PERFORMANCE CHARACTERIZATION OF CHARGE

CONTROLLERS: AN EXPERIMENTAL COMPARISON WITH

APPLICATION TO DEVELOPING NATIONS

BY

VISHAL CHANDRASHEKAR

B.E. P.E.S COLLEGE OF ENGINEERING (2013)

SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS

FOR THE DEGREE OF MASTER OF SCIENCE

DEPARTMENT OF MECHANICAL ENGINEERING

UNIVERSITY OF MASSACHUSETTS LOWELL

Signature of

Author: Date:

Signature of Thesis Supervisor:

Name Typed: Prof. Christopher Niezrecki

Co-supervisor:

Name Typed: Alessandro Sabato, PhD

Signature of other Thesis Committee Members:

Committee Member Signature:

Name Typed: Asst. Prof. Ertan Agar

Committee Member Signature:

Name Typed: Prof. Walter Thomas

PERFORMANCE CHARACTERIZATION OF CHARGE

CONTROLLERS: AN EXPERIMENTAL COMPARISON WITH

APPLICATION TO DEVELOPING NATIONS

BY

VISHAL CHANDRASHEKAR

ABSTARCT OF A THESIS SUBMITTED TO THE FACULTY OF THE

DEPARTMENT OF MECHANICAL ENGINEERING

IN PARTIAL FULLFILMENT OF THE REQUIREMENTS

FOR THE DEGREE OF

MASTER OF SCIENCE

IN

ENERGY ENGINEERING

UNIVERSITY OF MASSACHUSETTS LOWELL

2016

Thesis Supervisor: Christopher Niezrecki, PhD.

Chair, Professor, Department of Mechanical Engineering

University of Massachusetts Lowell

Thesis Co-Supervisor: Alessandro Sabato, PhD.

Postdoctoral Research Associate, SDASL, Department of Mechanical Engineering

University of Massachusetts Lowell

ii

ABSTRACT

Charge controllers (CCs) are essential devices for managing power between the solar

module, battery and the load in a SHLS (Solar Home Lighting System) unit. CCs

influence battery life, load compatibility, overall system efficiency and importantly,

system life cycle cost. A wide range of CC devices are available with varying degrees of

performance, protective measures and retail prices. It was decided to characterize and

analyze performance of 5 devices which broadly represent the different gamut of

products commercially available.

This work performs a comparison of different CC devices through experimental testing,

validation of data provided by the manufacturers, and estimating the suitability of a

particular charge controller for application in SHLS units by understanding device

behavior. A deep-cycle lead acid battery was discharged and charged using each of the

CCs and the voltages and currents to and from the modules, load, and battery were

sampled every 30 seconds during testing. Charging Discharging Cycle Profiles (CDCPs)

for the 5 devices were obtained for analysis. Two iterations of CDCPs were created; one

with and without a simultaneous cell-phone battery equivalent load. This was done to

simulate the charging of a cell-phone during the day and night time. A simulation for

calculating overall lifecycle cost of the system was also created.

iii

It was observed that the CDCPs without loading for two different specimen of the same

brand showed some variability in performance. The battery discharging times were varied

as well. Adherence to the set-points was found to be moderately close to the stated values

in the manufacturer specified data sheet. However, the two specimens showed slightly

different set-points which demonstrate a slight lack of reliability. The power consumed

by most of the devices was higher compared to the manufacturer specifications.

Life Cycle Cost (LCC) analysis using a theoretical cycle as standard revealed that the

overall cost of operation of a CC including its own cost varies by about $100 depending

on the device. The errors between the theoretical performance and the measured

performance did not exceed 3% for most of the devices.

iv

DEDICATION

This night is dark, the waves rise mountain high.

And a storm is raging!

What do the pedestrians know my plight moving

Upon the shore that’s safe and dry?

Hafiz

For the millions, who have been living and continue to live without lights: I hope this

work and the toil of those involved will create at least an iota of change.

To my parents: Arun and Lalitha, thanks for having faith in me. It is one of the things that

kept me going. I do not know what makes you think that I am capable of accomplishing

my dreams but I shall do my best. To my sister Sumukhi: you inspire me in ways that I

have not yet understood. Krish: I seek to duplicate your equanimity one day especially in

profession. Nishaan, few people believe in me like you do. “Miles and miles to go before

we sleep”. To Mahathi: you may want to read this when you grow up. To Cooby, my

eternal courage replenishment mechanism: I revel in your company even in your absence.

A special thanks to all of my family who have contributed to whatever I am today.

This work is dedicated to among others, my dearest friends Mohsin, Yao, Abiola, Gargee,

Anisha, Vyas, Vikas, Shashank, Kishan, Gautam, Mathews, Phaneendra, Ravi, Shyam,

and Arpitha: yes, I am still late at everything I do.

This has been a journey more spirited and unexpected than what I had imagined. I have

learnt a lot more than what have filled these pages.

Thank you.

v

ACKNOWLEDGEMENTS

I thank Prof. Niezrecki for his continued guidance, support and belief that I would come

up with something significant after two years. Thank you for your support and

encouragement. It was due to your vision that I was able to work on an important and

interesting topic.

I would like to thank all the committee members Prof. Thomas and Prof. Agar for their

constructive comments to add more substance to this work.

Sincere thanks to Alessandro for guiding me through the process writing this manuscript.

Thanks to Glen Bousquet and Don Bowden for troubleshooting as well educating me on

electronics and supplying me with necessary electrical components. Thanks to Jackie

Paradise for helping me with numerous issues.

Thank you all.

vi

TABLE OF CONTENTS

ABSTRACT ....................................................................................................................... ii

DEDICATION.................................................................................................................. iv

ACKNOWLEDGEMENTS ............................................................................................. v

TABLE OF CONTENTS ................................................................................................ vi

LIST OF FIGURES ....................................................................................................... viii

LIST OF TABLES ........................................................................................................... xi

I. INTRODUCTION ..................................................................................................... 1

1.1 Motivation ......................................................................................................................... 1

1.2 Energy access: problem and potential solution ............................................................ 2

1.3 Review of current solar devices enabling energy access ............................................ 6

1.4 Review of related literature ........................................................................................... 11

II. THEORY OF CHARGE CONTROLLERS AND BATTERIES ....................... 15

2.1 Overview ......................................................................................................................... 15

2.2 Classification and configuration of charge controllers ............................................. 17

2.2.1 Charge controllers based on shut off regulation ......................................... 18

2.2.2 Maximum Power Point Tracking (MPPT) and Pulse Width Modulation

(PWM) Circuits ........................................................................................... 26

2.3 Voltage set points ........................................................................................................... 29

2.4 Battery fundamentals ..................................................................................................... 33

2.5 Charging-discharging cycle plots ................................................................................. 36

2.6 Observed issues .............................................................................................................. 39

vii

III. METHODOLOGY .................................................................................................. 40

3.1 Overview ......................................................................................................................... 40

3.2 Equipment used and experimental setup ..................................................................... 41

3.2.1 Lighting and current sources ....................................................................... 43

3.2.2 Current and Voltage measurements ............................................................ 45

3.2.3 Battery properties ........................................................................................ 47

3.2.4 Charge controllers ....................................................................................... 47

3.2.5 Loads ..................................................................................................................... 51

3.3 Experiment 1: Setup of the CDCP experiment with no CBE ................................... 53

3.4 Experiment 2: Setup of the CDCP for the simultaneous loading case .................... 55

3.5 Theoretical model to estimate lifecycle cost .............................................................. 61

IV. RESULTS AND DISCUSSIONS ............................................................................ 63

4.1 Overview ......................................................................................................................... 63

4.2 Results: EXP. 1 ............................................................................................................... 65

4.3 Results: EXP. 2 ............................................................................................................... 75

4.4 Calculation of LCC using theoretical battery model ................................................. 82

V. CONCLUSION AND FUTURE WORK ............................................................... 88

VI. REFERENCES ........................................................................................................ 92

APPENDIX .................................................................................................................... 100

APPENDIX. 1........................................................................................................................ 100

APPENDIX. 2........................................................................................................................ 106

APPENDIX. 3........................................................................................................................ 109

viii

LIST OF FIGURES

Fig. 1.1 Access to electricity (in percentage) of population in developing countries

(Source: [4]) ....................................................................................................................... 3

Fig. 1.2 Modeled annual average radiation (Source: [11]) ................................................ 6

Fig. 2.1 Different kinds of PV systems ............................................................................ 15

Fig. 2.2 Different types of CC based on cycling .............................................................. 17

Fig.2.4 Block diagram representing the circuit schematic of a shunt type [39] .............. 20

Fig. 2.5 Current variation (top) and voltage variation (bottom) in a system operated using

a shunt type Interrupting Charging CC [41] .................................................................... 21

Fig. 2.6 Circuit representation of Series type CC [39] .................................................... 23

Fig. 2.7 Current variation (left) and voltage variation (right) in a system operated using a

series type Interrupting Charging CC [41]....................................................................... 24

Fig. 2.8 Theoretical I-V curve of a solar module [43] ..................................................... 27

Fig. 2.9 Schematic of a generic PWM CC [42] ............................................................... 27

Fig. 2.10 Schematic of a generic MPPT CC [42] ............................................................ 28

Fig. 2.11 Illustration of hysteresis in the regulation and disconnection regions of a typical

charge-discharge cycle [39] ............................................................................................. 32

Fig. 2.12 3-stage theoretical charge cycle [48] (left) and CDCP of a 12V LA battery [49]

(right) ............................................................................................................................... 36

ix

Fig. 3.1 Werker battery charger used to replenish the battery before starting each

experiment [50] ................................................................................................................ 42

Fig. 3.2 30W solar module selected [52] ......................................................................... 43

Fig. 3.3 Arrilite 1000W lamp ........................................................................................... 43

Fig. 3.4 CR5210-5 DC current transducer [53] ............................................................... 45

Fig. 3.5 Performance curve of the CR2510-5 transducer ................................................ 46

Fig. 3.6 NI USB-6001 DAQ device [54] (left) and NI LabView block diagram for data-

acquisition (right) ............................................................................................................. 46

Fig. 3.8 LED Strips used as load ...................................................................................... 51

Fig. 3.9 Portable battery pack used as cellphone battery equivalent [67] ........................ 52

Fig. 3.10 A step down buck used to charge the power bank [68] .................................... 52

Fig. 3.11 CBE discharging power resistor [69] ............................................................... 53

Fig. 3.12 Schematic of the discharging cycle .................................................................. 54

Fig. 3.13 Schematic of the charging cycle ....................................................................... 54

Fig. 3.14 CDCP with contemporary loading ................................................................... 56

Fig. 3.15 Entire experimental setup (1) PV module, 5) Digital multimeter) ................... 57

Fig. 3.16 Detail of the experimental setup (2) Current to Voltage Transducers, 3) DAQ,

4) Voltage dividers on breadboard, 6) LA Battery, 7) CC, 8) LED strip, 9) CBE, 10) Step

down buck)....................................................................................................................... 57

Fig. 3.17 Dynamic battery model utilized (source: [70]) ................................................. 61

Fig. 4.1 CDCP of the currents for the ten devices for EXP.1 .......................................... 67

x

Fig. 4.2 CDCP of the voltages for the ten devices for EXP.1 .......................................... 68

Fig. 4.3 CDCP of the power for the ten devices for EXP.1 ............................................. 69

Fig. 4.4 CDCP of the currents for the five devices for EXP.2 ......................................... 78

Fig. 4.5 CDCP of the voltages for the five devices for EXP.2 ........................................ 79

Fig. 4.6 CDCP of the powers for the five devices for EXP.2 .......................................... 80

Fig. 4.7 Theoretical CDCP for the LA AGM battery ...................................................... 85

A 1.1 CDCP of CMO1 (EXP. 1) .................................................................................... 100

A 1.2 CDCP of CMO2 (EXP. 1) .................................................................................... 101

A 1.3 CDCP of CTO1 (EXP. 1) ..................................................................................... 101

A 1.4 CDCP of CTO2 (EXP. 1) ..................................................................................... 102

A 1.5 CDCP of STO1 (EXP. 1) ..................................................................................... 102

A 1.6 CDCP of STO2 (EXP. 1) ..................................................................................... 103

A 1.7 CDCP of MS01 (EXP. 1) ..................................................................................... 103

A 1.8 CDCP of MS02 (EXP. 1) ..................................................................................... 104

A 1.9 CDCP of WN01 (EXP. 1) .................................................................................... 104

A 1.10 CDCP of WN02 (EXP. 1) .................................................................................. 105

A 2.1 CDCP of CM03 (EXP. 2) .................................................................................... 106

A 2.2 CDCP of CT01 (EXP. 2) ...................................................................................... 106

A 2.3 CDCP of ST01 (EXP. 2) ...................................................................................... 107

A 2.4 CDCP of MS01 (EXP. 2) ..................................................................................... 107

A 2.5 CDCP of WN03 (EXP. 2) .................................................................................... 108

xi

LIST OF TABLES

Table.1.1 Percentage population having access to electricity (Source: [5]) .......................... 4

Table 1.2 List of units and metrics used ................................................................................ 8

Table 1.3 Comparison of the SLS devices ............................................................................. 9

Table 1.4 Comparison of commercially available SHLS kits ............................................. 10

Table 2.1Comparison of the different features of PWM and MPPT CCs ........................... 29

Table 2.2 Definition of the commonly used set-points ........................................................ 31

Table 2.3 Typical Set points for a Lead Acid battery [39] .................................................. 32

Table 3.1 Figures of the Charge Controllers being used ..................................................... 49

Table 3.2 Specifications of the different CCs tested ........................................................... 50

Table 3.3 List of components used ...................................................................................... 59

Table. 3.4 Test matrix .......................................................................................................... 60

Table 4.1 Comparison of the features for the different CCs for EXP. 1 ............................. 74

Table 4.2 comparison of the features for the different CCs for EXP. 2 .............................. 81

Table 4.3 LCC calculation for the different devices ............................................................ 83

Table 4.4 Relation between DoD and life cycle till failure [73] ......................................... 86

1

I. INTRODUCTION

1.1 Motivation

Solar Photo-Voltaic (PV) modules are becoming more affordable and utilize the abundant

solar resource to generate electricity. This makes them suitable for being used in areas

characterized by lack or intermittent supply of electricity from the grid. Moreover, off-

grid LED lighting systems are cleaner, cheaper and healthier than kerosene lamps being

used today [1, 2]. PV modules alone cannot generate electricity; auxiliary components

such as batteries for energy storage and electronic control units are required to allow

users to connect their load and use the energy. Electronic control units such as charge

controllers (CCs) play a key role in the whole system as they direct energy from the

modules to the battery and loads. The purpose of this work is to compare and evaluate the

performance of different solar CC devices. The obtained results may be used to help

develop a PV system that can be operated inexpensively and used for lower-income

regions in third-world countries.

Small PV systems (less than 100W) comprising of PV modules, CC, wiring, batteries,

and lights bundled together are often referred to as Solar Home Lighting Systems

(SHLSs). Most existing SHLSs simply integrate components ordered from different

suppliers. Furthermore, most of these devices are imported; hence, do not encourage local

2

enterprise and also lack the desired robustness. Since the commercially available systems

usually embed the electronic components, they are not modular or expandable and are

very difficult to repair by end users.

A critical part of a SHLS is the charge controller (CC) and there is a need to better

understand the performance of the variety of CCs currently available on the market today.

This study consists of an experimental and theoretical analysis to better understand the

behavior of different market-available CCs and quantify their performance. To do this,

elaborate experiments were created and the Charge-Discharge Profiles (CDPs) for

different loaded and unloaded conditions were obtained and compared.

The thesis work is organized as follows: after chapter one where the problem of energy

access is discussed together with a short survey of the scientific literature addressing this

problem, some basic concepts concerning CCs, charging cycles and batteries are

discussed in chapter two. In chapter three, a detailed description of the experimental

setup and procedure are laid out. Chapter four comprises a detailed analysis of the

obtained results. To finish, the knowledge gained from this work is summarized and a

description of possible future work addressed in chapter five.

1.2 Energy access: problem and potential solution

According to the United Nations Secretary General’s Advisory group on Energy and

Climate Change, energy security is defined as “uninterrupted access to clean, reliable

and affordable energy services for cooking and heating, lighting, communications and

productive uses at an affordable and environmentally friendly price” [3]. Energy is vital

3

for survival regardless of the lifestyle. With reference to developing nations, several

studies have been performed by the World Bank (WB) which have shown that access to

electricity in many areas of the world is extremely limited. Figure 1.1 depicts the

percentage of people having access to electricity. From a preliminary analysis of the

image, it is observed that a lack of energy access characterizes developing nations and

areas such as the Sub-Saharan Africa, where access to electricity is very low and below

23%, or the Indian subcontinent where less than one out of two people have access to

electricity.

Fig. 1.1 Access to electricity (in percentage) of population in developing countries (Source: [4])

Furthermore, the grid does not connect to a large percentage of the population, especially

those living in rural areas as summarized in Table.1.1.

4

Table.1.1 Percentage population having access to electricity (Source: [5])

Region

People without

power

(millions)

Access to

electricity

(%)

Urban

electrification

rate

(%)

Rural

electrification

rate

(%)

Sub-Saharan

Africa 599 31 55.2 18.3

Malawi 14 7 37 1

Gabon 1 60 64 34

Democratic

Republic of Congo 62 9 26 1

Developing Asia1 615 83.1 95 74.9

India 306 75 94 67

Myanmar 25 49 89 29

Pakistan 56 69 88 57

Cambodia 9 34 97 18

Yemen 14.9 40 75 23

Latin America

Haiti 7.3 28 44 9

Peru 3 90 98 60

Nicaragua 1.3 78 98 50

For instance, it should be pointed out that India, despite an access rate to electricity equal

to 75%, has the higher number of people (306 millions) not connected to the grid. It is

due to the enormous population and to the disparity in energy access between

communities living in urban areas (94%) compared to rural areas (67%). The grid does

not reliably supply rural regions for they are sparsely populated and requires massive

investment to connect each and every village to the grid. This difference is even more

evident in the cases of regions like the Sub-Saharan ones are considered (e.g. Malawi).

Moreover, even if the grid connection exists, supplied power typically exists only for a

few hours each day and it is prone to outages. Also, transmission of electricity is another

issue for providing a reliable source of energy as it typically encompasses huge losses

1 Developing Asia includes China, India, Cambodia, Indonesia, Laos, Malaysia, Myanmar, Philippines,

Singapore, Thailand, Bangladesh, DPR Korea, Mongolia, Nepal, Pakistan, Sri Lanka

5

(usually from 11% - 54% including pilferage [6]) from the power plant to the consumer.

Theft of energy is also a major issue. On the other hand, population is growing especially

in those regions where access to electricity is low [7], simultaneously increasing the

demand for conventional energy supplies and at the same time there is need keep the cost

of electricity affordable [8].

On the other hand, conventional sources of energy are depleting at an alarming rate,

which makes the access to low-cost energy even more difficult. The exponential growth

in fuel consumption is now driven by shale discoveries and natural gas [9] especially in

the developed countries, which is yet more polluting compared to solar energy. As the

population increases, demand for oil increases too and CO2 emissions are estimated to

grow, leading to catastrophic consequences attributed to climate change [10].

As can be seen from Figure 1.1 and 1.2 – the countries lacking energy access are

typically the ones that have access to the solar energy resource. The regions where

unavailability of electricity is abundant are also the regions where the potential for power

generation using Solar Lighting Systems (SLS) are higher. In particular, Sub-Saharan,

developing Asia, and Latin America areas characterized by a scarcity of electricity access

are characterized by an annual average solar irradiation between 5.5 and 7.5kWhm-2

[11].

6

Fig. 1.2 Modeled annual average radiation (Source: [11])

Solar energy has the ability to partially supply the needs of the planet. The resource is

distributed and makes it easy to produce energy at the site of consumption. The

possibility of generating electricity where needed could help the business by creating new

customers, provide affordable lighting to people having no access to the grid, and prevent

much damage to the environment. By implementing SHLS and PV systems with battery

storage, it may be possible for people or communities to become independent of grid-tied

electricity.

1.3 Review of current solar devices enabling energy access

A simple solution currently employed to provide to access to lighting for the masses has

been the deployment of Solar Lighting Systems (SLS). These devices are palm sized and

usually have an embedded PV module to recharge a Lithium battery. The SLS may or

may not offer ability to charge a cellphone. The purpose of SLSs is to provide some

7

illumination mainly for task lighting during cooking, studying, cleaning etc. SLSs are

also compact and can be carried around to illuminate walking paths during night travel.

The SHLSs cater to slightly higher capacities and are usually stationary. These are

heavier, capable for larger loads and more loads can also be added. For instance, two or

more USB ports may be available in addition to LED bulbs which can be placed at

different points in the house to illuminate different areas simultaneously. SHLS devices

can either be sold as a kit or the user/ distributor/ installer may bundle together various

components of assorted manufacturers.

This section presents few of the popular devices in tabular form. Table 1.2 presents the

different parameters that shall be compared among different devices. Table 1.3 compares

different parameters of SLS devices. Table 1.4 compares different SHSL devices that are

sold as a kit.

These comparisons try to elaborate on the different devices available in the market in the

respective market segments. However, this thesis concerns the analysis of CC devices

that are not part of a kit and these devices form a part of bundled SHLS systems. The

devices in the Table 1.4 have larger capacity modules, more number of LED bulbs than

those devices in Table 1.3.

8

Table 1.2 List of units and metrics used

Measurement Unit Explanation

Luminous flux Lumen (lm)

Brightness of the luminary or LED bulb. Higher

the brightness of the bulb higher would be the

ease of sight in the region of illumination.

Battery capacity mAh

This is the amount of energy stored in the battery.

Higher the battery capacity means that the device

would be functional even during cloudy days or

when irradiance is low.

Unit cost of

luminance lm/$

This unit needs to be as low as possible in order

to maximize the customer’s willingness to buy.

Luminous efficacy lm/W

This is a measure of how the efficient the LED

bulbs which are used in the device are. Ideal is to

provide highest illumination whilst consuming

lowest battery power. These are calculated for

highest settings.

.

9

Table 1.3 Comparison of the SLS devices

Product Company Lumens PV panels Battery Cost

in $

Hours of

operation

on full

charge

Cost of

system

Lumen/

$

Luminous

efficacy

Lumen/watt

SunKing Solo

Greenlight

Planet 51

800 mW and

4.7 V

1000 mAh

3.2 V

Lithium

Ferro

Phosphate

24.94

[13]

5.8 hours in

Highest

setting

2.04 130 [14]

MiniSun 12H

SunLife NA

200 mW Poly

crystalline

[15]

NA 6 [15] 12 [15] NA NA

S20

dlight design 29 [16]

Mono

crystalline

silicon

0.4 W

[16]

Lithium

battery

10.31

[17] 6.5 2.81 NA

10

Table 1.4 Comparison of commercially available SHLS kits

Product Company Lumens PV panels Battery Cost

in $

Hours of

operation

on full

charge

Cost of

system

Lumen/

$

Other

Features

S300

dlightdesign

100/ 29

[18]

1.6 W Mono

Crystalline

silicon

1800 mAh

Lithium

Iron

Phosphate

38.34

[19]

High 5 hours

and low 26

hours

2.86 1 USB

charging port

Connect 600

Barefoot

Power

300 (4 lamps)

[20]

6.6 W

Poly

Crystalline

silicon

[20]

Sealed

Lead Acid

[20]

NA

11 hours

with 4 lamps

[20]

NA

2 USB

charging

ports + 1 x

12V DC port

[20]

Energy Station Plus

Futura 320 [21] 4.7 W [21]

4400 mAh

6.4 V

Lithium

[21]

NA

6.4 hours

with 3 lamps

[21]

NA

1 USB

charging port

[21]

11

1.4 Review of related literature

Much research has been done on the comparison, innovation, field testing, and economic

analysis of utility-scale Solar Lighting Systems (SLSs) or home lighting systems for

developed countries. This thesis hereby presented is an extension of these works but it

focuses on those CCs which are an integral part of Solar Home Lighting Systems

(SHLSs) which serve a slightly higher load. Some of the works focusing mainly on CCs

and stand-alone PV systems have been presented in this section to provide a preliminary

survey of the state-of-the-art of this technology.

One of the internationally accepted standards for performance of the charge controllers

are given by the International Electrochemical Commission (IEC) [22]. The IEC 62509:

2010 is currently being followed as far as battery CCs for PV systems. However, it is

interesting to note that none of the CCs purchased for this study did not mention

compliance to the IEC 62509 code.

During the 1990s, there were some standards that were used to determine the adequate

performance of CC devices. Some countries had set standards for CCs and implemented

them in their respected jurisdictional areas, for example: Basic Electrification for Rural

Households prescribed by GTZ in Germany and the Specifications for Solar Home

Systems prescribed by BPP Technologies in Indonesia. But none of the standards had a

truly global reach. Though PV modules’ performance is regulated stringently, the same

cannot be said for other solar system components such as lightening and controllers.

Egido et al. [23] analyzed the standards of different countries in 1998. In 2005 and 2010,

the International Electro-technical Commission (IEC) released two technical standards

12

for charge controllers regulation: the IEC 62093 (Balance-of-system components for

photovoltaic systems - Design qualification natural environments) and the IEC 62509

(Battery charge controllers for photovoltaic systems - Performance and functioning). The

parameters discussed in the standards were devised keeping in mind both the national

governments that intend to implement SHS and also to the CC manufacturers, who can

manufacture better and longer lasting devices. The final benefit goes to the consumer

who purchases a SHS devise. This work is a review of the Universal standard prescribed

by the European Commission [24].

Charge controllers have been tested and validated before: Diaz et al. [25] compared the

different batteries and charge regulators for application in Solar Home Lighting Systems

(SHLSs). This work was essentially the verification of above discussed proposed

Universal Technical Standards. A result of this study showed that though the cost of a

charge regulator was about 5% of the whole system’s cost, improper charging cycles due

to flawed regulators can lead to severe reductions in the life of the battery and therefore

increasing lifecycle costs. 20 charge regulators were tested in the research, out of which 3

failed completely. It was observed that the performance of these devices were unreliable,

varying and not well adapted to the batteries that was used for testing. The study

presented in this thesis is similar to the one performed by Diaz, with the difference that

the CDPs were also obtained for CCs of different price ranges. In particular, CDPs with

and without load have also been presented to gain a better understanding of the CC

behavior under different operational conditions. Also, the analysis presented in this thesis

was performed on more modern devices together with an estimation of lifecycle cost.

These features are not studied in the mentioned study, even if it should be noticed that

13

some of the critical performance characteristics pointed out by Diaz’s research were

confirmed by the experimental results presented in the thesis.

Different types of CCs, batteries and recommended practices have been elaborated in

Usher et al. [26] and Dunlop et al. [27]. In these studies, the schematics, mode of

operations, behavior, battery maintenance, and suitable applications for the considered

CCs have been analyzed and discussed with great detailed.

In large areas of Africa and other developing countries, deep-cycle batteries suited for

SHLSs applications are not easily available and quite expensive compared to abundant

automobile batteries. In general, the CCs are not compatible with automobile batteries as

their interaction can cause premature system failures. Masheleni et al. [28] developed an

idea to use microprocessors (SGS-Thompson microcontrollers, ST62E20) as CCs to try

to emulate the theoretical battery cycle for deep charging Lead Acid (LA) battery

applications. This study showed that the microprocessor could be easily programmed to

suit the requirements of an automobile if connected to the system, thus significantly

extending the battery life. Other advantages resulting from using microprocessors

included in-built system monitoring aides, reduced power consumption, elimination of

analog feedback, and simple modification of the circuit.

Few studies have been found which discuss the economics, feasibility, and Life Cycle

Cost (LCC) of small PV and wind systems. Nafeh [29] and Chel et al. [30] presented

models to analyze economics of the systems. In the latter study, using the electrical load

and daily average insolation on a tilted surface, capital cost and unit cost of electricity

were evaluated using LCC methods.

14

Some important technical papers were discussed above; now some outcomes of research

activities undertaken by respective institutions are presented. D-Labs at the

Massachusetts Institute of Technology (MIT) has been assessing the field performance of

SLS in various test sites in Africa and Central America [31]. A database of locally

available devices was created and sorted based on cost, performance, durability, lighting

output etc. [32].

The Lumina project [33] has published numerous studies on the performance analyses,

testing procedures, acceptability of products to the consumer, comparison of SLSs

against kerosene lamps, and adoption of SLSs into various other useful applications. An

important phenomenon of “market spoiling” concerning proliferation of LED lighting

devices was introduced by this group – this refers to “consumer skepticism” brought

about toward solar and LED lighting devices due to the consumers’ unsatisfactory first

experiences with these devices owing mainly to their lack of reliability and shorter than

advertised life. Rigorous testing and validation to help prevent “market spoiling” in the

realm of CCs in among of the aims of this work.

Lighting Global is an institution born out of the collaboration between the World Bank

and the Internal Finance Corporation (IFC). The goal of Lighting Global is to maintain a

quality standard for Solar Home Lighting System (SHLS) “that set a baseline level of

quality, durability, and truth-in-advertising to protect consumers”. Lighting Global tries

to make its standards and testing procedures having establishing laboratories or affiliated

testing facilities administered by regional organizations – Lighting Africa, Lighting Asia

and Lighting Pacific [34]. Lately, Lighting Global has established standards for ‘Solar

Home System Kits’ which are slightly larger capacity lighting devices [35].

15

II. THEORY OF CHARGE CONTROLLERS AND BATTERIES

2.1 Overview

SHLSs are widely adopted in regions where the access to a reliable grid is limited,

expensive, or nonexistent. Decrease in the solar modules and electronics’ cost have

propelled their growth and the trend is continuing in the near future [36].

Solar systems are classified based on their dependency on the grid into Stand Alone

Systems (SAS) and Hybrid systems as shown in Figure 2.1.

Fig. 2.1 Different kinds of PV systems

SAS systems are characterized by the absence of interaction with the grid, while the

hybrid systems by the presence of a photovoltaic system with another power generating

Hybrid PV

CLASSIFICATION BASED ON

GRID DEPENDANCY

Stand Alone PV

DC Loads AC

Loads

DC/ AC

Loads

16

energy source (e.g. wind, diesel engine). The schematic of a SAS is extremely simple and

includes, beside the presence of PV panels, a Charge Controller (CC), a battery bank, and

a load. Charge Controllers are basically DC-to-DC converters, which manage the power

output from the modules to the battery and from the battery to the loads. Several CCs

exist and the use of one type rather than another depends on the tasks being performed.

Loads can be of three different types (i.e. Direct Current (DC), Alternating Current (AC),

and DC/AC) and define the system further. It should be noticed that this study focuses on

the description of the DC loads SASs only, because their simplicity best fits the

necessities of remote and impoverished areas. Indeed, any AC conversion needs

accessory systems such inverters, which increase system’s complexity and cost [37].

In this chapter, a brief overview and characterization of the different CCs and their

respective circuit diagrams’ schematics are provided. This includes a discussion about the

relevance of the CC set-points to better understand the performed analyses. Then an

introduction about battery design is given, including an explanation of the theoretical

charging cycle. To finish, some generic issues CC devices experience during their

operations are described.

17

2.2 Classification and configuration of charge controllers

Generally, SHLSs have capacities within 100 W as they are mainly used for supplying

individual home lighting or small appliances only. Due to their characteristics, all the

energy needed by the system has to be generated and stored at any time on site.

Therefore, battery depletion or lack of sunlight must be taken into account before

designing a stand-alone system.

The features of the systems’ different components such as battery requirements and CC

characteristic depend on the applications the system is being designed for. For instance, if

the system is idle for a prolonged duration, the CC needs to top-up the depleted charge to

prevent battery failures under times of need. On the other hand, when the cycling rates

are higher, the CC needs to supply higher voltages for a certain time to break up the

Sulphation as will be specified in paragraph 2.4 [38]. Figure 2.2 shows a classification

based on the particular application CCs are used for.

Fig. 2.2 Different types of CC based on cycling

CLASSIFICATION BASED ON APPLICATION

Topping

Charge

Cycling Charge

Shallow Cycling Deep Cycling

18

As a small portion of the energy stored within the battery is used (e.g. during emergency

or black-out), the topping charge provide immediate replenishment of the used power by

means of the charger controller which allows the battery to be ready in the event of other

emergencies. In this situation, only a short percentage of the power stored within the

battery is used, and only a small amount has to be replenished. The system is idle for all

the other time. Such systems may be used in telephone towers and medicine storage

rooms where the shortest power outage cannot be tolerated. In cycling charge conditions,

the battery needs to be replenished many more times than topping charge since many

discharge and charge cycles occur. Two different kinds of cycling conditions can exist:

shallow and deep. In the former, the battery is partially discharged before being

recharged; while in the latter, the battery is fully discharged and then recharged. In deep

cycling charge conditions, the battery needs to be designed to accommodate a greater

Depth of Discharge (DoD) and the CCs need to recharge the batteries quicker.

2.2.1 Charge controllers based on shut off regulation

Another way to classify the CCs is based on the shut off voltage and voltage regualtion

mechanism as shown in Figure 2.3.

19

Fig.2.3 CC classification based on shut off and voltage regulation [39]

Based on the shut off mechanism, CCs are divided into Shunt type and Series type. In

Shunt type CCs the energy from the array is shut off as soon as a pre-determined voltage

is reached by shunting the circuit. This mechanism is quite simple, relatively inexpensive,

and it is generally used for systems having voltages lower than 24V [39].

As shown in Figure 2.4, where the block diagram of a shunt type circuit is shown, the

“control” switch is in parallel to the PV module. This means that when the control is

switched on (i.e. closed circuit), the power generated by the module is sent back and

cannot reach the rest of the system. It allows to maintain a constant voltage charging

cycle. No harm is caused to the PV modules by short circuiting them, since the PV

modules are basically current sources [40]. Also, the presence of a diode prevents the

battery from short-circuiting when the PV module is disconnected [40]. LVD is the Low

Voltage Disconnect which prevents over discharge and is explained in paragraph 2.3.

20

Fig.2.4 Block diagram representing the circuit schematic of a shunt type [39]

Due to the reduced complexity of the system, most CCs used to provide energy access are

of this kind. Figure 2.5 shows an example of current and voltage variation in a system

controlled by a shunt type CC over a 24-hour charge/discharge cycle.

In Figure 2.5, curve 1 represents the variation of PV module current, curve 2 the

variation of current input to the battery, curve 3 depicts variation of PV module voltage

and curve 4 the variation of the average battery current with respect to time.

21

Fig. 2.5 Current variation (top) and voltage variation (bottom) in a system operated using a shunt type

Interrupting Charging CC [41]

The charging cycle starts around 7 AM as sun irradiance begins to rise. It is observed that

the battery current (blue curve of top Figure 2.5) also rises correspondingly, but when

3

4

1

2

22

regulation starts (i.e. around 12 PM) the battery current starts decreasing to a value close

to zero at the sunset (i.e. around 6 PM). As soon as the charge controller begins to work,

the module is short circuited and it is utilized only for finishing charge (i.e. peaks on the

blue curve), and the load is completely absorbed by the battery.

When the Figure plotting the voltage is considered, it is observed that the voltage of the

battery (blue curve of bottom Figure 2.5) is around 12 V at 4AM, when the CC

disconnects the load. After sunrise, voltage starts to increase linearly and reaches its peak

around 12 PM, when regulation begins again. From that point on, the voltage of the

battery fluctuates, while the voltage of the module reduces and supplies power to the

battery intermittently. The difference between the current supplied from the module and

the current sent through to the battery is dissipated in the form of heat.

Instead, in Series type CC, the control is put in series with the module as observed from

the block diagram presented in Figure 2.6. In this case, when the controller recognizes the

battery as fully charged the control is switched off and the circuit is open. The PV

modules stop charging the battery and their voltage reach the open circuit value (VOC).

23

Fig. 2.6 Circuit representation of Series type CC [39]

As observed from the left plot of Figure 2.7, the series type CC essentially regulates the

incoming current of the module (red curve). Comparing the current of the module and

that of the battery, it is observed how similar these values are, while the module current

modulation does not exist in the shunt type CC. It implies higher energy wastage in the

shunt type CCs. When the regulation begins, the current in the array decreases because it

is used for charge topping.

In Figure 2.7, curve 1 represents the variation of PV module current, curve 2 the

variation of current input to the battery, curve 3 depicts variation of PV module voltage

and curve 4 the variation of the average battery current with respect to time.

24

Fig. 2.7 Current variation (left) and voltage variation (right) in a system operated using a series type

Interrupting Charging CC [41]

The array voltage approaches VOC (open circuit voltage) of the module. The regulation

voltages are usually lower for series type CC than shunt type CCs. Battery is charged at a

lower capacity in series CC compared to shunt CC [41]. These devices are more efficient

1

2

3

4

25

than the shunt type devices and provide better control, but are more expensive and

complex than their shunt type counterpart. It can be seen that the current from the module

(red line in the left curve) decreases close to zero as soon as regulation begins. This

prevents wastages of energy from the module.

A further classification of the charge controller takes into account the charging algorithm

employed. Interrupting Charging (ICH) and Constant Voltage Charging (CVC) can be

found in both Shunt and Series configurations as shown in Figure 2.3. ICH CCs are

usually referred to as pulsing CCs as they send the current from the PV module in pulses

between the two set-points. The charge controller recognizes when the voltage drops to

the lower set-point and instantly diverts power from the module. This “hysteresis” or

“pulsing” behavior is more prevalent during the later stages of each charging cycles. The

ICH shunt type CCs are the most popular and cheapest. However, their reliability,

performance, and associated lower battery life are worst compared to series CCs. Instead,

in the CVC types, the power from the PV modules supplied to the circuit depends on the

irradiation conditions, while the power supplied from the CC to the battery is at constant

voltage. This is done by a modulation circuit within the CC that allows for a constant

input to the battery. Then, the internal algorithm and control mechanism in this CVC

converts the supply power from the module to another one suitable for the battery by

modulating the current and keeping the voltage constant.

26

2.2.2 Maximum Power Point Tracking (MPPT) and Pulse Width Modulation

(PWM) Circuits

Selecting an appropriate theoretical charging model is beneficial as PV modules and

batteries operate with different voltages. This difference defines the kind of algorithms

that should be selected for charging the batteries. A brief review of two of the most

common models: Pulse Width Modulation (PWM) and Maximum Power Point Tracking

(MPPT) technology are discussed in this section. In the PWM model, the solar array and

batteries are in direct connection. The CC intervenes only to ensure that the charging is

consistent and conforms to the set-points. On the other hand, the Maximum Power Point

Tracking mechanism optimizes both power extraction from module, by using the MPPT

algorithm, as well as the power delivery to the battery. A detailed explanation and a

comparison between these two charging algorithms is presented here.

I-V (current – voltage) curves are characteristic features of a PV module. A qualitative

example of this kind of curves is shown in Figure 2.8. The solar module has a particular

voltage and current value when the power output is maximum. These current and voltage

values are called Imp and Vmp respectively. If the current and voltage values provided

from the PV module are not equal to its the theoretical values Imp and Vmp, it means that

the module is not operating optimally. The Vmp of a typical module is approximately 15-

17 V, while a 12V battery has an operating range between 10-15V [42].

27

Fig. 2.8 Theoretical I-V curve of a solar module [43]

In the case of PWM CCs, there is a direct connection between the module and the battery

as shown in Figure 2.9. This means that the module will have to supply energy in the

operating of the voltage range of the battery, so the energy from the module is not

extracted efficiently and as a result, the module’s efficiency factor is reduced. In this kind

of configuration, there is no intervention from the CC unless it is used to maintain set-

point conformity.

Fig. 2.9 Schematic of a generic PWM CC [42]

28

MPPT models are widely used in modern inverters in solar installations. A MPPT CC

embeds two printed circuit boards (PCB) with different functionalities as seen in Figure

2.10. One PCB (i.e. input board) is constantly trying to extract the maximum energy out

of the modules, while the other (i.e. charge board) is monitoring the battery level to make

sure that the supplied voltage and current values are conform to the default set-points.

Since MPPT CCs are more complex than PWM CCs, they are more expensive. A MPPT

CC is a DC-DC converter in its simplest format. Since the solar module output voltage is

not the same as that required by the battery, the MPPT CC is required to convert the

voltage from a higher value to lower one that can be stored in the batteries. It is done by

increasing the current over time and charging the battery at a higher current. The coil in

the center shown in Figure 2.10 is an inductor which serves as a DC-DC converter. Its

purpose is to supply uniform DC output given a particular DC input.

Fig. 2.10 Schematic of a generic MPPT CC [42]

Studies have determined that the MPPT CCs work marginally better than PWM CCs

under clear sky or unshaded environment, while the MPPTs’ performance can be as high

40% over traditional PWM mechanism when 1/3rd

of the module’s surface is covered

[42]. During clear sky periods, the MPPTs perform around 8% better than PWMs. This

same study argues that, despite efficiency increase during clear day is not significant,

29

over a longer time the cumulative savings makes the MPPT a worthwhile choice. Since

MPPTs convert voltages, the greater the difference in voltage is, the better these devices

will perform over PWMs. On the downside, the extent of deterioration due to increased

charging current is uncertain. For these reasons, it could be stated that the MPPT CCs are

better suited for larger systems where efficient modulation becomes a feature of

importance. For smaller systems, the gain in efficiency by use of MPPT CCs over PWM

CCs is not very significant. Table 2.1 summarizes the comparison of PWM and MPPT

CCs.

Table 2.1Comparison of the different features of PWM and MPPT CCs

Parameter MPPT CC PWM CC

Power extraction from the PV

module Active Absent

Regulation of charge to the

battery Active Active

Complexity Complex Relatively simple

Performance in cloudy weather More efficient Less efficient

Cost Expensive Cheap

2.3 Voltage set points

LA (Lead Acid) storage devices need to be charged in a predetermined fashion. How the

battery must be charged is specified by the battery manufacturer and executed

accordingly to an algorithm controlled by the CC. Charging cycles can generally be of 2-

stages or 3-stages.

30

Before discussing in detail the charge cycle specifications, a brief introduction of set-

points is presented for the ICH type chargers described in paragraph 2.2. Set-points are

extremely important as they provide the CC with basis of operation. If set-points are

misjudged, or wrongly measured, it causes the battery to operate a smaller number of

cycles than expected due to improper charging and excess depletion of capacity during

discharge. Set-points are determined based on a number of factors such as time required

for charging, life of battery expected, type of battery chemistry utilized, CC

characteristics, and cost of the equipment. Table 2.2 defines some of the terms that will

be used throughout this thesis. Recommended set-points for different battery types are

summarized in Table 2.3 [39]. In particular, Table. 2.3 shows the Voltage Regulation

(VR) and the Voltage Regulation Reconnect (VRR) values recommended for various

kind of batteries. It should be pointed out that the values of VR and VRR presented in

Table 2.3 are intended for 2V single-cell batteries and were provided for understanding

their order of magnitude only. This study will focus on the LA Absorbed Glass Mat

(AGM) class of batteries, where the electrolyte is not free flowing but it is absorbed on

the surface of layers of glass mats. In older batteries, the electrolyte is a free flowing

liquid. For the purpose of this thesis, only AGM LA batteries are discussed since these

are prevalent in stand-alone PV systems for their ability to deep cycle.

31

Table 2.2 Definition of the commonly used set-points

VR

(Voltage

Regulation)

This is the highest voltage that the charge controller will let

the battery reach. If the voltage of the battery measured by

the CC reaches this point, the CC will shut off the incoming

power from the module.

CHARGE

CYCLE REGULATION

VRR

(Voltage

Regulation

Reconnect)

When the battery voltage drops from VR to VRR, the CC

reverts the flow of energy from the module into the battery.

VRH

(Voltage

Regulation

Hysteresis)

The topping charge happens between VR and VRR. The

resulting on/off is the hysteresis referred to previously (§

2.2.1). Depth of the topping charge and duration may vary

drastically. Current is tapering during this time.

LVD

(Low Voltage

Disconnect)

As the battery reaches this point, the CC does not allow

further discharging of the battery. The battery has been

drained to the point that any further reduction of voltage

will damage the battery. LVD is typically chosen not too

low so that life cycles can be maximized.

DISCHARGE CYCLE

REGULATION

LVR

(Low Voltage

Reconnect)

When the apparent battery voltage increases to LVR the

load is connected and supplied with energy. LVR is reached

upon resuming of the charging state.

Self-

Consumption

During operation, the CC consumes some energy for its

own processes.

PERFORMANCE

CHARACTERISTIC

32

Table 2.3 Typical Set points for a Lead Acid battery [39]

To finish, Figure 2.11 illustrates the hysteresis cycle in the regulation (Voltage

Regulation Hysteresis) and disconnection regions (Low Voltage Disconnect Hysteresis)

described in Table 2.1.

Fig. 2.11 Illustration of hysteresis in the regulation and disconnection regions of a typical charge-

discharge cycle [39]

33

During the charging phases, the batteries receive power from the PV modules and

increase their voltage up to the Voltage Regulation point; after this, the CC disconnect

the flow of energy from the PV module to the battery and the voltage decreases up to the

Voltage Regulation Reconnect point because of inefficiencies in the charging process and

self-discharge mechanisms. As soon as this point is reached, the CC reconnect the two

sections of the circuit and the power rises to VR again. Instead, in the discharging phases

as soon as the battery’s voltage drops to the Low Voltage Disconnect point, the CC

disconnect the load from the battery and the voltage raises to the Low Voltage Reconnect

point. It should be observed that the discharging hysteresis is not as accentuated as the

charging one.

2.4 Battery fundamentals

This section will introduce the reader to some useful conceptual definitions of batteries

which shall be used repeatedly through this work. Generic definitions are presented here

and the same shall be used where necessary with appropriate substitutions.

Capacity: It is the quantity of the energy stored in the battery and it is commonly

measured in Ampere-Hours (Ah). As a solar system is designed, the capacity of

the battery has to be selected by taking into account the number of hours of stand-

by or autonomy, the loads being catered to, the available sunlight hours, and the

depletion of battery.

34

Depth of Discharge (DoD): It represents the amount of energy that can be safely

extracted out from the battery without affecting the future storage capabilities and

it is expressed as a percentage. Higher values of the DoD mean higher possibility

of irreversible failure. With each charging/discharging cycle, a minute reduction

in the actual capacity is observed. Usually, a 12 V battery reaches its end-of-

discharge state at around 10.5 V [44]. This means that at 10.5 V, the DoD is 100%

and the battery cannot longer be used without charging. Generally, DoD is

evaluated by measuring the voltage, but this parameter is not a fair indicator.

Therefore, internal resistance or specific gravity of the electrolyte serve as better

indicators.

C-rate: It is the number of Amperes that a battery can supply constantly for a

given time. For example: If the C rating is C/2 (i.e. 0.5C), the battery supplies 0.5

A for 2 hours [34]. As a result, a battery can supply a lower current for a longer

time or a higher current for a shorter time.

Sulphation: It is the phenomenon of Lead Sulphate (PbSO4) crystal depositions

on the cathode embracing some of the active area, which reduces the battery’s

capacity and performance [45]. It is a very common phenomenon for not

completely charged batteries such as the ones supplied with intermittent energy

from solar or wind. These sources, because of their discontinuous nature are not

able to supply enough energy for a full saturated charge. Sulphation can be

reduced by charging the battery properly for the whole duration specified by the

manufacturers without interruptions. Sulphation-preventive measures are

employed near the end of the charging cycle [39].

35

Life cycles: It is the time a battery can operate without much dissimilarity from

its original performances. This time can be quantified in terms of operational units

of cycles and represents the number of cycles until the capacity of the battery of

providing energy reaches 80% of its initial value.

Lifetime: It indicates how long the battery will last being loaded at a specific rate

[36] and can be evaluated using equation (1).

𝐿𝑖𝑓𝑒𝑡𝑖𝑚𝑒 𝑖𝑛 ℎ𝑜𝑢𝑟𝑠 = 𝐵𝑎𝑡𝑡𝑒𝑟𝑦 𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑦 (𝐴ℎ)

𝐿𝑜𝑎𝑑 𝐶𝑢𝑟𝑟𝑒𝑛𝑡 (𝐴) (1)

Charge factor: Takes into account that not all the energy supplied for the battery

is utilized to replenish the depleted capacity consumed by the loads [47]. Some

energy is lost because of thermodynamic inefficiency, chemical losses, heat and

internal resistance.

𝐶ℎ𝑎𝑟𝑔𝑒 𝑓𝑎𝑐𝑡𝑜𝑟 =𝐶ℎ𝑎𝑟𝑔𝑒 𝑒𝑛𝑒𝑟𝑔𝑦 (𝐴ℎ)

𝐷𝑖𝑠𝑐ℎ𝑎𝑟𝑔𝑒 𝑒𝑛𝑒𝑟𝑔𝑦 (𝐴ℎ) (2)

Sometimes in the evaluation of the battery’s efficiency, this factor of safety is also

considered in and results obtained from equation (1) are multiplied by this value

for improving the accuracy of the evaluation.

Gassing: Refers to electrolysis of water at the end of the charging cycle. Some

amount of controlled gassing is helpful to extend battery life, while gassing for

extended periods or shortened periods may result in faulty battery operation and

36

lower life [29]. Gassing helps by stirring the electrolyte solution to make it

homogenous.

2.5 Charging-discharging cycle plots

Charging-Discharging Cycle Plots (CDCPs) are graphical representation of voltages and

currents the battery assumes over time. They are representative of the battery

characteristics. Usually, these plots start from the fully charged battery and proceed until

the complete exhaustion of the charge under the supervision of a CC. Then the process

inverts and the battery is fully recharged to its initial state. Figure 2.12 (left) plots the

theoretical charge cycle diagram for a 2V battery and the adjoining figure (right)

represents the CDCP of a 12V LA battery, the different stages are labelled.

Fig. 2.12 3-stage theoretical charge cycle [48] (left) and CDCP of a 12V LA battery [49] (right)

In particular, the left image refers to a three-stages charging cycle, which is the most

recommended by manufacturers because a longer cycle makes the battery last longer,

while the right image refers to whole discharge and discharging cycle. The main aim of

this thesis consists in extracting the CDCPs when different CCs are used under different

37

loading conditions and to compare the obtained results with these theoretical curves.

With reference to the different sections shown in the right images of Figure 2.12, the

typical charge and discharge stages are described below:

Bulk Charging – Constant Current Charging (CCC): The battery has a State

of Charge (SoC) equal to 0% (100% DoD) as the charging is started. The battery

rapidly absorbs energy from the module and its voltage rises fast. Most of the

capacity depleted due to loading is recovered here. The voltage rises almost

linearly while the current remains more or less constant (as observed from the

first Stage depicted in the left image of Figure 2.12). This stage is not very

important since the delicate processes of topping up, gauging level of full charge,

and prevention of sulphation are not prevalent in this phase. During the bulk

charging time, the voltage need not to be continually monitored, hence on/off

cycling of the ICH CCs is not noticeable. The CDCPs of the experiments

conducted for this work will have Variable Current Discharge (VCD), since the

LED loads consume varying currents depending on the input voltage.

Absorption Charge – Constant Voltage Charge (CVC): At this point, the

battery has absorbed much of its charge. It now needs to complete the process by

fine-tuning itself. The CC starts monitoring the battery charges by sending the

charge into the battery at a controlled rate. The current will start to taper while

voltage is now constant (Stage 2 in left image of Figure 2.12). The ICH CC now

starts to closely monitor the battery to charge it slowly but thoroughly. Slow

charging is used to replenish the charge lost due to inefficiencies as previously

38

mentioned. This operation is also responsible for countering effects of sulphation.

In this section the hysteresis phenomenon described in the previous paragraphs

happens.

Float Charge or Charge Idle Time (CIT): During this stage, the CC maintains

the battery level constant by diverting current at a lower voltage. This is done to

compensate for the self-discharge phenomenon inherent to batteries.

Constant Current Discharging (CCD): In this stage, the load is connected and

the battery keeps supplying power until it reaches the LVD value described in

Table. 2.2. The curve’s profiles are very smooth and do not change much for

different CCs or batteries, while the slopes of the profiles depend on the

connected load.

Discharge Idle Time (DIT): After the battery is fully discharged it is no longer

operating. Voltage increases slightly due to termination of current extraction and

the battery is now idle until charging is started again.

Ideally, the charging process needs to provide the charge lost when the battery is

connected to loads, compensate for the energy lost due to the thermodynamic cycling,

and control the gassing at the end of the cycle to prevent stratification phenomena.

Therefore, these diagrams are extremely useful as they allow evaluating some

characteristics of the CC such as:

1. Conformity of the CC cycle to the theoretical model.

2. Comparison of performance of different CCs.

39

3. Lifecycle cost simulation of the CCs.

Using the analysis of CDCPs it is possible to understand their behavior from an

electronics standpoint and validate the performance claimed by the manufacturers.

2.6 Observed issues

During some preliminary tests performed to evaluate the characteristics of the CCs, it was

observed that they did not behave exactly as predicted in the manuals. Often the

information was inaccurate and in most cases insufficient for modelling or comparison

purposes. This is especially true with cheaper devices. These problems served as an

inspiration to devote full-fledged efforts into understanding these devices and are the

main motivation behind this thesis. The characteristics of the charge cycle being utilized

are not mentioned by the manufacturers.

After performing a few trials, it was noticed that the CC behavior is quite fluctuating too.

The charge profiles of subsequent tests with same battery and conditions seemed to yield

a slightly different curve. The same was observed when multiple units of the brand and

product line were compared. As mentioned before, conformity to the set-points and

theoretical CDCPs are crucial for long life of the battery. Therefore, a better

understanding of these problems is a highly desired to determine whether or not these

devices are suitable to be employed as reliable, low maintenance controllers for the

production of energy in remote and developing areas.

40

III. METHODOLOGY

3.1 Overview

The main objective of this work is to document the behavior of different types of CCs

and to understand which one is suitable for the installation within a PV system in remote

and developing countries. For this purpose, five different products were selected based on

their cost and technical specifications. Having reviewed the products available on the

market, it was decided to test CCs that are sold over a $10-$70 price range.

This thesis has two different components: an evaluation of the experiments performed

under different loading conditions and a simulation of the LCC. The experiments include

a characterization of the CCs both in absence and presence of loads to obtain the CDCP

for each device under the different loading conditions. In the first set of experiments the

CCs were tested without the application of simultaneous loads, while in the second set of

tests a simultaneous load representing a cell-phone being charged was added. CDCPs

with simultaneous loading were evaluated to characterize the performances of the devices

and compare them with those measured when no loads were applied. These data would

be helpful to estimate performance characteristics. Both experiments rely on very a

simple setup. In the first one a PV module (during charging phases), a LED strip (during

the discharging phases), and a battery only were used; while the same three components

41

and a cell-phone battery equivalent (i.e. a portable battery charger whose performance

and behavior approximate the behavior of a charging cell-phone) were employed in the

second one. During initial stages of the project, a Power Source (PS) was used to supply

the CC with energy in order to simulate the current production from a PV module. As

mentioned in the previous chapter 2.6, the CC’s behavior was negatively affected by the

PS. Hence, a 30W PV module was used to supply the CC with energy. The tests done

using the PS will not be discussed in detail in this work for the sake of brevity. To finish,

a simulation of the lifecycle costs was performed considering the non-conformity to the

theoretical set-points and other flaws affecting battery life cycles highlighted during the

experimental analysis.

3.2 Equipment used and experimental setup

Before presenting the details of the experimental setup, an understanding of the

equipment and experiment details is provided.

Before starting any test, the used battery was depleted to the LVD level and then charged

using the Werker Class 2 Battery Charger shown in Figure 3.1 [50]. It provides a 12V

output at 1A [50].

42

Fig. 3.1 Werker battery charger used to replenish the battery before starting each experiment [50]

The device switches off automatically once the battery is fully charged and has a LED

indicator to show the SoC of the battery. This procedure has been applied to ensure that

the battery has nearly the same amount of energy stored in it before starting each

discharging cycle and to ensure similar initial conditions in each of the tests performed.

In the first set of experiments, when the batteries are fully charged, a 12-hour discharge

cycle test is undertaken using a LED strip as a load. The CCs prevent over discharging

the batteries by shutting off the load. At the end of the 12-hour discharge cycle, after

resting the system, a 12-hour charge cycle is started using the PV module powered by

two 1kW incandescent lamps. This process was repeated for each of the 5 selected CCs.

In addition, for proving the experiments’ repeatability, two same-brand devices for each

of the five selected CCs were tested. A total of 10 surveys have been performed for the

first experiment set. The second experiment followed the same procedure, but a cellphone

battery equivalent was added in both the charging and discharging phases.

43

3.2.1 Lighting and current sources

As stated in the previous paragraph, energy was supplied to the system through a PV

solar module. To operate the 30 W PV module (Figure 3.2), two 1 kW lamps similar to

that shown in Figure 3.3 were used.

Fig. 3.2 30W solar module selected [52]

Fig. 3.3 Arrilite 1000W lamp

This solar module was selected because of its well-known electric characteristics [51] and

because of its low power [52], which makes it suitable for low-income and developing

areas. Furthermore, its nominal capacity is close to that normally used by households for

44

the dual purposes of lighting and cell phones charging. The module and the system would

be operated for quite a few years making the recovery of cost much more foreseeable and

realistic. In addition, the module could easily be used for catering slightly expanded

system capacity if desired by the user.

To extract the maximum current from the module, numerous spatial adjustments were

made. 1.6 A of current was extracted from the illuminated module which corresponds to a

charging C-Rate of around 0.114C. Also around 20-25 W of power were extracted from

the module during the course of the whole charging period. Despite the module was rated

at 30 W at 1000 Wm-2

, the maximum illumination that could be simulated using the

lamps was between 666-833 Wm-2

. As soon as the lamps were turned on, nearly 20W

was extracted and the module supplied this energy at a voltage between 12 and 12.5 V.

Probably, this variation depends on changes in the module input voltage over the

charging period, which is function of the battery properties.

From an analysis of the recorded CDCPs, it was found that the current extracted from the

modules remained almost constant through the bulk charging period, while the voltage

raised. Furthermore, during the tests, measurements of the temperature of the CC were

made regularly using a thermocouple to be sure that its operating temperature did not

significantly vary from room temperature and no temperature compensations were

required by the CC itself.

45

3.2.2 Current and Voltage measurements

The performed experiments rely on the measurement of both current and voltage. In

particular, for the first set of experiments two currents and two voltages values were

recorded through the whole duration of the test; while for the second set of experiments,

three currents and three voltages values were recorded.

To record the current output of each component in the system, current transducers were

used to convert component currents into voltages because the Data Acquisition (DAQ)

hardware used could only record voltage values as inputs. These transducers were

powered using a 24 V power source supplying between 17 and 20 mA per each device.

By diverting a current carrying conductor through the loop of the transducer, it was

possible to obtain a voltage output corresponding to the magnitude of the current flowing.

In Figure 3.4 the transducer employed is depicted, while Figure 3.5 shows the calibration

chart of the transducers employed, which shows a linear relationship between current and

voltage values.

Fig. 3.4 CR5210-5 DC current transducer [53]

46

Fig. 3.5 Performance curve of the CR2510-5 transducer

To acquire the voltage values, a NI USB-6001 DAQ [54] manufactured by National

Instrument and managed using a customized LabView code was used. Figure 3.6 shows a

picture of the DAQ and the block diagram of the executable code used.

Fig. 3.6 NI USB-6001 DAQ device [54] (left) and NI LabView block diagram for data-acquisition (right)

Furthermore, since the selected DAQ cannot measure voltage input greater than 10V and

considering that the PV module-battery system output may provide output voltage in the

order of 15-17 V, it was decided to use voltage dividers to obtain only half of the input

voltage and prevent any potential damage to the DAQ. The electrical circuit diagram of

the voltage divider that was used is depicted in Figure 3.7 and for each of the DAQ

0

1

2

3

4

5

6

0.2

5

0.5

0.7

5 1

1.2

5

1.5

1.7

5 2

2.2

5

2.5

2.7

5 3

3.2

5

3.5

3.7

5 4

4.2

5

4.5

4.7

5 5

Ou

tpu

t V

olt

age

(V

)

Current input (A)

47

channels used for acquiring voltage values, a divider was used. During the tests, data

were sampled every 30 seconds.

Fig. 3.7 Voltage divider circuit diagram

3.2.3 Battery properties

The battery selected was a Lead Acid Absorbed Glass Mat (LA AGM) type with a

nominal capacity of 14Ah or 168Wh at 12 V. This battery is sealed and does not need any

kind of maintenance. Two batteries of the exact same kind were used to expedite the

testing: a Duracell 14Ah AGM LA battery [55] and a Werker 14Ah AGM LA battery.

These batteries are suitable for being used in SHLS units since they are deep cycle

batteries capable of depleting to lower SoCs than the conventional LA batteries.

3.2.4 Charge controllers

The CCs are the most important component of the entire experimental process. As stated

before, the aim of this work is to understand how the different kinds of CCs behave. For

this reason, 5 different devices were purchased to be tested. Table 3.1 shows the pictures

48

of the different devices, while Table 3.2 summarizes their specifications and battery-

protective features. The abbreviations mentioned in Table. 3.1 are used for distinguishing

the CCs of different brands.

All of the information summarized in Table 3.2 have been taken from the products’

datasheet, while the eventual blank spaces represent either ambiguous data or missing

information. Furthermore, it has been observed that the datasheets of the cheaper devices

lack important information.

All the CCs used in this thesis are of PWM type.

49

Table 3.1 Figures of the Charge Controllers being used

Morningstar (MS)

SHS-6

Windy Nation (WN)

P10

Steca (ST)

Solsum 6.6F

CMP12(CM)

CMTP02 (CT)

50

Table 3.2 Specifications of the different CCs tested

Product name Cost

(USD)

VR

(V)

LVD/ LVR

(V)

Self

Consumption Other features

Morningstar

SHS-6 [56] 34.99 [57] 14.3 11.5/12.6 <8 mA

Series 4 stage PWM, reverse

current protection, high voltage

protection, short circuit and over

current protections [58]

Windy Nation

P10 [59]

21.99 14.4 11.1/12.5 <5 mA

Float at 13.6V

Equalization at 14.6V

[60]

Steca

Solsum 6.6F [61]

28.95 [62] 13.9 11.2/12.4 <4mA

Over voltage/ over current

protection, monthly maintenance

charge etc..

Boost/ equalization not specified

[63]

CMP12 9.99 [64] 14.4 [64] or 14 10.8 - -

CMTP02 [65] 22 [66] 14.4 10.8/12.6 - -

51

3.2.5 Loads

Two kinds of loads were used for the experiments. For the first set of experiments, where

the CDCPs of the CCs were obtained without simultaneous loading during the charge/

discharge period, the LED strip shown in Figure 3.8 was utilized to discharge the battery.

Fig. 3.8 LED Strips used as load

The strip has 120 LEDs and produces an illumination of around 450 Lumens which is

sufficient to light up a small hall/ kitchen. During the discharge period, it was observed

that the strips consume about 1.29 A of current, corresponding to a C rate of 0.092C. The

name of the manufacturer has not been mentioned on the product or the packaging.

For the second set of experiments, CDCPs were intended to be obtained with

simultaneous loading that means discharging the battery using two different loads (i.e.

LED and a small electronic device) and in charging them through the PV module as the

small electronic device was still connected to the grid. The load produced by the small

electronic device was chosen so as to simulate the same consumption pattern as a

cellphone. This is realistic since one can expect the user to charge a cellphone while the

entire system is charging and keep using it as the batteries are discharging. A

commercially available portable battery pack was used which serves as cell phone battery

equivalent (CBE) and it is shown in Figure 3.9. The storage capacity of this battery pack

52

was rated at 2,200mAh [67], close enough to the capacity of many medium size

smartphones.

Fig. 3.9 Portable battery pack used as cellphone battery equivalent [67]

Two portable CBEs were used during the test, connecting each of them to the system for

six hours for a total time of twelve hours. Both portable chargers were completely

discharged before starting each test so to not have any residual charge which can modify

the energy absorption from one test to another.

Step down bucks were used to charge the above mentioned CBE through an Universal

Serial Bus (USB) port supplying a constant voltage of 5V (Figure 3.10 [68]).

Fig. 3.10 A step down buck used to charge the power bank [68]

53

A step down buck converter is basically a DC-to-DC converter which takes the energy in

output from the CC and transforms it. The current fed through the CC to the step down

buck was acquired also acquired to control its variation over time. At the end of the sixth

hour, once the CBE was fully charged, it was replaced with the other one. The newly

removed CBE was then discharged using a power resistor similar to that shown in Figure

3.11 and kept ready for the next test [69].

Fig. 3.11 CBE discharging power resistor [69]

3.3 Experiment 1: Setup of the CDCP experiment with no CBE

Aim of this experiment is to evaluate how the CCs behave during the charging of LA

battery when no loads are connected to the CC and to evaluate the behavior of the same

device as a LED strip is used for discharging the battery. The schematic of the

experiment, both for the discharging and the charging cycles is presented in Figure 3.12

and 3.13.

54

Fig. 3.12 Schematic of the discharging cycle

Fig. 3.13 Schematic of the charging cycle

55

During the discharging phase, when only the LED strip was connected to the battery

through the CC, the residual voltage of the battery (Vb), the output voltage of the LED

strip (Vl), and the respective current values (Ib and Il) were acquired using the DAQ.

During the charging phase, the voltage of the battery (Vb), the output voltage from the PV

module (Vm), and the respective current values (Ib and Im) were acquired using the DAQ.

CDCPs for 10 devices were obtained, one each for the charging and discharging cycles.

A total of 20 data sets were obtained for the first set of experiments (EXP. 1) and the

collected data helped further analysis.

3.4 Experiment 2: Setup of the CDCP for the simultaneous loading case

The second sets of experiment (EXP. 2) is more complex than EXP. 1 due to the addition

of the Cellphone Battery Equivalent (CBE). Figure 3.14 shows the schematic for EXP. 2

and highlights the six channels of data recorded for this experiment.

During the discharge cycle, a fully charged LA was discharged using the LED strip in

addition to a fully discharged CBE in parallel. The discharge rate in this case was higher

than the previous case. After six hours, the CBE was replaced with another CBE which

had been already been fully discharged using the power resistors depicted in Figure 3.11.

The solar module was not illuminated during the discharging phase.

56

Fig. 3.14 CDCP with contemporary loading

During the charging phase, the module was illuminated using the 1000W lamps while the

CC supplied a portion of this energy to the CBE that was connected in tandem. A total of

20 CDCPs were obtained from EXP. 2.

The setup used for performing EXP. 2 is shown in Figure 3.15 and 3.16. In particular

Figure 3.16 shows a detail of the setup with particular emphasis on the devices used (i.e.

transducers, LA battery, stepdown buck, CBE, bread board on which the voltage dividers

were mounted and the LED strip).

57

Fig. 3.15 Entire experimental setup (1) PV module, 5) Digital multimeter)

Fig. 3.16 Detail of the experimental setup (2) Current to Voltage Transducers, 3) DAQ, 4) Voltage dividers on breadboard, 6) LA Battery, 7) CC, 8) LED strip,

9) CBE, 10) Step down buck)

1

5 See Fig. 3.16 for

enlarged area

7

+

6

3

1

8

9

4 2

58

The lab was maintained at 70-75ºF whenever the experiments were running. This was

done to reduce the impact of the temperature compensation during the charging phase. A

computer was the repository of the data recorded by the DAQ unit. A HP 24V Power

Source (PS) was used for supplying the three transducers connected in series to it.

The entire list of equipment using both tests is given in Table. 3.3. Table. 3.4 shows the

whole set of experiments that were performed. As can be seen, the abbreviations

introduced in Table. 3.1 are utilized.

59

Table 3.3 List of components used

Equipment used Number of

units Experiments utilized

Equipment

utilization phase

Illumination

Arrilite 1000W lamps 2 EXP. 1&2 CH only

Charging source

30W altE poly PV module 1 EXP. 1&2 CH only

Measurement and acquisition

CR Magnetics CR5210-5

current transducer

2 EXP. 1 CH & DIS

3 EXP. 2 CH & DIS

NI USB-6001 DAQ 1 EXP. 1&2 CH & DIS

Voltage dividers 2 EXP. 1 CH & DIS

3 EXP. 2 CH & DIS

Multimeter 1 - -

Storage and control

14Ah AGM LA battery 2 EXP. 1&2 CH & DIS

Charge controllers 10 EXP. 1&2 CH & DIS

Loads

LED strip

(during discharge only) 1 EXP. 1&2 DIS only

Cell Phone Equivalent

(only in the EXP.2) 2 EXP. 2 only CH & DIS

Auxiliary

Stepdown buck 2 EXP. 2 only CH & DIS

HP 24V Power Source

(for transducers) 1 EXP. 1&2 CH & DIS

Bread board

(for mounting voltage dividers) 1 EXP. 1&2 CH & DIS

Legend

EXP. 1 Experiment 1

EXP. 2 Experiment 2

CH Charging cycle

DIS Discharge cycle

60

Table. 3.4 Test matrix

Test

name Test description Morningstar Windynation Steca CMP12 CMTP02

DISCHARGING PHASE

EXP.1

(DIS)

A fully charged battery is gradually depleted till

LVD in supervision of a CC using a LED strip as

the load.

MS01 WN01 ST01 CM01 CT01

MS02 WN02 ST02 CM02 CT02

EXP. 2

(DIS)

A fully charged battery is depleted in supervision

of a CC using a LED strip together with a fully

discharged CBE connected in parallel. CBE

replaced after 6 hours.

MS01 WN01 ST01 CM01 CT01

MS02 WN02 ST02 CM02 CT02

CHARGING PHASE

EXP. 1

(CH)

The charging of a depleted battery (respective

preceding discharge cycle) managed by a CC

while energy is supplied from the illuminated PV

module.

MS01 WN01 ST01 CM01 CT01

MS02 WN02 ST02 CM02 CT02

EXP.2

(CH)

The charging of a depleted battery (respective

preceding discharge cycle) managed by a CC

while energy is supplied from the illuminated PV

module and simultaneously charging a CBE. CBE

replaced after 6 hours.

MS01 WN01 ST01 CM01 CT01

MS02 WN02 ST02 CM02 CT02

61

3.5 Theoretical model to estimate lifecycle cost

A theoretical model of a CDCP was created with the purpose to compare the measured

performances with the ideal behavior of a LA battery. There are many models that have

been used for simulating the characteristic performance of Lead Acid batteries [70]. The

most simplistic model is essentially a voltage source in series with a constant resistance

which represents the internal resistance of the battery. But the assumption of a fixed

internal resistance is major drawback since in reality, the internal resistance varies with

the state of charge and electrolyte concentration (Durr et al. [71]). Another drawback of

the model is the assumption of unlimited battery capacity. Therefore, other models were

developed which give a better picture of the battery’s CDCPs.

One of these is the dynamic battery model; a more complex, realistic, and accurate model

which is widely used to simulate battery behavior. Figure. 3.16 shows the schematic

representation of the dynamic battery model. The elements are modelled non-linearly and

regulated using the battery’s open circuit voltage (Voc), which is indirectly a function of

the State of Charge (SoC).

Fig. 3.17 Dynamic battery model utilized (source: [70])

In particular, the elements shown in the model assume the following meaning:

62

- Cb is the battery capacitance.

- Rp is the self-discharge resistance which takes into account the current small

leakage.

- Ric and Rid are the internal resistances during the charging and discharging

respectively, they account for the losses in the electrolyte as well as the

battery plates.

- C0, Rc0 Rd0 are the components of a branch of the circuit that accommodates

for the voltage drop as soon as the battery is connected to a load as well as

for over potential factors.

The non-linear equation used for the modelling of each of the above mentioned

components is described in equation (3).

𝐵𝐸 = 𝑘 × 𝑒(𝑊×(𝑉𝑚−𝑉𝑜𝑐))𝑓𝑓 (3)

BE represents each of the battery elements shown in Figure 3.17 (i.e. Cb, Rp, Ric, et.), while

k represents the gain factor, W the width factor, Vm the mean voltage, VOC the open

circuit voltage, and ff the flatness factor. The characteristic values for k, W, and ff are

taken from the theory and are different for each of the elements considered and

depending on the charging/discharging phases also. The flatness factor is assumed equal

to 2 for the purpose of this model. These constants have been derived from a work made

by Casacca [49, 72] and can be found tabulated there. Vm for this kind of battery is taken

as 12.4 V. A MATLAB model was created for the purpose of obtaining theoretical

CDCPs.

63

IV. RESULTS AND DISCUSSIONS

4.1 Overview

The CDCPs of the two experimental tests are presented as well as the LCC calculation

for each of the CCs. From the experimental data it was found that the CCs possessed

some variability. Some of them included boost or floating in the charging phasing while

others totally circumvented these stages. Individual plots for the currents and voltages are

also presented. Finally, a list of important characteristics is made and then discussed to

gain a better understanding of the collected data.

Prior to beginning of the comparisons, a brief description of some of the desired

characteristics is presented here and those features will be used for evaluating the

performances of the CCs later in this chapter. It should be noted that sometimes general

guidelines and recommended trends are given in those cases where specific values are not

available. This is because the Universal Standards and Lighting Global SHS standard do

not mention specifics for flooded AGM batteries, though these standards provide

adequate information for the set-points of other types of batteries.

LVD: As described in Chapter 2, the Low Voltage Disconnect is the value at

which the CC cuts off the power supply from the battery to the loads. This set-

point must not be too low as lower value results in excessive discharge and

64

therefore in a shorter battery life. Also, lower the LVD is, the longer it takes to

fully charge the battery assuming a completely discharged unit. It is

recommended by Lighting Global SHS Kit guidelines to set the deep discharge

disconnect at 1.87 V/cell for a flooded LA battery, which corresponds to 11.22 V

for the six cell 12 V batteries used in this work [35].

Discharge time: It is the amount of time the battery can supply a load at a

specified C-rate. In the case of two CCs of the same kind (e.g. brand, model, type,

etc.), this value must be similar. Similar values of discharge time are an indication

of repeatability and a feature attesting good performance for a given CC type.

Self-consumption: This parameter represents the difference between the energy

supplied and the energy diverged to the battery. If too much power supplied to or

from the battery is wasted, the overall system efficiency is reduced. The value of

this parameter should be kept as low as possible for overall efficient operations.

Charge factor: It is the ratio between the energy supplied to the battery and that

depleted during the discharge phase. The charge factor needs to be at least

between 1 and 1.05 for SHS [24].

Reverse current protection: All CCs must compulsorily provide protection for

the back flow of power from the battery into the PV module [24].

Conformity to set-points: For commercially available CCs the measured set-

points must be within 1% of the manufacturer specified values [24] for assuring a

good quality and accurate cycling.

65

Charging limit voltages: It a region defined by the following parameters: boost

voltage (2.4 V), VR (2.35 V) and VRR (2.20 V) [39].

4.2 Results: EXP. 1

The procedure and details of the setup for this experiment is presented in Section 3.3.

The CDCPs for all the devices are presented in the same graph for an easier comparison

of their performances, while individual CDCPs for each of the CCs used during the first

set of experiments (EXP. 1) are presented in Appendix 1. The current and voltage CDCP

is shown in Figures 4.1 and Figure 4.2, respectively. The first device of each kind has

been represented using a solid line of a particular color, while the CDCPs for the second

devices of the same kind has been represented using dotted lines of the same color. It

should be also pointed out that the first twelve hours of measurements refer to the

discharging cycle, while the following twelve hours correspond to the charging cycle.

It should be noted that, the obtained CDCPs for all the ten devices showed slightly

different starting voltages (in the order of ±0.2 V). It could imply different charging level

or capacity of the battery at the beginning of the test. Since the discharging profile of

each devices has been shown to be linear, it was possible to interpolate the curves to

obtain a common starting point of approximately 12.9 V. This would also give a more

realistic value for the discharge time, so that the batteries could be depleted to the same

level.

66

As can be seen in Figure. 4.3, the measured power are similar to the current curves. In all

of the devices, during charging the power curves have some variation. The most

significant variation is observed in the CT02 device which accumulates a lot of energy

during the topping/regulation phase. In most cases, the batteries are to be charged close to

80% SoC by the end of the CCC region. Surely, the power absorption of the CT01 is

lower than WN02 or MS01 during the bulk charging phase. It is possible that the device

compensates for that during the topping phase. The battery is also over charged by the

device and it is apparent in referring Table 4.1 since the CT01 device has the highest

charge factor meaning that it over charges the battery the most compared to other CCs.

67

Fig. 4.1 CDCP of the battery currents for the ten devices for EXP.1

0.0

0.4

0.8

1.2

1.6

2.0

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Cu

rre

nt

in A

Time in hours

CM01 CM02 CT01 CT02 ST01 ST02 MS01 MS02 WN01 WN02

12 HOUR DISCHARGING PHASE 12 HOUR CHARGING PHASE

68

Fig. 4.2 CDCP of the battery voltages for the ten devices for EXP.1

10.0

11.0

12.0

13.0

14.0

15.0

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Vo

ltag

e in

V

Time in hours

CM01 CM02 CT01 CT02 ST01 ST02 MS01 MS02 WN01 WN02

12 HOUR DISCHARGING PHASE 12 HOUR CHARGING PHASE

69

Fig. 4.3 CDCP of the power for the ten devices for EXP.1

0.000

5.000

10.000

15.000

20.000

25.000

30.000

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Po

we

r in

W

Time in hours

CM01 CM02 CT01 CT02 ST01 ST02 MS01 MS02 WN01 WN02

12 HOUR DISCHARGING PHASE 12 HOUR CHARGING PHASE

70

In Figure. 4.1, the point where the current curves drop to zero is the point at which the

discharge ends. Immediately before the battery reaches this point, the CC starts

monitoring the voltage, and as soon as it is reaching the LVD set-point it shuts off the

load ending the discharging phase. Though discharging is a much simpler process

compared to charging, it can be clearly noted that there is a disparity of performances

between the devices of the same type (i.e. same color curves) as well as between CC of

different manufactures. The discharge times varied as much as nearly four hours

depending on the CC used.

From the analysis of the charging phase, it can be observed that several differences exist

between the considered CCs. One dissimilarity is the different behavior as the full-charge

state is reached. Some devices exhibited both a float charging stage and boost stage while

other devices have only one stage. This is of particular concern, since these stages are the

stages where electrochemical, thermal losses and self-discharging are accounted for.

Therefore, missing one or more of these stages may compromise the LCC of the battery.

From a more accurate analysis of the data presented in the Figures 4.1 and 4.2, it is

possible to observe that the Steca devices ST01 and ST02 (represented by the green

curves) show clearly different discharge time of 8.35 and 7.81 hours respectively. The

starting voltages were 13.02 and 12.93 V respectively, which probably is the reason for

the discharge time disparity. The LVD points were measured at 11.57 and 11.83 V which

are higher than the 11.1 V reported in the data sheet. Despite the initial SoC disparity, the

CC is nonetheless expected to cut off supply to the load exactly at the LVD point. Hence,

conformity to set-points is lacking and the cycle is shut off nearly 0.6 V before the

stipulated value. The charging profiles were quite smooth but just as in the discharging

71

profiles, there was a clear difference in the behavior of the two devices in the last stages

of the charging cycle. As seen is Figure 4.2, the float charging of the two devices were at

13.65 V and 14.08 V respectively. Despite these drawbacks, the Steca CCs manage to

have reasonably good charge factors. The self-consumption during the bulk charging

phase was noticed to be around 6.5 times greater than that allowed by the datasheet. This

characteristic seems very high and it is an undesirable factor in SHLS applications.

The Morningstar products (represented by the beige curves in Figures 4.1 and 4.2) have

the closest discharge times for both the units, hence the most predictable performance

among all the CCs when it comes to discharging. The charging profiles of MS01 and

MS02 were also observed to be very similar to each other, which is the ideal behavior of

these CCs. The performance of these devices even conform to the set-points stipulated in

the manufacturer’s data sheet. However, the self-consumption can be as much as double

to what is specified during the charging phase. Charge factor, was also calculated to be

sufficient as can be observed from data summarized in Table 4.1. Apart from the high

self-consumption, the Morningstar products seem to perform optimally and being a good

fit for SHLSs.

CM devices (the blue curves in Figures 4.1 and 4.2) were the cheapest ones among those

chosen for performing this research. Detailed specifications were not provided by the

manufacturer. The Lighting Global regulations among others, require clear and detailed

labelling of the performance set-points. CM and CT devices have the lowest theoretical

LVD set-point fixed at 10.8 V. During the tests performed the measured LVDs for the

CM01 and CM02 have been calculated equal to 11.28 V and 10.78 V. The large disparity

in the found values could be due to variations in manufacturing or because a device was

72

not working properly, but since the tests have been performed considering two units only,

no particular conclusions on the quality of the CC can be done. Nevertheless, a very low

pre-determined LVD point may have an impact on the battery life as described in the

previous sections. Also, the power wastage during charging phases was highest among

these devices.

The most diverse comparative performance in the charging phase was exhibited by the

Windynation devices (black curves in Figures 4.1 and 4.2). These devices had a disparity

of discharging times of nearly one hour and half. Most interesting was that, even if the

specification mentions a boost charge value for the battery of 14.4 V, there is no evidence

of boost charging in the profiles of WN01 and WN02. The boost charge is maintained for

nearly 30 minutes at values below 14 V, and after that is kept at float charge until the end

of the cycle. In addition to this flaw, both the devices did not charge at the stipulated float

voltage of 13.6 V. Floating was clearly noticed being around 13.12 V and 12.97 V for the

two devices being tested. Furthermore, the charge factor was calculated below 1 meaning

that the battery would expel more energy during the discharging phase than it replenishes

during the charging phase. As it easy to imagine, this behavior cannot be sustainable

since each charge/discharge cycle further depletes the residual capacity of the battery

making it useless in a very short time. The reason for this behavior can be found

analyzing the current profile plotted in Figure 4.1. Here after a stationary phase in which

the current is kept constant (i.e. between 1.6 A and 1.7 A), the CC drastically drops that

value to zero, without any transitory period as observed for the other devices. Indeed, in

other devices, a tapering of the charging current is clearly noticed.

73

The CT devices (represented by the red curves in Figures 4.1 and 4.2) are the second

cheapest devices. Though the plots of CT01 and CT02 do not seem to be very dissimilar,

the two devices are characterized by a 16% difference in the value of the charging factor.

These devices are characterized by the longest discharge duration among all the CCs

analyzed, and by the highest value of regulation charge (nearly 14.6 V), but no float

charge period. Furthermore, despite the same LVD values for the CT and CM devices, it

is observed that the CT devices discharge for longer time compared to the CM charge

controllers even if the discharge load is exactly the same. This could be due to a

miscalculation of the voltage or to the absence of a low current disconnection protection

circuit, which does not shut the load completely off and permits to the load to still use

portion of the energy stored in the battery.

Except for Windynation, Steca and Morningstar devices, the other devices had no

mention of conforming to any recognized performance/component certification

requirements or mention the presence of reverse current protection. The cheaper CM and

CT devices did not specify any protective measures inbuilt into the CC. The self-

consumption values for these two devices were also mentioned.

To finish, Table. 4.1 summarizes some of the important findings from EXP. 1. Data

presented in brackets are those provided by the manufacture datasheets and manuals and

are reported as reference values. As observed from an analysis of the data summarized,

only MS02 and CT01 conform to the ±1% of the specified boost, VR and VRR voltages

specified by Usher et al. [39].

74

Table 4.1 Comparison of the features for the different CCs for EXP. 1

Parameter

CM CT Steca Morningstar Windynation

CM01 CM02 CT01 CT02 ST01 ST02 MS01 MS02 WN01 WN02

LVD

relevance (V) 11.28(10.8) 10.78(10.8) 10.94(10.8) 10.9(10.8) 11.57(11.1) 11.83(11.1) 11.46(11.5) 11.39(11.5) 10.92(11.1) 10.72(11.1)

Discharge

time

validation

(hours)

9.61 9.90 12.00 11.27 8.35 7.81 8.75 8.583 10.20 11.65

Regulation

point (V) 14.55(14.4) 14.29(14.4) 14.47(14.4) 14.68(14.4) 14.20(14.4) 14.61(14.4) 14.13(14.3) 14.14(14.3) - -

Floating point

(V) - - - - 13.65(13.9) 14.08(13.9) 13.88(-) 13.80(-) 13.12(-) 12.97(-)

Power

wastage (W)

DIS 0.098

CH 0.400

DIS 0.084

CH 0.379

DIS 0.064

CH 0.39

DIS 0.030

CH 0.465

DIS 0.090

CH 0.220

DIS 0.170

CH 0.267

DIS 0.195

CH 0.267

DIS 0.207

CH 0.287

DIS 0.034

CH 0.144

DIS 0.033

CH 0.075

Time for bulk/

total charging

(hours)

6.60/12 6.79/12 6.45/12 7.06/12 5.50/12 4.67/12 4.29/12 4.34/12 5.25/5.25 5.75/5.75

Charge factor 1.19 1.22 1.01 1.16 1.06 1.03 1.10 1.14 0.8 0.75

Self-

consumption

(mA)

DIS 2.5(-)

CH 8.1(-)

DIS 2.1(-)

CH 8.0(-)

DIS 2.0(-)

CH 3.8(-)

DIS 3.8(-)

CH 3.4(-)

DIS11.3(4)

CH 27.5(4)

DIS 7.5(4)

CH 11.4(4)

DIS 7.6(8)

CH 16.1(8)

DIS11.5(8)

CH 17.9(8)

DIS 3.3(5)

CH 4.1(5)

DIS 3.2(5)

CH 4.4(5)

Certifications - - - - CE CE, World Bank - -

75

4.3 Results: EXP. 2

In this set of experiments, the behavior of the different CCs has been studied as multiple

loads were connected simultaneously to the system above described. During the charging

phase, a Cellphone Battery Equivalent (CBE) was connected. During the discharging

phase, the CBE was connected to the load side of the circuit in addition to the LED strip.

A complete description of the experiment set up is discussed in the Section 3.4 of this

thesis.

The CDCPs recorded for five different devices during the second experiment (EXP. 2)

are shown in Figures 4.4 and Figure 4.5, where the recorded current and voltage values

are plotted against the time. The individual CDCP curves are not shown here for the sake

of brevity and are attached in the Appendix 2.

The CDCPs are much more smoother and behave as expected compared to the previous

EXP. 1. The first 6 hours of the discharging phase the nature of the curve is close to the

discharging profile of the Lithium battery which the CBEs are made of. In other words,

the increased slope of the curve between hours 5 and 6 is attributed to the CBEs being

fully charged. In this case, the CCs cut off the power around the same time. The

discharge time is exactly a function of the LVD and the initial SoC. In EXP. 2 all the

devices were charged to exactly the same level. On the contrary, in EXP. 1 the

discharging continued for longer than expected in some devices, probably due to the

tapering current of the LED strip which served as the load. This could demonstrate that

some cheap CCs might not have any provision for controlling a small continuously

reducing current. This hypothesis is also confirmed in the datasheets, which do not

76

mention the presence of over-discharge current protection. Protection of discharge using

voltage measurement is common in all devices, but the same protection unit may consider

this reducing current as a parasitic load, small enough to be ignored. For example, even

after the LVD point is reached, the LED battery level indicators embedded in the CC

keep consuming current. The CC does not cut off this consumption even if the SoC value

has overcome the LVD point. In contrast, EXP. 2 shows that a sudden increase in current

is registered clearly by the CC’s control unit when the CBE is replaced at the sixth hour

mark of the discharging phase since it was part of the experiment design. The CBE that

replaces the current one at the 6 hour mark is fully discharged and can charge at higher

rates; this is the reason for the sudden increase in current. The voltage decrease becomes

steeper if compared to the previous portion of the discharging curve since the CBE is

completely discharged and consumes energy more rapidly. Also, it is observed that the

CCs cut off the loads at the stipulated LVDs and that these values are very similar to

those measured in the first experiment.

Similar to what observed in the data measured during EXP. 1 for the Windynation

devices, the charging phase ends abruptly as soon as bulk charging is completed. The

same behavior highlighted in Figure 4.1 can be observed in Figure 4.4. Indeed, the

duration of the discharging phase in EXP. 1 was longer than the duration of the discharge

phase in EXP.2. Other consideration that can be made from analyses of the data plotted

is that the regulation and float voltages of the Windynation device are much lower than

those of other CCs. More investigation needs to be done in order to understand if this is a

systemic problem inherent to all Windynation devices.

77

Steca and Morningstar devices seem to cut off the load prematurely compared to the

other CCs. This is an important positive characteristic, which benefits the user in the form

extended battery life. On the other hand, the voltage fluctuations experienced by the

Morningstar CC during the final portion of the charging cycle are significant, and they

may not be beneficial to the modules.

Another issue observed was the supplying of load when charging is ongoing. Most

devices do not cut off the load when the module was illuminated. Some manufactures

program their CC devices to not cater to any loads when the LA battery is being charged.

This is favorable since all the energy supplied from the PV module goes into the LA

battery without a faction of input energy diverted to other loads. This way, charging of

the depleted LA battery is faster and complete. The Windynation device, as mentioned in

the manual, is not supposed to supply loads while the LA battery is being charged but this

was not observed in practice. On the other hand, the Morningstar device does not supply

any loads while the LA battery is being charged.

To finish, Table. 4.2 summarizes some of the important findings from EXP. 2. As in the

previous case, data in brackets are those provided by the manufacture datasheets and

manuals and are reported as reference values.

Figure 4.6 summarizes the change of power for the devices in EXP. 2. The behavior of

the Windynation device can be better understood, at around the 19.5 hour mark power

drops down to zero. Hence, the power is not input to the battery long enough. The power

follows the pattern very close to that of the currents. Also the sudden power surge during

the first half hour of discharge is not clearly understood.

78

Fig. 4.4 CDCP of the battery currents for the five devices for EXP.2

0

0.4

0.8

1.2

1.6

2

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Cu

rre

nt

in A

Time in hours

CM CT Steca Morningstar Windynation

12 HOUR DISCHARGING PHASE 12 HOUR CHARGING PHASE

79

Fig. 4.5 CDCP of the battery voltages for the five devices for EXP.2

10

11

12

13

14

15

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Vo

ltag

e in

V

Time in hours

CM Morningstar Windynation Steca CT

12 HOUR DISCHARGING PHASE 12 HOUR CHARGING PHASE

80

Fig. 4.6 CDCP of the powers for the five devices for EXP.2

0

5

10

15

20

25

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Po

we

r in

W

Time in hours

CM01 MS01 WN03 ST01 CT01

12 HOUR DISCHARGING PHASE 12 HOUR CHARGING PHASE

81

Table 4.2 comparison of the features for the different CCs for EXP. 2

Parameter CM01 CT01 ST01 MS01 WN01

LVD relevance (V) 10.77(10.8) 10.94(10.8) 11.47(11.1) 11.41(11.5) 10.91(11.1)

Discharge time validation (hours) 8.28 8.36 6.38 6.94 8.63

Regulation point (V) 14.55(14.4) 14.39(14.4) 14.00(14.4) 13.89(14.3) -

Floating point (V) - - 13.45/13.9 13.67 13.10

Power wastage (W)

DIS 0.435

CH 0.517

DIS 0.436

CH 0.660

DIS 0.502

CH 0.357

DIS 0.307

CH 1.012

DIS 0.3892

CH 0.253

Time for bulk/ total charging (hours) 5.95/12 5.94/12 5.48/12 4.67/12 7.07/7.07

Charge factor 1.17 1.11 1.12 1.10 0.94

Self-consumption (mA)

DIS 46 (-)

CH 8.3 (-)

DIS 48 (-)

CH 20 (-)

DIS 52 (4)

CH 12.81 (4)

DIS 42 (8)

CH 31 (8)

DIS 46 (5)

CH 4.5 (5)

82

4.4 Calculation of LCC using theoretical battery model

Using the theoretical exponential model described by equation (3) an ideal curve has

been computed and it is presented in Figure 4.7. The code used to generate the simulation

is presented in Appendix 3.

Once a theoretical model has been obtained, it becomes easier to compare the

performances of the CDCP evaluated from the experimental data to those evaluated

analytically. This was done by calculating the Relative Error (δ) between the theoretical

curve and the CC of interest. Equation 4 shows the equation used for evaluating the

Relative Error value used for this analysis.

𝛿 =1

𝑛∑ (|

𝑉1,𝑖−𝑉2,𝑖

𝑉1,𝑖| × 100)𝑛

𝑖=1 (4)

Where, V1, i is the generic theoretical value at time equal ti, V2, i the value of the

experimental set of data at the same time ti, normalized to the theoretical value.

The starting point of the theoretical CDCP was set at ~13.0 V which was close to the

point where the Werker battery charger stopped charging the battery. A LVD value of

~11.2 V was used as ending point for the discharge phase as previously mentioned at the

beginning of this chapter. The bulk charging phase was started at 12 V as soon as the 12

hour mark was reached, at this point the module is illuminated and produces constant

current of 1.6 A. The bulk charging phase was continued till 80% of the battery capacity

was reached (i.e SoC 80%). From this point on, the battery current is regulated and the

current curve starts to taper. The regulation stage continues until the SoC is 100%.

83

Regulation stage was maintained at 14.11 V [39], while floating was continued at 13.5 V

until the end of the charging phase [39].

Table 4.3 provides the evaluation of the performances of the different devices analyzed in

this study when a comparison with the theoretical values is performed. The data is taken

for EXP.1.

Table 4.3 LCC calculation for the different devices

CC Device

Relative Error

factor

(%)

DoD from

experiments

(%)

Number of

theoretical

cycles

Number of

replacements in

5 years

Total

LCC

(USD)

CM01 2.21 79.1 250 7.3 447

CM02 1.60 79.1 250 7.3 447

CT01 1.74 96 208 8.7 544

CT02 1.56 91 222 8.22 515

ST01 3.61 73 273 6.68 429

ST02 2.80 71 281 6.49 418

MS01 1.33 76 263 6.93 450

MS02 1.38 73 273 6.68 435

WM01 2.38 85 235 7.76 487

WN02 2.52 94 212 8.60 538

As can be observed the data reported, the theoretical curve and the experimental data are

in a good agreement. The relative error is always below 3%, with the only exception of

the ST01 device which records an error of 3.61%. The value of the DoD presented in the

Table 4.3 has been evaluated considering both the maximum power the battery is capable

to provide and the actual power used by the system during discharge. In particular, for

84

each device knowing the values of voltage and current in time it is possible to calculate

the overall energy consumed during the whole discharge phase as:

𝐸 = ∑𝑉𝑖×𝐼𝑖×𝑡𝑖

3600

𝑛𝑖=1 𝑊ℎ (5)

where the Vi and Ii are the values of voltage and current at the generic time ti, τ is the

time interval between two consecutive samples (i.e. sampling rate) and is equal to 30

seconds, while 3600 is a coefficient used for obtaining the result in Wh. On the other

hand, the maximum energy available from the battery can be evaluated using Equation

(6):

𝐸𝑏 = 𝐶𝑏 × 𝑉𝑛𝑜𝑚 𝑊ℎ (6)

where Cb is the battery capacity in Ah and Vnom the rated battery voltage equal to 12V.

For the battery used in this study, the energy was equal to 168 Wh. Therefore, the DoD of

the battery during the performed test can be evaluated as:

𝐷𝑜𝐷 = 𝐸

𝐸𝑏× 100 (7)

85

Fig. 4.7 Theoretical CDCP for the LA AGM battery

0

0.4

0.8

1.2

1.6

10

10.5

11

11.5

12

12.5

13

13.5

14

14.5

15

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Cu

rre

nt

in A

Vo

ltag

e in

V

Time in hours

Voltage Current

Discharge Bulk charging Regulation Idle time

86

Using the relative error value evaluated for each of the CC considered, and the theoretical

number of life cycle of the battery, it was possible to estimate the number of times the

battery needs to be changed during the operational life time of the SHLS operated using

the analyzed CCs. In particular, for a given DoD, the maximum number of cycle a battery

can withstand has been summarized in Table 4.4.

Table 4.4 Relation between DoD and life cycle till failure [73]

Depth of Discharge

(% of rated capacity) No. of cycles to end of life

10 2000

30 400

50 400

80 250

100 200

Most of the components of a SHLS are guaranteed for at least 5 years, therefore the cost

analysis performed in this research has been evaluated on that time span. It should be

pointed out that the batteries wear out much sooner and therefore, become the major

factor in the system cost. Though, the cost of the CC devices is not very dissimilar, the

LCC is more important. Most design projects generally give more emphasis to the initial

cost of the device rather than the cost of using that device for 5 years.

In this simulation, the cost of a battery is assumed to be $60 each. The cost reduction due

to purchase in large quantities, and the location variable costs are not accounted for.

Using the values summarized in Table 4.6 and the relative error value δ, one can estimate

87

the LCC of the battery for an entire operating range of 5 years. It is assumed that a 24

hour period comprises of discharging and charging each of 12 hours.

As can be seen from Table 4.3, though the numbers of cycles for different CCs are quite

different, the overall system cost for 5 years is not hugely different. These LCCs seem

very high. It is because of the high battery cost considered and also may be due to the

inaccuracy of the lifecycle values obtained. The reference [73] is for SLI (automobile)

battery since the equivalent for deep cycle batteries could not be found. Since the the SLI

batteries are not very compatible with deep cycling, the number of serviceable lifecycle is

lower than that of the deep cycle batteries. Further, it can be surely said that using

batteries capable of lower DoDs such as automobile batteries will drastically lower the

life time of the battery.

It is also important to mention that the DoD has a much larger effect on the battery life

than the non-conformity to ideal performance.

88

V. CONCLUSION AND FUTURE WORK

This work aims to determine the performances of several commercially available Charge

Controllers (CCs) which can be used within a Solar Home Lighting System (SHLS) in

developing countries. A number of experimental evaluations have been performed to

achieve this goal. Two different setups have been considered to simulate the discharge

and charging cycles that can be expected in real-life situations. In the first one (EXP.1)

only a load in the form of a LED strip has been used during the discharging phase, while

in the second experiment (EXP.2) a Cellphone Battery Equivalent (CBE) has been used

in addition to the LED load to simulate a scenario in which an end user is both charging a

cellphone while using the LED for task lighting. During the charging phase, a

photovoltaic (PV) module has been used for supplying input current to the exhausted

battery.

In EXP. 1, it can be seen that the discharge times varied for all the different devices

analyzed. The reason for this was due to the difference of Low Voltage Disconnect

(LVD) set-points among the devices. Some devices such as the CT (01 & 02) and the CM

(01 & 02) ones did not showcase float charging stages. However, it needs to be seen how

the profile will change upon extending the duration of the charging phase. Another

feature observed among most devices was the lack of adherence to the manufacture

specified voltage set-points.

89

Windynation (WN) devices were not recharging enough to compensate for the energy

lost during discharge. To better understand the behavior of the Windynation devices, the

CDCPs can be obtained using different kinds of changes to the test rigs to find out if the

device reacted negatively to the circuitry used for testing. Morningstar (MS) devices

behaved quite predictably. In Steca (ST) devices, a slight error in charging the batteries

up to the same initial level was noticed. An important future study may consist of

estimating the voltage measurement of the different devices. There may have been small

differences in recognizing the voltage as was observed while taking periodic manual

measurements.

Though there were dissimilarities in profiles of voltages and currents during EXP. 2, it

should be noted that the profiles were more predictable and smoother compared to EXP.

1. The LVDs were close to each other and not as far from the manufacturer specification

as was seen in EXP. 1. Though the exact reason for this was not understood, the reason

argued here is due to the increased response to larger currents. In most practical

discharging cycles, the current is constant. But that is not the same in the case of this

Thesis. So, the devices may work perfectly with constant current, which is also to be

ascertained. The variation of current during discharge may be as prevalent as variation of

charging current in the field since the irradiation is constantly varying. It is not certain

how well the constant discharging and charging assumption used while modeling the

batteries fits into practical situations. In the lab, constant illumination was provided

using the 1000 W lamps, but it will not be possible in the field. Another important study

for the future would be testing the responsiveness of currents among the different

devices.

90

The Windynation still behaved in a similar way in EXP. 2 as in EXP. 1. More theoretical

research into the behavior of the CCs, especially the Windynation devices needs to be

taken. The devices can be stripped down and thus, the visualized circuit can be compared

with measured performance. Self-consumption was rather high in most of the devices

during EXP. 2. Since the system in EXP. 2 is more complex owing to more components

and wiring, the losses may be also due to that.

A field testing of all the devices needs to be conducted at a later scale. Field testing helps

to better understand real life behavior. All experiments were conducted in controlled

environment and the performance will be different due to varying temperatures and

currents from the module.

In this Thesis, the batteries were assumed to be working without reduction in capacity,

despite these batteries having been used for at least 6-7 months on various experiments.

Previously, power sources were also connected into the system to simulate input from

module. It is not certain how much damage to the battery has occurred due to this.

The results of the simulation were also surprising since the life cycle costs for even the

best devices were so high (nearly $400). $100 difference between the best and worst

performing devices can be considered quite significant, especially for the families with

low household income. More research needs to be done to understand the effect of

charging/discharging conditions in a SHLS unit will have on the battery life. Another

important finding was that the relative errors were not very high, implying that the

difference between the ideal and actual performance of the CC were not dissimilar.

91

Finally, the theoretical model presented here can be made using more detailed and

complex models and studying the batteries to measure parameters such as width factor.

Temperature compensation also needs to be considered for increased accuracy purposes.

92

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96

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https://energypedia.info/wiki/Charge_Controllers#Shunt_Controller_Designs

41. Charge Controller Profiles, atperesources.com, 2010,

http://www.atperesources.com/old/PVS_Resources/PDF/ChargeControllerProfiles

.pdf

42. Comparison test between MPPT and PWM charger for solar generation, IZUMI

Corporation, 2011, http://www.schams-

solar.de/download/DESCRIPTION/comparison-mppt-pwm.pdf

43. IV curve, Solar Cells Explained, http://thesolarized.blogspot.com/2011/12/solar-

cells-panel-explained.html

44. ‘BU-402: What Is C-rate?’, Battery University,

http://batteryuniversity.com/learn/article/what_is_the_c_rate

45. ‘BU-804b: Sulphation and How to Prevent it’, Battery University,

http://batteryuniversity.com/learn/article/sulfation_and_how_to_prevent_it

46. ‘mAh Battery Life Calculator’, http://ncalculators.com/electrical/battery-life-

calculator.htm

47. ‘US Battery Charging Recommendations’, US Battery Manufacturing Company,

http://www.trojanbattery.com/pdf/U.S.%20Battery%20Charge%20Profile%20Ful

l%20%2011-12-13.pdf

48. ‘BU-403: Charging Lead Acid’, Battery University,

http://batteryuniversity.com/learn/article/charging_the_lead_acid_battery

49. Casacca, M.A, ‘Mathematical modelling of a Lead Acid Battery’, University of

Lowell, 1989

97

50. Werker Battery Charger, https://www.batteriesplus.com/charger/specialty-lead-

acid-battery/werker/slawk12v1000

51. 30W PV Module Specification sheet,

https://www.altestore.com/static/datafiles/Others/ALT30-12P_alte-solar-modules-

spec-sheet.pdf

52. 30W PV module, Alt-e-Store website, https://www.altestore.com/store/solar-

panels/alte-poly-30-watt-12v-solar-panel-p10350/

53. CR Magnetics CR5210-5 picture, http://www.crmagnetics.com/dc-current-

transducers/cr5210

54. National Instruments USB-6001 DAQ device,

http://sine.ni.com/nips/cds/view/p/lang/en/nid/212383

55. Duracell 14Ah AGM Battery Specifications,

https://www.batteriesplus.com/productdetails/wkdc12=14f2

56. Morningstar SHS-6 picture, http://www.morningstarcorp.com/products/shs/

57. Morningstar SHS-6 cost, http://www.ebay.com/itm/Morningstar-SHS6-6-Amp-

12-Volt-Solar-Charge-Controller-w-LVD-

/261734980687?hash=item3cf09edc4f:g:JpIAAOSw2s1Uts5g

58. Morningstar SHS-6 specification sheet, http://www.morningstarcorp.com/wp-

content/uploads/2014/02/SHS_ENG_R2_1_12lowres.pdf

59. Windynation P10 picture and cost, http://www.windynation.com/Charge-

Controllers/10A-P10-Solar-Panel-Charge-Controller-Regulator/-

/180?p=YzE9MTc

98

60. Windynation P10 specification sheet,

http://www.windynation.com/cm/10A_30A%20Controller%20Manual_R2%20JN

A.pdf

61. Steca Solsum 6.6F picture, http://www.conrad.com/ce/en/product/110678/Solar-

charge-controller-12-V-24-V-6-A-Steca-Steca-Solsum-66-F

62. Steca Solsum 6.6F cost, https://www.altestore.com/store/charge-controllers/solar-

charge-controllers/pwm-solar-charge-controllers/steca-solar-charge-controllers-

pwm/solsum-66f-6a-1224v-charge-controller-p7878/

63. Steca Solsum 6.6F specifications, http://www.steca.com/index.php?Steca-

Solsum-F-en

64. CMP12 charge controller cost, picture and specifications,

https://www.amazon.com/Controller-Charge-Battery-Regulator-

Protection/dp/B010FNO9NU/ref=sr_1_6?s=lawn-

garden&ie=UTF8&qid=1465724646&sr=1-

6&keywords=CHARGE+CONTROLLER

65. CMPT02 charge controller picture, http://diyprojects.eu/wp-

content/uploads/2014/08/CMTP02-30A-solar-charger-controller-top-view-2.jpg

66. CMPT02 charge controller cost, http://www.ebay.com/itm/10A-AMP-PV-Solar-

Charge-Controller-PWM-For-12V-Volt-Solar-Panel-Battery-RV-Boat-

/200970614849?hash=item2ecac83841

99

67. Portable charger – cellphone battery equivalent,

https://www.radioshack.com/products/radioshack-2200mah-lipstick-portable-

power-bank-red?variant=5717129349

68. Step down buck, https://www.amazon.com/Converter-Voltage-Regulator-

Regulated-

Voltmeter/dp/B00MZOJR8A/ref=sr_1_7?ie=UTF8&qid=1465734513&sr=8-

7&keywords=step+down+buck

69. Power resistor pictures and specifications, https://www.amazon.com/Yeeco-

Discharge-Monitoring-Detection-

Resistor/dp/B016KDWBYI/ref=sr_1_sc_3?ie=UTF8&qid=1465734869&sr=8-3-

spell&keywords=discharger+ressitor

70. Ceraolo, M., 2000, ‘New Dynamical Models of Lead Acid Batteries’, IEEE

Transactions on Power Systems, 15 (4)

71. Durr, M., Cruden, A., Gair, S. & McDonald, J. R., 2005, ‘Dynamic Model of a

Lead Acid Battery for Use in a Domestic Fuel Cell System’, Journal of Power

Sources, 161 (4), pp. 1400-1411

72. Salameh, Z. M., Casacca, M. & Lynch, W. A., 1992, ‘A Mathematical Model for

Lead-Acid Batteries’, IEEE Transactions on Energy Conversions, 7 (1)

73. Bartley, F. G., 2001, ‘The Avionics Handbook’, CRC Press,

http://www.davi.ws/avionics/TheAvionicsHandbook_Cap_10.pdf

100

APPENDIX

APPENDIX. 1

A 1.1 CDCP of CMO1 (EXP. 1)

0.0

0.4

0.8

1.2

1.6

10

11

12

13

14

15

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Cu

rre

nt

in A

Vo

ltag

e in

V

Time in hours

Voltage Battery LVD LVR RP Current Battery

VCD DIT CVC CCC

101

A 1.2 CDCP of CMO2 (EXP. 1)

A 1.3 CDCP of CTO1 (EXP. 1)

0.0

0.4

0.8

1.2

1.6

10

11

12

13

14

15

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Cu

rre

nt

in A

Vo

ltag

e i

n V

Time in hours

Voltage Battery LVD LVR RP Current Battery

VCD DIT CVC CCC

0.0

0.4

0.8

1.2

1.6

10

11

12

13

14

15

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Cu

rre

nt

in A

Vo

ltag

e i

n V

Time in hours

Voltage Battery LVD LVR RP Current Battery

VCD CVC CCC

102

A 1.4 CDCP of CTO2 (EXP. 1)

A 1.5 CDCP of STO1 (EXP. 1)

0.0

0.4

0.8

1.2

1.6

10

11

12

13

14

15

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Cu

rre

nt

in A

Vo

ltag

e i

n V

Time in hours

Voltage Battery LVD LVR RP Current Battery

VCD DIT CVC CCC

0.0

0.4

0.8

1.2

1.6

10

11

12

13

14

15

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Cu

rre

nt

in A

Vo

ltag

e i

n V

Time in hours

Voltage Battery LVD LVR RP Current Battery

VCD DIT CIT CCC CVC

103

A 1.6 CDCP of STO2 (EXP. 1)

A 1.7 CDCP of MS01 (EXP. 1)

0.0

0.4

0.8

1.2

1.6

2.0

10

11

12

13

14

15

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Cu

rre

nt

in A

Vo

ltag

e i

n V

Time in hours

Voltage Battery LVD LVR RP Current Battery

VCD DIT CIT CCC

CVC

0.0

0.4

0.8

1.2

1.6

10

11

12

13

14

15

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Cu

rre

nt

in A

Vo

ltag

e i

n V

Time in hours

Voltage Battery LVD LVR RP Current Battery

VCD DIT CVC

CCC CIT

104

A 1.8 CDCP of MS02 (EXP. 1)

A 1.9 CDCP of WN01 (EXP. 1)

0.0

0.4

0.8

1.2

1.6

10

11

12

13

14

15

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Cu

rre

nt

in A

Vo

ltag

e i

n V

Time in hours

Voltage Battery LVD LVR RP Current Battery

VCD DIT CVC

CCC CIT

0.0

0.4

0.8

1.2

1.6

10

11

12

13

14

15

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Cu

rre

nt

in A

Vo

ltag

e i

n V

Time in hours

Voltage Battery LVD LVR RP Current Battery

CCD

DIT CIT CCC

105

A 1.10 CDCP of WN02 (EXP. 1)

0.0

0.4

0.8

1.2

1.6

10

11

12

13

14

15

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Cu

rre

nt

in A

Vo

ltag

e i

n V

Time in hours

Voltage Battery LVD LVR RP Current Battery

CCD

DIT

CIT CCC

106

APPENDIX. 2

A 2.1 CDCP of CM03 (EXP. 2)

A 2.2 CDCP of CT01 (EXP. 2)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

10

11

12

13

14

15

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Cu

rre

nt

in A

Vo

ltag

e in

V

Time in hours

Voltage Battery LVD LVR RP Current Battery

VCD DIT CCC CVC

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

10

11

12

13

14

15

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Cu

rre

nt

in A

Vo

ltag

e in

V

Time in hours

Voltage Battery LVD LVR RP Current Battery

VCD DIT CCC CVC

107

A 2.3 CDCP of ST01 (EXP. 2)

A 2.4 CDCP of MS01 (EXP. 2)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

10

11

12

13

14

15

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Cu

rre

nt

in A

Vo

ltag

e in

V

Time in hours

Voltage Battery LVD LVR RP Current Battery

VCD DIT CCC CIT CVC

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

10

11

12

13

14

15

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Cu

rre

nt

in A

Vo

ltag

e in

V

Time in hours

Voltage Battery LVD LVR RP Current Battery

VCD DIT

CCC

CVC

CIT

108

A 2.5 CDCP of WN03 (EXP. 2)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

10

11

12

13

14

15

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Cu

rre

nt

in A

Vo

ltag

e in

V

Time in hours

Voltage Battery LVD LVR RP Current Battery

VCD DIT CCC CIT

109

APPENDIX. 3

This program has been developed by referring to the Thesis ‘Mathematical modelling of

a Lead Acid Battery’ [49]. This code pertains the CCC period which is being modelled.

k1=0.05; k2=0.02; k3=0.03; k4=0.04; m1=11.9; m2=11.9; m3=12.9; m4=12.9; w1=1; w2=1; w3=1; w4=1; ff=2; c1=20; kp=0.5; kc=110; wp=2; wc=-2; mp=14.3; mc=12.4; r0=92; c0=1; imax=1.6; yy=[]; zz=[]; aa=[]; bb=[]; uu=[];

for voci=12.0:0.0013:13.3

if voci==12.0; vc1i=0; else vc1i=vc1i; end

if voci==12.0; ipi=0; else ipi=ipi; end

if imax-ipi<0 rsi=(k3*(exp((w3*(m3-voci))^ff)));

110

r1i=(k4*(exp((w4*(m4-voci))^ff))); rxi=(kp*(exp((2*(12.4-voci))^ff))); rpi=((r0*rxi)/(r0+rxi)); cbi=(kc*(exp((-2*(12.4-voci))^2)))+c0; iri=vc1i/r1i; vc1i=(vc1i)+((imax-iri)/(c1*3600)); vbi=voci+(rsi*(imax))+vc1i; ipi=voci/rpi; voci=voci+((imax-ipi)/cbi/3600)

else rsi=(k1*(exp((w1*(m1-voci))^ff))); r1i=(k2*(exp((w2*(m2-voci))^ff))); rxi=(kp*(exp((2*(12.4-voci))^ff))); rpi=((r0*rxi)/(r0+rxi)); cbi=(0110*(exp((-2*(12.4-voci))^2)))+c0; iri=vc1i/r1i; vc1i=(vc1i)+((imax-iri)/(c1*3600)); vbi=voci+(rsi*(imax))+vc1i; ipi=voci/rpi; voci=voci+((imax-ipi)/cbi/3600);

end uu=[uu; vbi]; aa=[aa;iri]; end

for t=0:390.69:390690 t=t+1; yy=[yy; t]; end

disp('vbi'); disp(uu);

plot (yy, uu);

E