PROGRESS IN PHOTOVOLTAICS: RESEARCH AND APPLICATIONS

Prog. Photovolt: Res. Appl. 2010; 18:516–534

Published online 29 April 2010 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/pip.958

APPLICATIONS

Centralized solar lantern charging station under‘lighting a billion lives’ campaign: a technologicalevolution

Parimita Mohanty*, Nivedita Dasgupta and Arvind Sharma

The Energy and Resources Institute (TERI), Darbari Seth Block, India Habitat Center, Lodhi Road, New Delhi 110003, India

ABSTRACT

To mitigate the use of kerosene for rural lighting and to promote utilization of solar energy, solar lanterns prove to be a

viable and promising option. For addressing the issue of large-scale dissemination of solar lanterns, a rental model is

implemented though ‘Lighting a Billion Lives (LaBL)’ campaign. This paper deals with the technological development and

customization of the Centralized Solar Lantern Charging Station (CSLCS) under this campaign.

A single unit in a typical LaBL charging station consists of a Solar Photovoltaic (SPV) module feeding a junction box

(JB) containing multiple ports for charging of a certain number of lanterns simultaneously. The first version was developed

with an available Compact Fluorescent Lamp (CFL) lantern model. The design calculation of the various components

considering the various climatic conditions in India and other required parameters are presented. Further, the optimization

of the modular design of the charging station based on the above analysis is given. Subsequently, the second version was

developed with features addressing the challenges faced in the first version. The field demands and feasibility of

incorporating modifications addressing them are reported in detail. Further, a more advanced and customized third version

lanterns with additional features was developed. The versions also involved considerable modifications of the JB and

lantern circuitry. Comparative analysis of the obtained efficiencies of all the three configurations is presented.

The concluding section proposes methods that lead to the way forward in establishing a more rugged and customized

system addressing the issues of seasonal and technological constrains more efficiently. Copyright # 2010 John Wiley &

Sons, Ltd.

KEYWORDS

centralized solar lantern charging station (CSLCS); development and customization; efficiency; solar lantern

*Correspondence

Parimita Mohanty, The Energy and Resources Institute (TERI), Darbari Seth Block, India Habitat Center, Lodhi Road, New Delhi

110003, India.

E-mail: parimita@teri.res.in

Received 22 June 2009; Revised 31 October 2009

1. INTRODUCTION

Over 1.6 billion people in the world lack access to

electricity with roughly 25% in India aloney. Even the most

basic necessity, that of lighting, becomes a challenge after

sunset. Further, as per the latest survey, there are around

67.6 million rural households and 3.7 million urban

households in India who use kerosene as a fuel for lighting

applications [1]. Such huge amount of utilization of

kerosene not only creates a burden on the government for

providing heavy subsidy on kerosene but also pollutes the

yInternational Energy Agency; www.iea.org

516

environment due to CO2 emission and adversely affects the

health of the users. Minimizing the dependency of

kerosene and resorting to renewable energies such as

Solar Photovoltaic (SPV), surfaces as the most appropriate

route in alleviating this problem. Solar lantern can not only

provide better illumination, in the range of 30–130 lux at

1 feet distance from the centre point of the light source for a

2 W Light Emitting Diode (LED) lantern (as compared to

that of kerosene lamp which is 4–6 lux), but is environ-

mentally benign and even save the households from fire

hazards [2]. Several literature reviews mention that if a

SPV lantern is operated for 4 h a day for 300 days per year

(on an average), it saves about 60 L of kerosene [3].

Copyright � 2010 John Wiley & Sons, Ltd.

P. Mohanty et al. Centralized solar lantern charging station

Solar lanterns can be charged in two ways. One method

called the ‘Standalone Charging System’ involves charging

each lantern through a relatively low capacity dedicated

SPV module. The other method called ‘Centralized Solar

Lantern Charging Station (CSLCS)’ involves charging a

group of solar lanterns simultaneously through a common

SPV module of higher capacity with proper intermediate

protective circuits.

A standalone solar lantern setup consists of (i) a SPV

module of small capacity, typically of 5–10 W [4], (ii) a

Compact Fluorescent Lamp (CFL) or LED lamp as the

light source [5], (iii) an energy storage device such as

battery and (iv) an electronic interface. The size of the solar

lantern, in principle, can be specified either in terms of

power rating of the SPV module/CFL/LED lamp or the

capacity of the storage battery [3].

Standalone solar lantern setups are disseminated

through direct-sales where the user purchases the entire

setup. This in-turn involves higher upfront cost. On the

other hand, the CLSCS concept involves fee-for-service

model whereby the lanterns are rented out on daily basis. In

India, solar lanterns are generally disseminated as

‘standalone systems’ through various programmes by the

government and other organizations [6–8]. However, the

fee-for-service/rental model is found to be yet another

viable option as compared to direct-sales model on account

of affordability of lanterns by a larger number of

households [9]. Within this concept, every household pays

a nominal charge (Rs. 2–4 approx.) per day per lantern for

getting it charged in the centralized charging station.

Therefore the poorer community who has been using

kerosene for the lighting purposes would find the fee-for-

service model as the appropriate option over the direct-

sales model. The Energy and Resources Institute (TERI),

through its ‘Lighting a Billion Lives’ (LaBL—http://

labl.teriin.org/) campaign [10] has implemented CSLCSs

in various parts of rural India and is involved in a constant

endeavour in improving and customizing the technical

design of the charging station for its best suitability and

acceptance.

TERI initiated ‘Lighting a Billion Lives (LaBL)’

initiative in the year 2008 with an objective to bring light

into the lives of one billion rural people by providing them

solar lighting devices that not only provide high quality

light and smoke free indoor environment, but also reduce

consumption of kerosene and other fossil fuels used for the

purpose of lighting in power impoverished areas. Over the

past year and a half, LaBL has covered 108 villages in 10

Indian states. The total number of lanterns in field, as on

date is 5400 benefiting as many households and impacting

around 30 000 lives.

Although there are several aspects associated with the

CSLCS model, such as technical, financial and institutional

aspects, this paper focuses on the technical design and

customization of CSLCS and explains the design and

development of various versions under the LaBL

campaign. These have evolved based on the feedback

and requirements from the field. Finally, the way-forward

Prog. Photovolt: Res. Appl. 2010; 18:516–534 � 2010 John Wiley & Sons, LtdDOI: 10.1002/pip.958

to further improvement and customization of the of CSLCS

is presented.

2. CONCEPT OF CENTRALIZEDSOLAR LANTERN CHARGINGSTATION (CSLCS)

As described above, a CSLCS is a charging station where a

number of lanterns charge simultaneously through a

junction box (JB) from one or more number of SPV

modules, which are centrally located. The CSLCS option

offers possibility to use large capacity SPV modules that in

turn offer better efficiencies and lower unit costs (INR/Wp)

as compared to small capacity SPV modules that are used

individually and dedicatedly with each solar lantern.

A single unit in a typical CSLCS in the LaBL campaign

consists of a SPV module feeding a JB containing multiple

ports for facilitating the charging of a certain number of

lanterns simultaneously. Following are its major com-

ponents.

2.1. SPV modules

A set of SPV modules is installed on the shadow-free area

of the charging station. The voltage and current of each

SPV module is chosen in a way that it is capable of

charging a particular pre-determined number of lanterns.

2.2. Solar lanterns

A lantern is a portable lighting system consisting of

lighting device (lamp), a maintenance free storage battery

and electronics that are all placed in a case made of plastic

or fiberglass. During the day, the storage battery of the

lanterns is charged through the JB ports by the electricity

generated from the SPV module. When the lantern is fully

charged, it is disconnected from the JB and then can be

used as an independent portable lighting source. Lantern is

suitable for both indoor and outdoor lighting applications.

The specifications of the lanterns are generally based on

their light output and typical power rating.

2.3. Junction boxes

A JB basically contains the electronic interface circuitry

that is required between the SPV module and the lanterns.

It houses the necessary protections such as short-circuit

and reverse-polarity protections for effective charging of

the lanterns. For proper distribution of current and the

protection of the lanterns, the JB in CSLCS contains

current limiting circuits for each individual port.

Figure 1 illustrates the concept of a CSLCS. The

illustration shows that a cluster of houses in a village are

catered to by one central charging station. People from

the houses take the charged lanterns on rent daily from the

charging station.

. 517

Figure 1. Centralized solar lantern charging concept in a village.

Centralized solar lantern charging station P. Mohanty et al.

3. EVOLUTION OF CSLCS

If one studies the trend of any product/technological

development and customization over the years, then it is

observed that the trend is generally transformed through

development and restructuring based on the lesson learned

from the past [11]. Similar trend is followed in technology

development and customization process under this LaBL

campaign where the development and customization of the

CSLCSs have been evolved from the lessons learnt and

feedback obtained from the field. Therefore the authors

define different stages of development in designing and

evolving CLCS as:

(i) F

518

irst version CSLCS,

(ii) S

econd version CSLCS, and

(iii) T

hird version CSLCS.

These versions are presented in independent sections

and described in three stages each. The developmental

activities of each version of the CSLCS are introduced in

the first stage whereas the second stage describes the

configuration and features of each version of CSLCS which

were in accordance with the developmental activities. The

third stage presents, analyses and discusses the major

outcome that resulted from implementation of each of

CSLCS. The outcome of each of the version necessitates

the development/customization of next version CSLCS.

The following sections describe each of the versions.

4. FIRST VERSION CSLCS

The first version CSLCS was built to a large extent on the

basis of available lantern model for stand-alone solar

lantern system. The type of lantern used in the stand-alone

system and in CSLCS, in principle, is same. Hence the

lantern already available in the market for stand-alone

system is considered as a good starting point for the CLCS

model and thus being used in first version CLCS of LaBL

campaign. However one procedure was established for the

assessment of different lantern models and their alignment

Prog.

and suitability for using in CSLCS. For this purpose, an

extensive market survey [12] was conducted for identifying

and selecting the most appropriate lantern model for this

concept. For the assessment key players in the field of solar

lantern were identified and participated in the survey. The

results of the market survey with respect to the

configuration, lumen/lux output, hours of operation,

additional features available in the lantern, tentative price

range, etc. are summarized in Table I.

As per the survey, the most popular solar lantern model

is the 7 W CFL with 12 V, 7 Ah battery and individual solar

module of 12 V, 10 Wp (watt-peak) rating. The CFL

lanterns run for 3-4 h whereas the LED lanterns run for 8–

10 h. It has also been widely observed that there is hardly

any design modification and technological customization

has occurred in solar lantern ever since its inception.

4.1. Selection of appropriate lanterns forfirst version CSLCS

As a first step towards the selection, a comparative analysis

between variation of illumination of hurricane lamp and

commonly available solar lantern (5 W/7 W) with respect

to distance were studied. These findings indicated that the

illumination of the commonly available solar powered

lantern of 5 W/7 W is around 5 times higher than hurricane

lamp at all distance [13]. Further the standard illumination

norms were studied for identifying the appropriate level of

illumination required for different tasks in a house, which

can be met through a lantern. As per the IES lighting

handbook [14] the standard illumination for a working site

should be 5 lux and that of the reading and hand writing

place would be 7.5 lux a distance of 2 ft.

Keeping this standard illumination requirement as well

as maturity level, ruggedness, simplicity of usages, etc. of

the lantern, the 12 V, 7 W standard CFL lantern model was

selected for the first version CSLCS.

The first level short listing for selecting the appropriate

12 V, 7 W lantern under LaBL campaign was carried out

after assessing the performance features of the various

makes. Subsequently, several lantern models were procured

and in-house preliminary testing were conducted for finding

out the performance of the comparable models. The best

performing lanterns were chosen for first version CSLCS.

4.2. First version CSLCS: development andcustomization

As no design changes were incorporated in the lantern in

the first version CSLCS, the only developmental activity

that was carried out in this version was the development of

the JB, which is required for charging number of lanterns

simultaneously.

The basic design incorporation which was made in this

version (which is different from the standard stand-alone

solar lantern model) is the introduction of current limiting

Photovolt: Res. Appl. 2010; 18:516–534 � 2010 John Wiley & Sons, Ltd.DOI: 10.1002/pip.958

Table I. Summary of different lantern models available in the market.

Model Configuration Lumen output

(lm)

Hours of

operation (h)

Additional

features/features

Tentative price

range

(INR/model)

CFL 7 W CFL, 12 V,

7 Ah lead Acid battery,

12 V 10 Wp solar module

370� 5% 3-4 4300

CFL 7 W CFL, 12 V,

7 Ah lead Acid battery,

12 V 10 Wp solar module

350 3 Radio and mobile charging

option

3700

CFL 5 W CFL, 12 V 7/7.6 Ah battery,

12 V 10 Wp or 5 Wp solar module

230� 5% 4 FM Radio 3800/3990

CFL 5 W CFL, 6 V 4 Ah battery,

6 V 3 Wp or 5 Wp solar module

230 2 NA

LED 2.7 W LED 6 V,

4.5 Ah lead Acid battery,

6 V 3 Wp solar module

225 3-4 2200

LED 3.6 W LED 12 V,

7 Ah lead Acid battery,

12 V 5 Wp solar module

180–200 8–10 2400

LED 1.5–2.5 W LED 6 V,

4.5 Ah lead Acid battery,

9 V 3 Wp solar module

240 8–10 � FM radio stereo output 3450

� Mobile cell phone charger

� 1 GB audio flash memory

chip with preloaded music

and message, which can be

retrieved and played back

through built in amplifier

3 watts output

P. Mohanty et al. Centralized solar lantern charging station

circuit at each port of the JB. Since a smaller, individual

module is required for charging stand-alone lantern, it does

not require such limiting circuit. However when a number

of lanterns are getting charged from a higher rated module,

such circuit is required for safely charging each of the

lanterns without any damage.

With these changes, the CSLCS ensure the following:

(i) P

Prog.DOI: 1

rotects battery of each lantern from getting over-

charged, irrespective of the number of lanterns con-

nected to the JB,

(ii) P

rotects the battery of each lantern from reverse flow

if the state of charge (SoC) of the battery of different

lanterns is not equal, and

(iii) I

s able to optimally charge all connected lanterns

irrespective of the state of charge of their respective

batteries.

Two to three different models of JBs with different

current limiting options were developed with different

number of ports, e.g. one JB with 8 numbers of ports

(for simultaneously charging 8 number lanterns) and one

with 10 number of ports (for charging 10 number of

lanterns) are developed. The objective of introducing

different numbers of charging ports in the JBs was to test

out the optimum number of lanterns that can be charged

Photovolt: Res. Appl. 2010; 18:516–534 � 2010 John Wiley & Sons, Ltd0.1002/pip.958

from a prescribed SPV module under different field con-

ditions.

4.3. First version CSLCS: features andconfiguration

The development under first version CSLCS had led to the

configuration as tabulated in Table II.

4.4. First version CSLCS: user feedback onits appropriateness and suitability

Around 8–10 charging stations with first version CSLCS

have been installed at various locations in India under the

LaBL campaign. The post installation assessment was

conducted in order to examine the impact/appropriateness

of this version of CSLCS. The following sub-sections

present the points that were observed.

4.5. First version CSLCS: challenges

The challenges of CSLCS were analysed and can be

perceived in the following two perspectives:

. 519

Table II. Configuration of the first version of CSLCS

SPV module Lantern Junction box Overall efficiency

Configuration Five numbers of

70–75 Wp solar modules

50 numbers of lanterns

with the option of

charging upto 45 numbers

of lanterns

5 number of JBs 74%

Features Wattage: 7 W Number of ports: 8–9

Battery: 12 V/7 Ah

Lumen output: 350� 5% Features:

Duration for charging: 8 h � 12 V junction box

Duration of Operation: 3-4 h � Charging indicators

provided in all ports

Features: � Current limiting option for

charging at C/10 rate� Charging indication

� Low battery indication

Centralized solar lantern charging station P. Mohanty et al.

(i) F

zAcc

hour

of 1

from

520

rom the user’s and operator’s perspectives and

(ii) F

rom the implementation perspective.

4.5.1. Challenges from user’s/operator’sperspective.The challenges from the user’s/operator’s perspective,

which are most significant are the application and usages of

the lantern are the following.

4.5.1.1. Inconsistency in hours of opera-tion of lantern In several cases, the lanterns run for 6–

8 h in the initial days but fail to provide the same back up in

subsequent days. The inconsistent behaviour of the lantern

operating duration creates dissatisfaction amongst the

community.

4.5.1.2. Lack of variability in light out-put One of the typical requirements, which came from

the field, was that of a night lamp option in the lantern so

that it could be used throughout the night. The purpose of

such an option is not to illuminate the room or the work

space but just to provide the minimum light in order to

identify or locate any item.

4.5.2. Challenges from the operator’sperspective.

4.5.2.1. Limited charging of lanterns in aday The fully discharged lanterns require around 10–12 h

of peak sunshine (approximately 2 days) to get completely

charged if it is charged at the rated charging rate. In other

word, considering around 5–6 h of peak sunshinez per day,

only half of the lanterns got charged on daily basis, which

was not a desirable option for the operator of the CSLCS,

especially in a fee-for-service (rental) model.

ording to IEEE standards on PV Array sizing, ‘Peak sun

s’ is the length of time in hours at a solar irradiation level

kW/m2 needed to produce the daily solar radiation obtained

the integration of irradiance over all daylight hours.

Prog.

4.5.3. Challenges from implementationperspective.

4.5.3.1. Lack of standard design andconfiguration Past experiences suggest that many

product-oriented projects remained at the pilot demon-

stration stage and are yet to be replicated in larger numbers

as there are no standard design and configuration for mass

deployment. Lack of standard design and configuration

aggravated the implementation scenario as it made the

price of the system relatively high, the instruction for

installation procedure more complex, etc.

5. SECOND VERSION CSLCS

The second version CSLCS was based upon the feedback

and challenges obtained and the type of requirement that

came from the field through the implementation of first

version CSLCS.

As per the analysis of the problems occurring in the first

version of CSLCS, the solar lanterns available in the

market are meant for the stand-alone model, which had

been used and owned by individuals. The batteries of such

lanterns are designed with 3 days of autonomy. In other

words, if the lanterns are specified to run for 3 h in a day, its

batteries are designed/sized to provide 8–9 h back up

before reaching at its Low Voltage Disconnect (LVD)

point. Since in ownership model, each individual house-

hold use it for 3-4 h daily and again charge it on the next

day, it does not pose any problem. However the moment the

delivery model is changed from ownership model to fee-

for-service model, such operational practice changes. Here

in fee-for-service model, the lantern would continue to be

discharged completely before it comes to the charging

station for charging. Therefore, initially, the lantern runs

for 8–9 h. Once lanterns are fully discharged, it would take

2–3 days to be completely charged. If any lantern is

charged for one day only, then it cannot be completely

charged and hence cannot be used for 8–9 h. It can only

Photovolt: Res. Appl. 2010; 18:516–534 � 2010 John Wiley & Sons, Ltd.DOI: 10.1002/pip.958

P. Mohanty et al. Centralized solar lantern charging station

provide 3-4 h of backup if it is charged for a day under full

shine. This analysis was used while carrying out the

developmental activities for second version CSLCS.

In line with the challenges to be addressed in first

version CSLCS and the root cause analysis, the develop-

mental needs were identified, which were subsequently

reflected in the development and customization process of

second version CSLCS.

The developmental needs were articulated as follows:

(i) R

Prog.DOI: 1

equirement of lantern design which allows the lan-

tern (with existing lumen output) to run consistently

for 3-4 h in a day without any problem,

(ii) R

equirement of change in JB design, which can

charge a discharged lantern’s battery to its fully

charged condition within a day (with available full

sun shine hours),

(iii) R

equirement of a standard design and configuration of

CSLCS for mass replication,

(iv) R

equirement of lantern with variable lighting appli-

cations, and

(v) R

equirement of lightweight, portable lantern.

5.1. Second version CSLCS: developmentand Customization

Developmental activities carried out in second version

CSLCS were in accordance with the requirement of the

end-users and consisted of the following:

(i) C

ustomization of lantern with consistent supply of

light output,

(ii) C

ustomization of lanterns for multiple lighting appli-

cations,

(iii) D

evelopment of JBs for complete charging of a

number of lanterns simultaneously on daily basis, and

(iv) S

tandardization of CSLCS.

5.1.1. Customization of lantern with con-sistent supply of light output.Considering the reason behind inconsistent behaviour of

lantern, the in-house testing was started. A thorough study

based on the root cause analysis implied that the low

voltage disconnect (LVD) of the lantern should be elevated

to a point where the lantern cannot be discharged for more

than 5 h in any case. Such a design modification would

serve the following two purposes.

5.1.1.1. Prevent deep-discharge ofbattery It would not allow the lantern to get discharged

beyond certain hours (5 h) of operation, not even during

initial usage.

5.1.1.2. Improve battery-life The Depth of

Discharge (DOD) of the battery of the lantern would be

reduced from 80 to 50% which helps in improving the life

of the battery [15] (the lesser the DOD of the battery, the

more will be the life of the battery, up-to a maximum value

at certain DOD).

Photovolt: Res. Appl. 2010; 18:516–534 � 2010 John Wiley & Sons, Ltd0.1002/pip.958

Based on the in-house experiments, the Low-Voltage-

Disconnect (LVD) set point was chosen and fixed. The

necessary electronics were incorporated and lanterns were

made as per the modified set point values, which ensured 3-

4 h of consistent supply of light output of a lantern.

5.1.2. Customization of lanterns formultiple lighting applications.Provision of one LED, which can act as a night lamp was

introduced in the lantern. The night LED introduced was a

0.25 W LED, which could provide light output of 1 lux at

1 ft. The current drawn for operating the LED is very less

(around 15–18 mA) and hence it lasts throughout the night

even after the lantern is operated for 3 h with CFL mode.

Therefore the lantern with such a provision was used for

dual purposes: on one hand it was used as general purpose

light for conducting normal household activities and in

other hand it was used as night lamp for identifying and

locating items at night.

5.1.3. Customization of JBs for completecharging of number of lanterns on dailybasis.Here, the emphasis was placed on customizing the JBs for

complete and simultaneous charging of lanterns on daily

basis. Battery characteristics were studied through

extensive literature survey and several discussions were

carried out in this context, with battery manufacturers,

lantern manufacturers, etc. [16–17] It was revealed that if a

12 V VRLA battery is charged with C/10 rate and

discharged at C/10 rate upto 50% of the Depth of

Discharge (DOD) of the battery then the life of the battery

would be of 800–1000 cycles. That means, with this rate,

the battery needs replacement in every 3 years where as

with if a battery is charged with C/7 rate, the battery will

last for 2 ½ years with same discharging rate and DOD as

applicable for C/10 charging rate. From this analysis, it was

inferred that although C/7 charging rate would not reduce

the life of the battery drastically, but it would facilitate in

charging the battery fully in a day which is more critical for

a fee-for-service model.

In accordance with the above, JBs with current limiting

options at C/7 charging rate (e.g. current limiting at 1 A for

12 V, 7 Ah battery) was chosen. The approach was

validated through in-house dedicated testing and was in

line with the requirement. The electronic interface was

designed and developed based on the charging character-

istic and profile required for the battery, type of protections

required, etc.

5.1.4. Optimization and standardization ofCSLCS.Earlier in first version, the optimization and standardiz-

ation process had not been given enough attention.

However gradually, with implementation of several

CSLCS, it was realized that any large implementation

programme could be achieved within its stipulated time

period if the processes as well as the packages are

. 521

Centralized solar lantern charging station P. Mohanty et al.

standardized. Without a standard and optimized model, it is

difficult to implement projects of large magnitude such as

that of the LaBL programme.

There are several ways and approaches of optimizing

and standardizing the system configuration. This process

involved the following:

(i) B

522

alancing of energy supply and demand of a CSLCSand

(ii) S

tandard model based on the energy balance.

5.1.4.1. Balancing of energy supply anddemand of a CSLCS A comparative assessment

between the energy supply from a typical solar module

at different months, at different climatic regions and the

energy requirement for charging a number of lanterns were

conducted. The optimum configuration of the CSLCS was

depended on the solar radiation and the rated capacity of

the SPV module on one hand and on the energy require-

ment for charging a number of lanterns on the other hand.

Therefore under this optimization process, three different

sizes of SPV modules (75 Wp, 80 Wp and 100 Wp), JBs

with three different lantern-charging combinations (with 8

lantern charging, 9 lantern charging and 10 lantern char-

ging) and two different hours of operation per day(4 h/day

and 5 h/day) for the lantern were selected.

Under the optimization process, the maximum size/

capacity of 100 Wp solar module was proposed (for

charging maximum 10 numbers of 7 W CFL lanterns)

based on the fact that 10 Wp solar module is commonly

used for a 7 W CFL lantern. The similar reason was

followed for selecting 80 Wp solar module for charging 8

numbers of 7 W CFL lanterns. The other combinations,

which were considered under the optimization process was

the combination of charging 9 and 10 number of lanterns

with 75 Wp and 80 Wp solar modules, respectively. The

combinations were decided with the understanding that the

quality and efficiency of a larger SPV module was better as

compared to 10 Wp smaller SPV module and would

provide better energy output. Thus this puts forth the

requirement of smaller wattages of SPV modules per

lantern (i.e. 7–8 Wp instead of 10 Wp per lantern).

The step-wise approach followed in the optimization

process was articulated as below:

(i) C

alculation of energy available with different

modules per day under different climatic conditions,

(ii) C

alculation of energy required or energy demand per

day for different numbers of lantern,

(iii) C

omparison of daily energy available with energy

demand for every month throughout the year, and

(iv) D

evelopment of standard optimized model based on

the energy supply and demand scenario.

xModule performance is generally rated under Standard Test

Conditions (STC): irradiance of 1000W/m2, solar spectrum of AM

1.5 and module temperature at 258C.

Each of the steps was elucidated in details in the

following sections.

5.1.4.2. Energy availability at differentSPV modules under different climatic con-ditions The electrical output of solar modules strongly

Prog.

depends upon temperature, insolation and other conditions

like dust, wind speed, etc., which vary from one region to

other, typically for a vast country such as India.

Considering this, the standard climatic zone categoriz-

ation, which was made for the entire country, was adopted.

As per the climatic zone categorization, the Indian sub-

continent can be broadly divided into the following six

climatic zones [18–19].

Climatic Zone 1: cold and sunny (typical example area:

Leh).

Climatic Zone2: cold and cloudy (typical example area:

Shillong).

Climatic Zone 3: moderate (typical example area: Ban-

galore).

Climatic Zone 4: warm and humid (typical example

area: Chennai).

Climatic Zone 5: hot and dry (typical example area:

Jaisalmer).

Climatic Zone 6: composite (typical example area: New

Delhi).

Standardizing a CSLCS configuration considering the

disparate Indian climatic zones and field requirements was

a challenge. All the calculations and optimum design made

for CSLCS under LaBL campaign revolved around these

climatic zones. In order to calculate the energy available

with each of different SPV modules, the solar radiation

data were used. The month-wise global radiation data on a

horizontal surface (Igh) for a typical place in each of the

climatic zone were taken from the MNRE handbook [20].

The mean monthly global radiation on a tilted surface and

monthly mean ambient temperature for the six zones are

listed in Table III[20,21]. The global solar radiation on the

inclined modules (Y) was then calculated by multiplying

the available horizontal global radiation data (Igh) with correc-

tion factors (CF) for individual months of the year [18].

Y ¼ Igh � CF (1)

The module area and the rated conversion efficiencies

were taken from reputed solar manufacturers and listed in

Table IV[22].

However the conversion efficiency mentioned by any of

the reputed manufacturers is the rated efficiency that is

measured under Standard Test Condition (STC)x. There-

fore the conversion efficiency at the actual field condition

was calculated, while incorporating temperature correction

factor and other mismatch factor into consideration.

Conversion efficiencies (h) for mean temperature condition

and average insolation conditions were calculated using the

following expression [23].

h ¼ Voc � Isc � FF=A � G (2)

where G is the solar irradiation, Voc is the open circuit

voltage of solar module, Isc stand for short circuit current of

Photovolt: Res. Appl. 2010; 18:516–534 � 2010 John Wiley & Sons, Ltd.DOI: 10.1002/pip.958

Table

III.

The

mean

month

lyglo

balra

dia

tion

on

atilted

surf

ace

and

month

lym

ean

am

bie

nt

tem

pera

ture

for

the

typic

allo

cations

inth

esix

clim

atic

zones.

Leh

Shill

ong

Bangalo

reC

hennai

Jais

alm

er

New

Delh

i

Month

Radia

tion

(kW

h/

m2/d

ay)

Am

bie

nt

tem

pera

ture

(8C

)

Horizo

nta

l

radia

tion

(MJ/m

2/d

ay)

Radia

tion

(kW

h/

m2/d

ay)

Am

bie

nt

tem

pera

ture

(8C

)

Horizo

nta

l

radia

tion

(MJ/m

2/d

ay)

Radia

tion

(kW

h/

m2/d

ay)

Am

bie

nt

tem

pera

ture

(8C

)

Horizo

nta

l

radia

tion

(MJ/m

2/d

ay)

Radia

tion

(kW

h/m

2/d

ay)

Am

bie

nt

tem

pera

ture

(8C

)

Radia

tion

(kW

h/m

2/d

ay)

Am

bie

nt

tem

pera

ture

(8C

)

Horizo

nta

l

radia

tion

(MJ/m

2/d

ay)

Radia

tion

(kW

h/

m2/d

ay)

Am

bie

nt

tem

pera

ture

(8C

)

January

3.3

3�

21.1

14.1

13.9

0847

6.8

820.4

25.6

563

20.8

17.6

24.8

8074

24.4

4.6

115.3

13.3

23.6

8964

13�9

Febru

ary

4.2

9�

19.3

16.6

74.6

1759

8.9

523.3

56.4

680

23.4

121.0

75.8

3639

25.7

95.5

618.6

716.4

24.5

4834

16.5

5

Marc

h5.3

5�

15.7

19.2

75.3

3779

11.5

923.7

6.5

649

26.1

523.4

56.4

9565

27.9

96.4

924.5

820.6

45.7

1728

22.1

April

6.7

1�

11.3

21.1

35.8

5301

16.0

923.6

46.5

483

27.6

23.7

66.5

8152

30.1

7.4

830.9

824.0

76.6

6739

28.2

3

May

7.6

1�

618.4

15.0

9957

17.1

122.8

86.3

3776

26.7

22.5

46.2

4358

31.6

8.1

134.0

124.4

36.7

6711

31.8

7

June

8.3

90.3

16.4

24.5

4834

18.9

317.7

24.9

0844

24

20.5

95.7

0343

31.2

98.2

433.1

822.5

46.2

4358

33.2

9

July

7.9

95

16.0

64.4

4862

18.9

16.7

14.6

2867

23.1

919

5.2

63

30.2

57.4

431.1

819.0

75.2

8239

31.1

5

August

7.1

75

14.9

34.1

3561

19.3

416.1

64.4

7632

22.7

118.7

35.1

8821

29.5

7.0

830.2

717.7

94.9

2783

29.8

5

Septe

mber

6.7

90.7

14.0

33.8

8631

18.0

518.8

95.2

3253

23.4

319.4

15.3

7657

29.2

36.8

130.1

918.9

5.2

353

29.3

1

Octo

ber

5.4

4�

6.9

15.1

84.2

0486

15.9

118.4

25.1

0234

22.9

16.4

14.5

4557

27.7

76.0

629.0

616.8

4.6

536

25.3

3

Novem

ber

4.2

6�

14

15.6

34.3

2951

11.5

117.4

54.8

3365

21.8

814.3

93.9

8603

25.6

35

23.2

714.1

33.9

1401

19.4

8

Decem

ber

3.2

5�

18.7

14.4

33.9

9711

8.3

917.3

54.8

0595

20.5

314.9

64.1

4392

24.9

64.3

617.1

611.9

33.3

0461

14.6

7

Table IV. SPV module details.

Module

wattage

(Wp)

Area

(m2)

Conversion

efficiency (%)

(rated)

Conversion

efficiency (%)

(under typical

condition)

75 0.65 11.5 10.39

80 0.65 12.3 11.08

100 0.98 10.2 9.19

Prog. Photovolt: Res. Appl. 2010; 18:516–534 � 2010 John Wiley & Sons, LtdDOI: 10.1002/pip.958

P. Mohanty et al. Centralized solar lantern charging station

solar module, A is the area of the module and FF is the fill-

factor of the solar module.

Efficiency values were then calculated based on the

general expressions for Voc and Isc [23] and thus the total

daily energy output available from each module (75 Wp,

80 Wp and 100 Wp) was calculated. Based on the

conversion efficiency obtained under typical outdoor

condition and the global solar radiation falling on the

tilted surface of the solar modules (Y), the month-wise

daily energy obtained from different rated solar modules

for different climatic zones were calculated.

To show a typical case, the month-wise values obtained

for the 75 Wp, 80 Wp and 100 Wp modules for New Delhi

which features under the ‘composite’ climatic zone

following the above procedure are presented in Table V.

Similar approach was followed for all the other climatic

zones too and the month-wise daily energy output of

different rating solar modules were calculated and shown

in subsequent plots.

5.1.4.3. Daily energy demands for differ-ent numbers of lanterns The energy required for

each lantern for operating for different hours (4 h/day as

well as for 5 h/day) were calculated. For such applications,

a typical 7 WAC CFL lamp [24] with a lumen output of

370 lm is considered that works with a 12 V/7 Ah SMF

Lead–Acid battery. Table VI presents the energy required

by groups of 8, 9 and 10 lanterns, each for 4 h/day and for

5 h/day of lantern operation.

5.1.4.4. Balancing of energy supply withenergy demand The optimized configuration was

based on analysing and comparing the energy produced by

every SPV module (75 Wp, 80 Wp and 100 Wp) at each of

the climatic zone with the energy required by different

numbers of lanterns (8 or 9 or 10 numbers of lanterns).

Month-wise energy balance between supply of each of the

SPV modules and energy requirement of different numbers

of lanterns for all climatic zones were plotted in Figures 2,3

and 4. The following sections describe each of the plots in a

greater detail.

5.1.5. Analysis and explanation of plots.

5.1.5.1. Energy balance with 75Wp mod-ule With 75 Wp SPV module, 8 numbers of lanterns with

energy backup for 4 h(8 lanterns/4 h) will generally be

. 523

Table V. Daily energy output of different rating solar modules for every month in the climatic zone 6 ‘composite’ (typical example area:

New Delhi).

Month Horizontal

radiation

(kWh/m2/day)

Correction

factor

GI on tilt

(kWh/m2/day)

75 Wp SPV module 80 Wp SPV module 100 Wp SPV module

GI on

SPV module

(kWh/day)

Energy

delivered

by SPV

module

(kWh/day)

GI on

SPV module

(kWh/day)

Energy

delivered

by SPV

module

(kWh/day)

GI on

SPV

module

(kWh/day)

Energy

delivered

by SPV

module

(kWh/day)

January 3.69 1.461 5.39 3.50 0.36 3.50 0.39 5.28 0.49

February 4.55 1.312 5.97 3.88 0.40 3.88 0.43 5.85 0.54

March 5.72 1.125 6.43 4.18 0.43 4.18 0.46 6.30 0.58

April 6.67 0.993 6.62 4.30 0.45 4.30 0.48 6.49 0.60

May 6.77 0.912 6.17 4.01 0.42 4.01 0.44 6.05 0.56

June 6.24 0.89 5.56 3.61 0.38 3.61 0.40 5.45 0.50

July 5.28 0.903 4.77 3.10 0.32 3.10 0.34 4.67 0.43

August 4.93 0.952 4.69 3.05 0.32 3.05 0.34 4.60 0.42

September 5.24 1.057 5.53 3.60 0.37 3.60 0.40 5.42 0.50

October 4.65 1.243 5.78 3.76 0.39 3.76 0.42 5.67 0.52

November 3.91 1.446 5.66 3.68 0.38 3.68 0.41 5.55 0.51

December 3.30 1.578 5.21 3.39 0.35 3.39 0.38 5.11 0.47

Centralized solar lantern charging station P. Mohanty et al.

catered to in all the climatic zones and though the year

barring only 4 months in ‘cold and cloudy’ climate. With

the same module, 8 lanterns/5 h and 10 lanterns/4 h will not

be charged properly for 5 months in four different climatic

zones. For 10 lanterns for 5 h of backup, this module will

work only in ‘hot and dry’ and ‘cold and sunny’ climates

for most of the year. Similarly, for 9 lanterns for 5 h of

backup, this module will work for most of the year (8

months) only in ‘hot and dry’ and ‘cold and sunny’

climates.

Drawing a tradeoff, according to Table VII, this module

is suitable for charging a combination of 9 lanterns for

providing backup of 4 h each with satisfactory performance

for most of the year. The energy provided by the module in

Table VI. Parameters including ‘required energy’ for 8, 9

Parameter For 4

AC power required

Inverter efficiency

DC power required

Operating voltage

DC current required by the CFL

Charge to be given by battery per day

Battery efficiency

DoD

Charge to be supplied to battery per day

Efficiency of JB circuit and charge controller circuit

Nominal voltage of module

Energy required per day for one lantern

Energy required per day for 8 lanterns

Energy required per day for 9 lanterns

Energy required per day for 10 lanterns

524 Prog.

various climatic zones and that required by the various

combinations of ‘number of lanterns’ and ‘operation hours’

are plotted in Figure 2.

5.1.5.2. Energy balance with 80Wp mod-ule According to Table VIII, an 80 Wp module will be

able to successfully charge 8 lanterns for providing 4 h of

backup each. Similarly, with minor failure chances (only

for 2 months), this module is sufficient for 8 lanterns (5 h of

backup), 10 lanterns (4 h of backup) and even for 9 lanterns

(with 4 h of backup).

For charging 9 lanterns for giving 5 h of backup, this

module will not charge all 9 lanterns successfully for

almost 8 months in a year in four climatic zones.

and 10 numbers of lanterns with 4 and 5 h of backup.

h of operation For 5 h of operation Unit

7.00 7.00 WAC

92 92 %

7.61 7.61 WDC

12.00 12.00 VDC

0.63 0.63 ADC

2.54 3.17 Ah/day

88 88 %

0.60 0.60

2.88 3.6 Ah/day

90 90 %

12.00 12.00 V

38.43 48.03 Wh/day

0.31 0.38 kWh/day

0.35 0.43 kWh/day

0.38 0.48 kWh/day

Photovolt: Res. Appl. 2010; 18:516–534 � 2010 John Wiley & Sons, Ltd.DOI: 10.1002/pip.958

Figure 2. Energy plots showing feasibility of each combination in each climatic zone when a 75 Wp module is used.

P. Mohanty et al. Centralized solar lantern charging station

Finally, for 10 lanterns for providing 5 h of light, this

module will provide sufficient power in ‘hot and dry’ and

‘cold and sunny’ climatic zones only.

5.1.5.3. Energy balance with 100Wpmodules With marginal charging problems for 2 months

in some zones and barring ‘cold and cloudy’ climate, a

100 Wp module successfully charges all lanterns simul-

taneously for almost all of the combinations (summarized

in Table IX). Even for charging 10 lanterns simultaneously

for providing 5 h of backup, this module may fail only for

around 2 months in four climatic zones. Therefore, it is

apparent that a 100 Wp will not be fully utilized for most of

the configurations and lead to incurring of more cost per

watt of solar power.

Figure 3. Energy plots showing feasibility of each combinat

Prog. Photovolt: Res. Appl. 2010; 18:516–534 � 2010 John Wiley & Sons, LtdDOI: 10.1002/pip.958

5.1.5.4. Optimizing the configuration ofCSLCS The optimum, standardized configuration of the

CSLCS was the tradeoff between ‘overcapacity’ and

‘under capacity’ combinations. As per the analysis, there

were two options for charging ten (10) numbers of lanterns

simultaneously:

(i) S

ion in

.

electing 100 Wp SPV module and allowing wastage

of energy in most of the climatic region in several

months and

(ii) S

electing 80 Wp SPV module with buffer battery and

alternate charging options. The alternate charging

option would facilitate the charging of the lantern in

no or low sunshine hours.

each climatic zone when a 80 Wp module is used.

525

Figure 4. Energy plots showing feasibility of each combination in each climatic zone when a 100 Wp module is used.

Table VII. Feasibility of using a 75 Wp SPV module corresponding to the energy balance of various combinations of ‘number of

lanterns’ and ‘operation hours’ in particular months and climatic zones.

No. of lanterns/backup hours Duration and zone where the energy balance is infeasible

Month(s) Climatic zone

8 lanterns/4 h June–September Cold and cloudy’

8 lanterns/5 h June–October Cold and cloudy, warm and humid, composite, moderate

9 lanterns/4 h July-August Warm and humid, composite, moderate, cold and cloudy

June–September Cold and cloudy

9 lanterns/5 h January Composite, warm and humid, cold and cloudy and cold and sunny

May–December Composite, warm and humid, cold and cloudy and Moderate

10 lanterns/4 h June–October Cold and cloudy, warm and humid, composite, moderate

10 lanterns/5 h Most of the year All climatic zones except ‘hot and dry’ and ‘cold and sunny’

Centralized solar lantern charging station P. Mohanty et al.

Hence, the best tradeoff is to use a 80 Wp module for

catering to the demand of charging 10 lanterns for provid-

ing 5 h of backup each. Figure 5 illustrates the concept of a

typical LaBL CSLCS. Here, each module charges 10

lanterns and there are 5 such units; thus making it a

charging station for 50 lanterns.

Table VIII. Feasibility of using a 80 Wp SPV module correspondin

lanterns and operation hours in parti

No. of lanterns/backup hours Durat

Month(s)

8 lanterns/4 h

8 lanterns/5 h July-August (2)

June

9 lanterns/4 h July-August (2)

9 lanterns/5 h June-January (8)

10 lanterns/4 h July-August (2)

June

10 lanterns/5 h

526 Prog.

5.2. Second version CSLCS: features andconfiguration

The development under second version CSLCS had led to

the configuration as presented in Table X.

g to the energy balance of various combinations of number of

cular months and climatic zones.

ion and zone where the model is unviable

Climatic zone

Composite, moderate, cold and cloudy and warm and humid

Cold and cloudy and moderate

Composite, moderate, cold and cloudy

Composite, moderate, Cold and cloudy, warm and humid

Composite, moderate, cold and cloudy, warm and humid

Cold and cloudy and moderate

For entire year, it works only for two climatic zones

(mainly ‘cold and sunny’ and ‘hot and dry’)

Photovolt: Res. Appl. 2010; 18:516–534 � 2010 John Wiley & Sons, Ltd.DOI: 10.1002/pip.958

Table IX. Feasibility of using a 100 Wp SPV module corresponding to the energy balance of various combinations of number of

lanterns and operation hours in particular months and climatic zones.

No. of lanterns/backup hours Duration and zone where the model is unviable

Month(s) Climatic zone

8 lanterns/4 h

8 lanterns/5 h August-September Marginal problem in ‘cold and cloudy’ climate

9 lanterns/4 h

9 lanterns/5 h June–September Cold and cloudy

July–August (2) Moderate, cold and cloudy, composite

10 lanterns/4 h August-September Marginal problem in ‘cold and cloudy’

10 lanterns/5 h May–October Cold and cloudy

July-August (2) Moderate, cold and cloudy, composite, warm and humid

Figure 5. Configuration of CLSCS of LaBL programme.

P. Mohanty et al. Centralized solar lantern charging station

5.3. Second version CSLCS: challenges/userfeedback on its appropriateness andsuitability

Several charging stations (around 15–20 in numbers) were

implemented based on this version. The challenges that

Table X. Configuration of the

SPV module Lantern(s)

Configuration Five number

of 80 Wp

SPV module

50 numbers of 7 W CFL la

with 12 V/7 Ah battery eac

All can be charged simulta

Features Wattage: 7 W

Battery: 12 V/7 Ah

Lumen output: 350�5%

Duration for charging: 6 h

Duration of operation: 3-4

Features:

� Each lantern can provide

continuous 3 h of backu

� Night LED

Prog. Photovolt: Res. Appl. 2010; 18:516–534 � 2010 John Wiley & Sons, LtdDOI: 10.1002/pip.958

occurred in first version were resolved and, the lantern

started giving back up consistently for 3-4 h when fully

charged. Further, the lanterns have also been getting fully

charged within a day through the modified JBs. However

certain other requirements had come out from the field

after the implementation of the second version CSLCS.

second version of CSLCS.

Junction box (s) Efficiency

nterns

h.

neously

5 number of JBs 85%

Number of ports: 10

Features:

h

� Junction box for charging

12 V rating lantern

p

� Charging indicators provided

in all ports

� Circuit contains charging

and current limiting at 1 A

. 527

Centralized solar lantern charging station P. Mohanty et al.

The following feedbacks were obtained from the field.

(i) T

528

here was a requirement of providing more than 4 h of

back up as rural communities had started using the

lantern and thus their demand or expectation on hours

of operation of lantern had increased.

(ii) T

here was a demand of providing separate charging

port in the lantern itself for charging a mobile phone.

Such demands were region specific and applicable for

certain communities.

(iii) A

s per the feedback of the community, the lantern

users had stopped using kerosene. However since

there was no prior indication in the lantern before

the CFL was turned off, the users suddenly come into

complete darkness. Therefore there were demands for

providing certain prior indication before the CFL

lantern got completely extinguished were come out.

(iv) T

he requirement for light weight, portable lantern was

felt by most of the users as it would be easier for them

while commuting daily for taking and giving the

lantern at the charging station.

6. THIRD VERSION OF CSLCS

The third version CSLCS was based upon the feedback and

challenges obtained and the type of requirement came from

the field through the implementation of second version

CSLCS. Based on the findings obtained from the field, the

following future developmental requirements in the

CSLCS were listed out.

(i) R

equirement of lantern with extended hours of oper-

ation.

(ii) R

equirement of light weight, portable lantern.

(iii) R

equirement of prior indication before complete turn

out of the CFL.

(iv) R

equirement of multiple purpose lantern.

(v) R

equirement of providing external energy backup for

charging lantern in no- or low-sunshine hours.

6.1. Third version CSLCS: development andcustomization

According to the demands and the outcome of the second

version, the following key improvements/additions were

made in the lantern.

6.1.1. Development/customization oflanterns with extended hours ofoperation.This included two stages of development and customiza-

tion. One in which the operating hours of the CFL based

lantern was extended by slight changes in the circuit

parameters and the other in which LED based lanterns were

introduced as another option for longer operating hours as

an answer to the demands of certain communities.

Prog.

6.1.1.1. CFL based lantern with longerbackup (bright light for 4h) As mentioned earlier,

for certain group of community, there is a requirement of

bright-light (as that of the existing 7 W CFL) for around 4 h

for carrying out some of their tasks. Engaging a battery

with higher capacity for providing longer hours of charge

would incur higher cost and also increase the battery size

and thus the weight of the lantern. Further, the mould of the

base of the existing lantern model had to be changed to

accommodate a bigger battery. The following simpler and

more viable solution was thus resorted to. The battery

current that is drawn by the charging circuit for operating

the load was decreased slightly to provide prolonged

duration of charge and thus longer lamp backup. The rated

value for a 7 W CFL is 650 mA. The manufacturers were

consulted for scoping the effect of decreasing the value of

this on the brightness, blackening of the lamp and lamp-

life. The effects were, however, found negligible even

when the value was decreased to 600 mA. The reduction in

brightness due to this modification was not apparent and

was negligible.

6.1.1.2. Introduction of LED based lan-terns (with relatively less bright light formore than 4h of operation) For certain group of

community, the brightness of the light is relatively less

important than the duration of the availability of light. For

them extended hours of operation for more than 4 h and at-

least for 5 h is more desirable even if the brightness of the

lighting device is relatively less than 7 W CFL.

In this context another model, i.e. LED lighting system

were introduced in the LaBL campaign. As is known,

LEDs have certain advantages over CFLs, especially in

terms of providing longer lamp life, lesser power

consumption, greater efficacy, etc. Therefore, LED

lanterns with relatively lesser wattage were introduced.

These models were of 2.25 W with 12 V/4�5 Ah batteries.

To meet the requirement of varying illumination for

undertaking various tasks, an additional feature of

dimming was introduced in these LED based lanterns.

Additional feature of night LED was incorporated for

being used as a night lamp and also for the ease of

locating the lamp in dark. Hence, LED based lighting

proved to be viable in terms of longer backup and

multiple advantages.

6.1.2. Development of lantern with mobilephone charging.Recharging of mobile phones in unelectrified villages had

become an urgent need of late. In many villages, people are

required to go as far as 5 km to get a mobile phone charged.

To meet this demand, recharging the mobile phone battery

through solar power appeared to be a preferred option.

Based on this user requirement, the above-mentioned

newer LED lanterns were provided with mobile phone

charging ports, thus making them a multipurpose utility

reaching out to more eager users.

Photovolt: Res. Appl. 2010; 18:516–534 � 2010 John Wiley & Sons, Ltd.DOI: 10.1002/pip.958

P. Mohanty et al. Centralized solar lantern charging station

6.1.3. Development of lanterns withbattery state-of-charge indication.With the reduction in the usage of kerosene lanterns, the

dependency of households solely on solar lanterns

increased drastically. The lanterns were generally provided

with Green and Red indicators for showing battery-

charging and low-battery conditions respectively.

As soon as the low-battery indicator glows, the lamp

goes OFF simultaneously. Since, the low-battery indication

provided no warning of the battery getting exhausted and

the possibility of the lantern getting switched OFF, the

users often faced the problem of sudden switching OFF of

the lantern after the stipulated hours of backup. Hence, a

more detailed battery-status indicator was demanded from

the field. Thus, newer models of both the CFL and LED

based lanterns were introduced where a battery state-of-

charge indicator has been provided. This was basically

done to facilitate the users and the entrepreneurs (who are

responsible for maintaining the CSLCS) to be aware of the

battery status and plan the usage/charging optimally.

6.1.4. Development of lanterns with newerbatteries.A consistent demand from the field was to have a

lightweight and easily portable lantern for the ease of use

and also for the ease of being carried by the elderly and the

children. The key component adding to the weight of the

lantern is the battery [25]. The low-cost lead acid batteries,

which were being used in the lanterns, are relatively heavy

[15]. Ni-Cd batteries can withstand deep-discharges and

temperature extremes much better than lead–acid batteries

[26]. However, the main disadvantage is that such batteries

suffer from ‘memory effect’ in which a battery that is

repeatedly discharged to a certain percentage of its rated

capacity will eventually memorize this cycle and will limit

further discharge resulting in loss of life. In addition,

higher cost and limited availability hinder the large-scale

usage of such batteries. Another option is the NiMh battery.

Lighter batteries such as NiMh battery were introduced in a

newer model. NiMh batteries are compact, allow deep

discharge, have relatively longer life and are environmental

friendly. However, these are not as widely and easily

Table XI. Configuration of th

SPV module Lantern

Five number for 80 Wp SPV module Wattage: 7 W

Battery: 12 V/7 Ah

Lumen output: 350� 5%

Duration for charging: 8

Duration of Operation: 4

Features:

� Charging indication

� Low battery indication

� Night LED

� Battery status indicat

Prog. Photovolt: Res. Appl. 2010; 18:516–534 � 2010 John Wiley & Sons, LtdDOI: 10.1002/pip.958

available as lead–acid batteries and hence after-sale

services might also be unpredictable. Further, such

batteries are appreciably expensive and prove to be

techno-economically unviable. However, mass production

may eventually be useful for making their use in lanterns

more conducive.

6.1.5. Development of lantern withauxiliary charging.In a newer version of LED lantern, an additional mode of

charging has been incorporated under the LaBL campaign.

This is through hand-cranking which is a mechanical way

of charging the battery. This feature proves handy in case of

low sunlight days and for emergency charging of lanterns.

This lantern is still in the stage of testing and has not yet

been installed at any site.

6.2. Third version CSLCS: features andconfiguration

As an outcome of the developmental activities, the features

of the third version of CLCS are listed in Table XI.

6.3. Third version of CLCS: challenges

Even after significant developments and achieving

appreciable improvements in the CLCS model, there still

exists further scope for improvement in the CSLCS. The

key identified areas where future development/customiza-

tion can be done are as follows:

6.3.1. Requirement of complete chargingeven during no/low sunshine conditions.Since the SPV module output current strongly depends

upon the solar irradiation and temperature, there are certain

problems faced in lantern charging during low-sunlight,

cloudy and foggy days. As is also apparent from figures

(plots in second version), in certain months (typically from

June to August), all 50 lanterns are unable to get fully

charged in a single day. This problem demanded further

e third version of CSLCS.

Junction box Efficiency

Number of ports: 10 90%

Features:

� 12 V junction box

h

h

� Indicators on each row

(of five ports each) with indication

for presence of solar power

or

� Circuit contains only current

limiting at 1 A

. 529

Centralized solar lantern charging station P. Mohanty et al.

improvement to increase reliability of the model through-

out the year. Hence there is a requirement of additional

alternate charging option, specifically in low sunshine days

for charging all 10 lanterns in a day.

6.3.2. Requirement of developing highefficient bright LED lantern.For carrying out specific tasks, there were special demands

of LED lanterns with brightness as high as 5 W CFL

lanterns. Thus, there was a need of developing high-

efficient, brighter LED lanterns with appreciable hours of

backup.

These challenges and requirements prompted the

development of certain measures for determining the

way forward that shall be elaborated in Section 8. Figure 6

shows the complete progress chart consolidating the

developmental activities, feedback and the features of each

version and the way-forward.

As can be observed from Figure 7, the progress of the

various versions of CSLCS has been rapid and commend-

able development and results have been produced within a

relatively short duration.

7. EFFICIENCY IMPROVEMENT OFEXISTING CFL BASED CSLCS

The three versions of CSLCS were tested with the

respective JB and lantern combinations in the laboratory,

developed under the LaBL campaign. This exercise was

carried out for comparing the circuit efficiencies of each of

the versions. As illustrated in Figure 8, a SPV module

characteristic was simulated in the laboratory though a

regulated power supply based setup. An adjustable

resistance is connected in series with the power supply.

Negative I–V characteristic curve is generated at the

terminal of this setup when the load at this terminal is

varied (from open to short circuit). This simulates the trend

similar to that of the characteristic I–V curve of a SPV

module. This experimental arrangement provided a

laboratory-based controlled platform for comparing the

efficiencies of the three versions.

The adjustable resistor was fixed at a particular value

and the junction-box was connected to the terminal of this

setup. A fully discharged lantern is then connected to one

of the ports. Subsequently, the lantern is charged through

this JB by this power supply setup. As illustrated in the

figure, power at the output of the PV simulator (i.e. at the

input of the JB) and power that is fed to the lantern-battery

are recorded simultaneously at regular intervals during the

charging cycle. The efficiency of the combination of one

JB port circuit and one lantern charging circuit is recorded.

Likewise, the system-efficiencies for each of the versions

are calculated.

The Efficiency versus Input power curve for three

generations were plotted (Figure 9) and analysed. For the

analysis, the input power range was divided into two: (i)

when the input power is in the lower power range (3 W to

530 Prog.

10 W), which offers a consistent range for comparison and

(ii) the complete range of readings where the overall

efficiency was calculated.

It is observed that, for each efficiency curve, during low

input power range (as marked in the plot), at any instant of

the input power, the average system-efficiency increases

with each version. In this range, the efficiency of the

second version is greater than the first while that of the

third version is greater than the second. The average

efficiencies recorded in this working range are presented in

Table XII. Further, the percentage improvement in the

efficiency of second and third versions over their respective

previous versions is also tabulated in this table. It can be

observed that the circuit efficiency is significantly higher in

the final version of the charging station.

Similarly, the overall average efficiencies of the entire

charging range are also presented in Table XII. As is

observed, each improved version of the circuit of the JB

port and the lantern charging circuit has been achieved

along with appreciable increase in efficiencies.

8. WAY FORWARD

As discussed in sub-section 6.3, it is imperative to address

the challenges of the third version and to improve the

efficiency and robustness of the CSLCS. In order to achieve

these, the following measures are contemplated as the way-

forward.

8.1. Integration of buffer-battery in CSLCS

As discussed in sub-section 6.3, during a few cloudy and

foggy months in the year, all the lanterns might not

completely charge within 1 day. Thus, to improve the

reliability of the system throughout the year, an alternate

source of charge viz. a buffer battery of suitable capacity,

can be used as a backup option. This buffer battery shall

be installed in each charging station that shall be charged

with the additional power that is available from the solar

modules on clear days. This battery will have second

priority after the solar lanterns and shall be responsible

for providing the extra charge required when such

challenges are faced. The design of buffer battery

charging option are already finalized and in the final

stage of development.

8.2. Integration of maximum power pointtrackers with the modules

Direct connection of the SPV modules to the JB often leads

to underutilization of the available power from the SPV

modules since it does not work at the ‘peak power

operating point’. Electronic circuits [27–28] used for

optimizing the utilization of module power can be used. If

proved economically viable, this developmental activity

Photovolt: Res. Appl. 2010; 18:516–534 � 2010 John Wiley & Sons, Ltd.DOI: 10.1002/pip.958

Figure 6. Details of the development of the CSLCS configuration, features, feedback at each stage and way forward towards further

improvement.

Prog. Photovolt: Res. Appl. 2010; 18:516–534 � 2010 John Wiley & Sons, Ltd.DOI: 10.1002/pip.958

531

P. Mohanty et al. Centralized solar lantern charging station

Figure 7. Time chart for the three stages of development.

Figure 8. Experimental prototype for measuring the efficienc

Figure 9. Power versus efficiency plo

Table XII. Efficiencies of the

V

Average efficiency in initial power range (%)

Overall average efficiency (%)

Percentage increase in overall average efficiency

with respect to earlier version (%)

532 Prog.

Centralized solar lantern charging station P. Mohanty et al.

can significantly improve the overall efficiency of the

CSLCS model.

8.3. Brighter LED lanterns

The LED lanterns are energy-efficient and last relatively

longer. With the judicial use of batteries (Lead–Acid,

NiMh, etc.), power-LED based lanterns with brightness as

high as that of 5 W CFL are being developed. Use of newer

batteries shall also help develop lanterns with longer life

and lighter weight.

Incorporating the above features to CLCS would help

two-fold, viz. (i) This shall reduce the cost incurred per watt

of SPV power used and (ii) this shall present brighter and

more user-friendly lanterns with appreciable backup and

ies of the configurations of the three versions of CSLCS.

ts of the three versions of CSLCS.

three versions of CSLCS.

ersion 1 Version 2 Version 3

46.42 54.36 65.71

64.32 67.25 76.2

4.5 13.3

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P. Mohanty et al. Centralized solar lantern charging station

additional features that prove beneficial to the rural

community through the low-cost rental model of CLCS.

9. CONCLUSION

Rental model facilitating the dissemination of solar

lanterns to the rural areas has been implemented through

the LaBL campaign. The details of the technological

design and development of the CSLCS has been presented

in this paper. The technological and implementation-

related challenges are addressed in the various versions that

have been implemented through the developmental and

customization process. The criteria for improvement were

based upon the field feedback and requirements. The

overall system efficiency for the latest version was found to

be 76.2%. Several further measures for the improvement of

efficiency have been suggested in the way-forward in this

model.

ACKNOWLEDGEMENTS

This work is an outcome of the campaign ‘Lighting a

Billion Lives�—A TERI Initiative’ of The Energy and

Resources Institute, New Delhi, India. The authors are

grateful to Ms. Akanksha Chaurey (Director, Lighting a

Billion Lives�—A TERI Initiative) for her invaluable

suggestions and support during the development and for-

mulation of the technical design of the charging stations.

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