developing the next generation solar lantern
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Research, design and analysis of a new solar lantern.TRANSCRIPT
Developing the Next Generation Solar Lantern EWB and MEng research project investigating the success of the Glowstar Solar Lantern and
developing a next generation lantern
Chris White Pembroke College
Cambridge University May 2010
Supervisor: Dr P R Palmer Partner: Practical Action
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1 Abstract
Worldwide 1.6 billion people live without access to electricity, relying on expensive and
dangerous kerosene lanterns for light after dark. Kerosene for lighting can absorb up to 15%
of household income and produces very poor quality light. Grid expansion is expensive and
happening very slowly and so a new solution was sought. In 2003 the Glowstar lantern was
released to market. Developed by Practical Action Consulting (formerly ITC) and produced
and distributed by solar company Sollatek Ltd, it was designed to serve the world’s poorest
people by providing low cost, high quality lighting to eliminate the need to kerosene
lanterns. The Glowstar is a solar charged compact fluorescent lantern that continues to sell
worldwide but it has never enjoyed the success that was anticipated and has not spread as
far as the need for improved lighting. This project investigates the reasons for Glowstar’s
level of success using Kenya as a case study for the global situation seeks to design and
prototype a lantern design that can meet the needs of the target market more successfully.
The Glowstar is widely regarded in Kenya as a high quality, high performance
product. There are some issues with the battery life that have degraded its reputation
though underperformance but it is a rugged and durable product and backed by Sollatek’s
excellent 5 year guarantee. In Kenya however it has never made major inroads in the rural
mass market due to its high price that puts it beyond the reach of a large portion of the
target market and because of the limited geographic reach of the distribution network in
Kenya that is concentrated around provincial capitals but does not penetrate into the
countryside. Selling innovative products to the rural mass market requires a significant
marketing effort that has been lacking from the Glowstar project with the high impact
marketing coming through face to face training and hands on experience of the products.
Possible methods to improve penetration of the rural market include utilizing the mobile
phone distribution network that has grown at phenomenal rates in recent years, partnering
with micro-credit agencies to provide members with access to credit and training on the
product or building an extensive network of agents in towns and villages who are
knowledgeable about the product. The price of the lantern, at around $150 represents a
significant investment for the average rural person and is regarded by both users and
distributers as too expensive. A common consensus for a viable price is around $50.
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The requirements for a solar lantern have changed little since the Glowstar was
developed and there is still great interest in lanterns. The key requirements for a lantern are
a run-time of at least 6 hours, cost below $50 and provide sufficient light to illuminate a
4x4m room comfortably. To meet these requirements the advances in technology were
assessed and a system based on White high brightness LEDs and NiMH batteries is
proposed. The system is designed to be highly modular with each module being self
contained and able to interface with a wide range of alternative products. The intention is
that the solar lantern is the first step on the energy ladder and that a household will, at
some point in the future, wish to upgrade their system to higher powers and more capable.
The philosophy behind the concept for the lantern is that the modules should be capable of
integrating into a higher power system seamlessly while still operating efficiently as a
baseline system.
The system was prototypes performed well, proving that the concept is feasible. It
utilizes switch mode DC-DC converters in the lamp module and the battery module to allow
a wide range of input voltages and power while regulating the outputs to optimize
performance. The prototype cost in the region of $65 to produce falling to $55 for 1000
units.
The off-grid lighting sector is in a phase of rapid development and there are many
exciting opportunities for new lantern developments at this time if they are able to perform
and are combined with an effective marketing and distribution mechanism.
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2 Contents
1 Abstract............................................................................................................................... 1
2 Contents.............................................................................................................................. 4
3 Table of Figures .................................................................................................................. 6
4 Table of Tables .................................................................................................................... 6
5 Introduction ........................................................................................................................ 7
5.1 Solar Lanterns .............................................................................................................. 7
5.2 Glowstar background .................................................................................................. 8
5.3 Current situation ......................................................................................................... 8
5.4 Technology advances .................................................................................................. 9
5.5 Opportunities .............................................................................................................. 9
6 Methodology ...................................................................................................................... 9
6.1 Glowstar ...................................................................................................................... 9
6.1.1 UK based research ............................................................................................. 10
6.1.2 Kenya based research ........................................................................................ 10
6.2 Next generation lantern ............................................................................................ 12
7 Glowstar research results ................................................................................................. 12
7.1 Performance .............................................................................................................. 12
7.1.1 Technical assessment ......................................................................................... 12
7.1.2 Distributors ........................................................................................................ 13
7.1.3 Users .................................................................................................................. 13
7.2 Sales ........................................................................................................................... 14
7.2.1 Sollatek ............................................................................................................... 14
7.2.2 Distributors ........................................................................................................ 15
7.3 Market ....................................................................................................................... 15
7.4 Cost ............................................................................................................................ 16
7.5 Distribution ................................................................................................................ 16
7.6 Marketing .................................................................................................................. 17
7.7 Service ....................................................................................................................... 17
7.8 Perceptions ................................................................................................................ 18
7.8.1 Industry experts ................................................................................................. 18
7.8.2 Users .................................................................................................................. 18
7.9 Impacts ...................................................................................................................... 18
7.10 Competition and alternatives ................................................................................... 19
7.10.1 Market condition ............................................................................................... 19
7.10.2 Wider market ..................................................................................................... 20
7.11 Requirements for a lantern ....................................................................................... 21
8 Discussion and implications of research .......................................................................... 21
8.1 Success of Glowstar ................................................................................................... 21
8.1.1 Factor and opinions of success .......................................................................... 21
8.1.2 Successes and failures ........................................................................................ 22
8.2 Competition ............................................................................................................... 24
9 Conclusions about Glowstar ............................................................................................. 24
9.1 Reliability of information and conclusions ................................................................ 24
9.2 Degree of success ...................................................................................................... 24
9.3 Potential improvements............................................................................................ 25
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9.3.1 Product ............................................................................................................... 25
9.3.2 Distribution ........................................................................................................ 25
9.3.3 Marketing ........................................................................................................... 26
9.4 Other products .......................................................................................................... 26
9.5 Opportunities ............................................................................................................ 27
10 Next generation lantern development ............................................................................. 27
10.1 Requirements ............................................................................................................ 27
10.2 Technology options ................................................................................................... 27
10.2.1 Batteries ............................................................................................................. 27
10.2.2 Light Sources ...................................................................................................... 29
10.3 Technical considerations ........................................................................................... 30
10.3.1 LED light source .................................................................................................. 30
10.3.2 NiMH Batteries ................................................................................................... 31
10.4 Proposed solution ..................................................................................................... 32
10.4.1 Conceptual ......................................................................................................... 32
10.4.2 Technical ............................................................................................................ 33
Testing .................................................................................................................................. 35
10.4.3 Circuits ............................................................................................................... 35
10.4.4 Light bulbs .......................................................................................................... 37
11 Discussion of design process ............................................................................................ 38
11.1 Effectiveness of design .............................................................................................. 38
11.1.1 Output ................................................................................................................ 38
11.1.2 Efficiency ............................................................................................................ 39
11.2 Relevance to the problem ......................................................................................... 39
11.2.1 Performance ...................................................................................................... 39
11.2.2 Cost .................................................................................................................... 39
11.2.3 Usability ............................................................................................................. 40
11.3 Limitations ................................................................................................................. 40
11.4 Manufacture .............................................................................................................. 40
12 Conclusions ....................................................................................................................... 41
12.1 Further developments ............................................................................................... 42
13 The Future ........................................................................................................................ 42
13.1 Opportunities ............................................................................................................ 42
13.2 Challenges ................................................................................................................. 43
14 Acknowledgements .......................................................................................................... 43
15 Bibliography ...................................................................................................................... 44
16 Appendices ....................................................................................................................... 45
16.1 Risk Assessment Retrospective ................................................................................. 45
16.2 Appendix A – Glowstar specification ........................................................................ 46
16.3 Appendix B ................................................................................................................ 47
16.4 Appendix C: Design Specification for next generation lantern ................................. 48
16.5 Appendix D: Lamp Schematic .................................................................................... 49
16.6 Appendix E: Battery Module Schematic .................................................................... 49
16.7 Appendix F: Cost breakdown for lantern design ....................................................... 50
16.8 Appendix G: Circuit detail ......................................................................................... 51
16.9 Appendix H: Light bulb light distribution .................................................................. 52
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3 Table of Figures Figure 1 Glowstar Lantern ......................................................................................................... 8
Figure 2 Distribution model for Glowstar in Kenya ................................................................. 16
Figure 3 Barefoot Power marketing strategy .......................................................................... 17
Figure 4 Two examples of first generation lanterns on sale in Kenya. Energiser (left) and
Klassique (Right) ....................................................................................................................... 20
Figure 5 the history of the development of LEDs and other light sources (Osram, 2010) ...... 29
Figure 6 Ideas for providing 360 degree spread of light from LEDs ........................................ 30
Figure 7 Charge voltage and temperature of NiMH (GP Batteries) ......................................... 31
Figure 8 Function diagram of the next generation concept .................................................... 32
Figure 9 Functional diagram of the Lamp module ................................................................... 33
Figure 10 Functional diagram of the microcontroller code ..................................................... 34
Figure 11 Functional diagram of the Battery module ............................................................. 34
Figure 12 Lamp module ........................................................................................................... 35
Figure 13 Output of Buck MOS switch at 1.6Mhz.................................................................... 36
Figure 14 Graph showing Lamp module output characteristics .............................................. 35
Figure 15 Buck converter switch output .................................................................................. 35
Figure 16 Battery Module ........................................................................................................ 36
Figure 18 Graph of SEPIC output power against duty cycle .................................................... 36
Figure 17 Graph showing SEPIC converter efficiency .............................................................. 36
Figure 20 Light distribution for Phillips bulb ............................................................................ 37
Figure 19 Phillips bulb .............................................................................................................. 37
Figure 23 Light distribution for short 30° bulb ........................................................................ 38
Figure 21 Light distribution for phosphor coated bulb ........................................................... 38
Figure 22 Short 30° bulb .......................................................................................................... 38
Figure 24 Glowstar and next generation lantern side by side ................................................. 40
4 Table of Tables Table 1 sources of information during Kenya fieldwork.......................................................... 11
Table 2 Solar Lantern sales from Uchumi Supermarket, Meru Town during 2009 ................. 15
Table 3 List price for Glowstar lanterns in Kenya with estimates of US Dollar equivalent ..... 16
Table 4 Glowstar warranty period ........................................................................................... 17
Table 5 Example prices of off grid power systems in Kenya.................................................... 20
Table 6 Key characteristics of battery types ............................................................................ 28
Table 7 Potential light sources for a solar lantern ................................................................... 29
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5 Introduction
This report deals with two sections of related work, the first is investigating the Glowstar
lantern and assessing its impact and success and the second is developing a next generation
lantern.
5.1 Solar Lanterns
Worldwide 1.7 billion people live without access to electricity with rural access rates as low
as 2% in some countries (Lighting Africa). Those without access to electricity rely on
kerosene lamps, candles and battery powered torches to provide light at night. The quality
of these light sources is poor and the running costs are high, consuming valuable cash from
limited household budgets, accounting for 10 – 15% amongst the poorest households
(Lighting Africa). In addition the burning of kerosene produces smoke that is harmful to
health and poses a significant fire risk within the home.
The provision of electric lighting can provide a boost to families attempting to break away
from poverty through increased productivity resulting from an extended working day,
enabling children to study effectively after dark, reducing expenditure on consumables and
improving the health of the whole family. Grid expansion is expensive, especially into rural
areas where the distances are large and the population density is small resulting in very
slow progress. ‘By 2000, Kenya Power and Lighting’s rural electrification programme had
reached less than 70,000 households (about 2% of the population) after 15 years of activity.’
(Hankins, 2001). As a result it will take many years for the grid to reach all people, if indeed
it ever does, therefore a different solution needs to be found to extend access to electricity
and one method is the use of photovoltaic systems.
Photovoltaic (PV) systems are well suited to applications in the developing world as
much of the developing world receives high levels of insolation. In addition PV systems can
be low maintenance and installed in a variety of situations. The main drawback in this
context is the price which is falling as the global market develops but is still high, especially
when compared to the income levels of the poorest people.
The challenges with the cost of PV systems can be combated through the
development of small scale PV appliances dubbed ‘micro’ or ‘Pico PV’ that can be produced
at a cost that is compatible with rural household income in developing countries. The solar
lantern is one example of this that offers the potential to meet this large market.
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5.2 Glowstar background
The Glowstar lantern was developed between 1997 and 2003
by Practical Action Consulting, the consultancy arm of Practical
Action, formerly Intermediate Technology Development Group
(ITDG) with funding from the UK Department for International
Development (DFID). Practical Action is a development charity
founded on E.F Schumacher’s philosophy of ‘Small is beautiful’
(Schumacher, 1973) that ‘works to find practical solutions to
poverty’ through the application of appropriate technology
(Practical Action).
The Glowstar lantern (Figure 1) was designed to provide high quality, reliable and low
cost lighting to rural households in developing countries, replacing kerosene lanterns and
candles. The lantern was designed as a first step on the energy ladder and it was recognised
that this is not a long term solution to energy access for rural poor but a good short term
measure to improve lives. It was developed by Practical Action Consulting and transferred to
Sollatek, a UK based company specialising in solar energy amongst other products (Sollatek
(UK) Ltd), for further development, manufacture and distribution. The partnership with
Sollatek allowed the lantern to be produced and distributed worldwide through the
company’s existing distribution network.
The Glowstar is designed as a high performance, rugged and reliable lantern that can
be charged from Solar, the grid or a vehicle. The light source is a compact fluorescent lamp
with a sealed lead acid battery for energy storage and an external solar module. The
Glowstar is available in two models the GS5 and the GS7 (also called the Glowstar Basic and
Glowstar Plus). The main differences between the models are the inclusion of an auxiliary
output on the GS7 to allow for phone charging or powering a radio, the power of the
compact fluorescent lamp (CFL) and the battery capacity. The specification for each model is
included in Appendix A. The Glowstar lantern typically sells for around US$100 without a
solar module, rising to US$150 with a solar module.
5.3 Current situation
The current level of electricity access remains largely unchanged globally. Within this
environment the Glowstar lantern continues to be produced and sold worldwide but with
Figure 1 Glowstar Lantern
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sales volumes of tens of thousands not the hundreds of thousands anticipated and the
lantern has not reached as far as the need. The aim of this project is to investigate the
reasons for this underperformance of the Glowstar lantern and potential solutions to
improve the penetration of off grid electricity availability.
5.4 Technology advances
Since the launch of Glowstar there have been some significant advances in technology that
could be applied to this field including batteries and light sources. Perhaps the most exciting
of these is the development of the high power white LED that offers the option of solid state
general lighting.
5.5 Opportunities
There are many opportunities in this area and in recent years a significant focus has been
placed upon off grid lighting for developing countries from many organisations including
commercial, charitable and governmental. This has resulted in the development of new
products for the market and a greater understanding of the requirements through ongoing
research which are being made available to ease access into the market. On the back of all
of this there is great potential to be explored in the development of a next generation
lantern that could better meet the needs of the rural poor communities who would benefit
from access to improved lighting.
6 Methodology
The work in this project falls broadly into two areas, firstly the investigation of the Glowstar
project and secondly the development of a new lantern. This is reflected in the structure of
this report where the two areas are dealt with separately with the flow of useful
information from the first section to the second.
6.1 Glowstar
The aim of this part of the project was to understand the development, manufacture,
distribution and support of the Glowstar lantern and identify factors contributing to its
commercial success and social impact. To achieve these two areas of research were
undertaken, in the UK utilising published documents and information from people involved
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with the lantern and in Kenya to gather information from people marketing, distributing and
using the lanterns in the environment for which they were designed.
6.1.1 UK based research
The main focus of the UK based research was on documents, papers and reports produced
relating to Glowstar and off grid lighting in general. The Glowstar project was well
documented by Practical Action including honest post project assessment. The aim of this
project is to build on this assessment with the benefit of hindsight and seven years of
commercial release of the lantern. In addition information was gathered from those
involved in the development including Practical Action and DFID, it must however be stated
that this information was given informally but provides an insight into opinions held about
the Glowstar Project.
Research into the off grid lighting market in general helped to provide a context in
which specific research in Kenya could be based. There are several organisations that are
actively researching and publishing information relating to developing world off gird
lighting. The main organisations doing this are Lighting Africa and the Lumina Project as well
as other smaller contributors.
6.1.2 Kenya based research
Work in Kenya is a vital part of this research as it is vital to maintain a focus on the people
for which the product is designed as argued eloquently by Schumacher in ‘Small is Beautiful’
(Schumacher, 1973). It would be impossible to evaluate the lanterns success without input
from users, potential users and experts who understand the market. Kenya was the obvious
choice for a study location as it was the location of the original market research and
development activities for the Glowstar Lantern.
The aim therefore of travelling to Kenya was to gather opinions of Glowstar and
develop better understanding of the off-grid lighting market. Due to the time and resource
constraints of this project a large quantitative study of opinions, attitudes and experiences
was not possible, instead a range of opinions was gathered through discussions and
interviews across the range of stakeholders in the Glowstar distribution network and the off
grid lighting market. The structure of the research visit is outlined in Table 1.
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Group Details Research
Sollatek East
Africa
The East Africa branch of Sollatek
who have exclusive rights to import
of the Glowstar Lantern in East
Africa and therefore control the
distribution network within Kenya.
Interview with the regional sales manager for
Nairobi covering distribution, marketing,
sales performance and product performance
Solar product
agents /
distributers
Nairobi based companies that sell
and distribute the Glowstar
Lantern through their outlets
alongside other solar products.
Interviews with representatives who
understand the product and the market.
General points covered include sales
performance, customers, product
performance and potential improvements.
Local reseller Small local shops selling Glowstar
alongside other products. Also
including supermarkets that stock
Glowstar.
Two elements looked at, firstly a survey of off
grid lighting and solar products on sale and
secondly interviews with shop owners
covering sales performance, customers,
product performance and potential
improvements of the Glowstar.
Glowstar
Users
Owners and users of Glowstar,
both individuals and organisations
e.g. charities, schools, health
centres. Users were beneficiaries
of Practical Action and Rotary
sponsored distribution of lanterns.
Interviews covering lantern performance and
features, cost and value, other lighting
sources, overall opinion and potential
improvements
Other off grid
lighting
companies
Other companies producing solar
lighting products for off grid
applications
Discussion with a representative of Barefoot
Power covering their product range,
distribution and marketing strategies, the
solar lighting market and opinions of
Glowstar.
Related non-
commercial
organisations
NGOs and charities operating in
Kenya to promote the uptake of off
grid lighting including solar
lanterns.
Discussions covering the off grid market,
solar products available, distribution and
marketing, Opinions on Glowstar and
potential improvements
Table 1 sources of information during Kenya fieldwork
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6.2 Next generation lantern
The research into Glowstar provides a good background to a product development exercise
to design a new lantern to meet the needs identified. In addition to this new technology
options for achieving solar lighting need to be identified followed by a standard design
process for a new lantern. Research into technological advancements fed into the
requirements identified by the Glowstar research to form the basis of the design stage. The
design work focused mainly on the enabling technology rather than the form of the final
product but various concepts were explored and developed and the final design is intended
to enable the preferred concept.
7 Glowstar research results
The information gathered from the sources set out above provided impressions of Glowstar
from a broad range of parties. Inevitably there is considerable variation in the experiences
and opinions within this range however there were common themes and significant
correlations that can be identified. The following section aims to identify both the range of
opinions and the common themes within them.
7.1 Performance
7.1.1 Technical assessment
The most rigorous assessment of the technical performance of the Glowstar in comparison
to other solar lanterns on the market has been conducted by Deutsche Gesellschaft für
Technishe Zusammenarbeit (GTZ) who are a German ‘federally owned organisation working
worldwide in the field of international cooperation for sustainable development’ (GTZ).
Their study ‘Solar Lanterns Test: Shades of Light’ (Grüner, et al., 2009) compared 12 solar
lanterns from a variety of manufacturers including the Glowstar GS7. Each lantern was
subjected to a variety of tests including quality of workmanship, functionality, light output
and costs with scores being awarded for each of the 20 test undertaken.
The Glowstar fared poorly in results of this assessment, being placed 7th out of the
12 lanterns tested. The ‘Glowstar was criticised for wrongly designed circuitry’ and scored
poorly on efficiency, run time and deviation from specifications. The report concluded that
‘The Glowstar failed both the technical test and in terms of value for money. This unusually
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heavy and cumbersome lantern was a pioneer of the market sector, but exhibits defects in
workmanship and offers only a poor solar fraction and modest light duration.’
7.1.2 Distributors
The opinions of distributers and other industry experts vary as to the performance and
quality of the Glowstar. In general however the lantern is viewed as a high quality product
that performs well and has a good light output while being easy to use.
“Nice quality ... the product sells itself” (Distributor)
“Glowstar is very good quality” (Industry Profesional)
The Glowstar compares favourably to other solar lanterns in light output with many
alternatives providing less light with poorer battery lifetimes. Some consider the light
output to be excessive and too bright with one story of a lady being scared by the brightness
of the lantern. The batteries normally last two to three years before requiring replacement
and lanterns are rarely returned with problems.
Commonly identified problems with the Glowstar relate to the duration of light and
the lifetime of the battery. Many people identified that the duration of light after a full day’s
charge was often disappointing to customers and declined as the product aged. The lifetime
of the battery before it failed completely was also a common cause of disappointment with
customers. Estimates for the light duration on a full charge tended to start off at five to six
hours but declined to less than four within a year. Examples of battery life have been as
short as one year before replacement was required. In contrast, examples of lanterns that
have continued to operate for six years without the need for service or replacement parts
have also been reported.
More minor problems have been reported include incorrect battery status
indication, switches sinking into the lantern body and poor life of the CFL tubes.
7.1.3 Users
The experience of users of the Glowstar lantern varies in a similar way to the distributers
with some users being delighted by its performance while other are rather disappointed.
Once again the general impression is that the lantern is regarded as a good quality and high
performance product that meets the user’s requirements very well.
“The light output is very good, it is “quite ok” for reading by and will fill the whole
room.” (User)
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“The lanterns were very good at the beginning. They provided light from 7pm till 2am
on a full charge. The light produced was bright white light that had no effect on the
eyes and allowed people to read or work at night without eye problems.”(User)
The main frustration with the lantern is the degradation of performance that is often
experienced over time. The most significant of these seem to be reduced operation time on
a full charge and battery failure.
“The lantern does not now work well, it only works when connected to the panel and
this is temperamental, sometimes there is light but sometimes there is not.”(User)
From the small sample of users that were interviewed during this research most seemed to
get around two years of operation at the advertised levels before performance decreased.
“After two or three years the lanterns provided three to four hours of light after a full
day charging and after four years no light was produced at all. All the lanterns
stopped working in the same year.”(User)
“At first the lantern was very nice and provided around 5 hours of light. After two
years the light time had reduced.”(User)
7.2 Sales
As described in the introduction the sales of Glowstar globally since its launch in 2003 have
been disappointingly low. It has not been possible to acquire accurate sales figures but
Practical Action estimates, based on royalty payments from Sollatek, indicate that the level
is tens of thousands per year worldwide not the hundreds of thousands that was
anticipated. The distributers in Kenya were a little more forthcoming with information about
the level of sales of the lantern.
7.2.1 Sollatek
Samwel Odhiambo, the regional sales manager for Sollatek in Nairobi claims that Glowstar
enjoys around a 20% market share of solar lanterns in Kenya, a level that Sollatek are happy
with. He estimated that Sollatek sell around 100 Glowstar lanterns per month in Kenya,
mainly in Nairobi (“61 out of 100 last month”). Sales levels have decreased slightly since the
launch of the lantern, which is attributed to the emergence of counterfeit products from
China.
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7.2.2 Distributors
The general message from distributers is that sales of Glowstar lanterns are low in
comparison to alternative products and have declined in recent years.
“Sales have declined significantly on three years ago. They are now at around 10% of
those levels.”(Distributer)
“Sold in greater numbers when launched...no longer popular” (Sales Outlet)
Table 2 shows the sales figures for Uchumi Supermarket in Meru town, Kenya. Uchumi was
the only major supermarket chains in Kenya where the Glowstar was found with examples
in most of the stores visited around the country. It is worth noting that without exception
the Glowstar lanterns on the shelves in were old, dating back to 2006 and covered in dust.
The sales figures shown support this observation. Further details of the lanterns listed can
be found in appendix B.
Lantern Price (Ksh) Number sold
Glowstar GS7 7345 0
Osram 3000 1
Eveready RC102 8
Klassique LED 1745 1
Energiser emergency lantern 2200 6
Energiser RC105 (Round) 2000 10
Windsor emergency light 1990 2
Table 2 Solar Lantern sales from Uchumi Supermarket, Meru Town during 2009
7.3 Market
The sale of Glowstar lanterns is dominated by NGO’s, typically working in remote locations
including South Sudan and Northern Kenya. Sales to the individual consumers on the mass
market are very small. Distributers report that they get repeat business from NGOs who are
looking for replacement lanterns or lanterns for a new location. The suggested reason for
this is that NGOs working in remote areas value the reliability and robustness of the
Glowstar lantern and have the money available to buy them.
“Sales are now at 40 to 50% of original levels as a result of demand from NGOs falling.
Sales to the mass market have never been significant.”(Distributer)
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7.4 Cost
The list price for a Glowstar lantern in Kenya is set by Sollatek Kenya; they sell at trade
prices to distributers but at list price to consumers. The list price is shown in Table 3
(Sollatek (Kenya) Ltd, 2009).
Lantern model Recommended solar
module
Lantern list price Solar module list
price
Total price
Glowstar Basic
(GS5)
6Wp 7,200Ksh
US$100
3,300Ksh
US$50
10,500Ksh
US$150
Glowstar Plus
(GS7)
9Wp 10,100Ksh
US$150
5,000Ksh
US$70
15,100Ksh
US$220
Table 3 List price for Glowstar lanterns in Kenya with estimates of US Dollar equivalent
The current cost of Glowstar has remained constant for several years and is significantly
above the cost that was anticipated by Practical Action during its development and the price
indicated as acceptable by the market research for Glowstar of US$75 including the solar
module (ITC Ltd, 2003).
There was almost universal agreement that the Glowstar lantern is too expensive and
that this is the major obstacle to higher sales and wider market penetration, especially in
the consumer market and amongst rural poor. Suggestions for a reasonable cost for a
Glowstar lantern including a solar module ranged from 1,500Ksh to 8,000Ksh but a figure of
3,000Ksh (US$50) was the around the average and quoted by the majority of those asked
across the whole range of stakeholder.
7.5 Distribution
The distribution model for Glowstar in Kenya is
outlined in Figure 2. The distribution chain is
controlled by Sollatek Kenya as the only
authorised importer of Glowstar for East Africa.
Provincial distributors are located throughout
the country in the regional capitals but their
presence is imited in small towns and villages.
Sollatek UK
Sollatek Kenya
Provincial Distributors
End users
Community Groups Retail units
Figure 2 Distribution model for Glowstar in Kenya
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Feedback from users and community organisations suggests that the distribution channels
do not extend close enough to the rural consumers. This limits their access to the product
and to after sales service and spare parts and inherently limits the penetration of the rural
market. Several of the users interviewed had non-functional lanterns but had not taken
them for service due to the long distances to service centres.
7.6 Marketing
The main target market for Glowstar is NGOs as they
have the money available for purchase. As a result of
this there is little marketing effort undertaken to the
mass market. Methods that are employed include
partnering with NGOs and community organisations to
promote the product and educate people about the
benefits of solar lanterns and partnering with banks and
credit schemes to ease money restrictions on potential
customers. The biggest focus in marketing is on face to
face training to create awareness.
Experience from other solar lighting companies
and NGOs promoting solar lighting is that raising
awareness of the products and training people about
the benefits is the best way to grow demand amongst
the rural poor target market, and the best way to do this is through face to face contact.
One strategy employed by Barefoot Power and Solar Aid is outlined in Figure 3.
7.7 Service
Sollatek’s reputation for after sales service in Kenya is
excellent and the company appears to be committed to
the Glowstar warranty (Table 4). This level of warranty is
unusual in Kenya where many products are sold without
any warranty and cheap, poorly manufactured products
are commonplace. This is a very strong selling point of the Glowstar lantern.
Part Warranty period
Lantern 5 years
Battery 2 years
CFL bulb 6 month
Table 4 Glowstar warranty period
Mobilise Leaders “Tell them the good news
about our product”
Train in the use of the product
Provide examples for them to use and test
Encourage them to spread the news in their communities
Use existing distributors and shops to provide local access to
the product
Figure 3 Barefoot Power marketing strategy
18
To obtain repairs under warranty the product must be returned to Sollatek at the
expense of the owner, as discussed above this can be a considerable expense due to the
limited geographic spread of service centres.
Outside of warranty replacement batteries cost 1000-1800Ksh and CFLs around
500Ksh however neither is commonly available away from service centres.
7.8 Perceptions
7.8.1 Industry experts
The Glowstar is generally regarded as a high performance product amongst industry experts
partly due to the good light output and the long warranty that is offered. Opinions vary
however, with many aspects of the design and performance detracting from the positive
image. The performance issues related to the battery life have damaged the reputation of
the Glowstar and affected its sales as customers move to new products. In addition the
lantern is big and heavy, with a large solar module that limits the portability although the
design offers robustness and a good spread of light. The cost is a major constraint to sales.
The inclusion of additional features, especially mobile phone charging is a great bonus to
the product. LEDs are considered to be an improvement as they are perceived as brighter
and more efficient than CFLs.
7.8.2 Users
The general response from users of the Glowstar to its design was positive with the lantern
considered attractive, easy to use and rugged. The lighting performance (output and
duration) was expressed as the most important criteria for the lantern rather than its
appearance or additional features. The ability to charge a mobile phone was identified as a
useful additional feature but a recurrent message was that a simple lantern that works well
is better than lots of features that are unreliable.
7.9 Impacts
The Glowstar lantern has had a number of impacts in the area of off grid lighting which are
potentially much wider reaching than simply providing lighting solutions to poor rural
people.
The project successfully developed a good quality lantern that was taken on by a
private company and marketed worldwide. This has been an experiment in partnerships of
19
this nature which will provide interesting lessons for the future. The direct social impact of
the lantern on poor rural people has been very limited due to poor market penetration;
however where the product has been used within this market users reported that the
lantern was very useful and replaced kerosene for lighting. In addition to this most of the
users interviewed for this research now have alternative supplies of electricity installed
either from a solar system or mains. This is not a strong basis for conclusions without
further research but appears to suggest that the Glowstar lantern was a first step on the
energy ladder.
The lantern has been used extensively by NGOs in remote areas and continues to sell
today in significant numbers worldwide.
The Glowstar was one of the first lanterns designed for this market and as such
played a role in establishing the market that has continued to develop.
No official reports by DFID are available however the experience of the Glowstar
development was apparently viewed as a total failure by some staff at DFID and perhaps
had an impact on future funding decisions in related areas.
The original intention was for the lantern to be manufactured in Kenya in keeping with
the philosophy of Small is Beautiful (Schumacher, 1973) advocating local manufacture of
appropriate technology. This aim was later abandoned on practical and economic grounds
but provides an interesting experiment in the application of this philosophy. The current aim
of most organisations involved in off grid lighting is to provide lights to the maximum
number of people possible rather that to develop local industry resulting in the majority of
products being produced in China.
7.10 Competition and alternatives
7.10.1 Market condition
The solar market in Kenya is well established and growing with a high level of awareness of
solar power. The extent of the grid is limited with poor reliability and high costs. This
combined with a growing awareness of environmental concerns has led to a high level of
enthusiasm for solar power. The government has responded to support the market by
introducing strict import standards and rigorous checks to ensure that products are not
substandard and has removed VAT (16%) from solar products.
20
The solar market in Kenya “is very price sensitive and consumers have short memories”
(Chege, 2009) about products.
7.10.2 Wider market
The wider off grid lighting market is quite broad incorporating solar lanterns, solar home
systems and fuel based generators as well as traditional kerosene lamps and candles. In
addition new schemes are being trialled based on an energy kiosk idea where energy is
bought as a product from a central kiosk, mini grids covering one village and generating
local power from alternative fuels e.g. biogas. Example prices for some alternative systems
are shown in Table 5.
Product Details Price
Solar module and battery
The most basic type can consist of a 14Wp panel and 50Ah.
7995Ksh (offer from Chloride Exide)
Full solar home system (installed)
Including solar module, battery, charge controller, lights and installation
25,000Ksh to 90,000Ksh and upwards for very large systems
Generator Running on petrol or diesel 10,000Ksh to 70,000Ksh
Hurricane lantern Traditional enclosed kerosene lantern 300 – 500Ksh Table 5 Example prices of off grid power systems in Kenya
The solar lantern market is also developing rapidly with two generations of lantern evident.
The first generation, contemporaries of Glowstar, tend to be large CFL and lead acid based
lanterns. The new generation of solar lighting is emerging on the market now and is often
LED based with a range of prices and power options. The companies producing the new
generation include number of social enterprises that have been established to tackle the
problem of providing modern lighting to rural people; examples include Barefoot Power and
Tough Stuff Solar, but also include some big corporate names including Phillips and Osram.
There is a wide variety of lanterns available in Kenya,
however only a small number are equipped with solar
charging. Few outlets stock solar lanterns, mainly specialist
solar shops however this is beginning to change with the
companies mentioned above actively pursuing the rural mass
market. Current lanterns (usually mains charging) cover a
wide range of prices and performance and include both
compact fluorescent and LEDs as the light source. A couple of
typical lantern designs are shown in Figure 4, one CFL and one LED. Many new generation
solar lights make use of LEDs although often for task light or small home systems. Lighting
Figure 4 Two examples of first generation lanterns on sale in Kenya. Energiser (left) and Klassique (Right)
21
Africa has recently announced the winners of their ‘Best off-grid lighting products in Sub-
Saharan Africa’ (Lighting Africa, 2010), the winners are shown in Appendix B. There appear
to be no lanterns that have a Glowstar type design (portable room lighting) that use LEDs
and provide high quality light of a comparable level.
7.11 Requirements for a lantern
It would seem that little has changed to the requirements for a solar lantern since the
market research was carried out for the Glowstar except for the desire for six hours of light.
Detailed market research by Lighting Africa (Lighting Africa, 2008) and this project research
have led to the summary of key requirements as follows:
Provide light for 6 hours on a day’s solar charge
Light a whole room (based on rooms 4x4m) sufficiently to undertake a range of
activities in the room
Enable light to be used in multiple rooms/locations
Price should be below $50 (US)
Lantern must be chargeable from solar PV
Lantern should look and feel of high quality
Lantern life should be a minimum of two years with no servicing
8 Discussion and implications of research
8.1 Success of Glowstar
The stated aim of the Glowstar development project was to “Develop, produce and market
an affordable, reliable micro solar lantern in Kenya, meeting the needs of large numbers of
poor rural people for better quality cheaper lighting” (ITC Ltd, 2003).
8.1.1 Factor and opinions of success
It is important at this stage to consider the requirements and factors for success. The
impacts of Glowstar has had impacts that do not directly achieve its purpose and have had
knock on effects that are difficult to analyse. As a result it would be inappropriate to label
the Glowstar project as a success or failure based purely on sales performance and market
penetration but rather more appropriate to consider the elements of Glowstar’s impact.
22
8.1.2 Successes and failures
On a basic level of direct benefit to poor rural people the project cannot be classed as a
success based on experience in Kenya. The lantern has failed to reach the target market in
any significant numbers and has been effectively out of the reach of the intended
customers. The main reason contributing to this must be the cost, which places the lantern
outside the financial reach of even average income rural people let alone the poorest and
even with the availability of credit schemes it may still not accessible. A GS5 lantern is equal
to the average household monthly income and if directly replacing a kerosene lamp (typical
running costs are US$2.80 to US$8.06 per month for a simple wick lamp and hurricane
lantern respectively (Lighting Africa, 2008)) it has a payback period of 18 months to four and
a half years. This is clearly a very high capital outlay and significant payback period for the
target market and the maintenance requirement of batteries and bulbs provides additional
cost within this payback period. Penetration of the target market is also hindered by the
distribution network in Kenya which does not bring the product close enough to the
intended customers and a marketing strategy that seems to have abandoned the mass
market, with its great marketing challenges and high workload, in favour of the lucrative and
easier NGO sector.
The project has successfully produced a high quality product that is very well suited to
the intended purpose, with the caveats about battery performance outlined previously. This
is highlighted by the continuing sales and demand from NGOs for use in remote areas where
reliability is of high importance. The project also explored a new market segment when it
was developed, being the first to specifically target the poor rural mass market, and
therefore helped highlight the need and opportunities in this sector through the high profile
coverage that the project enjoyed (ITC Ltd, 2003) and (ITC, 2001). This is likely to have
played a part in promoting the development of the market sector to what is now a very
active industry and therefore in an indirect way has helped improve access to modern
lighting in the rural mass market. Lessons learnt from Glowstar will also informed
subsequent developments of lanterns by other organisations yielding better products. The
danger of high profile coverage of Glowstar is that it may have caused disillusion amongst
stakeholders and interested groups, for example DFID, as the investment did not result in
direct success on the stated aims. There is also the possibility of wider market spoiling by
products that do not perform to their expected levels.
23
It is an interesting experiment in collaboration between charity and private enterprise
that offers points to guide future developments. The partnership between Practical Action
and Sollatek clearly brought many advantages to the Glowstar project, not least the quick
and easy access to manufacturing capability and distribution networks worldwide. This will
have significantly sped up the entry of Glowstar to market and reduced the work involved in
getting it there but also introduced compromises in the philosophy behind the product. As
highlighted in the Glowstar Final Report (ITC Ltd, 2003) the primary aims of development
organisations and private enterprise are fundamentally different, with the former seeking to
improve lives while the latter is more concerned with profit. This is evident with Glowstar
which lost the pro-poor focus when control was transferred to Sollatek with the result of a
high market price and limited the market penetration. Sollatek have focused on higher
margins at low sales rather than mass sales.
To effectively and sustainably market this type of product requires the interlinking of
pro-poor ethos with commercial approaches throughout the whole product lifecycle,
without a transition occurring from one to the other in the middle. Several recent start-up
social enterprises are experimenting with this model and producing some excellent
products. The road to establish a company, manufacturing and distribution network
however is long and difficult. It is also very exciting to see some big corporate companies
entering the market driven by both social and commercial considerations. These companies
have significant resources and experience available to develop good products and strong
supply networks.
The final major experiment was the aim to develop indigenous industry as well as
providing affordable lighting services. This is a worthy aim for a development organisation
but the project did not succeed due to the limitations of industrial capability in Kenya. This
aim was abandoned late in the project, possibly causing unnecessary expenditure. It is
important to identify early on what the overriding objective for a project is to be and the
realities of meeting it to allow focusing of resources on achievable aims. It is interesting to
note that most organisations involved in the solar lantern market now are aiming to provide
the improved lighting to the maximum number of people rather than aiming for industrial
development.
24
8.2 Competition
As explained earlier the solar market in Kenya is well developed and growing providing a
context for the position occupied by Glowstar. Sollatek have done well to maintain the
image of the product as high quality, in large part due to the excellent warranty. Glowstar’s
price puts it in direct competition with a basic solar home system which can be bought from
around 8,000Ksh. These have the barebones components offering low performance and
limited lifetime due to the absence of a charge controller but they can power lights in two
rooms. When portability of light is not required two fixed lights are likely to be preferred to
a single lantern.
The range of second generation lanterns that are now emerging on the market is going
to increase competition to Glowstar. These products are generally smaller, lighter and
cheaper than Glowstar or offer greater functionality, i.e. small solar home systems.
9 Conclusions about Glowstar
9.1 Reliability of information and conclusions
It must be stressed that the results presented above are based on interviews with
stakeholders in the Glowstar distribution network in Kenya and not on extensive
quantitative research. The results as presented are based on common themes that were
repeated by the majority of those interviewed and therefore provide a reasonable basis on
which to base conclusions. These results and conclusions focus on the situation in Kenya and
without further research cannot be considered representative of the global situation.
9.2 Degree of success
The Glowstar project cannot be heralded as an absolute success however neither can it be
branded a complete failure. The project has elements of success within its aims, both stated
and implied and potential wider consequences that will have benefitted the target market.
In terms of the stated aims of the project, it has not succeeded in either directly providing
affordable modern lighting to the masses or in nurturing industry in Kenya. It is highly likely
that they project has indirectly contributed towards these aims through development of the
sector.
25
9.3 Potential improvements
With the benefit of hindsight and based on the experience of Glowstar, which provides
many positive learning points, there are several recommendations for changes to the
project if it were to done again.
9.3.1 Product
The functional aspects of potential future lantern designs will be dealt with in more detail in
the following section on next generation lantern development. However the following
conclusions relate to the Glowstar specifically.
The key characteristic of the lantern is the price which must be minimise as the
market is very cost sensitive. The current cost of the lantern is too high and a target
of US$50 is a more acceptable price.
The light runtime needs to be guaranteed at a minimum of six hours and the lantern
needs to perform consistently
The appearance of the lantern was well liked but is considered large and heavy
The inclusion of mobile phone charging is valued.
9.3.2 Distribution
For a product to be self sustaining it needs to be sold on a commercial basis. Charity funded
give-aways are inherently not and they degrade the perceived value of the product with the
risk of market spoiling. To quote Tough Stuff Solar “There’s a built in feedback loop when
you sell something – people only pay for something they want. That just doesn’t happen
when you give things away.” (Rocky Radar, 2009).
The Glowstar distribution network in place in Kenya is inadequate for rural market
penetration. The product must be available locally coupled with knowledgeable advisors for
effective distribution. This requires a local focus on a nationwide scale and will inevitably be
labour intensive. The availability of credit will be a major boost to sales from some sections
of society. Spares and servicing also need to be local to users and tie in with distribution.
There are a large number of small outlets in rural towns and villages that sell
electrical goods and could sell lanterns. The owners of these shops would presumably be
technology aware enabling them to be trained in the basic servicing of lanterns. Accessing
these small outlets will be a resource intensive task as each must be contacted and most will
want to trial the products before stocking them.
26
Utilising the mobile phone distribution network is a possible solution. Mobile phones
use has exploded in Kenya in recent years so the inclusion of mobile phone charging with a
solar lantern provides a promising route into accessing a widespread distribution network. A
subtle change in emphasis to a phone charger with attached light may be required, but the
net effect is the same and mobile phone dealers are going to be technology aware providing
a good basis on which to understand the product.
Partnerships with micro credit agencies and community groups has been explored by
the Glowstar project but could be expanded to provide an effective distribution network by
combining a solution to capital availability access to large numbers of people.
9.3.3 Marketing
The marketing of a lantern plays a key role in creating awareness of the product. The target
market will not necessarily be technology aware, or know about the benefits the product.
The purchase of a lantern will represent a significant expenditure for the household and
therefore the costs and benefits need to be fully understood. Marketing in rural areas is
going to be a highly resource intensive process and has strong links to the distribution
network as the most effective method of marketing is likely to be face to face contact.
Marketing through mass media may have some effect but this is unlikely to be able to
demystify the product and its operation while sharing of personal experiences and gaining
hands on experience of a product play a significant role in earning peoples.
The marketing process employed by Barefoot Power is very promising (see section
6.6), where influential figures in each community are identified and introduced to the
product and encouraged to share their experiences. Creating excitement about the product
is important through public events as awareness of the product spreads it will begin to
snowball if sufficient excitement can be created in an area.
9.4 Other products
The implications for Glowstar with the emergence of the second generation of solar lanterns
will be seen over the coming years. There is a high possibility that new lanterns will take
market share away from Glowstar, especially the Phillips Uday lantern that is of a similar
design one third of the cost. The key to this will be the new lanterns performance compared
to Glowstar. In terms of the rural mass market many of the new solar lights have the
potential to perform well with appropriate marketing, distribution and support. This is an
27
exciting time for the solar lighting market in Kenya with the potential to have big impacts on
peoples’ lives.
9.5 Opportunities
With the current state of the solar market in Kenya there are good opportunities for new
products if they meet the needs of the market. It remains to be seen over the coming years
how the new entrants to the market will perform, but until they are established the entire
rural poor market remains untapped and under-served providing exciting opportunities for
new lantern developments. The Kenyan Government is working to protect the solar market
from substandard products. Considering the strength of the competition that is emerging
with the second generation of lanterns there is little point in launching a new lantern
development unless something new can be brought to the product that will enhance the
benefit the user. Many NGOs promoting off-grid lighting should help stimulate and
accelerate the market.
10 Next generation lantern development
10.1 Requirements
The specification for a new lantern design based on this research is included in Appendix C.
The key constraints of the requirements are:
Cost – below $50 and as low as possible
Light Duration – minimum of 6 hours on a day’s charge
Easy to operate and maintain
360 degree light distribution Some industry experts felt that general room lighting, rather than directional task lighting is
a higher priority for domestic users.
10.2 Technology options
10.2.1 Batteries
The main battery types available are Nickel based (NiCad and NiMH), lithium based (Li-ion,
Li-polymer) and Lead Acid. The key characteristics related to solar lanterns are set out in
Table 6. (Buchmann, 2005)
28
Type Advantages Disadvantages
Ni-Cad Standard sizes and commonly available
High cycle life
Well suited to solar charging
Low energy density
Heavy metal content
Memory effect and high self discharge
NiMH Standard Sizes and commonly available
No Toxic metals
Good energy density and Low self discharge
Poor performance at slow charging rates
Intolerant of overcharge
Moderate cycle life
Lead
Acid
Well suited to solar charging
Low self discharge
No memory effect
Bulky and heavy
Low energy density
Lead content – Environmental concern
Li-ion High energy Density
No memory effect
Custom sizes – not commonly available
Complex charge control required
Expensive
Table 6 Key characteristics of battery types
NiMH batteries offer a good compromise between cost and performance with good energy
density, reasonable cycle life and low self discharge in standard packages for a reasonable
price. NiCad are to be avoided due to their cadmium content and potential for
environmental damage is discarded and lead acid batteries are large, bulky and are not
available in standard packages. Li-ion batteries are expensive and require more complex
control circuitry to operate safely.
The availability of NiMH in standard sizes allows for much easier replacement when
the batteries reach the end of their life as they can be sourced and replaced by the owner
without specialist knowledge. NiMH batteries lifetime is typically quoted by manufacturers
as 500 to 1000 cycles which gives them a life of 1.5 to 3 years if charged everyday. The use
of easily replaceable batteries is a trade-off between protecting performance of the lantern
with a custom battery and ease of maintenance where substandard batteries could be
installed that will degrade the performance of the whole product and therefore risks
spoiling the reputation of the product. On balance the benefits to the user with easy
maintainability outweigh the risks.
29
10.2.2 Light Sources
Possible light sources for a solar lantern are set out in Table 7.
Source Description
Bioluminescence Microorganisms that produce light, therefore avoiding electrical parts. Requires
a food source that could be provided by photosynthesis during the day. Levels
of light output are very low and impractical.
Phosphorescence ‘Glow in the Dark’ materials that store up light during the day and emit it at
night. Levels of light output are very low and there is no control over the
output.
Laser with
fluorescent
Use low powered blue or UV lasers to excite a phosphor that produces white
light. The laser could illuminate a ball of phosphor or be swept over a phosphor
surface to produce more diffuse light. While potentially practical the cost of
blue lasers is prohibitively high for this application starting from £120 for a
120mW laser diode.
LED The development of high power white LEDs make these a potential solution
CFL Compact Fluorescent lamps provide efficient white light output and are a
potential solution.
PHOLEDs Phosphorescent Organic LEDs have the potential to provide very high efficiency
lighting (Universal Display Corporation, 2009). Thin film Sheets of PHOLED can
be produced that would provide a diffuse light source instead of a point source
as in conventional LEDs. The technology is not yet mature and is unfeasibly
expensive.
Table 7 Potential light sources for a solar lantern
LEDs and CFLs are potential
solutions with many examples of CFL
lanterns on the market. The rapid
development of LEDs is illustrated in
Figure 5 (Osram, 2010) and shows
that the efficacy of LEDs is rising
rapidly. The latest efficacy record to
be announced was over 130lm/W by
Cree (Electronic Products, 2010).
These quoted efficacies are measured under specific laboratory conditions and do not
include driver circuitry, therefore the practically obtainable efficacy will be lower however
they still appear compare favourably to CFLs.
LEDs they have other good features including long life (up to 100,000 hours quoted by
manufacturers) and being mechanically robust. This means that they do not need to be
Figure 5 the history of the development of LEDs and other light sources (Osram, 2010)
30
treated as a replaceable part in a lantern and can greatly reduce the maintenance burden of
a product.
10.3 Technical considerations
10.3.1 LED light source
The main challenge with using LEDs is that they produce directional light. This is ideally
suited to task lighting but requires modifying for general room lighting with 360 degree
spread of light. Some potential methods to achieve this are shown in Figure 6 and are based
on the principles of non imaging optics, total internal reflection or diffusion media.
Figure 6 c makes use of the fact that white light from LEDs is produced by a blue LED chip
with a yellow phosphor layer over the top with the combination of blue and yellow giving
the appearance of white. By separating the phosphor layer it may provide a more diffuse
and less directional light source.
A common method is to use multiple LEDs to provide multidirectional light but high
power LEDs have better performance characteristics with higher efficacy and therefore a
single LED approach is preferred. From the designs shown in Figure 6 b, c, e and f look most
promising as they are simple geometric shapes and therefore easier to manufacture.
LEDs should be driven with a constant current, which becomes more important the
higher the power used. The use of a DC-DC converter allows constant current control while
a) Based on a black hole lens. Light would be emitted mainly sideways.
b) Simple frosted bulb.
c) Phosphor coated bulb illuminated by a blue LED.
d) LED held at top of bulb shining onto a convex reflective surface.
e) Perspex cylinder with inverted cone to reflect light sideways.
f) Tall Perspex cylinder with inverted cone and frosted sides.
g) TIR lens to distribute LED light to 360 degrees.
Figure 6 Ideas for providing 360 degree spread of light from LEDs
31
efficiently matching the battery voltage to the typical forward voltage of 3-4v for white
LEDs.
10.3.2 NiMH Batteries
NiMH offer good characteristics
for a solar lantern but must be
looked after to maximise their
life. They are intolerant of both
overcharge where hydrogen can
be evolved and electrolyte lost
through the safety valve and
over discharge where cell
reversal can occur in multi-cell
batteries (Buchmann, 2005). To
protect against these the batteries
should not be discharged below 1v per cell and charging should be stopped promptly on
reaching full charge.
Solar charging poses unique challenges in detecting full charge due to the variation
in supply current and voltage experienced throughout the day resulting from cloud cover
and the motion of the sun (Cadini, et al., 2008) and (Boico, et al., 2007). Figure 7 shows the
voltage and temperature of NiMH cells during charging at different rates (GP Batteries),
from which the two standard methods for detecting end of charge can be seen. In a typical
fast charger (rate 0.5 – 1.0C) full charge is detected by negative dv/dt or increase in
temperature, commonly both are used along with a back up timer to avoid excessive
overcharge. There are many specialised ICs that include this functionality available.
As can be seen in Figure 7, these full charge indications are most pronounced at fast
charge rate, however to minimise cost the solar module must be small, giving a low rate of
charge. In addition fluctuations in environmental conditions can lead to these standard
termination methods giving false indications when solar charging as cloud cover will reduce
the supply current, giving a negative dv/dt and sudden direct sunlight will cause rapid
temperature rise. Various charging methods and algorithms are proposed in (Boico, et al.,
2007), (Cadini, et al., 2008) and (Hussein, et al., 2009) to overcome these problems.
Figure 7 Charge voltage and temperature of NiMH (GP Batteries)
32
10.4 Proposed solution
10.4.1 Conceptual
Solar lanterns are a very
good first step on the
energy ladder, but they are
not a long term solution
and it is likely that
customers will seek to
upgrade to higher power
systems with more
functionality when their
finances permit, perhaps
using the money saved by
not buying kerosene for
lighting. When a larger system is installed the solar lanterns become redundant, or act as a
backup light source and new lighting systems are purchased. This concept aims to improve
the scalability of Pico solar systems and allow them to be easily upgraded to suit all
requirements. The lighting system concept is described in Figure 8.
The basis of the system is a smart solar lighting unit that offers flexibility while remaining
simple to use and maintain. The basic lantern is split into three elements: the lamp, Battery
pack and solar module. Each is a standalone appliance and can be used with seamlessly with
the others as well as other products.
Lamp
The lamp consists of a high power, high efficiency LED with a driver circuit that allows input
voltages of 4 to 15 volts. This allows the lamp to be run from a 4xAA NiMH battery pack or a
12V lead acid solar battery in a solar home system (SHS). Therefore if the household
upgrades to a SHS they can use their existing high quality lamps.
Figure 8 Function diagram of the next generation concept
33
Battery pack
The battery pack holds four AA NiMH batteries which can be replaced by the owner and
used as individual batteries in other appliances as well as in the battery pack. The battery
pack has over-discharge protection for the batteries and a charge controller that will accept
power between 6 and 24 volts allowing a range of solar modules to be used to charge it.
This allows seamless upgrading to higher power solar modules without rendering the
battery pack useless. The battery pack can clip into the lamp to provide a single lantern unit,
or it can be attached via wires for permanent light fittings in the house with the batteries at
a central location. The battery pack can also be utilised for other applications e.g. phone
charging or powering a radio.
Solar module
The basic lighting pack would be supplied with a 2Wp solar module to minimise cost but as
described above any other size of panel could be used to suit the household budget.
10.4.2 Technical
The proposed design that will enable this concept is set out below with prototypes built and
tested.
Lamp
The light source is a 3W Cree XP-G
white LED that produces 340lm at
1A. This is driven by a constant
current buck converter allowing
input voltages in the range 4 – 15V.
The buck converter is driven by a
555 PWM circuit (555 Timer
Circuits, 2010) that provides three light output levels. A functional diagram is shown in
Figure 9 and the full schematic can be found in Appendix D. The circuit makes use of a buck
converter IC which integrates an NMOS power switch, current sense and PWM driver to
maintain the output current. The device operates at 1.6MHz to minimise the size of the
inductor required and requires a current feedback voltage of 0.205v to minimise power
dissipation.
Figure 9 Functional diagram of the Lamp module
34
Battery Pack
The battery pack contains four AA NiMH batteries that are
charged by a microcontroller controlled PWM Single Ended
Primary Inductor Converter (SEPIC) (Wikipedia, 2010). A SEPIC
converter (Boico, et al., 2007) (National Semiconductor
Corporation, 2008) was chosen as it allows step-up and step-
down and also has continuous current from the solar module.
A buck converter would have been less efficient as energy is
wasted when the switch is open. The microcontroller operates
a dithering maximum power point tracker, measuring the
current delivered to the battery to maximise it up to a limit
where it is maintained at 0.6A. The microcontroller also
monitors the temperature of the batteries and terminates
charge when an increase relative to ambient is seen. Ambient
temperature is measured on an equivalent thermal mass (in
this case a dead battery). A safety timeout is inherently
provided by the length of the day. The over discharge
protection circuit cuts off the battery when the output voltage
falls below 4V.
A functional diagram is shown in Figure 11 and the full
schematic can be found in Appendix E. A functional diagram
of the microcontroller code is shown in Figure 11.
Figure 10 Functional diagram of the Battery module
Figure 11 Functional diagram of the microcontroller code
35
Testing
10.4.3 Circuits
Lamp Module
The lamp module, Figure 12 and Appendix G, works
well, regulating the current supplied to the LED across
the whole voltage input range. In addition the PWM
dimming works as expected and the middle setting has
been calibrated to provide eight hours of light (the 6
hours specified plus a margin).
The output characteristic
of the lamp module, shown in
Figure 14, show that the output
current delivered falls short of
the intended 1A and varies with
the input voltage, as does the
efficiency. An explanation for the
reduced performance is not
obvious as the circuit values are
correct and there is margin on all the
components to avoid saturation or
overloading, however the circuit is switching
at high frequency (1.6MHz, see Figure 15)
and noise on the signals could be affecting
the internal limits in the driver IC. The lamps
performance at the primary operation point
of 4.8v is reasonable at 0.5A and 65%
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0
20
40
60
80
100
3.0 5.0 7.0 9.0 11.0 13.0 15.0
Ou
tpu
t C
urr
en
t /
A
Effi
cie
ncy
/ %
Input Voltage / v
Lamp Module Efficiency and output voltage at full power setting against input voltage
Efficiency I out
Figure 12 Lamp module
Figure 14 Graph showing Lamp module output characteristics
Figure 13 Buck converter switch output
36
efficiency. The LED driver IC remains cool during operation, maintaining a temperature of
35°C while operating at full load at room temperature.
Battery Module
The battery module, Figure 16 and Appendix
G, comprises the SEPIC converter,
microcontroller and the low voltage cut off.
The low voltage cut off circuit works
well, reliably turning the batteries off when
the voltage drops below 4V and preventing
them being latched back on
until the voltage rises.
There is a standby current
of 3mA which is not ideal as
this equates to a power
drain of 12 mW however
this can be eliminated by
turning off main the switch,
which completely isolates
the battery.
The PIC
microcontroller drives the
SEPIC MOSFET with a
250kHz PWM signal to
control the output current
to the battery and also
controls an indicator LED to
show that the battery is
being charged. The
microcontroller includes
Figure 16 Battery Module
0
20
40
60
80
100
0.0 2.0 4.0 6.0 8.0
Co
nve
rte
r Ef
fie
icn
cy /
%
Output Power / W
SEPIC Converter Efficiency against output power at Vin = 10v
Figure 18 Graph showing SEPIC converter efficiency
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
0.00 0.10 0.20 0.30 0.40 0.50
Ou
tpu
t p
ow
er
/ W
SEPIC Duty Cycle
SEPIC output power against Duty Cycle at Vin = 10v
Figure 17 Graph of SEPIC output power against duty cycle
Figure 15 Output of Buck MOS switch at 1.6Mhz
37
analogue to digital converters (ADC) to allow the battery temperatures to be monitored for
full charge detection and to monitor the current to the battery to close the control loop and
implement maximum power point tracking (MPPT). These ADC functions have yet to be
implemented but the functionality is present and just requires further work to implement.
The SEPIC converter, under the control of the microcontroller operates very well.
Figure 18 shows the efficiency of the converter when stepping down from Vin = 10v to the
battery voltage. The average efficiency recorded is 80.6%. The output voltage is fixed by the
battery therefore the duty cycle controls the power as shown in Figure 17. It is clear that the
converter is very sensitive to a small range of duty cycles which has implications for the
microcontroller program. Similar results to these are seen when the converter is stepping up
from a low voltage input as can be seen in Appendix G.
At an input power of 2W, the design power of the solar module for the basic lantern the
current to the battery is 0.3A. This equates to a C/7 charge rate giving approximately 8-9
hour. There will be some additional power consumption by the microcontroller and
monitoring circuitry, but this should be small and not impact the charging time too greatly.
10.4.4 Light bulbs
The light distributions from all the bulb designs are
presented in Appendix H. Each of the bulbs was tested
using the lamp module driven from the battery in a
photographic dark room. Measurements were taken with a
light meter at 30cm away from the LED at a range of angles
from the vertical.
The most even light distribution
was obtained from the Phillips light bulb,
shown in Figure 19, which was removed
from an LED mains bulb. The bulb (Figure
20) appears to have a polymer coating on the inside of the glass that
reflects and diffuses the light arround resulting in a very uniform emmision of light from the
bulb.
Figure 19 Light distribution for Phillips bulb
0
100
200
300
Light distribution (lux): Phillips light bulb with Cree
LED
Figure 20 Phillips bulb
38
It is difficult to judge on te best light distribution, but perhaps the
most promising from the designs proposed in section 10.3.1 is the short
bulb with
inverted conical
top (Figure 23).
The light distribution, shown in
Figure 21 is not uniform with
peaks at certain angles however
the spread of light to the sides is
good. It may be possible, through
development of the design, to
tweek the light distribution, for
example round off the corners and cone apex may smooth out the light distribution.
The use of the phosphor coatings with a blue LED gave very nice light distirbutions as
shown in Figure 22. There is potential for improving the output from the phosphor through
optimisation of the coating and bulb design.
11 Discussion of design process
11.1 Effectiveness of design
11.1.1 Output
The light output from the lantern is bright and if effectively distributed then it should be
sufficient to meet the requirements for the lantern. Lighting levels are quite subjective and
depend on the task undertaken so it is difficult to make definite assertions that the light
level is suitable or not. The Lumina project have undertaken some interesting work into
minimum illumination levels for night market vendors in Kenya (Johnstone, et al., 2009)
which showed that the minimum illumination acceptable at a distance of 1m from the light
source is in the order of 2 lux. Based on the Phillips bulb the illumination at 1m from the
lantern should be around 18lux and is therefore well in excess of the minimum level found
by Johnstone et al. In addition the lamp module should maintain that illumination level right
down to battery cut-off.
0
50
100
150
Light distribution (lux): phosphor bulb with blue LED
0
100
200
300
Light Distribution (lux): Short bulb 30° + dif with
Cree LEDFigure 23 Short 30° bulb
Figure 21 Light distribution for short 30° bulb
Figure 22 Light distribution for phosphor coated bulb
39
The results from the bulb light distributions show that there is potential in these
simple approaches to yield good performance for minimal cost and great simplicity. Further
development of the bulb shapes is required but it is clear that the technique is a successful
one. An additional possibility would be to buy in bulbs of the Phillips type that give very
even light distribution.
11.1.2 Efficiency
The efficiency of the charging circuit is very good at around 80% however there should be
scope for further improvement with more development. The biggest area for improvement
is in the lamp module where the efficiencies are disappointingly low across a large range of
input voltages and further work is needed to optimise the circuit.
11.2 Relevance to the problem
11.2.1 Performance
As discussed above, the light output of the lantern seems to be suitable for the intended
users. To gain a better idea of the suitability requires testing prototypes with a sample of
potential users and gaining feedback on its suitability as there is not a definite academic
answer that can be determined otherwise.
11.2.2 Cost
The cost of the parts for the prototype lantern is around £40 (approximately US$65). To
produce 1000 prototype lanterns would reduce the cost per lantern to £35 (approximately
US$55). This is still too expensive to meet the target of sub US$50 as this does not include
the casings, transport, mark-ups and taxes that will be imposed on a product going to
market. There are going to be savings in the economies of mass production that will drive
the cost down but it is difficult to quantify that amount. The total production cost will have
to be brought down to around US$25 in order for the final retail price to be on target,
however this may be possible to achieve with the current design. The full cost breakdown
for the lantern is included in Appendix F.
40
11.2.3 Usability
The design, when appropriately packaged can be intuitive and
easy to operate with plug and play design and three controls to
master. The operation could be simplified further by a change of
design to the low V cut-off to eliminate the need to have a
separate switch just for its initialisation.
Figure 24 shows the relative size of the Glowstar and the
lantern developed here and clearly illustrates the significant large
difference between the two, which are of similar performance
specification. There is clearly more work to be done to package
the new lantern appropriately but once done it should address
the issue of Glowstar’s size and weight giving a much more
portable, easy to handle product.
11.3 Limitations
This design is not a solution to the problems of energy access globally, but it is a good
interim measure to start households on their way to improved energy access with the
benefit of all the components still being useful after a household upgrades their energy
supply whether to a solar home system or grid connection.
The light output of the lantern is inherently limited and will never be able to compete
with a grid connection in terms of light output; however with development of LEDs
progressing rapidly the output of the lantern can be upgraded as better LEDs become
available. The lantern is however a significant step up in performance from fuel based
lighting products.
11.4 Manufacture
The aim of the Glowstar project to enable production in Kenya was very worthy and an
interesting exercise. This design has not been developed with the same target but, if the
lantern were to be produced, local manufacture or assembly is an interesting proposition as
it provides employment and skills and also increases the maintainability of the product in
country through the availability of spare parts skill labour. As with Glowstar, wholesale
production of the lantern in Kenya is unlikely to be achievable due to the limitations of
Kenya’s industry however assembly of the final product from imported and locally sourced
Figure 24 Glowstar and next generation lantern side by side
41
parts is possibility e.g. circuit boards from China, Solar cells from US or Europe and batteries
from the general world market with final assembly in country. Careful analysis would need
to take place before such a scheme was implemented to define the costs, benefits and
wider implications.
12 Conclusions
Glowstar pioneered a new market sector ten years ago and was in many ways a ground
breaking innovation. As has been discussed in this project much advance has been made in
technology in the intervening decade that now allows new options to be explored and there
are many factors, social and technological, that make a next generation lantern
development a very exciting prospect.
Technical:
LED technology has developed new, efficient and robust lighting possibilities that are
proven in service
LED technology continues to advance rapidly promising better, brighter and more
efficient products in the future.
A great array of very capable and affordable ICs is now available on the market that
can simplify the design and reduce costs.
Battery technology has advanced significantly and continues to expand the options
for off-grid applications including NiMH and lithium chemistries.
Social:
The need for improved off-grid lighting has not diminished with a huge underserved
market
There is great desire and enthusiasm amongst un-electrified communities
The potential benefits to people are still huge and potentially life-changing
There is an unprecedented global focus on off-grid lighting through projects such as
Lighting Africa
Access to relevant information is easier than ever before
Governments, communities and individuals are increasingly aware of the potential
benefits including environmental issues resulting from the worldwide concern over
climate change.
The coincidence of the above factors makes now a very good time for a new lantern
development and indeed there are many companies in various stages of the process. The
design proposed here perhaps offers a new level of modularity and flexibility of use to the
design that can benefit users.
42
This prototype successfully proves that the concept design can be feasibly
implemented, in an easy to use product and near to the target price. The performance of
the lantern isn’t yet up to the expected levels in terms of efficiency and light output, but
further work should help to optimise the circuit and improve performance. As it stands the
lantern seems to attain a suitable level of performance to meet the requirements set out by
the market research.
12.1 Further developments
The performance of the lantern can be improved in several areas. The charge control and
MPPT need to be implemented with further development to the microprocessor code. The
microprocessor has excess capacity that will allow more sophisticated charging algorithms
to be implemented for example dT/dt termination and dV/dt termination of charging as
proposed in (Boico, et al., 2007), (Cadini, et al., 2008) and (Hussein, et al., 2009). The
performance can also be improved through optimisation of the lamp drive to enable full
current to the LED and improved efficiency and on the low V cut-off to minimise the standby
current. The circuit would also benefit from being constructed on a well designed PCB.
Full testing and characterisation of the design needs to be carried out to establish how
robust the design is and the ongoing performance level attainable.
Further work should then concentrate on packaging the modules to attain the
functionality set out in the concept design with the opportunity to develop additional
accessories for the system.
13 The Future
13.1 Opportunities
With further development this design could form the basis of a high performance, scalable
and affordable solar lantern that can help to address the need for off-grid lighting in Kenya
and beyond. There is the potential to reach huge numbers of people through a suitable and
scalable development, manufacturing and distribution program building on the lessons
learnt from the Glowstar project and subsequent market experience. A proportion of local
manufacture and assembly is a feasible option given the design of the lantern with benefits
for both the host country and the business viability through improved maintainability, local
43
servicing and building of local skill which may help to stimulate the local market through
indigenous innovation.
13.2 Challenges
The challenges in a lantern development are clearly large and numerous, but not
insurmountable. The main considerations are:
Obtaining funding to pursue the development as returns on investments is likely to be slow due to the nature of the market and the need to sell many products at low mark-ups.
Setting up a successful distribution network because to be effective it is likely to be highly labour intensive and needs to be geographically diverse.
Marketing the product successfully to a target group who are geographically diverse, may not be technology aware and have little spare cash available.
Making the product affordable by keeping the cost to a minimum and seeking ways to enable capital poor people to purchase the product
Building a strong brand through high product performance and providing good after sales service.
14 Acknowledgements
Dr Patrick Palmer, Project supervisor, Cambridge University Engineering Department
Mike Brown, Technician, Cambridge University Engineering Department
Stephen Hunt, Senior Energy Consultant, Practical Action Consulting
Leo Blyth, Technical Advisor, Lighting Africa
Tameezan wa Guthui, Energy Specialist, Practical Action East Africa
Ray Holland, EUEI PDF Manager, GTZ
Maina Mumbi, Off-Grid energy technician, Lighting Africa
Nienke Stam, consultant, Tiodos Facet
Norman Chege, Solar Manager, Davis and Shirtliff
John Maina, Executive Co-ordinator, SCODE Nakuru
John Kiama, Technical Consultant, Solagen Power Nairobi
Samwel Odhiambo, Regional Sales Manager, Sollatek Electronics (K) Ltd
Richard Mburu, Sales Engineer, Studertek Power Systems Kenya
Antony Mwangi, General Manager, Green Planet and Natural Light
John Kangiri, Glowstar owner
Duncan Muchiri, Technician, SCODE Nakuru
Kakamega Environmental Education Programme (KEEP), Kenya
Jane Muthoni, Glowstar owner
George Michieka, Smart Solar / Barefoot Power Kenya
John Keane, Regional Manager, Solar Aid
Chris Cleaver, EWB intern, Global Village Energy Partnership Kenya
44
Daniel Machariah, Global Village Energy Partnership Kenya
Auto Electric Care Ltd KEEP, Kakamega Environmental Education Project Powerpoint Karen Fearon, Student, Liverpool University
Katie Cresswell-Maynard, Research Programme Manager, EWB UK
EWB UK Bursaries
Pembroke College Cambridge Travel Grants
15 Bibliography
555 Timer Circuits. 2010. PWM Controller Circuit. 555 Timer Circuits. [Online] 2010. [Cited:
11 04 2010.] http://www.555-timer-circuits.com/pwm-controller.html.
Boico, Florent, Lehman, Brad and Shujaee, Khalil. 2007. Solar Battery Chargers for NiMH
Batteries. s.l. : IEEE, 2007.
Buchmann, Isidor. 2005. Battery university. [Online] 2005.
http://www.batteryuniversity.com.
Cadini, D and Marola, G. 2008. Solar Battery Charger for NiMH Batteries. s.l. : IEE, 2008.
Chege, Norman. 2009. Davis and Shirtliff. [interv.] Chris White. 15 12 2009.
Electronic Products. 2010. LED breaks brightness barriers - Cree. Hearst Electronic Products.
[Online] 04 01 2010. [Cited: 23 01 2010.]
http://www2.electronicproducts.com/LED_breaks_brightness_and_efficiency_barriers_--
_Cree-article-poyrc01_jan2010-html.aspx.
GP Batteries. Nickel Metal Hydride Technical Handbook. Hong Kong : GPI International
limited.
Grüner, Roman, et al. 2009. Solar Lanterns Test: Shades of Light. s.l. : GTZ, 2009.
GTZ. About Us. GTZ. [Online] [Cited: 22 05 2010.] http://www.gtz.de.
Hankins, Mark. 2001. The Kenya PV Experience (Draft). s.l. : Energy and Development
Research Centre, University of Cape Town, 2001.
Hussein, Ala Al-Haj, et al. 2009. An Efficient Solar Charging Algorithm for Different Battery
Chemistries. s.l. : IEEE, 2009.
ITC. 2001. Glowstar in the Press. Practical Action Glowstar Website. [Online] Practical
Action, 2001. [Cited: 23 05 2010.] http://www.itcltd.com/glowstar/articles.htm.
ITC Ltd. 2003. Glowstar Final Technical Report. s.l. : Intermediate Technology Consultants
(Practical Action Consulting), 2003.
Johnstone, Peter, et al. 2009. Observed Minimum Illuminance Threshold for Night. s.l. : The
Lumina Project, 2009.
Lighting Africa. 2008. Kenya Qualitative Off-Grid Lighting Market Assessment. s.l. : IFC -
World Bank, 2008.
—. 2008. Lighting Africa Market Assessment Results: Quantitative Results - Kenya. s.l. : IFC -
World Bank, 2008.
45
—. Lighting and Development. Lighting Africa. [Online] [Cited: 21 05 2010.]
http://www.lightingafrica.org/node/326.
—. 2010. Winners picked as best off-grid lighting products in Sub-Saharan Africa. Lighting
Africa. [Online] 20 05 2010. [Cited: 22 05 2010.] http://www.lightingafrica.org/node/78616.
National Semiconductor Corporation. 2008. Application Note. Designing a SEPIC Converter.
2008.
Osram. 2010. History of LED. Osram. [Online] 2010. [Cited: 20 01 2010.]
http://www.osram.com/osram_com/LED/Everything_about_LED/History_of_LED/index.htm
l.
Practical Action. What We do - Our Approach. Practical Action. [Online] [Cited: 21 05 2010.]
http://practicalaction.org/about-us/approach.
Rocky Radar. 2009. Tough Stuff: Bringing Solar to the Developing World. Rocky Radar.
[Online] 01 09 2009. [Cited: 23 05 2010.] http://www.rockyradar.com/cleantech/?p=341.
Schumacher, E.F. 1973. Small is Beautful, A study of Economics as if people mattered. s.l. :
Blond and Briggs, 1973.
Sollatek (Kenya) Ltd. 2009. Retail Price List. Sollatek. [Online] 2009. [Cited: 22 05 2010.]
http://www.sollatek.co.ke/static/uploads/pricelists/Kenya-Pricelist.pdf.
Sollatek (UK) Ltd. Sollatek. [Online] [Cited: 21 05 2010.] http://www.sollatek.com/.
—. 2006. Glowstar Brochure. 02 2006.
—. Solar Products > Solar Lights > Glowstar. [Online] [Cited: 22 05 2010.]
http://www.sollatek.com/product-detail.asp?id=970.
Universal Display Corporation. 2009. PHOLEDs. Universal Display. [Online] 2009. [Cited: 23
05 2010.] http://www.universaldisplay.com.
Wikipedia. 2010. SEPIC Converter. Wikipedia. [Online] 30 04 2010. [Cited: 01 05 2010.]
http://en.wikipedia.org/wiki/SEPIC_converter.
16 Appendices
16.1 Risk Assessment Retrospective
Aside from the usual risks associated with working with low voltage electronics and
prototyping the main hazard in this project was the use of high brightness LEDs. These LEDs
are typically Class 2 optical devices for which the risk of permanent damage is low. The risk
assessment was reasonably accurate as there have been no major issues however one
recommendation for future is to consider the use of sunglasses while operating the LEDs as
it was a common occurrence to get ‘spots in front of the eyes’ after glancing at a high
brightness LED. Sunglasses were used on a number of occasions and seemed to reduce the
effect of the LEDs on the eye, especially when trying to observe patterns of light requiring
prolonged observation of the area around the LED. There are no other deviations from the
risk assessment or issues to note.
46
16.2 Appendix A – Glowstar specification
Glowstar product specification and charging modes (Sollatek (UK) Ltd).
Model Glowstar GS5 Glowstar GS7
Lamp 5W 7W
Battery 4.4Ahr 7.2Ahr
Operating Temp -10'C - +45'C -10'C - +45'C
Running time (from full charge)
5.5 hours 8 hours
Aux Output - Yes
Dimension H: 420mm D: 135mm
H: 420mm D: 135mm
Weight 2.4kg 3.3kg
5W (25W GLS) 6 hours 10 hours
7W (40 W GLS) 5.5 hours 8 hours
9W (60W GLS) 4 hours 6 hours
Lamp life 10,000 hours 10,000 hours
47
16.3 Appendix B
Details of solar lanterns available in Kenya
Some of the Lighting Africa competition winners May 2010
Other Lanterns
Green Light
Planet Sun King
Price $20 0.5W 4.5v panel included a-si. 10 LED (5mm) Li-polymer 4-16hrs runtime 1 year warranty
Philips Uday Lantern
Price $50 5W panel 5W CFL Lead Acid battery 4-5hrs runtime Mains charger included
Barefoot power Firefly
Price $20 1.5W panel 12 LED Battery 3xNi-Cad 600mAh 5-6hrs runtime 1 year warranty
Hada Solar lamp
Price $20 Small solar panel built in Multiple LED 2xNi-Cad 600mAh Poor Quality
D.Light Nova
$45 Panel power unknown 3W LED 3-12hrs runtime 3 models
Energiser RC102
Price $30 Not solar 7W CFL 6hrs runtime
Other Solar Lanterns Interchange ‘Captain Green’ lantern radio
Price $30 Small built in Panel 12 x LED light 3xNi-Cad batteries 700mAh 5-10hrs runtime Built in radio Wind-up mechanism
Tough Stuff Solar
light
Price $15 1W, 5.6v Panel 4LED Battery 1.3Ah 6-30hrs runtime Variable brightness Modular system
Osram LED
Solar 1
Price unknown Solar panel 0.95W, 3.9v 1.2W LED with conical relector 4x NiMH 17Ah batteries 7-10hr runtime
Topray ‘powerpack’
Price $100 LED cluster Bulbs (two bulbs) Lead Acid Battery 7Ah 12V 8-16hr runtime Mini Solar home system
D.Light Kiran
Price $10 0.3W panel built in LED light 4-8hrs 8hr charge
48
16.4 Appendix C: Design Specification for next generation lantern
Essential
Provide light for 6 hours on a day’s solar charge
Light a whole room (based on rooms 4x4m) sufficiently to undertake a range of
activities in the room
Enable light to be used in multiple rooms/locations
Price should be below $50 (US)
Lantern must be chargeable from solar PV
Lantern must gain a full charge in one sunny day
Lantern should look and feel of high quality
Lantern life should be a minimum of two years with no servicing
Lantern must be able to operate in direct sunlight and shade in extremes of climate
in -5 to 45°C air temperature and 0 to 100% humidity
Lantern must be able to withstand a drop of 2 meters onto a hard surface without
damage to the product or performance
Lantern must not degrade under exposure to UV light
Desired
Provide lighting for toilets/washrooms separate from house
Provide portable lighting
Price should be as low as possible
Lantern should be chargeable from other sources e.g. mains adaptor, car adaptor
The product should be able to be offered in a range of performance levels and prices
to suit different people
The light output should be variable
The product should be capable of charging a mobile phone or powering an auxiliary
device
49
16.5 Appendix D: Lamp Schematic
For component values see Appendix F: Cost Breakdown.
16.6 Appendix E: Battery Module Schematic
For component values see Appendix F: Cost Breakdown.
50
16.7 Appendix F: Cost breakdown for lantern design
Part list and costs Lamp module Part Component Value quantity Price (one off) Price (1000pcs)
LED1 LED
1 4.5 3.8
IC3405 Buck IC
1 1.71 0.915
R5 resistor 0.22 1% 1 0.125 0.07
L1 Inductor 10uH 1 0.664 0.526
C3 Capacitor 10uF 1 0.083 0.032
C5, C6 Capacitor 1uF 2 0.058 0.034
C4 Capacitor 0.01uF 1 0.005 0.002
D3 Diode
1 0.079 0.036
D4 Diode
1 0.045 0.045
IC555 555 timer
1 0.219 0.219
S2 switch
1 0.397 0.381
S1 switch
1 0.397 0.194
C1 Capacitor
1 0.01 0.005
C2 Capacitor
1 0.01 0.005
R1 resistor variable (prototype) 1 0.001 0.001
R2 resistor variable (prototype) 1 0.001 0.001
R3 resistor variable (prototype) 1 0.001 0.001
R4 resistor variable (prototype) 1 0.001 0.001
PCB
1 # #
Heat Sink
1 0.583 0.437
Casing
1 # #
Light diffuser
1 # #
Dc connector
1 0.243 0.162
Total for lamp 9.132 6.867
Battery module
Batteries 2100mAh 1 5.39 5.23
battery holder
1 0.386 0.242
Microcontroller PIC18F1220 1 1.98 1.37
5V regulator 7805 1 0.284 0.092
L1, L2 Inductor 100uH 2 0.94 0.746
MOS1 MOSFET
2 0.34 0.122
D1 diode
2 0.568 0.568
C1 capacitor 10uF 2 0.166 0.064
C2 capacitor 47uF 1 0.155 0.06
Temp sensor
5 1.215 0.7
C3 Capacitor 0.1uF 5 0.02 0.01
R1 Resistor 0.22ohm 1 0.125 0.07
DC connector
2 0.956 0.778
LED
2 0.098 0.048
resistor 330ohm 2 0.002 0.002
V ref 2.495 1 0.094 0.062
R3,R4 Resistor 1Mpot 1 0.019 0.01
R5 Resistor 100k 1 0.041 0.014
switch
1 0.292 0.17
op-amp
1 0.3 0.2
Total for Battery Module 13.371 10.558
Solar Module
Solar Module 2.1Wp 9v 1 17.99 17.99
DC connector
1 0.243 0.162
Total for Solar Module 18.233 18.152
Total for lantern 40.736 35.577
51
16.8 Appendix G: Circuit detail
1) Whole lantern system connected and operating 2) Standard DC connectors for simple connection
3) Lamp module top and solder side including surface mount components on the solder side
4) Detail of Buck driver IC (left, SMD on adapter) and
555 (right)
5) Battery module top side. SEPIC and microcontroller to the left, Low V cut-off to the right
6) Solder side of SEPIC and microcontroller showing
surface mount components
7) Solder side of Low V cut-off
showing surface mount components
52
16.9 Appendix H: Light bulb light distribution
All measurements are in Lux, taken at 30cm from the LED.
Diff refers to a diffusion paper that can be added to the outside of the short bulbs.
0
100
200
300
Light distribution: Short 10 ° Diff, Cree LED
0
100
200
300
Light distribution: Short 30 ° Diff, Cree LED
0
100
200
300
Light distribution: Short 30 ° No Diff, Cree LED
0
100
200
300
Light distribution: Short 10 ° No Diff, Cree LED
0
100
200
300
Light distribution: Phillips , Cree LED
0
100
200
300
400
Light distribution: Pearl bulb, Cree LED
53
0
50
100
150
Light distribution: Phospho coat1, Blue LED
0
50
100
150
Light distribution: Phospho coat3, Blue LED
0
50
100
150
Light distribution: Phospho coat2, Blue
LED
0
100
200
300
400
Light distribution: Tall Diffusion, Cree LED
0
200
400
600
Cree No bulb
Cree Phillips
0
50
100
150
Avago blue No bulb
Avago Blue Phosphor outside 1
Figure above shows the different bulbs left to right: Tall diff, short 10°, short 30°,
phospho1, phospho2, phospho3, Phillips.