Assembling a solar lamp at a NEST workshop in Secunderabad, India.

In India, an estimated 100 million households use kerosene wick lamps as their main source of light. These produce poor quality light and unhealthy fumes, and present a serious fire risk particularly when used in thatched homes.

NEST won a 2005 Ashden Award for developing a very small solar lantern, the Aishwarya, as a safe substitute for the kerosene wick lamp.

Now with the light, we don’t have any problem with insects crawling into the food, so whatever we are eating now has no bugs. Secondly, as it’s so light, we are able to take the solar lantern into the hills, where all the pigs that used to come and disturb our crops no longer come near.

Village elder Laxmi Menawat

Poor quality and irregular lighting blights lives. When that light comes from kerosene wick lamps, it not only strains eyes, but produces dangerous fumes and the risk of fire. Yet in India 100 million homes use just this form of lighting.

Solar lighting is an obvious solution. What Noble Energy Solar Technologies (NEST) achieved was to develop a solar lantern which is small and practical and yet which is also cost-effective for its users. Costing about US$35 each, the lanterns are self-funding in one to two years depending on the kerosene saved.

There is no subsidy involved. Indeed NEST is a private company using a network of independent dealers who maintain the lamps and organise the financing. This is a model of commercial enterprise delivering sustainable, environmental benefits.

Key points

  • PV lantern similar in size to kerosene lamp which uses a 3 W high-efficiency compact fluorescent lamp (CFLs) producing 60 lumens of light, with a 3 Wp detachable PV module. 
  • Lantern costs about US$35. Customers able to buy on credit from dealers and pay back over eight or 16 months. The lantern pays for itself from savings on kerosene in one to two years. 
  • Dealership network used to maintain lanterns properly, replace parts and ensure prompt payment by users. 
  • By 2005, 65,000 PV lanterns produced and distributed throughout the states of Andhra Pradesh and Maharashtra, benefitting over 300,000 people.     
  • Each PV lantern reduces CO2 emissions by about 0.21 tonnes/year CO2 through avoided kerosene use, giving a total saving of about 14,000 tonnes/year CO2.
  • Light from PV lantern is five times brighter than a single kerosene lamp and much better for reading, allowing children to study in the evenings. 
  • Inhalation of fumes, eye irritation and risk of fire in the home reduced through use of PV lanterns.

The technology

How does it work? 

The NEST PV lantern is a similar size to a simple kerosene lamp, lightweight so that it can easily be carried even by children, and affordable by the poorest households who have no other alternative but kerosene.  The design of the lantern allows for easy replacement of key parts, rather than repair.  NEST also produces larger PV lanterns (for street vendors and street lighting) as  well as solar-home systems. 

The basic components of the lantern are common to all PV lighting systems: a PV module to supply the electrical power, rechargeable battery for energy storage, lamp and electronic controller. The lanterns are assembled at the NEST  workshop in Hyderabad. Rigorous attention is paid to quality, with checks on all individual components and on the finished lanterns. 

Using the light, we can get good gum from the raw gum and sell it in the market for extra cash. With the light, this is now possible. Before, with the kerosene lamp, it was impossible to see the gum properly.

Villager

The technology in more detail

The lantern uses 3 W high-efficiency compact fluorescent lamps (CFLs), which produce about 60 lumens of light output – five times as much as a kerosene lamp. This small size CFL is manufactured specially for NEST, by Osram.  NEST makes the 3 Wp polycrystalline PV modules at its own factory in Bangalore, using 3 Wp modules to provide up to three to four hours of light per night. The PV module is mounted with an angled bracket on the roof or outside wall of a house, and plugged into the lantern to charge it during the day.  The lead-acid battery (rated 4 Ah at 6 V) is the heaviest part of the lantern and is mounted in the base to give stability. The lantern base also has a socket to power a small fan or radio if desired. To ensure quality, NEST designs the electronic controllers and purchases the components, but outsources the manufacture to a small electronics business in Hyderabad. 

The lantern design and manufacturing systems were developed over a period of three years, and commercial production started in 2001. 

How much does it cost and how do users pay? US$1 = Rs 44 (Indian Rupees) [June 2005]

NEST specifically intended the Aishwarya lantern to be sold as an unsubsidised, commercial product in remote, poor  villages.  To achieve this, it established a network of dealers based in small towns.  Dealers are independent businesses, sometimes selling other goods or services as well as lanterns. Each dealer recruits a number of sub-dealers who work on commission at  village level.  

The cost of an Aishwarya lantern is about US$35 (Rs 1,500). Most customers cannot afford this price upfront, but are able to buy on credit from the dealers.  Typically they pay US$5 (Rs 200) per month for eight months, or US$2 (Rs 100) per month for 16 months. NEST will sometimes reduce its own profit in order to allow the dealers to give free credit, but this is the only form of subsidy offered.

A kerosene wick lamp used in a home for three hours per night burns about seven litres of kerosene per month. With subsidised kerosene this costs about US$1.50 (Rs 70). However, poor families often can’t get hold of subsidised kerosene, and may pay twice this amount. Thus the lantern pays for itself in one to two years through kerosene savings.  

Because the sub-dealers know their individual customers, they are able to collect regular payments, even from people who do not have a formal address.  Customers often need to extend their repayment period, but the overall track record of repayment is good, with only about  3-4% defaulting. 

How is it maintained? 

NEST gives a one year guarantee on its products, but the lantern is expected to last at least ten years, and the PV modules about 25 years.  The dealership network, which provides an effective route for sales, is also crucial for training, providing replacement parts, after-sales service and recycling. Sub-dealers have to make sure that each user knows they must recharge their lantern every day, otherwise it will not provide the intended three to four hours of light each evening. It is an advantage for sub-dealers to recruit a number of customers in a given village, so that several people can share experience of using lanterns.

Each dealer is provided with a full set of spare components. Sub-dealers carry a few spare controllers, batteries and CFLs which can be swapped in if needed during the guarantee period, but this is not often needed. 

Few lanterns give problems, and when they do it is usually because the battery has not been regularly charged.  The lifetime of the battery is typically three years if it is used carefully (about 1000 daily cycles of discharge and recharge), after  which it is exchanged by the NEST dealer at a cost of about US$3.50 (Rs 150 ). The CFLs have a similar lifetime and are replaced at a cost of about US$1.40 (Rs 60 ).  Both CFLs and batteries are returned to their manufacturers for recycling. 

Assembling a solar lamp.

Benefits

By 2005, over 65,000 lanterns had been produced and distributed. About 75% were sold through the dealer network and the remainder bought by donor and government programmes.  With over five people per household, the lanterns benefit an estimated 320,000 people. 

Environmental benefits 

A single wick lamp burning seven litres of kerosene each month produces about 210 kg/ year of CO2. Thus the lanterns which had been distributed in 2005 save about 14,000 tonnes/year CO2.

Social benefits 

An Aishwarya lantern provides between three and four hours of light each evening. Using the lantern avoids the dangers associated with kerosene wick lamps: inhalation of fumes, eye irritation and the risk of fire in the home if they are knocked over. Poor villagers often go without light at night if they run out of kerosene or simply cannot afford it. There are great benefits to having the Aishwarya lantern available whenever it is needed, particularly for urgent matters like delivering babies or dealing with accidents. Most lanterns provide the sole source of light to a family of typically five people – and sometimes two families share one lantern. 

The Aishwarya lantern is about five times brighter than a single kerosene lamp and provides much better quality light for reading, allowing children to study in the evenings.  Some people have also been able to carry out income-generating work in the evenings.  

NEST has provided PV street lights for some government programmes, as well as donating them to some of the slum communities around Hyderabad. Within this thriving, modern city there are still many people without access to the benefits of electricity.

Employment benefits 

NEST has generated employment for a growing number of people.  In 2005, there were about 50 dealers (five of whom were women) working full or part-time selling Aishwarya lanterns, each of these providing part-time employment to sub-dealers.  The small businesses which manufacture charge controllers and plastic parts work exclusively for NEST and employ a further 60 people.  

Update: what happened next?

NEST has developed and recently launched an LED version of the Aishwarya lantern, the AISHWARYA-WOW lantern, and is hoping to expand its market with this new product. NEST is also involved in the development of high purity quartz, which has potential to bring down the cost of solar silicon for photovoltaic cells.

In a 2009 test report by GTZ (German Technical Cooperation), with technical cooperation from the Fraunhofer Institute for Solar Energy, the Aishwarya solar lantern was found to give the best performance for price out of twelve solar lanterns assessed in detail.