Solar home systems and solar lanterns Brochure

Ashden technologyPhotovoltaic solar home systems and solar lanternsAshden technology | Photovoltaic solar home systems and solar lanterns 1A solar-home-system uses a photovoltaic (solar-electric) module and a rechargeable battery to provide a stand-alone power supply. Lanterns are the smallest systems, designed to be portable and cheap. Solar home systems and lanterns bring huge benefits to off-grid homes, by replacing smoky, dangerous kerosene lamps and powering radios and mobile phone chargers. – Millions of solar-home-systems and solar lanterns are in use.– High quality lanterns retail for as little as US$10 each.– 1 Wp of PV provides enough electricity for a small light and phone charger.Read on for more information about solar-home-systems, or go to our database for films and case studies of Ashden Award winners who use solar home systems.How a solar-home-system works Photovoltaic (PV) modules use semiconductor materials to generate dc electricity from sunlight. A large area is needed to collect as much sunlight as possible, so the semiconductor is either made into thin, flat, crystalline cells, or deposited as a very thin continuous layer onto a support material. The semiconductor must be sealed into a weatherproof casing, with suitable electrical connectors. info@ashdenawards.orgwww.ashdenawards.orgA home for street children can show football on television, powered by a solar-home-system from Zara solarMaking charge controllers for solar-home-systems at a Grameen Shakti technology centrePV ratingPV modules are specified by their ‘watt-peak’ (Wp) rating, which is the power generated under standard conditions, equivalent to bright sun in the tropics (they still work at lower light levels though). Most solar-home-systems use modules between about 10 Wp and 100 Wp rating, although modules for lanterns are often 1 Wp or less.The rechargeable batteries store spare electricity on sunny days, so that it is available at night and on cloudy days. They also provide a stable voltage for the devices which use the electricity. Standard lead-acid car batteries can be used, but they don’t last long if they are heavily discharged, so specially-made solar versions are strongly recommended. Other types of rechargeable battery like nickel-cadmium and nickel-metal-hydride are increasingly used, particularly in small systems like solar lanterns. They are more expensive, but easier to make small and portable, and more tolerant of being heavily discharged.All equipment run directly from the PV supply must be designed for dc operation. Efficient lights and appliances make best use of the limited supply of electricity. Efficient dc fluorescent lights are available down to about 3 or 4 W power rating, in both tube and compact forms. LED lights are even more efficient, and are now sufficiently cheap and reliable to be used as well. In most systems, an electronic charge-controller is used to protect the battery from being overcharged (when it is very sunny) or over-discharged (when people try to get too much electricity from the system). The charge controller usually has lights or a meter to indicate the state-of-charge of the battery. How solar home systems are used A solar-home-system should be designed with sufficient PV capacity (Wp) to provide the daily electricity demand throughout the year, and typically three days storage capacity in the battery, so that the system keeps working during a cloudy period. For example, a typical solar-home-system sold by Ashden Award-winner SELCO in India has a 35 Wp PV module and a 90 Ah/12 V battery to power four 7 W dc fluorescent lights for about four hours per day and a socket. Recently the Solar Energy Foundation in Ethiopia has introduced a 10 Wp system which powers four small LED lamps.The PV module is fixed to the roof of a home at the angle which collects maximum sunlight. A framed 35 Wp module made from crystalline cells has an area of about 0.3 m2, or about 0.7 m2 if made from lower-efficiency thin film materials, so it is easy to handle and install. The battery is kept indoors, and the terminals should be covered so that they cannot accidentally be touched or short-circuited. The PV, battery, lights and socket are all wired carefully to the charge-controller, ideally by a trained technician. Larger systems can run a TV as well, and often include an inverter (dc to ac converter), so that standard mains-voltage equipment can be run from the solar home system. Solar-home-systems can be very reliable and need little maintenance. Users must be trained to check the battery, keep the PV module clean and make sure that connectors are secure. It is important not to over-discharge the battery (and very tempting to do so, to get a bit more light or TV). Even with careful use, batteries deteriorate and need to be replaced every four or five years.Solar lanterns Some small solar-home-systems are designed to be portable. Several participants of the REDP PV programme in China produce small portable PV systems for herders who move seasonally with their animals. Another approach is to use solar lanterns for lighting, to bring down the cost. A solar lantern has a high-efficiency light, usually an LED, and a rechargeable battery, in a case which is easy to carry and can stand on the ground or a table, or else hang from the ceiling. Ashden Award winner D-light’s smallest lantern includes a small built-in PV module, while its larger ones have detachable modules. 2011 finalist ToughStuff provides a detachable module that can also be used to power a mobile phone or a radio.What are the benefits of solar home systems?The amount of electricity supplied by a solar-home-system is small, typically about 0.1 kWh per day for a 35 Wp system. However, the benefits can be huge.Electric light avoids the fumes and the fire risk of kerosene lamps. They are also much brighter, and give opportunities for study, income-generating work and recreation after dark. Ashden technology | Photovoltaic solar home systems and solar lanterns 2A Grameen Shakti solar technician in Bangladesh installs the PV module for a solar-home-system on a roofBattery and charge controller for a solar-home-system installed by SELCO in India, covered up to keep them clean and safeSmall D-light lantern with built-in PV module on the topAshden technology | Photovoltaic solar home systems and solar lanterns 3Being able to listen to a radio without the expense of dry-cell batteries allows people in remote areas to keep in touch. Mobile phones bring money-transfer services as well as communications, and solar-home-systems or lanterns with phone-chargers allow people in off-grid areas to benefit from these, without the time and expense of going to a phone-charging shop. Solar lanterns are attractive for market stall holders as well as homes, because they give good-quality light for displaying and selling produce after dark. They are also used by midwives and traditional birth attendants, to deliver babies more safely.Cost Costs of solar-home-systems vary between countries. In Bangladesh, a 20 Wp system sold by Grameen Shakti costs about US$230, and a 50 Wp system US$430. This is a significant capital investment for a poor household, but usually no more than would be spent on kerosene for lighting and dry-cell batteries over three years. Outside Asia, costs tend to be higher. For example, 10 Wp systems provided by the Solar Energy Foundation in Ethiopia cost about US$260, and 50 Wp systems sold by ECAMI in Nicaragua cost about US$600.Several Ashden Award winners have made solar light and power affordable to more people at the bottom of the income pyramid, by developing and mass-producing solar lanterns. The cheapest D-light lantern retails for US$10 in India, and a ToughStuff kit of lantern, PV module and phone-charging lead retails for US$18 in Kenya.NumbersThe number of solar-home-systems currently in use is difficult to estimate, but is likely to be several million. Several Ashden Award winners have been involved in large scale programmes. The work of the REDP led to the installation of over 400,000 systems in rural China and Grameen Shakti and Rahimafrooz Renewable Energy have between them installed over 600,000 in Bangladesh. Solar lantern sales have grown rapidly in the past few years, with over 300,000 sold by D-light alone.The futureThe number of solar-home-systems and lanterns in use globally is difficult to estimate, but it is probably at least ten million. Bangladesh has seen remarkable growth in the use of solar-home-systems since 2003, thanks to a national fund to provide microfinance for off-grid households to buy them. In May 2011 the country achieved one million installations, and 600,000 of these were provided by Ashden Award winner Grameen Shakti. The work of another winner the REDP has led to the installation of over 400,000 systems in rural China. Solar lantern sales have recently escalated, with over 300,000 sold globally by D-light and 140,000 by ToughStuff.Useful linksView our Photovoltaic solar home systems and solar lanterns photo collection on flikr If you’ve found this interesting, then you might want to read some of the other technology papers on our website www.ashdenawards.orgLead author: Dr Anne WheldonPhotovoltaic solar home systems and solar lanterns v1.0, last updated June 2011A 20 Wp module provides power to this home in rural NicaraguaWith solar lighting, goods can be well displayed on a market stall at nightBanking by mobile is crucial for many in Kenya. Being able to charge your mobile phone at home makes it possible in off-grid areas