Solar lanterns and solar home systems
Some 1.3 billion people across the developing world don’t have electric light in their homes. Solar lanterns and solar home systems that harness the power of the sun replace smoky, dangerous kerosene lamps and power mobile phone chargers and radios, helping transform lives and offering a window on the world.
- 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.
How solar home systems and solar lamps work
Solar home systems and lamps use photovoltaic (solar-electric or PV) cells and rechargeable batteries to provide electrical power away from the mains grid. Lamps provide a single light (and sometimes phone charging) and are portable. Solar home systems are fixed in a home and can supply several lights, phone charging and other small appliances.
PV cells are made from semiconductor materials, such as silicon, and generate dc electricity from sunlight. A number of cells can be connected together and sealed in a weatherproof casing to form a PV module.
PV cells and 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). Solar home systems use between about 5 and 100 Wp of PV, solar lanterns between about 0.5 and 2 Wp.
The rechargeable batteries store electricity, so that it is available at night and on cloudy days, as well as when the sun is bright, and they also provide a stable voltage for the appliances that use the electricity. Larger solar home systems normally use lead-acid batteries designed specifically for solar use – standard car batteries don’t last long with the deep levels of discharge needed in a solar system. Nickel-cadmium and nickel-metal-hydride batteries have been used in lanterns and smaller systems because they are easier to make portable and in small sizes. But lithium-ion batteries are rapidly becoming the most popular because, with good electronic controllers, they last longer.
An electronic charge-controller protects the battery from being overcharged (when it is very sunny) or over-discharged (when people try to get too much electricity from the system). Other features can also be built into the controller, like different brightness setting for lamps.
Appliances that are powered directly must operate at the dc voltage of the battery but an inverter (dc to ac converter) can be included in a larger system so that standard mains-voltage equipment can be used.
How solar home systems and solar lamps are used
The PV module of a solar home system should be fixed in a position that collects as much sunlight as possible, ideally on an unshaded roof – this also reduces the risk of theft. The battery is kept indoors with the terminals covered so that they cannot accidentally be touched. The PV, battery, lights and sockets for appliances are wired to the charge-controller.
Customers usually buy solar systems based on the service that they provide (for example: ‘charge one phone and run two lights for six hours each day’). It’s up to the supplier to make sure that there is sufficient PV capacity to provide this service throughout the year, and sufficient battery capacity to keep the supply running even when there are several cloudy days in a row. It pays to use the most efficient lights and appliances, so LED lights are now most commonly used, although larger systems also use fluorescent lights.
Ten years ago, most systems were provided as individual components, and installed on site by a trained electrician. However, small systems are increasingly produced as ‘plug-and-play’ kits for DIY installation. The advantage of kits is that the manufacturer is responsible for the sizing, matching and quality of all components. Increasingly, kits are designed so that they can be upgraded.
In a solar lamp, the LED light, battery and charge controller are all in a casing which is easy to carry and can stand on a table, or hang from the ceiling. Some have small plug-in PV modules, like solar home systems, but others have the PV cell mounted on the casing. This cuts the cost, but has the disadvantage that the whole lamp has to be out in the sun to recharge the battery.
Solar-home-systems and lamps can be very reliable and need little maintenance, although in many countries there are cheap, poor quality products on the market as well. Users must be trained to check the battery, keep the PV module clean and make sure that connectors are secure. Even with careful use, batteries deteriorate and need to be replaced every few years.
What are the benefits of solar home systems and solar lamps?
The amount of electricity provided by solar home systems and lamps is surprisingly small: the 20 Wp module supplies about 50 watt-hours (0.05 kWh) per day, and the cell on a small lamp only about one watt-hour (0.001 kWh). However, the benefits can be huge.
The main use of a solar home system is to provide better lighting. Many homes without access to grid electricity use kerosene lamps, which are dangerous - producing health-damaging fumes and a constant risk of fires. Children are particularly at risk, so Ashden winner SolarAid has focused on selling solar study lamps, which can be used on a table for homework. Even these smallest solar lamps give more light than a kerosene lamp. And it is not just studying that is easier and safer with better light. Housework is faster, midwives can deliver babies more safely, shopkeepers can display goods, cattle can be tended and farm produce sorted and packed.
Mobile phones keep people in touch with family and friends, and give access to information, entertainment and mobile money. Being able to charge a mobile phone at home with solar power enables people in off-grid homes to stay connected to the world, without the cost and effort of sending phones to be charged in town. Solar systems can also power radios, providing entertainment and information, and larger systems run TVs as well.
Costs of solar home systems and lamps vary between countries, and have come down rapidly over the past ten years. In 2014, you’d pay about US$150 to buy a 20 Wp Barefoot Power kit including five LED lights and a phone charger in East Africa, or to have a 20 Wp system with three lights and phone charger installed on your home by Grameen Shakti in Bangladesh. Even though many families spend more US$150 on kerosene and phone charging in a year, it is a large amount to pay in one go, and the upfront cost can be prohibitive. In South Asia, microfinance has been used successfully for many years to make solar home systems affordable. More recently there has been growing interest in providing systems on a ‘pay-as-you-go’ basis, with businesses like Off Grid Electric in Tanzania encouraging customers to pay with their mobile phones.
There are probably more than ten million solar home systems in use. Over three million homes have been supplied through the IDCOL programme in Bangladesh, in which Ashden Award-winners Grameen Shakti and Rahimafrooz Renewable Energy are major partners. The work of the REDP led to the installation of over 400,000 systems in rural China. Kenya is the largest market for solar home systems in Africa, with a large number of independent businesses involved and about 350,000 systems in use.
The Lighting Africa and Lighting Global initiatives have helped to improve the quality of solar lamps and small plug-and-play systems, and sales have grown rapidly over the past five years. Ashden winner d.light has sold over 6 million solar lamps, helped by SolarAid in Africa.
1.3 billion people in the world don’t have access to electricity, most of them in low income countries. For example, in Tanzania less than 15% of the population are connected to the mains electric grid. Even in India where three quarters of the population have grid power within reach, the supply is unreliable with frequent and lengthy power cuts in many places. Solar home systems don’t provide the level of power that the grid offers – you can’t run a refrigerator or power tools on 50 Wp of PV – but they have huge potential to provide reliable access to electric lighting, communications and mobile money. System costs will decrease as the global PV market continues to grow, and the improving efficiency of lights and appliances will provide increasing better services.
Author: Dr Anne Wheldon