Solar Home System

A solar-home-system uses a photovoltaic (solar-electric) module to provide power for lights and small appliances. The system also needs a rechargeable battery, so that power is still available at nigh


A solar-home-system uses a photovoltaic (solar-electric) module to provide power for lights and small appliances. The system also needs a rechargeable battery, so that power is still available at night and on cloudy days.

Solar-home-systems bring huge benefits to homes in developing countries which aren’t connected to the mains electricity grid. They replace smoky, unsafe kerosene lamps with brighter light, allowing work, study and social activities after dark. They also power radios and cellphone chargers, enabling families to be in contact with the wider world. The smallest systems are solar lanterns, which can be moved around the home or carried outdoors.

Solar-home-systems and solar lanterns already provide power to millions of homes in Asia, Africa and Latin America. Similar systems are also used in off-grid schools and health centres.

How a solar-home-system works

Photovoltaic (PV) modules use semiconductor materials to generate d.c. 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.

Layout of a solar-home-system

PV 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.

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 (usually 12 V) 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 12 V d.c. operation. Efficient lights and appliances make best use of the limited supply of electricity. Efficient d.c. 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.