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Solar lighting is often used for solar garden lights, since lamps in the garden are exposed to sunlight throughout the day. Since a renewable energy source is used, electric power is saved, no electric wiring is required and there is no problem of electric shock from exposed cables during the rains.
Solar lighting usually consists of solar cells , batteries, LEDs and associated electronic circuitry. Several solar cells are connected together to generate sufficient voltage and current to charge the batteries. The solar energy is usually stored in NiCad (Nickel Cadmium) or NimH (Nickel metal hydride) batteries during the day.
A diode in the solar lighting circuit prevents the current from the battery flowing through the solar cells at night. After exposure to more than 5 hours of direct sunlight, the batteries of the solar light are fully charged and charger electronics prevents overcharging
At night, the photo resistor (photocell) in the solar lighting turns on the LED and the energy stored in the batteries is discharged at night. Unlike conventional batteries used in cars, the batteries used for solar lighting are deep discharge batteries and can withstand several cycles of charging and discharging. The LEDs used in solar lighting consume very little power and the light output is similar to that of candles.
Solar lighting is not widely used since monocrystalline silicon which
is used for manufacturing photovoltaic (solar) cells is still expensive.
The light output depends on location of the solar cell and weather
conditions. On a cloudy day, less energy is stored in the batteries. Also
the LED light output is the maximum in the first few hours of
operation at night and gradually decreases. The battery used for solar
lighting usually has to be replaced after a year, but the LED and solar
cells work for several years.