Solar panels. An array of photovoltaic cells (solar panels) on a roof. The cells convert sunlight directly into electricity. Solar power is a renewable source of energy and does not contribute to global warming. The only pollution associated with these cells is during their manufacture. Photovoltaic cells are made from semiconductor materials such as silicon or gallium arsenide. As photovoltaic cells do not work in low light, residences which use solar power must have a reserve power supply. This can either be batteries which store excess power during the day or a connection to a conventional electricity distribution network. Photographed in Germany.