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Solar panels for water purification. Solar panels are collections of photovoltaic cells (black squares), which use a light-absorbing material to generate electricity from sunlight. The material used here is silicon. Electricity from solar power is a clean form of energy compared to electricity distributed from coal-fired power stations, as solar panels do not produce pollutant gases. These solar panels are for the water purification station of Meze, France. (KEYSTONE/SCIENCE PHOTO LIBRARY/PATRICK DUMAS/EURELIOS)