A solar hot water system requires a hot water storage tank that keeps the water at a high temperature. In a two-tank system, water is heated with solar collectors and then stored in the first tank. A one-tank system has a single cylinder with twin coils.
Solar cell efficiency tells us the amount of solar insolation that is converted into electricity. It usually lies between 12.5 and 15%. In laboratories, scientists are working on solar cell efficiency constantly.