Geothermal energy is the power extracted from heat stored in the earth, coming from the original formation of the planet, from radioactive decay of minerals, and from solar energy absorbed at the surface. Geothermal energy doesn't create any pollution, is very efficient, an alternative source of energy, which means that by using it we get less dependent on coal and oil, and perhaps the most important advantage of geothermal energy is that, unlike energy derived from carbon-based sources, geothermal energy will never run out.
Heating water using solar energy was used long before our energy system being dominated by fossil fuels. Thus, solar heating principles are known for thousands of years. A black surface exposed to the sun becomes hot, while a light colored surface remains cooler, with white being the coldest.
