Energy according to the source can be divided into three categories: (1) the energy from the sun.Including direct energy from the sun (such as sunlight radiation) and indirect energy from the sun (such as coal, oil, natural gas, oil shale and other combustible minerals and fuel wood and other biomass energy, hydropower and wind power, etc.).(2) the energy from the earth itself.One is the interior of the earth is geothermal energy, such as underground hot water, steam, dry...