Coal 1. a breakable black or dark brown rock consisting of mainly carbonized plant matter, found mainly in underground deposits and widely used as fuel.
solar 1. Solar energy technologies use the sun's energy and light to provide heat, light, hot water, electricity, and even cooling, for homes, businesses, and industry.
Geothermal 1. amount of heat generated by the Earth's core. 2. eothermal areas dependent on a reservoir of hot water, the volume taken out can be reinjected, making it a sustainable energy source.