Abstract
In this paper, we present five basic types of renewable energy sources, namely: wind turbines, solar cells, small hydroelectric plants, biomass, and geothermal sources of energy. Wind turbines transform energy of wind into electrical energy, solar cells transform energy of sun into electric energy, hydroelectric plants transform energy of water into electric energy, devices or machines can be constructed to transform energy of biomass into heat energy, and geothermal energy into some form of energy. In this paper we present basic information and reasons why there is need today to use these forms of energy—called green energies, we present how these devices or machines function, and we propose for future work design of typical devices or machines that will satisfy basic functional needs