Most renewable energy is obtained, directly or indirectly, from the sun. Solar energy can be used directly to heat and light up buildings, for generating electricity, and for heating and cooling at levels suitable for commercial and industrial process purposes.
Weather patterns, and particularly winds, are also driven by the heat of the sun. Wind energy is captured with turbines to generate electricity or for mechanical pumping purposes. Winds and the heat of the sun, in turn, evaporate water. The resulting water cycle provides the opportunity to capture hydro energy through electricity generating turbines and other mechanical devices.
Along with sunlight, the precipitation and runoff of the water cycle cause plants to grow. The organic matter that makes up those plants is known as biomass. The associate bio-energy of the carbon content of the biomass can be used effectively to produce electricity, transportation fuels and chemical products. Hydrogen also can be found in many organic compounds, as well as water. Once separated from the organic compounds or water, hydrogen can be burned as a fuel or converted into electricity.
Ocean energy comes from a number of sources. In addition to tidal energy, due to the gravitational pull of the moon and the sun upon the earth, there is the energy of the ocean's waves, which are driven by both the tides and the winds, and currents, also ascribe to wind patterns that are caused by the rotation of the earth. The sun also warms the surface of the ocean more than the ocean depths, creating a temperature difference that can be used as an energy source. All these forms of ocean energy can be used to produce electricity.
Geothermal energy is another renewable resource that is not attributable to the sun. Here the internal heat of the earth is used in a variety of ways, including electric power production, and the heating and cooling of buildings and processes.