Solar power also has great potential. In a single year, we receive twice as much energy from the sun as that contained in all the earth’s remaining non-renewable resources, such as coal, oil, natural gas, and uranium. For practical purposes, the sun’s energy is infinite. We can capture some of this energy by designing smart buildings, for example, ones in the northern hemisphere that have most windows facing south and few facing north. This is known as passive solar power. Another way is to use the sun’s energy to convert water to steam and have this steam drive an electric generator. A third way is a use a solar cell to produce electricity directly. Solar power holds great promise, but its reliability in the far north and south is questionable.