Most of the world depends on fossil fuels for both electricity generation and transportation. Two factors will put tremendous pressure on fossil fuel use in the twenty-ﬁrst century: global climate change, and concerns about resources and geopolitics, especially of oil. These factors make it prudent to consider sources of energy that are not likely to be depleted; such sources are called renewables. Examples include wind, water, solar, and biomass. The term renewables implies that this source is continuously being renewed, either through natural events, as in wind or solar energy, or through human intervention, such as energy crops. Energy sources that are harvested and then regrown are also known as sustainable energy sources. Renewables do not rely on localized concentrations in seams or reservoirs, as fossil fuels, but can be used almost anywhere. Therefore renewables are not nearly so likely to be impacted by concerns of geopolitics and possible embargoes as are the fossil fuels. If there were such a thing as an ‘ideal’ energy source, it would:
(1) be essentially limitless, so that we need not worry about the lifetime resources; (2) produce little or no pollution and no radioactive waste; (3) produce no net increase in atmospheric CO2; and (4) be a domestic resource, eliminating any nation’s concern about dependence on foreign sources. Various energy sources meet these criteria to some extent; renewables come closest.