The US Department of Energy and the Department of the Interior’s Bureau of Land Management have released the “Final Programmatic Environmental Impact Statement” (FPEIS) for utility-scale solar energy operations on public lands in Arizona, California, Colorado, Nevada, Utah, and New Mexico. This “solar roadmap” estimates we will be able to harness 23,700 megawatts from 285,000 acres of developed lands, enough to power 7 million US homes with renewable energy.
285,000 acres might sound substantial, but everything we do involves trade offs. Deciding to pursue one opportunity inherently means not pursuing another, hence the name opportunity cost. But 285,000 acres only make up one ten-thousandth of the United States’ total acreage, meaning that from one hundredth of one percent of our land we could supply power to 2.3% of our country’s population. Seems like a good trade off to me. To the sun god!
JM Kincaid
tothesungod 
Water, solar, and wind.Oddly enough the most coolmnmy found and under-utilized is probably methane. From human sewer systems to landfills, from animal production farms to compost production systems, there is a readily renewable source of methane. A number of folks consider methane to be less than environmentally friendly as its use does generate CO2. A number of folks consider it to be less than practical because one one source is likely to be a sole solution for an area/greater. A number of folks discount it because it is not necessarily a magic bullet that can be sold as the solution for use by all across the country, nor particularly by a private utility company. Still it exists and is not particularly being used for productive purposes.
It all comes from the sun, directly or inderictly and it varies with where you are. If you are in the NE USA, around the fall line, water power is feasible. If you happen to be around Mecca, in Saudi Arabia, solar panels would be ideal. That area gets the most insolation on Earth. Not a good spot for river power, though. Tidal power works well if you are along the ocean and nearer the poless than the equator, as in the Bay of Fundy. Wind power is dependable on the Great Plains and id dependent on local topography to a large extent.