There's also geothermal energy -- which uses the differential between near-constant temperatures below-ground and temperatures up here to create energy.
Because geothermal energy equipment is of necessity buried, it costs a bit more to maintain it. But total costs tend to average around 10 cents a kwh -- similar to wind, and not much more than hydro. But again, a heck of a lot cheaper than solar. Indeed, at the Geysers power plant in California, geothermal energy is sold for as little as 3 cents a kwh.
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