Solar and wind are attractive sources of renewable energy, but neither one is available constantly. But there's another resource that is, and projects to tap into it are heating up.

California already has a leg up on most other areas in the development of geothermal power, observes Karl Gawell, Executive Director of the Geothermal Energy Association. He expects that will only expand, as the state ramps up renewable energy production in order to meet its greenhouse gas reduction targets.

But the proliferation of geothermal production sites in the future will look quite different than large, concentrated facilities such as The Geysers, Gawell predicts. Instead, they will be smaller, less visible, and scattered across the state.

Such a future is entirely plausible, even expected, for much of California and the West, Gawell says, while other areas, farther removed from areas of geothermal activity, may still regard it as something speculative or far-fetched.

You can expect to be hearing more about geothermal energy this week, as the GEA is hosting its Geothermal Energy Expo 2012 in Reno, NV.