More than 30 states have passed or are considering “renewable energy portfolio standards” that require utility companies to generate some portion of their electricity from renewable sources. Geothermal power plants, which tap hot subterranean water or steam, are high on many lists.

Most utilities have not pursued geothermal energy primarily because up-front costs, including exploratory drilling, can be high. (Geothermal taps deep reservoirs, not groundwater, which collects much closer to the surface.) But once in operation, the plants consume no fuel and create few if any emissions. “When looking at the true costs over a plant’s lifetime, geothermal is on par with or better than a coal plant,” the least expensive conventional option, notes Gerald Nix, geothermal technology manager at the National Renewable Energy Laboratory in Golden, Colo.

This article was originally published with the title Heating Up.

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