The first geothermal generator in 1904 lit exactly four light bulbs
On 4 July 1904 at Larderello in Italy, Prince Piero Ginori Conti hooked a generator up to volcanic steam and switched on four light bulbs. Seven years later the same spot hosted the first commercial geothermal power station, and for over half a century Italy remained the only country producing geothermal electricity on an industrial scale.
That monopoly ended in 1958 when New Zealand opened its Wairakei station, the first to use flash steam. In 1960 Pacific Gas and Electric started up the first successful American plant at The Geysers in California; its original turbine ran for over 30 years. Earlier experimental generators had been tried at Beppu in Japan and at The Geysers in the 1920s. By 2022, 32 countries operated geothermal plants, and Iceland, Kenya, Costa Rica, New Zealand, El Salvador and the Philippines each drew more than 15 percent of their electricity from underground heat.
The planet holds an enormous store of heat, constantly topped up by radioactive decay, but most of it seeps out far too thinly to capture. The crust acts like a thick blanket that must be pierced by magma, hot springs or drilled wells. Away from tectonic plate edges, temperature climbs only 25 to 30 degrees Celsius per kilometre of depth, so power wells there would need to go several kilometres down, and drilling beyond 4 kilometres usually costs tens of millions of dollars.
Three designs dominate. Dry steam plants, the oldest and simplest, pipe natural steam of at least 150 degrees straight into turbines. Flash steam plants let very hot pressurised water boil as the pressure drops; they make up over half of installed capacity. Binary cycle plants pass warmer water past a second fluid with a lower boiling point, and one in Alaska generated power from water at just 57 degrees Celsius.
Geothermal plants convert only 7 to 10 percent of the heat into electricity, but unlike wind or solar they run almost continuously, with capacity factors up to 96 percent demonstrated. Emissions average 45 grams of carbon dioxide per kilowatt-hour, under a twentieth of coal. Wells can cool or run dry, though: when steam at The Geysers dwindled, operators began injecting treated municipal sewage water to revive it.
Source: Geothermal power
