The Earth’s core contains radioactive metals that constantly give off heat. Where this heat reaches the surface, it can fuel roiling hot springs or erupt in explosive geysers.

The first geothermal power plants were built on these natural sources of steam. Steam from hot springs turned a turbine to power a generator, just like in a coal-fired power plant.1

Modern geothermal plants find or make steam deeper underground. A pair of wells is drilled into the Earth, up to around 3 kilometers (nearly 2 miles) deep, where the rock is boiling hot.2 Water is pumped into the first well to seep into pores and cracks in the rock below. As the water heats up, it emerges from the second well and becomes steam that turns a turbine. Water can be continuously recycled through this system, making electricity all the while.

These power plants must be built on a very specific geology, with permeable rock and high heat near the Earth’s surface. This has mostly limited geothermal power to regions with lots of tectonic activity, like California, Indonesia, the Philippines, and Central America.

In small countries with rich underground heat, geothermal can be an important part of the power mix. Kenya gets almost half its electricity from geothermal,3 and Iceland uses geothermal for 30% of its electricity and nearly all its home heating.4 But globally, only around 0.3% of electricity comes from geothermal.5

Modern drilling technology is pushing these limits. As the cost of drilling falls, several countries have explored building geothermal power outside tectonically active areas, in places where the high heat needed lies deeper underground.

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