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Far, far below your feet lies a source of nearly endless energy. Earth's core is about as hot as the surface of the Sun, so hot that it melts the rocky layers above it into magma, or liquid rock. Wouldn't it be great if we could tap into all that energy? In some places, we do!
The Geysers is an area north of San Francisco in California where magma's heat turns a reservoir of underground water into steam. This region is home to 18 geothermal power plants. The steam rises up through spaces between the rocks underground, a bit like how steam pours from a teakettle boiling on a stove. The power plant has pipelines that send the steam into the turbines (涡轮机) where electricity flow is generated. Once the steam leaves the turbine, it goes into a cooling tower where it turns back into liquid. Then it's piped back into the reservoir to be reheated again. Other kinds of geothermal power plants pump hot groundwater into the power plant. Then the pressure is reduced, causing the liquid to flash into steam that turns the turbine and generates electricity flow. Once the steam cools and turns back into liquid, it's pumped back down into the reservoir to begin the cycle again.
So why don't we all heat our homes with free steam from the earth? First, the heat has to be close enough to the surface for us to reach it. Next, there has to be plenty of underground water to be heated. Finally, there has to be a layer of rock that water or steam can flow through. So in places where all three of those things come together, geothermal energy can be a powerful renewable energy source. Besides, when a geothermal plant returns water back into the hot rocks of a reservoir, it makes the rock crack a bit, which can cause small earthquakes. There's another danger that comes with drilling near magma-pipes and other equipment might melt if they hit a pocket of magma or are caught in an eruption. One geothermal plant in Hawaii was partially buried by lava in 2018. But engineers are hopeful that the repaired plant will generate even more power. Geothermal energy isn't the answer for everywhere, but it's a piece of the puzzle to help slow climate change.
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