When it comes to renewable energy, solar and wind power take the spotlight. Their power plants are highly visible and iconic: most people instantly recognize solar panels and spinning wind turbines. But ask someone to describe a geothermal plant and the task is more challenging.
Despite this, use of geothermal power is growing fast. Over 450 geothermal plants are in production around the world, up from just 30 several years ago. About 175 of those are located in the US. The world’s only green-powered country, Iceland, gets nearly 30% of its electricity from geothermal power (and almost 90% of its heat and hot water).
So how does it work? As the name suggests, geothermal harvests the energy produced by the earth’s hot core. Pipes are drilled into the ground and the steam or heat that escapes is either used to generate electricity or is directed straight to a building for space heating. You can usually find billowy white clouds of steam surrounding a geothermal power plant.
Unlike conventional energy sources like coal and gas, geothermal power doesn’t produce dangerous greenhouse gases like carbon dioxide or methane. One of Iceland’s most iconic tourist spots, the Blue Lagoon (pictured above), was created by diverting water unearthed by a nearby geothermal plant. Geothermal also has an advantage over other renewable technologies in its consistency: the heat produced by the earth’s core never wanes.
It’s not just utility companies that are taking advantage of geothermal power. Individual homeowners are building smaller geothermal installations too. Geothermal heat pumps (also known as “ground source heat pumps”) that draw heat from the ground beneath one’s home or business can slash HVAC costs. More than 600,000 U.S. homes and other buildings already use such pumps, which are placed at a depth of 20 feet or deeper.
Harvesting geothermal energy doesn’t come without its challenges. Large power plants can only be built in certain regions, typically near fault lines. It takes time and money to find the best place to put one. So far the US has geothermal plants in Alaska, California, Hawaii, Idaho, Nevada, Oregon, Utah, and Wyoming (although smaller systems can be installed just about anywhere).
In large systems that aren’t “closed-loop”, sulfur dioxide (SO2) from the steam can be a minor pollution concern – although SO2 emissions are about 30 times lower per megawatt-hour than from coal plants, the nation’s largest source of SO2 emissions. Drilling for geothermal has also been known to cause small earthquakes and certain designs can compete with other users for freshwater, albeit significantly less than conventional forms of energy like coal.
Want to learn more about solar and wind’s unsung yet powerful cousin? Visit the Union of Concerned Scientists’ page on geothermal energy or Google’s comprehensive map of geothermal resources. Interested in learning more about the role of this and other often overlooked renewable resources? Listen to this EESI Congressional briefing. And if you’re interested in installing your own geothermal heat pump, the Department of Energy has great resources to get you started.