This article is part three of a short series for October’s National Energy Awareness Month by National Geographic Geography Intern Hannah Dempsey. Find part two on biopower here, and part one on tidal energy potential here.

 Reliable. Constant. Ancient. Geothermal energy is as old as the Earth itself, and we take advantage of this naturally occurring phenomenon to make electricity.

Geothermal energy powers three and a half million homes in the United States—namely in California, Nevada, and Utah. It provides up to 30% of the electricity in Iceland, the Philippines, and El Salvador.

Harnessing Earth’s Energy

Intense energy generated in Earth’s interior naturally fuels geothermal activity associated with volcanoes, geysers (like Old Faithful in Yellowstone National Park), and hot springs.

We take advantage of geothermal energy in different ways. Water—in the form of natural hot springs or water piped through the ground—can be used to heat homes, sidewalks, or spa “lagoons.”

Geothermal energy provides the opportunity for homeowners to reduce their heating and air conditioning costs. Referred to as geothermal HVAC, homeowners can actually buy a geothermal heat pump and have pipes installed deep in the ground outside of their house. Warm water is piped in during the winter, and cool water is piped in during the summer.

Similarly, power plants pipe hot water from the depths of the Earth to create steam, and ultimately, electricity.

Advantages and Disadvantages

The single greatest advantage of geothermal energy is that it is completely renewable and reliable for the next four billion years or so.

Geothermal power plants are relatively cheap to maintain, last for a very long time, and tend to have small physical footprint when compared to hydroelectric or fossil fuel-based power plants.

Of course, geothermal heat is not a perfect energy source. Harvesting geothermal energy remains a challenge for scientists and engineers.

First, geothermal energy isn’t equally accessible across the whole surface of the Earth. We are limited to collecting energy from places that are hot, contain liquid, and are permeable. This is largely why Iceland and the Philippines can take advantage of geothermal heat; they are in great hotspots for geothermal activity. Iceland sits on the Mid-Atlantic Ridge where tectonic plates are spreading, while the Philippines rests on the Ring of Fire.

Second, while geothermal systems don’t require large quantities of freshwater, it is possible for leaks to pollute drinking water sources and aquatic habitats. Geothermal plants also emit small amounts of hydrogen sulfide and carbon dioxide—although at a much lower rate than fossil fuel plants.

Lastly, the initial cost of constructing geothermal plants is quite high, prohibitively so for developing nations.

So, it’s not a perfect solution, but geothermal energy is an important sector to invest in because the ecological concerns are largely preventable, and there is so just much potential we could tap into.

Let’s seek the heat!