It’s been called a “limitless” source of energy by advocates, and “volcano fracking” by critics - but exactly what is geothermal energy?

From the Core of the Planet

Hot Water Geothermal

Diagram illustrating power generation from a hot-water hydrothermal system (Photo credit: US federal government)

The term actually defines itself: “geo” refers to earth, and “thermal” means heat. A geothermal power plant extracts heat from deep within the earth. The intense heat from hot magma rises, which boils pools of water buried in crust rock.

The water then generates high-temperature steam that spins turbines in a power plant onsite. The energy is ultimately sourced from the feverish core of the planet, which produces a virtually eternal source of intensive heat.

Conventional geothermal production features virtually zero emissions and creates no harmful byproducts. Additionally, this source is not subject to the vagaries of wind and solar - geothermodynamics work full-time, year-round. While the sun doesn’t always shine, and the wind doesn’t always blow, geothermal currents never stop moving.

Geothermal energy production is reliable as long as seismic activity and magma flows remain at low levels; this makes geothermal energy an extremely attractive renewable energy source. Let’s take a look at how the emerging science of geothermal extraction actually works.

Development Boom

According to an air emissions analysis published by the Geothermal Energy Association, hydrothermal production is a big boon to public health as well as the environment. The U.S.-based trade group’s data suggested that California and Nevada save some $117 million annually in diverted pollution by developing geothermal energy.

Geothermal works are filling a surfacing market that has caught the attention of companies and governments worldwide. From Turkey and Indonesia to France and East Africa, nations are increasingly investigating and developing their own geothermal resources.

Meanwhile, the UK hopes to construct a huge vulcan underwater pipeline from Iceland to its own shores in a bid to access cost-effective exports of the cheap, greenhouse gas-free energy source.

How Does It Work?

Conventional Operations

How does geothermal energy work? There are two basic models of geothermal production, and their usage depends first and foremost on the real estate at hand. In the richest reservoirs, there is enormous potential for local energy independence and sustainability. The heart of Iceland, a “land of fire and ice,” is a perfect case-in-point.

Nesjavellir Power Plant in Iceland

Nesjavellir Geothermal Power Plant in Iceland (Photo credit: Gretar Ívarsson)

Here, you can dig a deep well and simply plant a production facility on top. Steam power is constantly available from ever-boiling underground water. “Enhanced” extraction techniques aren’t necessary in a place where the earth’s hot magma readily intrudes through the crust and hot springs freely flow.

The North Atlantic island itself is a product of these processes over geological history. It straddles the seam separating the American and European tectonic plates, which are slowly being torn apart over time. That’s why geothermal works so well for Icelanders: it’s local, abundant and cheap.

Today, it is a huge part of how the nation maintains one of the world’s only 100% renewable electricity grids. Big glass greenhouses sprinkle southern Iceland, using heat from below to grow food that could not otherwise survive in the above-ground climate.

Sonoma Calpine 3 geothermal power plant

Sonoma Calpine 3 geothermal power plant at "The Geysers" (Photo credit: Wikipedia)

More rarely, earthen power comes from dry rocks superheated by underground water, most notably north of San Francisco, California in the “Geysers.” Here, 22 plants and 350 wells collectively produce the world’s largest geothermal output. The installation provides electricity to several hundred thousand local homes, pollution-free.

Enhanced Operations


Diagram illustrating an enhanced geothermal system (Photo credit: Wikipedia)

Most places lack the abundant natural springs that fuel conventional geothermal installations. Currently, a wave of commercial projects is underway to overcome these built-in limitations, using an emerging technology called “Enhanced Geothermal Systems” (EGS) to extract magma-warmed heat from artificial reservoirs.

EGS is still in the early stages of research and development, but promises exponential returns compared to traditional geothermal methods. It could be a viable way to bring geothermal energy into mass production. However, the technique is not without risks.

EGS has been associated with some negative ecological impacts. While a true geothermal reservoir is a source of naturally heated water, EGS involves fracturing bedrock and injecting the cracks with water where none exists. This process has been linked to induced earthquakes and groundwater contamination.

The Future of Geothermal Energy

Conventional geothermal power shines as a high-potential source of cheap, clean and sustainable baseload power for stressed electrical grids. Meanwhile, “enhanced” geothermal operations have large-scale potential, but the cost-benefit balance is still unclear.

Overall, geothermal represents a positive step toward renewable power. It doesn’t get much more clean and reliable than the steam continously formed by the earth’s rocks and all-natural hot springs.