Heat from below
Deep beneath your feet, Earth is very hot. The temperature rises about 25–30 °C for every kilometre you go down. Earth’s core is about as hot as the surface of the Sun. Geothermal energy is the heat that comes from inside Earth. The word comes from Greek: geo (Earth) and therme (heat).
Where does the heat come from?
Earth’s interior is hot for two main reasons:
- Leftover heat from when Earth formed about 4.6 billion years ago.
- Radioactive decay of elements like uranium, thorium and potassium in rocks, which keeps releasing heat.
In some places, magma comes close to the surface, heating underground rocks and water. These areas have the most geothermal energy, often near volcanoes and plate boundaries.
Natural signs of geothermal energy
| Feature | What it is | Example |
|---|---|---|
| Hot spring | Groundwater heated by hot rock rises to the surface | Banff Upper Hot Springs, Alberta; Harrison Hot Springs, BC |
| Geyser | Hot water and steam erupt regularly | Old Faithful in Yellowstone erupts about every 60–110 minutes |
| Fumarole | Vent releasing steam and volcanic gases | Iceland, Yellowstone |
| Mud pot | Bubbling pool of hot mud | Yellowstone, New Zealand |
People have bathed in hot springs for thousands of years. The ancient Romans built public baths over hot springs, including the famous baths in Bath, England.
Generating electricity
A geothermal power plant uses steam or very hot water from deep underground.
- Wells are drilled 1–3 km deep into hot rock or underground reservoirs.
- Hot water or steam rises up the well.
- The steam spins a turbine connected to a generator, making electricity.
- Cooled water is pumped back underground to be reheated.
| Plant type | How it works |
|---|---|
| Dry steam | Uses steam directly from the ground |
| Flash steam | Very hot water "flashes" into steam when pressure drops |
| Binary cycle | Moderately hot water heats a second liquid with a low boiling point, which turns to vapour and spins the turbine |
The first geothermal power plant opened in Larderello, Italy, in 1904.
Leading countries
| Country | Notes |
|---|---|
| United States | World’s largest producer (California’s "The Geysers" is the largest geothermal complex) |
| Indonesia, Philippines | Many volcanoes |
| Iceland | About 25–30% of electricity and about 90% of home heating from geothermal |
| New Zealand | Major producer |
| Kenya | Gets nearly half its electricity from geothermal |
Canada has strong geothermal potential in BC, Yukon, NWT, Alberta and Saskatchewan. Canada’s first geothermal power projects are being developed in several of these places.
Geothermal heat pumps
You don’t need volcanoes to use geothermal energy at home. A few metres underground, the temperature stays about 5–10 °C all year in much of Canada, warmer than winter air and cooler than summer air.
A geothermal heat pump (also called a ground-source heat pump) circulates fluid through pipes buried in the ground:
- Winter: it collects heat from the ground and moves it into the house.
- Summer: it moves heat from the house into the ground, cooling the building.
These systems can be three to four times more efficient than electric baseboard heaters.
Direct uses
Hot water from underground can be used directly to:
- heat homes and greenhouses
- warm fish farms
- melt snow on sidewalks (as in Reykjavík, Iceland)
- dry crops and timber
Advantages and disadvantages
| Advantages | Disadvantages |
|---|---|
| Renewable energy: Earth’s heat won’t run out | Big power plants need hot rocks near the surface |
| Works 24/7, rain or shine | Drilling is expensive |
| Very low greenhouse gas emissions | Can release small amounts of underground gases |
| Takes up little land | Deep drilling has occasionally triggered small earthquakes |
| Reliable, steady supply | Wells can cool down if overused |
Common mistakes
- Thinking geothermal only works near volcanoes. Heat pumps work almost anywhere.
- Thinking geothermal heat comes from the Sun. It comes from inside Earth.
Try it yourself
- Measure the temperature of soil at the surface and 30 cm down on a cold day and a hot day. Compare.
- Find the nearest hot spring to where you live on a map.
- Make a chart comparing geothermal with solar and wind energy.
Quick recap
- Geothermal energy is heat from inside Earth.
- It comes from Earth’s formation and radioactive decay.
- Power plants use underground steam to generate electricity.
- Heat pumps use steady ground temperatures to heat and cool buildings.
- Geothermal is renewable, reliable and low-emission, but limited by location and cost.