Geothermal power plants

Steam or hot water from underground reservoirs drives turbines.

Capture · Geothermal · No. 34

• Capture
• Output: Electricity

Geothermal plants turn only about 12% of their underground heat into power, yet run about 85% of the time.

Chart: Illustration: Geothermal power plants

Where it comes from

Chart: Map of where it comes from

Heat from deep inside the Earth warms water held in porous rock. Wells bring it up as steam or hot brine; dry steam fields such as Darajat in Indonesia convert up to 21%.

Three things to know

1. The ground at Wairakei in New Zealand has sunk about 15 m in 50 years as fluid was drawn from beneath it.
2. Some Turkish plants release 400-1,300 g CO₂/kWh from reservoir gas, while binary plants that reinject everything emit almost nothing.
3. A 50 MW flash plant needs about 21 wells: 15 to bring hot fluid up and 6 to send it back down.

The journey

1. 1 Deep heatHot rock warms water underground
2. 2 WellsBring up steam or hot brine
3. 3 Power plantDry steam, flash or binary turbine
4. 4 ReinjectionSpent fluid pumped back to hold pressure
5. 5 GridSteady power around the clock

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