How does geothermal energy work

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Last updated: April 8, 2026

Quick Answer: Geothermal energy harnesses heat from Earth's interior, typically from depths of 3-10 kilometers where temperatures reach 150-370°C. The first geothermal power plant began operating in Larderello, Italy in 1904, generating 250 kW. Today, geothermal provides about 0.3% of global electricity but supplies over 25% of Iceland's power needs. Enhanced geothermal systems (EGS) can potentially access heat resources up to 10 kilometers deep.

Key Facts

Geothermal energy taps into Earth's internal heat, which originates from radioactive decay and residual heat from planetary formation
The first commercial geothermal power plant started in Larderello, Italy in 1904
Geothermal provides approximately 0.3% of global electricity generation
Iceland generates over 25% of its electricity from geothermal sources
Enhanced Geothermal Systems (EGS) can access heat resources at depths up to 10 kilometers

Overview

Geothermal energy harnesses heat from Earth's interior, originating from both the planet's formation approximately 4.5 billion years ago and ongoing radioactive decay of isotopes like uranium-238, thorium-232, and potassium-40. This thermal energy creates temperature gradients increasing about 25-30°C per kilometer depth in most regions. Humans have utilized geothermal heat since Paleolithic times for bathing, with the Romans building elaborate bath complexes around hot springs. The first industrial use began in 1827 when Francesco Larderelli extracted boric acid from geothermal steam in Italy. Modern geothermal power generation started with Prince Piero Ginori Conti's 1904 plant in Larderello, which initially produced 250 kW. Today, geothermal energy provides renewable baseload power in over 20 countries, with the United States leading at 3,700 MW installed capacity as of 2021.

How It Works

Geothermal systems extract heat through three primary methods. Hydrothermal systems access naturally occurring reservoirs where water circulates through permeable rock, heated to 150-370°C at depths of 1-3 km. Wells drilled into these reservoirs bring hot water or steam to the surface, where flash steam plants (for temperatures above 180°C) or binary cycle plants (for 100-180°C) convert thermal energy to electricity. Enhanced Geothermal Systems (EGS) create artificial reservoirs by injecting water into hot dry rock at 3-10 km depths, fracturing the rock to improve permeability. Direct use applications employ heat pumps for space heating, utilizing consistent 10-16°C ground temperatures just 1-2 meters below surface. Geothermal heat pumps achieve 300-400% efficiency by moving heat rather than generating it.

Why It Matters

Geothermal energy provides reliable baseload power with capacity factors exceeding 90%, compared to 20-40% for solar and wind. It emits minimal greenhouse gases—typically 5% of coal plants' emissions per kWh—and uses less land than other renewables. Beyond electricity, direct geothermal heating serves district systems in cities like Reykjavik and Paris, while agricultural applications include greenhouse heating and aquaculture. The geothermal industry supports approximately 100,000 jobs globally. With technical potential estimated at 200 GW for conventional systems and potentially 100 times more for EGS, geothermal could significantly contribute to decarbonization goals while providing grid stability through dispatchable renewable power.