Earth's heat: Abundance
Millions of years of supply, mostly out of reach
Millions of years of supply, mostly out of reach What this tab covers How much of this energy there is: the natural flow or stock, the share that could be harnessed, and how much is used today, compared with world primary energy use (592 EJ in 2024).Heat flows out of the Earth at about 47 TW, around 2.5 times world primary energy use, and the heat stored in the crust alone is millions of years of human demand. But only hot spots are usable: geothermal supplied about 99 TWh of electricity and 245 TWh of direct heat in 2024, about 0.2% of world primary energy.
A flow: renewed continuouslyHow much there is
| Measure | Value | Compared with world energy use | Note |
|---|---|---|---|
| Total heat flow from the interior | 47 +/- 2 TW2 | about 2.5 times world primary energy (about 1,480 EJ/yr vs 592 EJ) | Davies and Davies (2010) from 38,347 measurements, higher than earlier published estimates |
| Radiogenic part of the heat flow | about 20 TW5 | about 1.1 times world primary energy | From KamLAND and Borexino geoneutrino measurements of uranium and thorium decay; models add about 4 TW from potassium-40 |
| Heat stored in the Earth's crust | about 5.4 x 10^21 MJ4 | about 9 million years of world primary energy at 2024 rates | Whole Earth about 12.6 x 10^24 MJ; most is far too deep or too diffuse to reach |
| Technical potential for electricity | about 210 GWe4 | about 1.1% of world primary energy if run continuously (about 6.6 EJ/yr) | Most likely value (Stefansson 2005), conventional hydrothermal resources; an earlier estimate (Bertani 2003) ran from 35-70 GWe to 140 GWe |
| Use in 2024: electricity | about 99 TWh6 | about 0.06% of world primary energy (0.36 EJ) | From about 15.1 GW of capacity at end 2024 |
| Use in 2024: direct heat | about 245 TWh (882 PJ)6 | about 0.15% of world primary energy | District heating, greenhouses, baths, industry |
Geothermal is technically a flow (the steady outward leak of heat) drawn from an enormous stock (the heat stored in rock). The outward flow is more than twice what humanity uses, but it is spread thinly over the whole planet, including the ocean floor.
In practice a geothermal field is mined like a stock: wells withdraw heat faster than the surrounding rock replaces it, and a field can cool or lose pressure over decades unless fluid is reinjected. Enhanced geothermal systems, which fracture hot dry rock and circulate water through it, could open up far more of the stored heat; they are not included in the 210 GWe estimate.
Sources
- Earth's surface heat flux (Davies and Davies, Solid Earth 1, 5-24) Copernicus / European Geosciences Union, 2010
- World Energy Resources 2013: Geothermal World Energy Council, 2013
- Radioactive decay fuels Earth's inner fires (KamLAND geoneutrino results) ScienceDaily / Lawrence Berkeley National Laboratory, 2011
- Renewables 2025 Global Status Report: Geothermal REN21, 2025