Geothermal Power: Tapping Earth's Internal Heat Engine

simulator intermediate ~10 min
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Output: 8.4 MW_e at 200C, 80 kg/s, 12.5% efficiency

A geothermal plant with 200C reservoir, 80 kg/s flow at 3 km depth produces 67 MW thermal and 8.4 MW electrical at 12.5% cycle efficiency. This powers about 7,000 homes continuously with near-zero carbon emissions.

Formula

Q_thermal = m_dot * cp * (T_reservoir - T_reject)
eta_Carnot = 1 - T_cold / T_hot
P_electric = Q_thermal * eta_cycle

Earth's Hidden Power

Beneath our feet lies an enormous reservoir of thermal energy. The Earth's core, at roughly 5,500C, continuously radiates heat outward through mantle convection and radioactive decay. Geothermal power plants tap this heat where it approaches the surface - at tectonic plate boundaries, volcanic regions, and hot spots. Unlike solar and wind, geothermal provides continuous baseload power, operating 24/7 with capacity factors exceeding 90%.

From Reservoir to Grid

This simulation models the thermodynamic conversion of geothermal heat to electricity. Hot geothermal fluid arrives at the surface carrying thermal energy proportional to its temperature and flow rate. A power cycle (flash steam or organic Rankine cycle) converts a fraction of this thermal energy into electricity. The efficiency is inherently limited by the relatively low source temperature - even ideal Carnot efficiency at 200C is only about 38%, and real cycles achieve 25-40% of Carnot.

Deep Wells and Hot Rocks

Reaching economically useful temperatures typically requires drilling 2-5 km deep, where temperatures increase along the geothermal gradient (typically 25-30C per km, but up to 100C/km in volcanic regions). The visualization shows the temperature profile from surface to reservoir depth, the wellbore path, and the plant at the surface. Deeper wells access hotter rock but cost exponentially more to drill.

The Future: Enhanced Geothermal

Conventional geothermal is limited to locations with naturally occurring hydrothermal reservoirs - hot rock with permeability and fluid. Enhanced Geothermal Systems (EGS) aim to create reservoirs anywhere by fracturing hot dry rock at depth and circulating injected water. If successful at scale, EGS could provide hundreds of gigawatts of clean baseload power globally, transforming geothermal from a niche resource into a major energy source.

FAQ

How does geothermal power work?

Geothermal power plants use heat from the Earth's interior to generate electricity. Hot water or steam from underground reservoirs is brought to the surface through wells. Flash steam plants directly use the steam; binary cycle plants transfer heat to a secondary fluid. The cooled fluid is typically reinjected into the reservoir.

What types of geothermal power plants exist?

Three main types: Dry steam plants use steam directly from the reservoir (rare, e.g., The Geysers, California). Flash steam plants depressurize hot water to create steam (most common, for T > 180C). Binary cycle (ORC) plants use a secondary working fluid and work at lower temperatures (80-180C).

Is geothermal energy truly renewable?

Yes, Earth's heat is essentially inexhaustible on human timescales - the Earth's core temperature is about 5,500C and heat production from radioactive decay continues. However, individual reservoirs can be depleted if extracted heat exceeds natural recharge. Sustainable management requires matching extraction to the reservoir's thermal recovery rate.

What is Enhanced Geothermal Systems (EGS)?

EGS creates artificial geothermal reservoirs by hydraulically fracturing hot dry rock at depth, then circulating water through the fractures. This dramatically expands the geographic potential of geothermal energy beyond naturally occurring hydrothermal reservoirs. EGS could theoretically provide hundreds of GW globally.

Sources

Embed

<iframe src="https://homo-deus.com/lab/renewable-energy/geothermal/embed" width="100%" height="400" frameborder="0"></iframe>
View source on GitHub