Geothermal Energy's Untapped Potential in the Global Energy Shift

Nesjavellir Geothermal Power Station
Nesjavellir Geothermal Power Station
Maksim Kontić
Maksim Kontić
6 min

Hidden beneath the surface of our planet is an immense, untapped energy potential: geothermal energy. This thermal energy, which is generated by the decay of radioactive substances such as uranium, thorium and potassium in the Earth's core, is an almost inexhaustible resource. Although it is overshadowed by solar and wind energy, geothermal energy has the potential to become a respectable participant in the global energy transition due to its unimaginable reserves.

Despite its great potential, geothermal energy is unevenly distributed and often lies at inaccessible depths, which makes it difficult to exploit. However, in areas with a high geothermal gradient, it is possible to drill for liquid or solidifying magmatic bodies that release heat, or for aquifers with high pressure and temperatures that can exceed 300°C.

There are different types of geothermal systems: hydrothermal reservoirs, hot dry rock geothermal systems, magmatic geothermal systems and geopressured systems. Hydrothermal wells are most commonly used in geothermal power plants to generate electricity due to their lower technical requirements. Depending on the type and temperature of the well, different technologies have been developed for its optimal use, including dry steam power plants, flash steam power plants and binary cycle power plants.

Dry steam power plants use steam directly from the reservoir to drive turbines. The steam is piped to the turbines, then condensed and returned to the reservoir. Although they are very efficient, they are rare due to the special geological conditions required for their operation, such as extremely high water temperatures. The largest geothermal power plants, such as those in the USA and Italy, are of this type.

Most of today's geothermal power plants are flash-steam power plants that use water from hydrothermal reservoirs with temperatures between 180°C and 370°C. As the water flows through the pipes, it partially vaporizes due to the pressure drop. In the separator, the steam is separated from the liquid and fed to the steam turbine, while the remaining water is returned to the reservoir via return channels. The quality of the steam or the steam/water ratio is crucial for maintaining sufficient pressure in the turbine and maximizing output. Modern plants with two separators can generate 20-30% more energy compared to plants with one separator.

Binary cycle power plants use a secondary medium with a low boiling point, such as pentane or butane, to generate electricity. Water or steam transfers heat to the secondary medium via a heat exchanger and causes it to vaporize. The vaporized liquid then drives the turbines. The binary cycle is expected to become the most common type of geothermal power plant as it can utilize lower temperature resources and is therefore suitable for a wider range of locations.

Although this type of renewable resource is significantly limited by geographical restrictions and complex implementations compared to other renewable sources, examples from the USA, Italy, Kenya, Mexico, the Philippines and Iceland are shining examples of its application. By 2023, over 16 GW of geothermal power capacity has been installed in 32 countries worldwide. In Kenya, these sources account for up to 45% of capacity, and in Iceland almost 27%. The Geysers in California is the largest geothermal complex in the world with a capacity of 1,517 MW, while Larderello in Tuscany, the oldest geothermal power plant in the world (since 1913), is now the second largest geothermal complex with 769 MW. Other significant capacities are Cerro Prieto (Mexico) with 720 MW, Olkaria (Kenya) with 700 MW and Makiling-Banahaw (Philippines) with 458 MW.

Geothermal energy stands out as one of the most promising solutions for a sustainable energy future. Its unique ability to deliver a stable and continuous energy supply, in contrast to the intermittent nature of solar and wind sources, makes it an invaluable addition to the energy mix. As technology advances and binary cycle plants evolve, we can anticipate unlocking the full potential of geothermal energy, making it viable for an ever-growing number of locations with lower geothermal potential.

References

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