Geothermal Power Plant

Rising energy demand, declining fossil fuel reserves, increasing pollution, and concerns about global warming have directed countries worldwide toward clean and renewable energy sources. In this context, the Paris Agreement has established international protocols that require nations to set emissions reduction targets and promote the transition to renewable energy to lower greenhouse gas (GHG) emissions. Among renewable resources such as hydropower, wind, solar, biomass, and geothermal energy, geothermal energy stands out due to its continuous availability and low environmental footprint.

Geothermal, derived from the Greek words "geo" (earth) and "therme" (heat), refers to the thermal energy stored within the Earth’s interior. This energy is continuously generated by the slow decay of isotopes in the Earth’s core, such as potassium-40 and thorium-232. The Earth has four main layers: a solid iron inner core approximately 1,500 miles in diameter, a liquid outer core 1,500 miles thick composed of molten material, a mantle 1,800 miles thick made of magma and rock, and a crust 15–35 miles thick beneath continents or 3–5 miles thick beneath oceans. While temperatures in the core exceed 5,000°C (approximately 10,800°F), temperatures at the mantle boundaries range between 392°F and 7,230°F. This heat rises toward the surface along plate boundaries and manifests in natural features such as geysers, hot springs, and fumaroles.

Geothermal energy is renewable because the heat production in the Earth’s core has continued for billions of years and will persist unless an unforeseen event occurs. Humans have used this energy for thousands of years for bathing, cooking, and heating. Today, geothermal power plants have been developed to generate electricity from this resource.

Principles of Operation of Geothermal Power Plants

Geothermal power plants convert the Earth’s internal heat into electrical energy. They operate similarly to coal or nuclear plants but use the Earth’s natural heat instead of fossil fuels or reactors as the heat source. Three essential elements are required for electricity generation: heat (abundant energy stored in deep rocks), a fluid (water or steam to transport heat to the surface), and permeability (pathways allowing the fluid to move through rocks). Systems where these elements occur naturally together are called conventional hydrothermal resources.

Principle of Operation of a Geothermal Power Plant

Power plants operate by extracting hot water or steam from underground. Typically, high-pressure hot water is pumped to the surface through wells located at depths of 1–2 miles. When the pressure drops at the surface, the water flashes into steam, which drives turbines to generate electricity. The used water is usually reinjected into the reservoir, ensuring system sustainability. Geothermal power plants are classified into three main types: dry steam, flash steam, and binary cycle.

1. Dry Steam Plants: These use naturally occurring dry steam from underground. The steam is directed directly from wells to turbines, and after electricity generation, it condenses and is reinjected into the reservoir. This is the oldest type of geothermal power plant, with the first example built in 1904 in Larderello, Italy. The Geysers in Northern California is the largest example of this technology, operating with a capacity of approximately 1.5 GW. However, its application is limited to areas with sufficiently high temperatures.

2. Flash Steam Plants: These are the most common type and utilize reservoirs with water temperatures above 182°C. High-pressure water from underground is released into a low-pressure tank at the surface, causing it to “flash” into steam. This steam drives turbines, while the remaining water can be reused in a second flash tank or reinjected. This technology is widespread in volcanic regions such as Iceland and provides both electricity and direct heating.

3. Binary Cycle Plants: These utilize lower-temperature resources (107–182°C). Hot water passes through a heat exchanger to vaporize a secondary fluid with a low boiling point, such as pentane or butane. This vapor drives the turbines, and since the water and secondary fluid remain separate, emissions are minimal. Binary cycle technology is expected to play a major role in the future due to its potential for broader geographic application.

In addition, when natural conditions are insufficient, Enhanced Geothermal Systems (EGS) are employed. EGS creates artificial reservoirs by injecting water into hot but dry or low-permeability rocks. The 2019 GeoVision analysis in the United States estimated that EGS could supply energy to 40 million homes by 2050, while the 2023 Enhanced Geothermal Shot analysis projects this number could reach 65 million.

Geothermal Power Plants in Türkiye

Türkiye is one of the world’s top five countries in geothermal energy production, alongside the United States, the Philippines, Indonesia, and Kenya. The country’s geothermal potential stems from regions with active tectonic plates. Installed capacity, which stood at 1,064 MW in 2017, rose to 1,696 MW by 2021, with a compound annual growth rate (CAGR) of 12.3%. It is projected that capacity will reach 2,785 MW by 2030, growing at a CAGR of 5.61% between 2020 and 2030. Electricity generation, which was 8,151 GWh in 2021, is expected to reach 13,183 GWh by 2030. In 2023, geothermal energy accounted for 2% of Türkiye’s total installed capacity and 3% of its energy production.

Amendments to the Renewable Energy Law in 2011 aimed to encourage the installation and widespread adoption of geothermal plants by offering incentives such as price guarantees, low connection fees, priority grid access, and simplified permitting procedures.

Advantages and Disadvantages

Geothermal energy produces about one-sixth of the average carbon dioxide emissions of natural gas plants and, unlike other renewable sources such as solar or wind, is available continuously. It offers advantages such as a stable infrastructure, long lifespan (decades), and low water consumption. However, challenges remain, including high initial costs, the risk of microseismic events, and the potential for reservoirs to cool over time. While technologies like EGS offer hope for overcoming these issues, implementation costs and technological development requirements remain high.

Geothermal power plants provide a sustainable and clean energy source by harnessing the Earth’s internal heat. Countries with high geothermal potential such as Türkiye are utilizing this resource for both electricity generation and direct heating, and efforts continue to expand its adoption.