1. Dry steam geothermal power plants utilize steam produced from underground natural reservoirs to drive turbines and generate electricity.
2. Binary cycle geothermal power plants use low to medium temperature geothermal fluids to heat a working fluid which in turn drives turbines and produces energy.
Types of Geothermal Power Plants
Geothermal power plants harness the natural heat stored within the Earth's crust to generate electricity. By tapping into this sustainable and renewable energy source, these power plants contribute towards reducing greenhouse gas emissions and diversifying the energy mix. There are three main types of geothermal power plants: dry steam, flash steam, and binary cycle.
1. Dry Steam Power Plants
Dry steam power plants are the oldest and most conventional type of geothermal power plants. These plants utilize naturally occurring steam directly from the geothermal reservoir to power turbines and generate electricity. In a dry steam power plant, high-pressure dry steam is extracted from underground and directed towards a turbine. As the steam passes through the turbine, it causes the blades to rotate, thus generating electricity. After going through the turbine, the steam is condensed and reinjected back into the geothermal reservoir, maintaining a closed-loop system.
Dry steam power plants require geothermal reservoirs with high-temperature steam, typically above 150°C (302°F). These reservoirs are relatively rare and can be found in tectonically active regions, such as geothermal fields near volcanic or geologically active areas. One of the oldest and largest dry steam power plants is located in Tuscany, Italy, known as Larderello. It has been operational since 1913 and currently produces around 800 MW of electricity.
2. Flash Steam Power Plants
Flash steam power plants are the most common type of geothermal power plants, accounting for over 50% of the installed geothermal capacity worldwide. These power plants utilize water from the geothermal reservoir that is at a high temperature but remains in a liquid state due to the high-pressure conditions underground. As this hot water (known as geothermal brine) is extracted from the reservoir and brought to the surface, a portion of it flashes into steam due to the drop in pressure.
The steam obtained through the flashing process is then directed towards a turbine, which drives the generator to produce electricity. After passing through the turbine, the spent steam is condensed and reinjected back into the reservoir. In flash steam power plants, the non-flashed, liquid portion of the geothermal brine is also reinjected, minimizing the environmental impact of the operation.
One of the largest flash steam power plants is located in the Geysers Geothermal Field in California, United States. This field has a capacity of approximately 1,500 MW and has been in operation since the 1960s, making it one of the oldest geothermal fields still producing electricity.
3. Binary Cycle Power Plants
Binary cycle power plants are a relatively recent development in geothermal power generation and have gained popularity due to their vast application potential. Instead of using the direct steam or hot water from the geothermal reservoir, binary cycle power plants utilize a secondary fluid with a lower boiling point to generate electricity. The primary fluid, typically hot geothermal water, is pumped from the geothermal reservoir to a heat exchanger, where it transfers heat to the secondary fluid.
As the secondary fluid, which has a lower boiling point, vaporizes, the resulting high-pressure vapor is directed towards a turbine, generating electricity. After passing through the turbine, the vapor is condensed back into a liquid state using cooling towers or air coolers. The condensed fluid is then pumped back into the heat exchanger, where the process starts again.
Binary cycle power plants are highly flexible and can operate with lower temperature geothermal reservoirs, typically ranging from 90°C to 150°C (194°F to 302°F). This widens their potential application in areas with geothermal resources but with lower temperatures, making it a more accessible option for geothermal power generation.
Conclusion
Geothermal power plants provide a sustainable and renewable source of clean energy by leveraging the Earth's natural heat. Dry steam power plants, flash steam power plants, and binary cycle power plants are the three main types that harness this heat for electricity generation. Each type has its own specific requirements, including geothermal reservoir temperature, making them suitable for different geological conditions. As governments and organizations focus on reducing carbon emissions and transitioning to renewable sources, geothermal power plants continue to play a crucial role in the global energy landscape.