Does Geothermal Energy Use Electricity?
What is geothermal energy?
Geothermal energy is thermal energy generated and stored in the Earth (U.S. Energy Information Administration, 2023). It comes from the Greek words geo, meaning earth, and thermal, meaning heat. Geothermal energy is a renewable energy source because heat is continuously produced inside the Earth (TWI, 2023).
There are three main types of geothermal energy systems (Energy.gov, 2023):
- Hydrothermal systems use hot water or steam reservoirs found deep beneath the Earth’s surface to generate electricity. The heated water can also be used directly for heating homes and buildings.
- Enhanced geothermal systems inject water into hot dry rock reservoirs to create a geothermal reservoir and enable energy extraction.
- Direct-use and geothermal heat pump systems use stable ground or water temperatures near the Earth’s surface for direct heating and cooling.
How geothermal energy works
Geothermal energy harnesses heat from inside the Earth to generate electricity and provide heating and cooling. The heat originates from the original formation of the planet, radioactive decay of minerals, and volcanic activity. To utilize this heat, wells are drilled into underground reservoirs to pump hot underground water or steam to the surface. The steam can then drive turbines to generate electricity. For heating and cooling applications, geothermal energy systems pump water or antifreeze through pipes buried underground to transfer heat between the earth and buildings.
Geothermal power plants use wells and pumps to bring hot water and steam from deep underground reservoirs to the surface. The steam then turns turbines that power electric generators. For electricity generation, a well is drilled into a hot water or steam reservoir about 1-2 miles deep. Pipes bring the hot water or steam up through the well to the power plant at the surface. In a dry steam reservoir, steam is piped directly to a power plant to drive a turbine. For a geothermal reservoir containing hot water, the water is brought to the surface and flashed into steam which then drives the turbine. After passing through the turbine, the steam is condensed back into water in a condenser and recycled back into the reservoir to be used again.
For heating and cooling, a geothermal heat pump system consists of pipes buried underground, a heat pump unit, and an air delivery system. The pipes called a loop are installed underground, either vertically or horizontally. A fluid circulating through the loop pipes absorbs heat from the earth and carries it into the building. In summer, the process is reversed and indoor heat is extracted and transferred outside. The geothermal heat pump unit, which looks like a traditional air conditioner or furnace, uses a refrigerant to transfer heat between the building’s air and the loop fluid. An air delivery system consisting of traditional ductwork distributes the heat inside.
Geothermal Power Plants
There are three main types of geothermal power plants: flash steam, dry steam, and binary cycle plants. They each use geothermal reservoirs of hot water or steam located deep underground to generate electricity.
In flash steam plants, high-pressure hot water travels up production wells to the power plant, where the pressure is reduced, causing some of the hot water to flash into steam. The steam is then used to turn turbine generators to produce electricity (1).
In dry steam plants, geothermal steam is piped directly from underground wells to power plant turbines without being converted into water. The steam goes through a rock catcher to remove small rocks before moving into the power plant to spin the turbine generators (2).
Binary cycle power plants differ because the water or steam from the geothermal reservoir never comes in contact with the turbines. The geothermal water is passed through a heat exchanger, which heats a separate organic fluid with a low boiling point. This causes the organic fluid to turn into vapor, which then spins the turbines (1).
The spinning turbines in all three types of plants drive generators that produce electricity. After passing through the turbines, the geothermal fluid is injected back into the reservoir to be reheated and reused (2). This makes geothermal power a sustainable and renewable energy source.
(1) https://www.energy.gov/eere/geothermal/electricity-generation
Uses of geothermal energy
Geothermal energy has several uses for both industrial and residential applications. The three main uses are:
Electricity generation
Geothermal energy can be used to generate electricity. Geothermal power plants use steam from reservoirs of hot water found deep underground to turn turbines and generate electricity. According to the U.S. Department of Energy, geothermal power plants produced about 17 billion kilowatt-hours of electricity in 2020, which was 0.4% of total U.S. electricity generation [1].
Heating and cooling
Geothermal energy can be used to heat and cool buildings. Geothermal heat pumps use shallow ground or water temperatures to control building temperatures. According to the U.S. Energy Information Administration, geothermal heating is used in about 50,000 U.S. homes and buildings [2].
Other applications
Other uses of geothermal energy include food dehydration, gold mining, milk pasteurization, greenhouse heating, and hot spring bathing. Geothermal energy can also be used for melting snow on roads and sidewalks.
Geothermal electricity generation
Geothermal power plants convert thermal energy from underground reservoirs into electricity that can be fed into the power grid. The thermal energy comes from naturally occurring pockets of steam or hot water thousands of feet below the earth’s surface.
At a geothermal power plant, wells are drilled into the geothermal reservoir to bring the hot water or steam to the surface. The steam then drives a turbine connected to a generator to produce electricity. The steam condenses into water and is injected back into the reservoir to be reheated and reused.
According to the U.S. Department of Energy, there are three types of geothermal power plants:
- Flash steam plants use water with temperatures over 360°F that is naturally in the form of steam when brought to the surface. This high-pressure steam is directed into a turbine.
- Dry steam plants use steam from underground reservoirs and route it directly into turbines without having to flash the fluid to steam.
- Binary cycle power plants transfer the heat from geothermal hot water to another liquid. The heated liquid vaporizes and drives the turbines.
The electricity generated can be transmitted via power lines to utilities and consumers. In the U.S., geothermal power plants are located in states like California, Nevada, Utah, Hawaii, and Alaska where geothermal resources are prevalent.
Geothermal systems for heating/cooling
Geothermal energy can be used to heat and cool spaces directly through geothermal heat pumps and the direct use of geothermal reservoirs. Geothermal heat pumps take advantage of the constant temperatures underground to regulate indoor temperatures. They can be used for space heating and cooling as well as water heating.
Geothermal heat pumps use a system of pipes called a loop that is buried underground, either vertically or horizontally. The pipes contain a water or antifreeze solution that absorbs heat from the earth in winter and rejects heat into the earth in summer. This provides both heating and cooling capabilities.
According to the U.S. Department of Energy, geothermal heat pumps can reduce energy consumption up to 60% compared to conventional heating and cooling systems (source). This makes them an energy efficient and environmentally friendly heating and cooling solution.
Direct use of geothermal reservoirs involves tapping into naturally heated water reservoirs below the Earth’s surface. The hot water can be used to provide space heating or to heat water. This eliminates the need for boilers or furnaces.
Does geothermal use electricity?
Geothermal energy can produce electricity, but the systems also require some electrical input to operate. At geothermal power plants, naturally heated fluids from underground are brought to the surface to turn turbines and generate electricity. This makes geothermal a renewable baseload energy source that provides consistent power around the clock. However, the plant’s pumps and other equipment need electricity to run, representing about 10-30% of the gross power generation, according to the Department of Energy (DOE).
For geothermal heating and cooling systems, like ground source heat pumps, electricity is needed to power the pumps and compressors. But this electrical input is much lower compared to the equivalent heating and cooling energy provided. According to one analysis, the added electrical cost for geothermal heat pumps may be around $500-600 per year, versus potentially thousands saved on fossils fuels for heating and cooling (Reddit). The geothermal system uses 25-50% less electricity overall than conventional HVAC systems.
So while geothermal does require some electrical input, the net electricity produced and energy savings generally make it a very efficient renewable energy source.
Efficiency of geothermal
Geothermal power plants have very high capacity factors compared to other renewable energy sources. The capacity factor for geothermal plants is typically over 90%, whereas wind turbines have capacity factors around 35% and solar PV around 25% [1]. This means geothermal plants can generate electricity consistently around the clock, unlike wind and solar which depend on weather conditions.
Geothermal energy is also highly efficient at converting the earth’s heat into electricity. Geothermal power plants essentially tap into pockets of hot water or steam underground. This geothermal fluid is brought to the surface and its heat is converted into electricity using a steam turbine or binary power plant system. Only about 10-20% of the thermal energy from the geothermal fluid is converted into electricity, but the remaining heat can be used for other applications like district heating systems [2].
Overall, geothermal power can operate with 90% less downtime than wind or solar systems. The consistent generation from geothermal allows it to serve as a reliable baseload power source.
Pros and Cons of Geothermal Energy
Geothermal energy has several advantages as well as some disadvantages compared to other energy sources:
Some of the key pros of geothermal energy include:
- It is a renewable and sustainable energy source, as thermal energy within the Earth is constantly replenished.
- Geothermal power plants have low emissions and a small land footprint compared to fossil fuel plants.
- Geothermal energy can provide reliable baseload power, with capacity factors over 90%.
However, there are also some cons to be aware of:
Sources:
https://www.energysage.com/about-clean-energy/geothermal/pros-cons-geothermal-energy/
https://www.solarreviews.com/blog/geothermal-energy-pros-and-cons
Conclusion
In summary, geothermal energy does not inherently require electricity to generate power or provide heating/cooling. The natural heat within the earth’s crust is directly harnessed through geothermal power plants and geothermal heat pump systems. While the equipment used does utilize some electrical components, the geothermal energy itself does not need electricity to be produced.
Geothermal energy has an important role to play as a renewable and sustainable energy source. Geothermal power plants provide constant baseline power, unaffected by weather fluctuations like solar and wind power. Geothermal heating/cooling systems provide an energy efficient method to heat and cool buildings. Overall, geothermal energy offers a reliable way to meet energy needs while reducing dependence on fossil fuels.
