Deep inside the Earth there is a constant decay of radioactive materials, like uranium. This decaying process gives off an incredible amount of heat. Layers of rock absorb this heat and melt, creating hot magma. When this magma rises, it is under a lot of pressure, and can shoot out through volcanoes on the Earth’s crust.

Meanwhile, water is constantly draining deeper into the Earth through cracks in rock layers. The water will eventually heat up to temperatures of nearly 700 degrees Fahrenheit. This hot water and steam is exactly what geothermal power plants use to create energy.

Geothermal energy can be used in:

·         Electricity generation

·         Heat pumps

·         Direct use

Electricity generation

Geologists must first find an area with a geothermal reservoir underground. These reservoirs are typically found along fault lines and are filled with very hot water or steam that is under pressure. There are three different ways that geothermal energy can be produced into electricity:

·         Flash Power Plants

·         Dry Steam Power Plants

·         Binary Power Plants

Flash power plants

These power plants drill a deep production well, one to two miles deep in the Earth’s crust, until they hit a geothermal reservoir. The power plant will pump hot water out of the geothermal reservoir through the production well and into a flash tank where the water will convert to steam. The steam is then forced through a turbine which then turns a generator, producing electricity. The used steam, or excess water, is then returned to the geothermal reservoir through the injection well that is drilled near the production well.

 

Dry steam power plants

Dry steam plants are just like flash power plants, but instead of driving hot water up through the production well, hot steam is pumped up. This steam is extremely hot and under a lot of pressure. As soon as it reaches the turbine, it pushes past the blades, creating a spin of the turbine which runs a generator, creating electricity. Once the steam is rushed past the turbine, it will return to the reservoir in the form of steam or condensed water through the injection well.

Binary power plants

This type of geothermal power plant pumps hot water up through the production well, just like the other plants, but instead of entering a flash tank or turbine, the hot water enters a heat exchanger. The heat exchanger is filled with fluid that will typically have a lower boiling point than water. Once the heat exchanger’s fluid is heated it will travel up, as a gaseous vapor, and be forced through the turbine just like other geothermal power plant systems. The heat exchanger fluid is recycled back into the heat exchanger and the geothermal water is returned back to the geothermal reservoir through the injection well.

Binary power plants increase the efficiency of geothermal energy because the heat exchanger fluid will boil and turn into vapor at lower temperatures than water. The result is a lower emission rate.

Geothermal heat pumps

Geothermal heat pumps, or ground source heat pumps, are the easiest way to benefit from geothermal energy. These pumps can be used in any type of building, including residential houses. Geothermal heating pumps can also be used under sidewalks or roads to keep them thawed in winter, or under swimming pools in summer. These pumps can be used almost anywhere in the world, and are not restricted to being near a deep geothermal reservoir.

A geothermal heat pump consists of tubing that is buried roughly 10 feet underground and filled with a fluid, like antifreeze. The fluid is pumped through the tubing circuitry underground and back up into the building. Once inside the building it enters a heat exchange where air is pumped past the tubing and either heated or cooled depending on the time of year.

Since the ground remains a constant temperature year round, the heating fluid will come into the heat exchange at that temperature.

The EPA has said that geothermal heat pumps are the most energy efficient, environmentally clean, renewable and cost-effective space conditioner systems that are available.

Direct use

Geothermal energy can be used to directly heat buildings. A geographical area with large buildings can use geothermal energy for heat instead of burning fossil fuels, or consuming electricity. This type of group heating system is referred to as district heating. Reykjavik, Iceland uses district heating in 95% of their buildings because they are so close to geothermal energy sources.

Once a production well has been drilled into an identified geothermal reservoir, or hot spring near the surface, the geothermal water or steam is pumped up and circulated through each building, or pumped into a heat exchange unit, where a heating fluid is warmed, and then circulated. The geothermal water or steam is then recycled back to the geothermal reservoir or hot spring through the injection well. The process is very similar to geothermal power plants, but the geothermal water or steam makes a circuit without passing any turbines.

Future of geothermal energy

Geothermal energy is a very efficient source of energy. Although start up costs are usually high, geothermal energy pays for itself quickly. Geothermal heat pumps in residential buildings pay for themselves within 2 to 10 years according to the US Department of Energy. Government programs can help with start up costs for geothermal energy projects as well.

New geothermal power plant facilities can produce electricity for between 4.5 and 7.3 cents per kilowatt-hour, according to the California Energy Commission. Oil can produce electricity for 5.3 cents per kilowatt-hour, according to Stanford.

Earth has 42 million megawatts of geothermal power inside it, an inexhaustible supply of energy, estimated by the Geothermal Energy Association. In the US alone, the US Geological Survey estimates that geothermal energy potential is between 95,000 and 150,000 megawatts. Of that, 22,000 are suitable for electricity generation.

Geothermal energy can be used so efficiently that its future is extremely promising. Geothermal power plants and heating systems will become more popular over time with decreasing start up costs and increasing efficiency. Geothermal energy is energy of the future.

-Colvin