How Does Geothermal Energy Work?

How Does Geothermal Energy Work

Geothermal energy is energy which is generated and stored in the Earth. If you suddenly decided to dig a big hole in the middle of the U.S. and keep going, you wouldn’t find China. Instead, you would feel that as you delved deeper and deeper, the temperature would start to rise. This rise in temperature is because far down inside the Earth is heat, and lots of it. This heat is known as geothermal energy and it is a sustainable energy source which can be captured and powers entire countries such as Iceland.

Geothermal energy is a natural resource which is renewable and does not cause any pollution. Although drilling wells is required, this is not nearly as environmentally harmful as traditional fossil fuels or nuclear energy.

Geothermal Power Plants & Heat Pumps

We have two primary means of capturing this geothermal energy: through geothermal power plants; and through geothermal heat pumps.

Geothermal power plants use this heat from deep inside our Earth to generate steam which creates electricity through powering turbines. A geothermal power plant digs wells miles down into the earth and pumps steam to the surface. Geothermal power plants are more common in areas where there is lots of natural volcanic activity (i.e. Iceland) because in these parts of the world, there is a lot of heat just below the surface and wells don’t need to be dug very far.

Geothermal heat pumps, on the other hand, transfer heat by pumping water through a system of pipes below the surface of the Earth where there is a constant temperature of around 60°F. Whilst these heat pumps do not generate electricity, they are a sustainable way to heat up water which can be used in our home’s central heating systems or to warm up swimming pools.

How Geothermal Power Plants Work

At the moment, there are geothermal power plants in almost 100 countries, including the United States and developing countries such as Indonesia and Kenya. You may be surprised that the U.S. has geothermal power plants. After all, it is not a particularly volcanic country!

The U.S. was the first country to build a geothermal power plant, up in the Mayacamas Mountains just north of San Francisco. The Mayacamas Mountains is actually the world’s most geothermally active location and there are now over 20 geothermal power plants which call the Mayacamas home.

There are three different types of geothermal power plant:

  1. Dry Steam Plants - These are the most common types of power plant which use hot steam from underground. Dry steam plants make up around half of the world’s geothermal plants and they pipe this hot steam directly into turbines which powers a generator to create electricity. After the turbine has been powered, the stream turns into water and is sent straight back into the Earth through an injection well.
  2. Binary Cycle - In a binary cycle plant, hot water is pumped directly from underground through a heat exchange which heats a secondary liquid to turn it into steam. The primary difference between dry steam and binary cycle plants is that the steam from underground never comes into contact with the turbines and, instead, pumps water from geothermal reservoirs through the heat exchange.
  3. Flash Steam - Much like the binary cycle plant, flash steam plants pump hot water directly from underground up to the surface into what is known as a “flash tank”. When water reaches this flash tank, which has a low ambient temperature, the water very quickly turns into steam due to the temperature gradient which is then used to power turbines.

Although these three types of geothermal power plant work very differently, they all do the same thing: use heat generated from below the earth to power a turbine and create electricity.

How Geothermal Heat Pumps Work

All year round, the temperatures below the surface of the Earth do not fluctuate and are at a constant ~60°F year-round. There are two types of geothermal heat pump:

  • Closed Loop Systems - With a closed loop system, a mixture of antifreeze and water travels around a loop of pipes which lay underground. During the winter, temperatures below ground remain warmer than the surface and so the water heats up as it is pumped through the system of pipes. When the heated water travels back up above ground, heat exchangers transfer the heat into the building and used in central heating systems.
  • Open Loop Systems - With an open loop system, water comes directly from a water source and travels into a heat pump where it is either recycled back into the original source or a different one. It is known as an open loop system because it does not use the same mixture of water and antifreeze, instead using fresh water each time. An open loop system requires a plentiful water source which is capable of being pumped from and provide power or heat to your home.
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