Geothermal Energy is Gaining Steam

If someone were to ask you to list renewable energy sources, I'm sure geothermal energy isn't the first thing you think of. Most people don't know the details of geothermal energy, but its use has been steadily increasing throughout the years. 

Geothermal energy is thermal energy generated and stored in the Earth. This thermal energy originates from the formation of the Earth and the radioactive decay of uranium and potassium in Earth's core. The difference in temperature between the core of the Earth and the surface is known as the geothermal gradient, which is what provides energy in a form of heat from the core to the surface (How Stuff Works).

Courtesy of  How Stuff Works

The core of the Earth is about 4,000 miles beneath the surface and can reach temperatures of up to 7,600 degrees Fahrenheit. At this temperature, rocks melt and the resultant molten rocks are known as magma. Magma's density is less dense than the rocks surrounding it which causes it to rise to the surface. Sometimes, the magma that rises to the surface escapes through cracks, erupting out of volcanoes. But, volcanic eruptions don't happen constantly, since most of the time, the magma stays beneath Earth's surface. This magma heats any surrounding rocks and the water trapped within these rocks. Some of the water escapes through cracks in the surface and forms pools of hot water, or bursts of hot water and steam known as springs and geysers respectively. The rest of the heated water stays in pools under Earth's surface, known as geothermal reservoirs (Union of Concerned Scientists).

Geothermal energy is mainly used in three ways: direct geothermal energy, geothermal heat pumps, and geothermal power plants. Direct geothermal energy is used in areas where hot springs or geothermal reservoirs are located so the hot water can be piped directly in to heat homes or office buildings. The geothermal water is pumped through a heat exchanger, which transfers heat from the water into the building's heating system. This water is then pumped back down into a well and cycled back through to be reheated and used again (The Conversation). 

A geothermal heat pump is located a few feet under the ground, where the soil or water remains a constant 50-60 degrees Fahrenheit year round. This seemingly small amount of heat is used to heat or cool homes and offices as fluid circulates through a series of pipes (called a loop) underground or beneath the water of a pond or lake and into a building. During the summertime, this process is reversed to cool the building. The pipes draw the heat away from the house and carry it to the ground where it is absorbed (Water Furnace). 

Courtesy of Water Furnace

Finally, the last way to use geothermal energy is through a geothermal power plant. Hot water and steam from deep underground is piped up through underground wells and used to generate electricity in the power plant. There are three types of geothermal power plants. Dry steam plants use the hot steam to spin turbines which generate electricity. Flash steam plants use water that's between 300 and 700 degrees Fahrenheit that is brought up from a well. Some of the water turns to steam which turns turbines, and when the steam cools it condenses back into water and is returned to the ground. Lastly, binary cycle plants use moderately hot geothermal water, and passes it through a heat exchanger. Here, heat is transferred into a liquid that boils at a lower temperature than water. When that fluid is heated it turns to steam which spins turbines. 

Courtesy of Union of Concerned Scientists

The first recorded use of geothermal energy occurred more than 10,000 years ago by American Paleo-Indians who utilized the water from hot springs for cooking, bathing, and cleaning. The first geothermal electric power plant which used steam to generate power was invented in 1904 by Italian scientist, Piero Ginori Conti. 

Courtesy of Unione Geotermica Italiana

Improving upon Piero Ginori Conti's design, the first geothermal plant in the USA was started in 1922. It had a low capacity of 250 kilowatts, producing little output and was eventually shutdown due to a technical glitch. Later on, in 1946, a fully functioning geothermal heat pump was installed in Portland, Oregon. In 1973 due to the oil crisis, many countries began looking for a renewable energy source that reduced heating and cooling costs. This increased the popularity of geothermal heat pumps. Today, geothermal power supplies less than 1% of the world's energy, but it is projected to supply 10-20% of the world's energy requirement by 2050 (Conserve Energy). 

Geothermal energy is such an appealing source of energy because it is such a stable and reliable source of energy. The power output of a geothermal power plant can be predicted with extreme accuracy, which means it's good for meeting the base load energy demand, as opposed to less stable sources of energy such as wind and solar. Second, harnessing geothermal energy doesn't involve any fuels, which leads to stable electricity prices and prevention of cost fluctuations. Finally, geothermal energy doesn't take up a lot of land since it can be build partially underground. 

With it's advantages also comes disadvantages. The main problem being certain environmental issues that are associated with geothermal energy. Greenhouse gases below the surface of the earth tend to accumulate near geothermal power plants. Also, geothermal power plants are associated with sulfur dioxide and silica emissions and reservoirs can contain traces of heavy metals including mercury, arsenic and boron (Triple Pundit). 

Geothermal energy in general is regarded as environmentally friendly, sustainable, and reliable, which makes it a no-brainer in some areas, but heavy upfront costs prevent us from realizing the full potential. How much influence geothermal power will have really depends on technological advancements, energy prices, and politics. We'll just have to see what the situation will look like in the next couple decades.