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Describe the use of geothermal energy in power generation and its effects on the environment.

Geothermal Energy

Humans have used geothermal energy for thousands of years for bathing, cooking, eating, and warmth. More recently, we have learned to tap into geothermal energy to heat and cool buildings and homes and to generate electricity.

The heat in the interior of the earth emanates from the decay of radioactive particles. Scientists estimate that the inner core of the earth is nearly as hot as the surface of the sun at 10,800 degrees Fahrenheit!

A diagram of Earth’s layers, highlighting both compositional and mechanical properties. The left side details the compositional layers: crust, mantle, and core. The right side outlines the mechanical layers: lithosphere, asthenosphere, mesosphere, outer core, and inner core. — **Geothermal energy takes advantage of the heat produced in the interior of the Earth.**

This heat finds its way towards the outer edges of the lithosphere in the form of molten magma, volcanic action, and hot springs. Geothermal energy is considered a renewable energy source because heat is constantly being produced in the interior of the earth.

a map of Iceland highlighting geothermal activity and volcanic zones. Red dots indicate hydrothermal systems hotter than 150°C, located near Reykjavik, Hengil, Geysir, and Krafla. — **Iceland is ideal for geothermal** **energy,** **and they have taken advantage of this, increasing their geothermal energy capacity by 340% between 2000 and 2022!**

Geothermal energy uses naturally heated water or steam to heat buildings or drive turbogenerators. Iceland pioneered the use of geothermal energy along with other renewable energies, helping it go from one of the poorest energy-dependent countries to a country with a high standard of living.

Geothermal energy production is growing at a rate of 20% per year.

As of 2014, around 85% of Iceland’s energy was derived from renewable energy with about 66% of that coming from geothermal energy. Nearly 30% of Iceland’s electricity comes from geothermal power plants.

When done correctly and under the right conditions, geothermal energy reliably provides a constant source of energy.

Explore the map below to learn more about geothermal energy production. As you can see, the United States is a world leader in geothermal energy production. Most of our geothermal resources in the United States are located in the western states.

Geothermal Heat Pumps

Geothermal heat pumps are used to both heat and cool homes and buildings. Residential geothermal heat pumps involve loops of buried pipes filled with antifreeze circulated by a pump connected to an air handler. The blower moves air from the house through the heat pump and distributes it throughout the house via ductwork. This type of energy production saves money in the long run and is considered “trouble free.”

The diagram below shows a home, but a similar, larger setup can be used to heat and cool much larger buildings. The left frame depicts geothermal energy in action during cold weather and the right frame, hot weather.

the thermal dynamics of a geothermal house during winter and summer. — **Geothermal energy can cool a house in the summer and heat a home in the winter!**

During cold weather, water or another liquid is sent down into the earth to absorb heat (#1 and #2 in the diagram). When the heated liquid returns to the heat pump, the heat pump distributes the heat energy throughout the house (#3). After the heat is removed, the cooled liquid is sent back into the ground to absorb more heat (#4) to continue the process.

During hot weather, the system runs in reverse (right frame in the diagram). The heat pump removes heat from the home and adds it to the liquid. The hot liquid is sent into the earth (which is cooler than the liquid) and the earth absorbs the heat from the liquid. The cooled liquid returns to the heat pump ready to absorb more heat out of the home and return it back to the earth in a continuous cycle.

Geothermal Power Plants

On a larger scale and in the right locations, geothermal energy can provide enough energy to create significant amounts of electricity.

There are three types of geothermal power plants.

Dry steam plants use steam piped directly from a geothermal reservoir to turn generators.
Flash steam plants take high-pressure hot water from deep inside the Earth and convert it to steam to drive generator turbines. When the steam cools, it condenses and is injected back into the ground so it can be used again.
Binary cycle power plants transfer heat from geothermal hot water to another liquid. The heat causes the second liquid to turn to steam, which is used to drive a generator.

In places where the heat from the earth creates hot springs, geysers, or volcanic activity, the heat from the earth’s interior is much closer to the earth’s surface. At these locations, wells can be drilled up to two miles deep to tap into steam or high temperature water that is pressurized (#1 in the diagram):

a diagram of the Enhanced Geothermal System (EGS), illustrating the process of producing hot water from a well in hot granite, pumping it to the surface, converting it into energy, exchanging heat, and re-injecting cool water back into the ground. — **Geothermal power plants can take advantage of Earth's heat, but they still require deep wells and expensive infrastructure to work.**

The steam or pressurized hot water is drawn into a chamber (#2) and the pressurized hot water is depressurized, causing it to turn into steam. The steam is used to turn the blades of a turbine which engages a generator (#3). The generator produces electricity which is sent out over powerlines to the electrical grid. The steam is cooled back into a liquid at the cooling tower (#4) then pumped back into the earth to heat up again (#5).

Essential Knowledge

Geothermal energy is obtained by using the heat stored in the Earth's interior to heat up water, which is brought back to the surface as steam. The steam is used to drive an electric generator.

Environmental Effects of Geothermal Power

There are some limitations associated with geothermal energy, despite it having very little environmental impact.

Let's explore a few of these advantages and disadvantages. After reading through the pros and cons, what do you think? Are the disadvantages of geothermal power worth the benefits?

✅ Low Environmental Impact (click to reveal)

Geothermal heat pumps and other direct uses of geothermal energy have almost no impact on the environment. In fact, using geothermal energy instead of fossil fuel energy results actually lessens air pollution.

✅ Reliable Source of Power (click to reveal)

Geothermal energy can provide power 24 hours/day, 365 days/year, regardless of the weather conditions, making it a reliable source of power that can meet baseload energy demand.

✅ Renewable Energy Source (click to reveal)

Geothermal energy is a clean, renewable energy source that can help reduce reliance on fossil fuels.

✅ Cheap to Maintain (click to reveal)

Long-lasting infrastructure that can operate for many years with minimal maintenance.

❌ Only Possible in Areas with Lots of Heat (click to reveal)

Geothermal energy is not readily available everywhere. In the United States, the western half of the country has the lion’s share of geothermal possibilities.

Geothermal power plants can only work if they are sited in areas where there is a high level of heat near the earth’s surface. The Pacific Ocean’s “Ring of Fire” is a circular area surrounding the Pacific Ocean at which there is a lot of volcanic activity. Areas near the Ring of Fire are prime locations for geothermal power plants.

the ‘Ring of Fire,’ a horseshoe-shaped zone of high seismic and volcanic activity around the Pacific Ocean. — **Areas near the ring of fire are ideal for geothermal energy production.**

Other areas conducive to good geothermal energy use included countries such as Iceland, which is located directly atop the geothermally-active “mid-ocean ridge” which occurs at the divergent boundary between two tectonic plates.

❌ Can Release SO₂ (click to reveal)

Geothermal power plants can release small quantities of sulfur dioxide (a component of acid rain) and carbon dioxide (a greenhouse gas) but those gases that are released are over 95% less than the gases released by a fossil fuel power plant.

❌ Expensive to Construct (click to reveal)

Geothermal systems can be expensive to build so their up-front cost can be a deterrent to its use. The systems can pay for themselves, however, so the “payback period” should be considered when thinking about installing one.

❌ Can Generate Waste (click to reveal)

It can generate waste, such as brine, steam, and gases, that need to be disposed of or treated.

❌ Can Cause Earthquakes (click to reveal)

Unfortunately, large scale geothermal electricity generation may cause surface instability and earthquakes, especially in areas with high seismic activity or near fault lines.

All in all, geothermal energy holds a lot of promise (in the right locations) as a reliable energy source for the future.

Essential Knowledge

The cost of accessing geothermal energy can be prohibitively expensive, as is not easily accessible in many parts of the world. In addition, it can cause the release of hydrogen sulfide.

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