The more we learn about renewable resources, the more we are presented with sustainable and renewable options. One of these options has been residing underground, below the earth’s surface, for centuries.
How Does Geothermal Energy Work
The center of the earth contains a core so hot that it melts rocks, creating magma. As this magma moves through weaker layers and points far underground, they meet with or near themselves to underground water reserves. These water reserves, in turn, heat to a boiling point. Technology has allowed us to access this hot water and use it to heat and cool buildings and homes using geothermal power.
Geothermal plants are already in use in over 80 countries, according to the Geothermal Energy Association (GEA). The United States is currently the leader in geothermal power, with Turkey, Kenya, and Indonesia working toward their own expansion of these plants.
Geothermal energy isn’t an advanced concept. In fact, it has been witnessed for thousands of years and can still be witnessed without the use of technology today in natural occurrences such as hot springs, volcanoes, and geysers.
Geothermal literally translates to “heat from the earth,” with “geo” meaning “from the earth” and “thermal” meaning “heat.” Thus, this term indicates energy or heat that is harvested or occurs in the earth. The lava from volcanoes and steam from geysers results from an intense heat underground that pushes melted rocks, steam, and/or hot water to the surface. This energy is obtainable, and thus, we can put it to use for our own heating and cooling needs.
In the 1960s, the first geothermal plant was built in the Mayacamas Mountains just north of San Francisco, California, by Pacific Gas and Electric. This plant, called The Geysers, is located on the world’s largest geothermal field and now has 22 geothermal power plants, which make up the Geysers Complex. Not only is it the home of the largest geothermal field, but this also makes it the largest geothermal plant in the world.
Main Benefit of Geothermal Energy?
The main benefit and draw from using geothermal energy instead of traditional forms of energy are that it doesn’t require or use any fossil fuels. The system purely uses the naturally occurring steam from the underground reservoirs. Once the water has been used, it is returned, untainted, to the reservoir to be naturally reheated and used again. This process creates a renewable and clean energy source.
While the seasons can affect the surface temperature of the ground, once the depths get to four feet, the ground temperature stays the same, regardless of the time of year (approximately 55°F). A geothermal heating system consists of piping that goes further underground, pumping a liquid through the pipes, which is heated by the naturally occurring underground heat and returns this liquid to the surface and to a home or building to be heated. This is one of the reasons (among many) why it is important to ensure that you call 811 before beginning any excavation projects that might interrupt underground piping.
Once the liquid has been returned to the designated building, a device called a “heat exchanger” transfers the heat to heat the air inside.
Geothermal systems don’t only heat a home or building but can also act as a cooler as well. It applies the same concept but instead reverses the process: the liquid absorbs the heat from inside the home and moves it back into the earth. Rather than blowing cold air in, it simply removes the head.
This type of system is quite energy-efficient. There is little, if any, the energy that is wasted, and thus can make for a cost-effective energy bill during the winter months.
Geothermal Power Plants
There are three ways that geothermal heat is being used in plants to create power in different ways: dry steam plants, flash steam plants, and binary cycle plants.
Dry Steam Plants
These are the most common geothermal power plants. Dry steam plants account for half of the functioning geothermal plants and work by drawing steam from the underground reservoirs via piping and directing it straight to turbines. This then powers generators to create electricity. Once the steam has powered these turbines, it returns to a water state and is returned to the reservoir through an injection well, where it can be heated to a gas state again and reused.
Flash Steam Plants
The difference between dry steam and flash steam plants is that while dry steam plants use steam to power the turbines, flash steam uses hot water from the reservoirs. The hot water is pumped straight to the surface using pressure naturally generated from the underground heat. The water goes into what is called a “flash tank” above ground.
The flash tank is at a lower pressure and quickly turns the hot water into steam, which is then used to power the turbines. When the steam returns to a water state, it moves through the injection well to the reservoir.
Binary Cycle Plants
Unlike dry and flash steam, the water never comes into contact with the turbines but is pumped into a heat exchanger. The heat exchanger then utilizes the hot water to heat to boil another liquid such as isobutene. Isobutene boils at a lower temperature than water.
Once this second liquid boils, it, like water, turns to steam which then powers the turbines. The hot water that heated the isobutene is returned to the underwater reservoir through the injection well. In contrast, the isobutene (or equivalent) is recycled through the heat exchanger for further use.
Geothermal Heat Pumps
Geothermal pumps mean that through cultivating underground temperatures, you can heat or cool your home or building. While surface temperatures fluctuate with the weather and seasons, the underground temperatures remain relatively consistent, perhaps only fluctuating between 50°F and 60°F.
There are four types of pumps that can be divided into two categories: closed-loop systems (of which there are three types) and open-loop systems (one type). Each type of system depends on the climate conditions, the available land, and the soil.
Closed-Loop Horizontal Systems
Close loop horizontal systems are best used for larger residential areas and larger commercial buildings as they’re the most cost-effective. To keep these costs down, these types of systems generally are constructed under ponds or lakes. These systems stretch underground as deep as 400 feet.
Closed-loop systems use a mixture of water and antifreeze to circulate through the piping, which either runs underground or under a body of water and then into a building. As you can see above, in the winter, the ground temperatures are warmer than surface temperatures and thus mean that the mixture in the pipes is warmer. As this liquid moves through to a building, an electric compressor and heat exchanger moves this heat from the pipes, through the ducts, and into the building.
In the summer, this process is reversed, as the pipes use the liquid to draw the heat away from the building, which is then put into the ground or into the water to cool. This takes the pressure off the heater in the winter and the AC in the summer.
Open Loop Systems
Open-loop systems take the water directly from a water source and to a heat pump. It is then circulated back into its source or moved to another water source without any pollutants. The water is only altered in temperature, meaning that nothing is added or detracted from the water during the circulation process. The water is warmer when it goes in than when it comes out. While these systems can often be cheaper, they have more requirements than a close loop system in that it needs to be ensured that there is steady water flow powerful enough to power your home.
These four types of geothermal pumps are accessible and can be utilized all over the country because of a fairly consistent underground temperature. However, the location might cause variation in how efficiently these systems work and how cost-effective they might be.
Technology, though, is moving this power form forward. A noteworthy advancement toward a geothermally energized future is developing the Enhanced Geothermal System (EGS). While up to yet, geothermal power has required a geothermal reservoir to be functional (which is mostly within the Western part of the U.S.. California has already taken advantage of this and uses geothermal power to provide 60% of the energy in Northern California.), this new system allows for the creation of synthetic water reserves. That is to say that the EGS can engineer geothermal reservoirs by pumping cold water deeper, thousands of feet deeper, to allow for access to hot water, which will then produce steam to power the geothermal power plants.
Related: Pros and Cons of Nuclear Energy
One of the best aspects of geothermal energy is that it is a renewable and natural resource, meaning that it won’t run out like wind or solar power. However, there is some additional maintenance that is required over time. Drilling new wells might be necessary to keep up consistent power production. However, this is little concern for the most part, as the earth always gives off heat from its core. Proof of this heat can be seen in natural wonders such as Old Faithful, the famous geyser in Yellow Stone National Park. It’s the same energy that shoots this water into the sky that is used for geothermal-powered electricity.
The Geothermal Resource
The closer you get to the earth’s core, the hotter it gets. This heat creates molten rock or magma. With the decay of naturally occurring radioactive materials such as potassium and uranium, heat is constantly produced. Delving down 10,000 meters (of 33,000 feet), there is enough energy in this outer layer of the earth’s crust to put the natural gas and oil industry to shame, containing more than 50,000 times more energy than all these industries in the world.
Where there are geologically youthful volcanoes, there is a higher underground temperature. These are the results of weak or thin places within the earth’s crusts, along tectonic plate boundaries, which allow for the heat and energy from underground to the surface. Often nicknamed the Ring of Fire, the Pacific Rim is lined with active volcanoes to indicate these hot spots. These weak points are found in Alaska, California, and Oregon, to name a few places on the eastern line of the Rim. Likewise, Nevada is rife with these hotspots in the northern part of the state.
Volcanoes go hand in hand with seismic activity. For example, San Francisco is known for regular earthquakes (though generally quite harmless). These earthquakes work with the magma to break up the upper/outer layer of the earth’s crust to release the building pressure and allowing the underground water to circulate. As this water rises to the surface, hot springs and geysers form, whose temperatures can get as hot as 200°C (430°F).
However, places with seismic activity are not the only places that geothermal energy can be located. Milder heat, which can be used for direct heating purposes, can be found anywhere on the planet. The depths at which this heat is found can be anywhere as shallow as ten feet to a few hundred feet underground. Furthermore, a great deal of heat energy can be mined from dry rock formations even deeper (from 4-10km) below the surface. Advancing technology allows access to this deep heat, such as the aforementioned Enhanced Geothermal Systems (EGS). Such technologies allow us to harness this energy on a greater scale than existing and applied technologies. Although still in the development stages, one of the first demonstrations of an EGS project in 2013 allowed for enough power to enable grids in the U.S. and Australia.
If geothermal resources can be widely applied, they would resolve many economic and ecological issues as such a vast and plentiful electronic production. In 2012, the United States National renewable energy laboratory (NREL) found in 13 states that a conventional application of geothermal sources, or hydrothermal sources, had the potential capacity of 38,000 MW. This translates to approximately 308 million MWh of electricity every year.
While spreading information and understanding this power source is beneficial; it is unlikely to come to full fruition without state and federal policies to push developers into this potential over the next few years. However, that isn’t to say that it isn’t happening. According to the Geothermal Energy Association (GEA), an estimated 125 projects are underway across the country, which could provide 2,500 MW of new capacity.
With the improvement of GEA technologies, there is competition in the marketplace, which can only enhance the existing technologies to make them more efficient and accessible. Thus, the more untapped geothermal potential is being strived for. The RNEL study found that the use of hot, dry rock resources could produce another four million megawatts of capacity, which would meet the U.S.’s current electrical need, and then some.
The geothermic resource potential in the United States is immense and is a consistent power potential. The NREL reports that the ratio of the actual electricity generated over time compared to what would be produced if a geothermal plant was running uninterrupted around the clock during a given period of time, or the capacity factors, are comparable to those of coal and nuclear power plants. Considering the combined resource base size and the consistency of the energy, geothermal energy can be an essential player in striving for cleaner and sustainable power.
Mini-FAQ
How does geothermal heat produce energy?
The steam brought up from an underground water reservoir is brought to the surface directly or indirectly to push a turbine into motion. This turbine then activates a generator which produces electricity. This isn’t new and is used though less ecologically or sustainably. Currently, fossil fuels are used in power plants to boil the water for steam. However, with geothermal power plants, the steam used is from the naturally occurring reservoirs with naturally heated hot water from local molten deep below the surface.
What are the 3 main uses for geothermal energy?
Three systems use geothermal energy:
- Direct use and energy heating systems
- Electricity generation power plants
- Geothermic heat pump
