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Geothermal Energy

Geothermal energy is an enigma to many people because it is hard to define something that you cannot easily point to and say ‘that is geothermal’. It is easy to point to a solar panel and say that is solar energy, and the same with a wind turbine. Hydro-electric power is widely recognized by dams.

Geothermal energy is most often recognized from geysers, but they are a small part of geothermal energy. The easiest way to define geothermal energy by breaking the word down in to its roots. In its simplest terms geo means ‘earth’ and thermal means ‘heat’. In other words geothermal energy is heat or energy derived from the earth.

The source of geothermal energy is predominantly the radioactive decay at the center of the earth that radiates outward toward the surface, especially with respect to geothermal electricity generation where super-heated fluid temperatures can reach several hundred degrees.

But even at the surface of the earth the temperature maintains a relatively constant 55 degrees Fahrenheit throughout much of the US. This constant temperature does not fluctuate like ambient air temperatures, so it is warmer in the winter and cooler in the summer. Animals have known this for eons. The steady ground temperature allows for efficient heating and cooling of buildings.

Geothermal energy has many uses and applications from ice melting to space heating, agricultural production and industrial processes, as well as electricity generation. To define geothermal energy as one specific use limits the scope of the resource and does not convey its full potential.

The Earth itself is probably the most appropriate symbol of geothermal energy because it is the source of the energy. One of the benefits of geothermal energy is the variety of applications it can be used for, and the flexibility of the resource. Solar, and wind in particular are primarily used to generate electricity but geothermal can be used in situations where electricity is not practical.

Benefits of Geothermal Energy

There are numerous benefits from the development and use of geothermal energy at both a national and individual level. Geothermal energy reduces our dependence on fossil fuels and consequently our carbon footprint. We become more self-sufficient by developing renewable energy resources and increase job growth.

Geothermal is a clean and renewable source of energy that lasts for decades if properly managed.  The Geysers electric power plant in California has been in operation for forty years. Geothermal energy also does not require transport as it can be used on site, or in the case of electricity, distributed through the grid.

A large percentage of the public believes it is necessary to have a geyser in your backyard to be able to use geothermal energy. This is a misconception because it would be difficult to build a home next to a geyser. A geyser would only be practical for generating electricity because it indicates a high quality resource that contains a substantial amount of heat.

Geothermal energy also has a much smaller footprint in terms of electricity generation. Coal power plants require destruction of the landscape to remove the coal, or deep mines that jeopardize water supplies and are subject to explosions. A ground loop for a geothermal heat pump is buried underground where it is not even visible.

Basically any process or product that requires heat can be accomplished or produced with geothermal energy. The flexibility of the resource makes it extremely valuable from a commercial or industrial application perspective. Many companies are developing co-generation applications where the resource is used to generate electricity and the waste heat is used for industrial processes. Geothermal energy is good for the environment and for local economies.

Geothermal electricity generation is so reliable it is considered a base load power source in the same way that coal, nuclear and natural gas fired power plants are base load. It is a consistent, dependable source of power that is much more environmentally friendly than the other resources.

Natural gas fracking is a highly controversial method of extracting natural gas from the earth. Advanced technologies such as Enhanced Geothermal Systems can provide electricity at a comparable rate to fossil fuel energy resources. They also have modular plant designs which allows for flexibility in development.

Enhanced Geothermal Systems (EGS) is a process of injecting cold water in to fracture networks deep below the surface. The water is super-heated in the fracture networks where temperatures are several hundred degrees. The water flashes to steam and is brought to the surface and passed through a turbine to generate electricity.

After the water is cooled it is re-injected back in to the ground to absorb more heat. EGS shows much potential for generating electricity in the Western half of the US where most high temperature resources are located.

Geothermal energy does not produce greenhouse gas emissions that contribute to climate change. Developing any form of energy resource will have an impact on the environment but the question is to what degree. In the case of geothermal energy that impact is much lower than conventional energy sources.

The International Geothermal Association estimates there are potentially 2700 TWh/yr of electricity in North America and more than 120 TJ/yr of heat energy. These are sizeable figures that represent tremendous potential.

Geothermal heat pumps are a direct use form of geothermal energy that is three to five times more efficient than conventional furnaces and twice as efficient as air source heat pumps. They do not use fossil fuels because they utilize the ground as a heat source and a heat sink.

They use electricity to circulate anti-freeze through a ground loop that extracts heat in the winter and rejects heat in the summer. Utilizing heat from the ground is more efficient and avoids the use of highly polluting fossil fuels.

History of Geothermal Energy

Geothermal energy is nearly as long and old as that of the earth itself. It is difficult to say what early people may have done with geothermal energy before recorded history, but it must quite a mystery to them. Recorded uses of geothermal energy included bathing and cooking. The presence of volcano’, hot springs, and geysers as well as other surface manifestations indicated to early humans the interior of the Earth was hot.

Since recorded history geothermal hot springs have been used for bathing and food preparation.  In modern times geothermal is used for a variety of uses including ice and snow melting, agricultural food processing, space heating and industrial processes, district heating, as well as electricity generation.

Geothermal energy has been in use longer in a rudimentary form than any other renewable energy resource. During the 16th and 17th centuries when started subsurface mining exploration they discovered that temperature increased with depth.

Native Americans began using geothermal waters for medicine and cooking as early as 10,000 years ago. The Greeks and Romans also used it for bathing purposes in ancient times. The healing qualities of geothermal energy have been known and understood for centuries. Today in the US there are 100’s of hot springs in commercial use throughout the Western US.

Historically development of geothermal resources in the US has been slow largely due to the fact that government funding has most often been limited and sporadic. Additionally, natural gas and propane prices have consistently impeded development of renewable energy.

The controversy surrounding fracking with respect to contamination of water supplies and environmental pollution should lead to renewed interest in geothermal energy. A primary benefit of geothermal energy is that it does not contribute to environmental degradation on the scale of fossil fuels.

Geothermal energy has been waiting in the wings to get acknowledged and recognized as a viable, economically efficient and environmentally sensitive energy resource. The complications associated with continued natural gas development will only bode well for geothermal energy, which does not contribute to greenhouse gas emissions or water and air pollution.

Geothermal energy is a long-term solution to our energy dilemma: how to produce the energy we need without destroying the environment we depend on to survive. The future is undoubtedly bright for geothermal energy.

Geothermal heat pumps were first conceived by Lord Kelvin around 1870, and were first installed in the US in the 1940’s. Since then there have been over 1,000,000 geothermal heating and cooling systems installed in the US. Every year another 50,000 units are installed. The Department of Energy has stated they are a mature technology and most units are rated by Energy Star. Finding an economical way to reduce equipment and installation costs is essential for them to gain broad based market acceptance.

Interesting Geothermal Facts

According to the Geothermal Resources Council, the average global temperature gradient is 20° C per kilometer of depth. For every kilometer of depth the ground temperature increases by 20° C.  In areas where high temperature resources are located the gradient closer to 100° C/Km.

That is the primary reason why geothermal energy is so consistent and reliable. The constant heat radiating out from the center provides a virtually infinite source of energy. The video below does an excellent job of illustrating how a geothermal electric power plant operates. It is an example of a hydrothermal plant, which uses hot water directly from the ground rather than an EGS plant, but the concept is still the same.

The first geothermal energy plant was constructed in Lardello Italy in 1904. Globally geothermal generates about 7000 Mw of electricity annually and the US produces the most electricity from geothermal energy by sheer volume at 2700 Mw. The Geysers in Northern California has been in operation since the 1960’s and is the largest geothermal power plant in the US.

Globally, it is estimated there are thousands more megawatts worth of geothermal resources that could be developed. Improvements in drilling technology will allow us to tap in to geothermal resources even in areas that do not have water reservoirs. This is where EGS technology will be instrumental.

The International Geothermal Association has estimated there is approximately 42 x 1012 W of thermal energy in the mantle of the Earth, mostly from radioactive decay of U238 and U235, Th232 and K40 isotopes. Average temperatures at the base of the mantle have been relatively constant at about 4000° C for the past 3 billion years. The constant temperature of the mantle and the inner core which radiate outward towards the surface provides a reliable source of energy for generating electricity as well as thermal applications.

In 2003 geothermal energy generated approximately 8,402.21 Mwe of electricity around the world. Direct use applications provided 190,699 TJ/yr of thermal energy globally in 2000.  The uses of geothermal energy make it the most diverse and flexible of all the renewable energy resources. It is used in agricultural applications to keep the soil warm in order to extend the growing season.

Fish farming, or aquaculture is the process where certain types of fish prefer warmer waters to grow. It can be used for dehydration and pasteurization, as well as deicing and snow melting. Virtually any process that requires heat can be accomplished using geothermal energy. Space heating and district energy are another form of geothermal energy application. Space heating using geothermal heat pumps is feasible anywhere, while geothermal district energy systems are predominantly found in the West.

Globally, the most intense geothermal activity is located along areas where tectonic plates come together, as this is where magma can rise closer to the surface. Typically it is necessary to drill several miles below the surface to reach a geothermal reservoir or a rock network. As the magma gets closer to the surface it reduces the amount of necessary drilling.

Drilling is the most expensive and risky aspect of geothermal development because there is no way to know with certainty what is located below the surface. The technology is advancing but it is still a somewhat speculative endeavor. This is why government funding is so critical for geothermal development.

The most famous area for geothermal activity is what is known as the ‘Pacific Ring of Fire’, located in the Pacific Ocean. It extends along the boundary of the Pacific tectonic plate along the coast of North and South America as well as along Asia. This is coincidentally where many of the geothermal power plants in the world are located. The countries that produce the most electricity from geothermal energy located along the Ring of Fire.

Geothermal electric power plants provide some of the most reliable electricity available in the world. It is considered a base load power because it generates electricity twenty-four hours a day, seven days a week. The only time is does not produce electricity is when the generators are down for maintenance. The plants can operate non-stop because the resource is consistent and reliable. It renews itself due to the heat from the center of the Earth, which is theoretically infinite. When properly managed a geothermal reservoir or rock network can last for decades.

Iceland is an example of a country that is steeped in geothermal energy development. Over 90% of the homes in the capital of Reykjavik are heated with geothermal district energy, and as a result it is one of the cleanest cities in the world. An impressive 25% of the countries electricity generation is supplied by geothermal power plants, compared to less than 1% for the US.

Historically the country depended on imported peat and coal for its energy supplies which created a substantial amount of air pollution. In 2011, 84% of the countries energy demand was supplied by renewable energy resources and 66% of that came from geothermal energy. Iceland is an example of how to become energy independent.

Geothermal heat pumps are a direct use form of geothermal energy that can be used virtually anywhere for heating and cooling purposes. They are especially ideal for remote rural areas where public services are not readily available. They do not depend on a steady supply of fossil fuels because they utilize the temperature of the ground for heating and cooling.

Heat generally flows from areas of high temperature to low temperature, but a heat pump is able to reverse this process through the use of refrigerant and a heat exchanger. Refrigerant has a lower boiling point than water so it will flash to steam easier.

An anti-freeze solution is circulated through a ground loop to absorb heat from the ground in the winter because it typically stays warmer than the air at four to six fee below the surface. The anti-freeze is able to extract about ten degrees of heat from the ground which is then transferred to the refrigerant.

The refrigerant is then passed through a compressor to raise the temperature to about 120° F. After leaving the compressor the refrigerant is circulated through an air coil and a fan distributes the heat throughout building in the case of duct work. If the building has a radiant floor system the fluid is circulated through pipes.

A geothermal heat pump only uses electricity to circulate fluids and to run a fan motor to distribute heat. There is no direct consumption of fossil fuels with a geothermal heat pump. A geothermal heat pump can also heat domestic hot water as a by-product of the space heating and cooling process. In the summer, excess heat extracted from the home is used to heat domestic water. Essentially hot water in the summer time is free.

Summary

Geothermal energy is an incredibly versatile and flexible energy resource that has a vast amount of development potential. Any process or product that requires the application of heat can be resolved through the use of geothermal energy.

The US currently leads the world in electricity production from geothermal energy, but there are still thousands of megawatts that could be tapped in to around the world. Direct use applications present the most widespread potential because their required temperature range is much lower. The uses of low temperatures resources are as varied as the places they are utilized; basically anything that requires heat can utilize geothermal energy. Geothermal heat pumps are another form of direct use application.

They can be used virtually anywhere in the world. They are most effective in extreme climates where the air temperature has wide fluctuations.

According to the UN Intergovernmental Panel on Climate Change investment in renewables needs to triple in order to avert the worst effects of climate change by 2100. We have the technology but lack the political will to enact change. We cannot afford to wait any longer. Our childrens future is at stake.

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