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Will geothermal energy be the next big renewable resource?

30 August 2013
Will geothermal energy be the next big renewable resource?

Ben Barnes writes:

The US produces more geothermal energy than any other country, with more than 3,000 megawatts (MW) generated in eight states—enough to power about .04% of the US population. Geothermal energy generation has increased gradually over the past few years with an additional 100 MW added to the power grid between 2011 and 2012.

But the nation has the potential to produce so much more. According to an assessment by the U.S. Geological survey, if all conventional geothermal resources could be tapped in the United States they could potentially produce up to 73,000 MW of energy. An MIT report suggests the potential is even higher with enhanced geothermal technology. If new technologies receive reasonable investments, MIT predicts the nation could produce 100 gigawatts (100,000 MW) of geothermal electricity by 2050—enough to replace 100 coal power plants.   

Geothermal energy isn't just viable for the United States. Other countries have been working to harness the renewable energy as well. Iceland, for example, generates enough geothermal power to supply 25% of Iceland's electricity. And Australia started a pilot power plant in July that focuses on enhanced geothermal technology. The hope is that after 100 days of operation, the plant will contribute valuable information for the success of future geothermal technologies. 

What is geothermal energy?

Hot molten rock, or magma, located under the earth's crust produces massive amounts of heat. These high temperatures rise toward the earth's surface and can be captured as an energy resource. In fact, at just 33,000 feet under the surface, underground temperatures contain 50,000 times the energy of all the oil and natural gas resources in the world.

Geothermal energy taps into water resources typically a mile or two below the Earth's surface by drilling down toward the resources. The extremely hot water or even the steam a geothermal reservoir releases can be used to generate electricity. The resources brought up from the reservoir pushes a turbine, which creates electricity as it turns. Once the energy is produced it is purchased by a utility or retail energy company, such as TXU, in a power purchase agreement. Then the renewable power is placed on the electric grid and transported to homes and businesses across the United States.

Geothermal energy is considered a renewable energy resource because the electricity can be generated by utilizing natural resources without burning fossil fuels. In addition, geothermal can be produced 24 hours per day and 365 days per year, unlike solar which doesn't generate energy at night or wind that doesn't always blow. It's this constant supply of power, or base load power, which makes geothermal energy so valuable.  

The power grid requires a continuous supply of electricity to keep up with the demand of the nation. And this need for base load power is why fossil fuel-generated power is so widely used across the country—it can be generated at any time. However, with enough geothermal resources, the nation could produce a constant supply of power while reducing reliance on coal and oil.

Environmental concerns surrounding geothermal energy

Geothermal energy might be considered a green energy source, but the process is not without a carbon footprint.  Take a look at some of the environmental issues surrounding the production of geothermal energy.

Geographical location

The optimal location for a geothermal plant is near geological hotspots, such as volcanoes, hot springs or geysers. These areas make it easy for drillers to tap into the earth's steamy pockets of water to generate energy.  However, because they are typically located along fault lines, these optimal areas are prone to earthquakes. In addition, drilling at geothermal plants can prompt a greater frequency of earthquakes, which can be especially dangerous in heavily populated areas.

Water quality

Water pumped from the earth's surface is typically high in sulfur, salt and minerals. If the substances leaked into drinking water supplies, the water would be contaminated and unsafe for consumption. However, most geothermal sites use a closed-loop water system, which eliminates the concern. This system pumps the geothermal liquid right back into the reservoir where it's contained in a steel well that's cemented off from surrounding rock. According to the Union of Concerned Scientists, there have not been any reported incidents of water contamination at geothermal sites in the United States.

Water use

The process of harnessing geothermal energy also requires the use of large quantities of water. In the United States, all geothermal power plants use wet-recirculating technology and cooling towers which require between 1,700 and 4,000 gallons of water per megawatt-hour of energy generation. The process helps cool the super-hot steam found in the earth's core so it can be used again to generate electricity. Many geothermal plants use freshwater for cooling, but some reuse geothermal fluids to reduce the plant's water use.

Air emissions

Though most geothermal plants use closed-loop water systems, a few plants use an open-loop system that causes unwanted air emissions. In an open-loop system, geothermal plants emit carbon dioxide, methane, ammonia, hydrogen sulfide and boron.  Hydrogen sulfide emissions give geothermal plants a distinct smell—similar to rotten eggs. Once in the atmosphere, the gas converts to sulfur dioxide, which causes acid rain. However, it's important to note that closed-loop systems are more widely used and are also much safer because gases released from the well are injected back into the ground, minimizing air emissions.

Land use

Though the amount of land needed for a geothermal facility depends on the equipment used and the size of the resource reservoir, the plants can be quite expansive. The largest geothermal plant in the world is The Geysers, located in California. The site covers 45 square miles in Northern California.

Sinking land

In some cases the removal of water from a geothermal reservoir causes the surface land to sink. The phenomenon, called land subsidence, can usually be prevented. Geothermal plants that operate in closed-loop systems and inject wastewater back into the ground, decrease the risk of land subsidence.

Is geothermal a viable alternative to coal?

It's important to note that while geothermal energy has a carbon footprint, it produces fewer emissions than a coal power plant. And if all geothermal plants switched to closed-loop water systems, which have minimal emissions and even reuse the salient water from geothermal wells, geothermal energy could be the next big renewable energy generation craze. As countries around the globe continue to improve upon geothermal technology, it's possible the U.S. could eventually reach the 100,000 MW geothermal capacity that MIT predicts and replace many of its polluting coal power plants.

Ben Barnes is a graduate student with experience in the energy sector. His work concentrates on efforts to increase the sustainability of renewable energy sources and reduce the carbon footprint in the world we live in.

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