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Geothermal research may lead to alternative energy options for farmers
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Geothermal - heat from the earth - is an alternative energy source that could join the ranks of solar, wind, water and biomass.
The earth gets progressively warmer as you near its center, where the temperature is over 7,600 degrees F. Scientists and developers are looking for ways to tap into some of that heat created as result of the decay of radioactive material.
The University of North Dakota (UND) recently received a $400,000 grant from the Department of Energy to study geothermal energy.
The grant has two major objectives, said Ahmad Ghassemi, UND associate professor in geological engineering and principal investigator.
Scientists hope to learn more about water/rock interactions based on how rocks fracture. They will also study the affect of fracture width, or the size of the opening, on water/rock interactions.
“The idea is there is a significant energy resource available in rocks in the earth - but those rocks do not have significant open space in them so one can circulate water to extract the heat,” said Ghassemi, who was reached by phone at his UND, Grand Forks office. “The interest is to create those fractures and maintain them open throughout the life of a particular reservoir.”
Two types of geothermal energy are high-grade and low-grade.
Low-grade geothermal energy heats a liquid near the earth's surface - 10' to 500' down. Geothermal piping and heat pumps circulate the liquid in the winter to draw warmth from the earth to heat buildings. The same piping and pumps can circulate liquid in the summer to transfer heat to the earth to cool buildings.
High-grade geothermal energy focuses on the generation of steam or hot water for the production of electricity.
Hot rocks heat water to produce high-grade geothermal energy. Old Faithful in Yellowstone National Park is an example of high-grade geothermal energy.
According to Internet sources, the continental United States produces about 2,700 megawatts of geothermal-generated electricity. That's enough electricity to power about 1.5 million households.
Professor Ghassemi sited a United States Geological Survey that estimates the U.S. could produce about 100,000 megawatts of electricity for 30 years by using geothermal energy available in rocks that are three kilometers deep (9,842 feet or 1.86 miles). That much electricity could supply the power needed for 26-30 million homes.
Much of the geothermal energy resource is available in the western United States. In central and northern California, treated sewage effluent is piped into geothermal fields where it replenishes steam produced for power generation.
New Mexico, Nevada, Oregon, Idaho, Arizona and Utah are also developing high-grade geothermal energy.
At certain locations in the West, magma or molten rock pockets located near the earth's surface remain at high temperatures. Porous rock formations allow liquid to travel through these warm temperature zones. As the water rushes to the surface under pressure, it begins to cool and may turn to steam.
The research being conducted by Ghassemi and others could uncover ways to take advantage of geothermal energy in the central and eastern United States. The West, however, will remain the primary location for production of electricity using the earth's heat.
In areas with no magma bodies near the surface, the earth warms by an average of 30 degrees C (86 degrees F) for every 3,300 feet down from the surface.
In areas where the rocks heat up at a higher rate, the temperatures can reach and exceed 150 degrees C (300 degrees F) at 9,800 feet. The water could be heated sufficiently to produce electricity when it is brought to the surface, said Ghassemi.
The challenge is to provide enough fractures - or to connect the pre-existing ones - in rocks at that depth to A) allow the water or liquid to travel from an injection well to an extraction well, and B) create enough rock surface area to allow the liquid to heat sufficiently.
At the same time, scientists need to make sure there are no fracture short cuts that would allow the liquid to reach the extraction well without getting sufficiently heated.
Ghassemi, colleagues and graduate students will be using computer simulations to study these challenges.
They want to look at how the change in the temperature of rocks can enhance formation of a crack or fracture in the right locations. If there are ways to fracture rocks at a depth of 1.5 miles, there is no limit on the locations where geothermal energy could be produced.
Ghassemi wants to also provide new information on the percolation of water and the chemical interactions of water and rock fractures.
“If you have the opportunity to see some veins in rocks - in certain outcrops, you'll see there are some minerals in these veins or cracks that are different from the rest of the rock,” Ghassemi said. “Many of those are the result of water/rock interaction. When they happen, they plug the fractures and prevent water from flowing through them.”
In addition to computer simulations, Ghassemi will be using data from current geothermal facilities. He will be studying the changes in pressure and water temperatures in the injections and extraction wells with hopes of understanding the response of rocks in various scenarios.
Ghassemi believes there are opportunities to develop geothermal energy in the upper Midwest - particularly in western North Dakota, Montana, Western Nebraska, Wyoming and Colorado.
He encourages landowners to look for opportunities to use this alternative energy. Federal grants may be available to some landowners to develop geothermal energy.
Although geothermal sounds very exciting, if developers have to drill very deep to access warm rocks, geothermal energy could become less economically feasible than some other methods of energy production, said Ghassemi.
“There are alternatives. One can heat the water partially by using the heat from rocks, but also using other sources of energy to make steam and generate electricity,” he said. “That could potentially happen in western North Dakota. In eastern North Dakota, the best idea is using a heat pump approach to produce low-grade geothermal energy.”
University of North Dakota will conduct research for two years and release the results of their work in about three years.
“There are opportunities to take advantage of geothermal resources, particularly in the farming community,” Ghassemi said.
The potential for one day running ethanol plants using geothermal energy would be an exciting way to produce renewable energy for cars and trucks.
In the case of geothermal energy, the earth - not the sky - is the limit.
For more information, please visit http://www.geothermal.org/what.html or http://www.eere.energy.gov/geothermal/geomap.html
