Beneath Minnesota’s often cold surface is a hot heart of granite that could serve as an energy source in the future.
Scientists studying the Earth’s crust in Minnesota have discovered that the geothermal potential is much greater than originally thought, especially in the western and central parts of the state. If harnessed, that energy source could replace today’s power infrastructure at a competitive price.
“When you look at all the energy emitted from the core of the Earth every day, it amounts to three times the amount of energy used in the world,” said Donald Fosnacht of the University of Minnesota-Duluth’s Natural Resources Research Institute. “It’s basically lost to space.”
As director of the institute’s Center for Applied Research and Technology Development, Fosnacht oversaw a recent study of the state’s geothermal potential. The government-funded research found that Minnesota had three times the energy potential than had been estimated in earlier geothermal studies.
In fact, the Earth could conceivably produce enough electricity for the entire state through the construction of “enhanced geothermal systems” (EGS) plants, he said. The greatest potential lies in counties where geothermal heat is closest to the Earth’s surface (about 6 to 7 kilometers, or 3.7 to 4.3 miles).
Those counties include Wilkin, Otter Tail, Pope, Clay, Stevens, Swift, Meeker, Aitkin, Carleton and even Stearns, as well as northern St. Louis County. The Twin Cities area has less potential because energy developers would have to drill to 7 kilometers to reach a layer with temperatures high enough, Fosnacht said.
With the Midwest’s integrated power grid, the location of geothermal plants matters less since the electricity the plants would produce could be shared across the region through transmission lines, he suggested.
Minnesota has much greater stability than much of the country because it lies on no major earthquake fault lines. “Minnesota is pretty darn stable, so if you’re drilling here you’re not going to have mini-earthquakes and that sort of thing,” he said. “We have older rocks, which are much more stable.”
The key to making a geothermal plant functional would be a minimal temperature of 125 to 150 degrees, at levels from 6 to 7 kilometers beneath the surface, Fosnacht said. To capture the thermal heat embedded in granite formations, water or carbon dioxide would be used to create the steam necessary for electricity production, he said.
One idea under study is for coal or ethanol power plants to sequester CO2 then use it in a combination with a geothermal plant, he said.
Steve Hauck, program manager for the UMD institute, pointed out that research by other experts suggests a 50-megawatt geothermal plant would cost more than $140 million and produce power for $88 to $94 per megawatt.
That price range is competitive with other energy sources, including natural gas, Hauck said. Other advantages include no need for fuel in an operation and the fact that EGS is base-load energy, which means it continues to provide power constantly, unlike solar and wind, he said.
A geothermal plant is one-ninth the size of a typical coal plant and employs a closed loop system that reuses the water and organic mixture involved in creating steam, Hauck said. A geothermal plant basically requires little to no additional energy after operations begin, he said.
The idea of large-scale geothermal heating seems to be on the rise. The University of Minnesota announced last month that it has spun off a technology it developed to a South Dakota company that uses carbon dioxide instead of water.
The process would create more energy than a water-based geothermal plant does and sequester CO2, the leading cause of global warming.
Still, there are challenges. The up-front capital costs that include drilling, itself risky, make EGS less than a clear winner as a future energy source in Minnesota. The drilling itself might disrupt the environment in unpredictable ways, Hauck said.
Geothermal plants have operated in California, Hawaii and Nevada for years, but those states have the advantage of a belt close to the surface of radioactive heat-producing rock that carries high temperatures.
Now researchers or an energy company should hone in on the best locations for a geothermal plant, Hauck said. “This report just shows the possibility of doing geothermal in Minnesota,” he said. “The next step would be to take a much closer look to pinpoint good areas for geothermal.”
University of North Dakota geophysicist William Gosnold said that while Minnesota’s geothermal landscape looks promising, North Dakota has even greater potential. In the Williston Basin an energy developer would only have to drill down 3 kilometers to reach geothermal potential, he said.
Gosnold, who helped with mapping Minnesota’s geothermal areas during the study, is involved in five other geothermal research projects with the U.S. Department of Energy.
A geothermal plant in Minnesota “would have to be deeper than anywhere else in the U.S.,” he said. “The farther west you go towards the mountains and Montana, the better you find the potential for geothermal.”
Still, the report revealed much greater potential than was found in previous studies, he conceded. The latest research was funded by the Office of Energy Security at the Minnesota Department of Commerce with money provided by the Xcel Energy Renewable Development Fund.