Low Temperature Geothermal Resources

“I was reading about the geothermal plant utilizing the binary system and a relatively low temperature recently built in Alaska. I can imagine that practically any place with a nearby hot spring can produce geothermal energy for electricity production. Am I correct on that?” –Manny M., Michigan, USA

The first Chena geothermal power plant in Alaska, online as of late July 2006, is the lowest temperature geothermal resource to be used for commercial power production in the world. The plant uses resources at 165 degrees F. In the past, experts assumed that geothermal fluids needed to be at least 225 degrees F for power uses. This low temperature technology will significantly reduce Chena’s high energy costs through a reliable, renewable, environmentally friendly power source. On December 26, 2006 a second power unit began operating at the Chena resort. Together, the two power units are contributing to owner Bernie Karl’s goal of making Chena the first totally renewably powered and fueled community in the United States. These rankine-cycle, binary units are produced by United Technologies Corporation. Here’s how Chena describes their facilities: “Because the geothermal water at Chena Hot Springs never reaches the boiling point of water we cannot use a traditional steam driven turbine. Instead a secondary (hence, “binary”) fluid, R-134a, which has a lower boiling point than water passes through a heat exchanger with 165 degree F water from our geothermal wells. Heat from the geothermal water causes the R-134a to flash to vapor which then drives the turbine. Because this is a closed loop system virtually nothing is emitted to the atmosphere.” For more information about the Chena project please visit their website: http://www.yourownpower.com/Power/ So, what does this mean for geothermal development? According to the folks at the Chena plant, “moderate temperature is by far the most common geothermal resource and most geothermal power plants in the future will be binary cycle plants.” Even so, power can’t be economically produced from every single hot spring. While the presence of a hot spring or other surface manifestation indicates the existence of a geothermal resource, in most cases a power plant needs hotter, deeper resources. And if a resource is too deep, it will be too expensive to develop. Also, most resources do not have any surface manifestations, so we shouldn’t limit our sights to hot springs. There’s no question that our ability to produce power from lower temperature resources expands geothermal’s potential for development. The availability of small power units makes distributed generation much more viable, with such uses possible in areas like Arkansas, Georgia or even New York. Power could likewise expand throughout the West, into the Gulf States, and perhaps into the northern Great Plains over time. New technology will have significant applications in many oil and gas fields, which produce large quantities of hot water. (Visit http://www.smu.edu/geothermal/ for more information.) But, it is difficult to know the extent of subsurface geothermal resources capable of economically producing power from small systems like those at Chena. The last geothermal resource assessment was conducted by the US Geological Survey almost thirty years ago, in 1978, and that report did not examine the potential for what would be called “medium” temperature resources. That’s why Congress mandated that the US Geological Survey (USGS) complete a new national resource assessment in the Energy Policy Act of 2005. We hope their report will shed light on these and other questions. Meanwhile, it’s exciting to see entrepreneurs like Bernie Karl working to find new ways to tap our largely unused geothermal resources. I wish I could say that the Department of Energy will be helping them, but we still don’t know the fate of the federal geothermal research program for 2007. We hope that the new Congress will convince the Administration and Department of Energy that Bernie was right when he testified last year before the Senate Energy Committee about the importance of supporting new technology and geothermal research: “The power generation project at Chena would not be possible without support from the United States Department of Energy’s Geothermal Technologies Program, which is currently threatened with elimination…New technologies that hold tremendous promise for tapping moderate temperature geothermal resources, including those associated with oil and gas production are emerging. Without validation in real world operating conditions and a stable, sustained commitment to financial incentives, the necessary investment will not be made and these technologies will never penetrate the market resulting in lost opportunities for renewable domestic energy production and the associated economic and environmental benefits.” (Testimony by Bernie Karl, Proprietor, Chena Hot Springs Resort, Fairbanks, AK, Senate Energy and Natural Resources Committee, Hearing on Geothermal Energy, July 11, 2006) Karl Gawell has been the Executive Director of the Geothermal Energy Association since 1997. He was formerly Director of Government Affairs for the American Wind Energy Association and has held senior positions at the National Wildlife Federation and The Wilderness Society.