DOE Awards $20 Million for Geothermal Technologies
DOE has selected seven projects to research, develop, and demonstrate cutting-edge geothermal technologies involving low-temperature fluids, geothermal fluids recovered from oil and gas wells, and highly pressurized geothermal fluids.
Today's geothermal power plants draw on underground reservoirs of water or steam that are heated by "hot spots" in the Earth's crust. While traditional geothermal plants require reservoirs at temperatures greater than 360°F, hot enough to easily generate steam, the latest generation of power plants use binary-cycle technology to draw on lower-temperature resources.
New technology employs a "working fluid" that, when passed through a heat exchanger, vaporizes at lower temperatures than water. The vapor drives a turbine, which spins a generator to produce power. The vapor is then condensed and reused in a closed cycle. Because the geothermal fluid is kept separate from the working fluid, the two fluids form two separate cycles, hence the name "binary-cycle" technology. See the description and illustration of binary-cycle power plants on the Web site of DOE's Geothermal Technologies Program.
Three projects are designed to advance binary-cycle technology, including a scale-resistant heat exchanger that could increase power production 40%, and systems that use carbon dioxide and ammonia-water mixtures as working fluids. A fourth project aims to extract more energy from geothermal fluid by developing a generator that can run on waste heat from an existing geothermal plant. The geothermal fluid would be used as the heat source for a heating system, a greenhouse, and a fish farm. This "cascading" use of the geothermal resource would improve the economics of tapping nearly 1500 potential low- to moderate-temperature well sites in towns and medium-sized cities throughout the West.
The three other projects seek to tap unconventional sources of geothermal energy. In one case, ElectraTherm, Inc. will aim to draw power from hot geothermal fluids that oil and gas wells often generate as a byproduct. They plan to develop a low-cost, modular, mobile power plant that can be moved from well site to well site, reducing the need to generate on-site power from diesel generators.
The other two projects will aim to draw power from geothermal fluids that exist at high pressures under certain geological conditions, particularly along the Gulf Coast. Such "geopressured" fluids often contain high concentrations of dissolved natural gas. Louisiana Geothermal will produce power from a resource in Cameron Parish, Louisiana, and NRG Energy will demonstrate cost-effective recovery of heat, kinetic energy, and natural gas from geo-pressured resources. See the
DOE press release.
