Region 5: The Basin and Range

Like the Columbia Plateau region, active tectonism yields an opportunity for the growth of geothermal energy in the Basin and Range. Hydroelectric power development is associated with the region’s steep topography, in particular that of the Snake River, which flows from western Wyoming through the Snake River Plain of southern Idaho and discharges water at a rate of over 1500 cubic meters per second (54,000 cubic feet per second). The largest hydroelectric plant in the Basin and Range is Palisades Dam on the Snake River, though it is less than half the size (about 175 MW) of the largest hydro plant in the Columbia Plateau region.

Geothermal energy comes from heat within the Earth, which is created on an ongoing basis by radioactivity. This energy powers mantle convection and plate tectonics. The highest-temperature conditions exist in tectonically active areas, including the Basin and Range, Iceland (a mid-Atlantic ridge), Japan (an area of subduction), and Hawaii and Yellowstone (areas with hot spots). Idaho’s Basin and Range is home to the Raft River Geothermal Power Plant. Operated by Geothermal, Inc., the plant is actually a former US Department of Energy (USDOE) geothermal research and demonstration facility (Figure 7.17). The facility uses a “binary” energy system developed and tested by the USDOE. Unlike typical geothermal power plants that make direct use of vapor from heated water to spin turbines, this system passes hot geothermal water through a heat exchanger to heat a secondary liquid that vaporizes at a significantly lower temperature than water. This enhances the energy capture capacity of the system, thus increasing energy production.

Figure 7.17: The 13 MW Raft River Geothermal Plant near Malta, Idaho was the first commercial-sized binary cycle geothermal plant in the world. The plant’s condensers and heat exchangers are pictured here.

Figure 7.17: The 13 MW Raft River Geothermal Plant near Malta, Idaho was the first commercial-sized binary cycle geothermal plant in the world. The plant’s condensers and heat exchangers are pictured here.

How does geothermal energy work?

Geothermal power stations use steam to power turbines that generate electricity. The steam is created either by tapping a source of heated groundwater or by injecting water deep into the Earth where it is heated to boiling. Pressurized steam is then piped back up to the power plant, where its force turns a turbine and generates power. Water that cycles through the power plant is injected back into the underground reservoir to preserve the resource.

There are three geothermal sources that can be used to create electricity. Geopressurized or dry steam power plants utilize an existing heated groundwater source, generally around 177°C (350°F) in temperature. Petrothermal or flash steam power plants are the most common type of geothermal plant in operation today, and they actively inject water to create steam. Binary cycle power plants are able to use a lower temperature geothermal reservoir by using the warm water to heat a liquid with a lower boiling point, such as butane. The liquid butane becomes steam, which is used to power the turbine.