Geothermal
Geothermal power is an alternative source of energy that harnesses the Earth’s heat in order to generate electricity. In locations with shallow ground water at high temperatures, wells are drilled in order to extract the steam or hot water. There are three types of geothermal energy generation plants in use today. The first type is called a dry steam plant, which harvests steam from fractures in the ground. The steam is directly used to drive a turbine that spins a generator, an example of this process is shown below:
Geothermal Energy Used for Dry Steam Plant (above)
Since steam is used directly, the cost of boilers and boiler fuels are eliminated. This provides energy at a very low cost. However, the technology is bounded by the extremely rare resources of dry-steam. The geysers in California are the only existing source in the United States.
The second type is called a flash plant, which collects ground water with temperatures of over 360 degrees Fahrenheit from beneath the surface of the Earth. The water boils in its ascent and is sprayed into a tank held at much lower pressure than the fluid. This causes the fluid to vaporize rapidly, or “flash.” The vapor then drives a turbine to run the generator. Some plants utilize a second tank in order to flash any remaining fluid for more energy. A diagram of how a flash plant operates can be seen below:
Diagram of Geothermal Flash Plant (above)
The third and final type is called a binary plant, which extracts water under 400 degrees Fahrenheit from beneath the surface of the Earth. Hot geothermal fluid and a second organic fluid, consisting of a much lower boiling point, are passed through a heat exchanger. The geothermal fluid produces heat that flashes the organic fluid to vapor, which in turn, drives the turbines. This is the most common source of geothermal energy production due to its abundance of moderate-temperature water found in the Earth. An example of a binary plant is shown below:
Diagram of Geothermal Binary Plant (above)
With all three of these methods, the left over condensed steam and geothermal fluids are returned to the Earth in order to generate more heat.
The Earth’s heat is so immense that harnessing it could power the entire world would while only utilizing a small fraction of its total heat. The Earth’s magma and dry rock will provide cheap, clean and nearly unlimited energy as soon as the technology for extraction is developed. Before geothermal electricity can be regarded as a key component of the U.S. source of energy, it must first become economically competitive with the other forms of power generation in place today. The Department of Energy is working with the geothermal industry in order to attain a price level of $0.03 to $0.05 per kilowatt-hour, which is projected to occur within the next decade.