How Geothermal Works
Human use of geothermal energy is neither new nor revolutionary. It’s one of our oldest sources of clean energy, and it’s used the world over for everything from cooking, bathing, and heating homes and factories, to driving some of the largest, most technically advanced energy systems.
Unlike winds, solar and other alternative energy sources, geothermal is consistent, firm, dependable base-load power. It feeds directly into existing energy distribution networks, as well as the new “smart grids” that monitor usage to maximize efficiency,
IDG’s approach to geothermal energy production is unique. We customize our technology to fit the local environment. And out community-based business model means benefits are shared more equitably among investors, land and mineral rights owners, the state, and local communities.
- Dry Steam
Dry steam geothermal technologies are used in geothermal resources where there is primarily steam. The steam comes up a pipe, is cleaned for debris, and goes directly to the turbine, which generates electricity. The steam is then reinjected in the reinjection well after passing through a condenser, or used for some other heating purpose. This is the simplest source of geothermal energy, but is very rare to find an economical geothermal resource that is mainly steam.
Examples: The Geysers, CA. Lardarello, Italy.
- Flash Steam
Flash steam geothermal technologies are only used when hydrothermal fluids are above 360 degrees Fahrenheit. This technology is used in geothermal resources where there is liquid and vapor present. The hydrothermal fluids are brought up in the production well under pressure, and sprayed into a flash tank, where the pressure is greatly decreased, lowering the boiling point, and causing the liquid present to turn to vapor. This vapor then drives the turbine, to generate electricity. If liquid still remains, a second flashing process, and additional ones, can take place in order to extract all possible energy. The hydrothermal waste, excess liquid and brine, is then pumped back down into the injection well, after passing through the condenser.
Examples: Cal Energy Navy at Coso Geothermal Field. Kokonoe, Kyushu, Japan. Hachijojms Island, Japan. Bouillante, Guadeloupe. CGPV Azores, Portugal.
- Binary Cycle
Binary Cycle power plants are for moderate and low temperature geothermal resources. This would be in the temperature range between 160 and 360 degrees Fahrenheit. In this process, the hydrothermal fluids are pumped up the production well, and passed through a heat exchanger, where the heat from the hydrothermal fluid is transferred to another fluid, usually one with a lower boiling point, such as pentane or hexane. After transferring this heat, the hydrothermal fluid is then pumped directly down the injection well, never coming into direct contact with the turbine. The secondary fluid, now as a vapor, drives the turbine to generate electricity.
Examples: Puna, Hawaii. Mammoth Pacific at Cada Diablo geothermal field. Fang, Thailand.