Renewables - Geothermal Energy | Alabama Power

Geothermal Energy Program


Geothermal energy (derived from the root words "geo", meaning earth, and "thermal" meaning heat) is generated from heat energy contained deep within the earth. By taking advantage of the warmth of the earth, both utilities and homeowners can utilize a renewable source of energy that can be used to produce power or heat and cool a home efficiently.


Geothermal Power Plants

Various forms of geothermal power production methods may be implemented depending on the deep-earth conditions in an area. There are three basic types of geothermal power plants: dry steam, flash steam, and binary cycle plants.


Dry steam plants

Dry steam plants tap into geothermal steam deep beneath the surface of earth. This released and captured steam then drives power plant turbines directly to product electricity. Dry steam plants were first used at the beginning of the 20th century in Italy. This is the most desired form of geothermal power production, which can also be seen at the Geysers in California today.


Flash steam plants

Flash steam plants bring hot, pressurized water and steam from deep within the earth to surface piping where the steam-water mixture travels into separation vessels. In the separation vessels, steam separates (or "flashes") from the water. This steam is then routed to the turbines to produce power, while remaining water in the bottom of the vessel is pumped back into the earth.


Binary-cycle plants

Binary-cycle plants bring hot water from within the earth, at times from relatively shallow depths. The geothermal water is piped through a "heat exchanger" and is simply used to heat another liquid running through adjacent pipes in the heat exchanger, hence the term "binary". The secondary liquid flashes into a vapor and then powers a turbo-expander to produce electricity. The now cooled geothermal water is injected back into the earth without ever having been exposed to the outside air. During normal operation, virtually nothing is emitted to the atmosphere as a result.

In 2005, Southern Company acquired the 30-megawatt Puna Geothermal Venture (PGV) in Pahoa on Hawaii Island, and then leased it back to Ormat Technologies, one of the largest geothermal corporations in the world, under a long term lease. The PGV binary-cycle plant provides approximately 15% of the power for the big island of Hawaii in a renewable-friendly manner.

Geothermal Heat Pumps

Although homeowners do not drill wells into the earth to find steam and hot water, geothermal heat pumps provide a technology that utilizes the near-constant ground temperature in order to heat and cool your home. To find out more about geothermal heat pumps, visit our Geothermal Heat Pump page.