Skip to main content.
Header Image
Header Image

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. 


What is a GeoExchange heat pump?

An electrically powered device that uses the near-constant temperature of the earth to heat and cool your home.

What components make up a GeoExchange system?

The heat pump unit, the underground closed-loop system and the ductwork.

What is a closed-loop system?

A continuous loop of special buried plastic pipe connected to the indoor heat pump. Unlike an open-loop system that draws water from a well, a closed-loop system recirculates the same water under pressure, functioning as a heat exchanger with the earth. Because the water is sealed inside the piping, it remains pure, requiring less filtering and less potential maintenance.

How long will the pipe last?

High-density polyuethylene pipe properly heat-fused should last over 50 years. This material is unaffected by chemicals normally found in soil and has good conducting properties. PVC pipe should not be used.

Can anyone install the system?

Do-it-yourself installation is not recommended. It is best to employ IGSPHA or manufacturer-certified technicians and contractors to install your GeoExchange system. Retrofits in buildings with existing ductwork are typically easy to install. Consult your local dealer to determine any modifications that might be necessary.

What if I need heating but have no ventilation?

GeoExchange uses no combustion and therefore needs no outside venting.

How effective is this underground system?

Conceived in the 1940s, refined heat pump designs and improved pipe materials make GeoExchange systems the most efficient heating and cooling options available today.

Will the buried pipes affect my lawn or landscape?

After installation, closed-loop piping has no affect on grass, trees and shrubs. Installation requires displacement of some turf, which can be restored with grass seed or sod.

Can a GeoExchange system also heat water for my house?

Yes. Using a device called a "desuperheater," GeoExchange systems can preheat tank water to save up to 50% on water heating bills.