Geothermal energy is created beneath the Earth’s surface from the heat contained in hot liquid magma. This heat naturally creates hot water and steam in vents which can be piped to the surface. When the hot water and steam reach the surface it can be used to turn a steam turbine and generate electricity. Geothermal energy is also obtained by piping water underground to be heated by dry rocks beneath the surface. The heated water is then returned to the surface to turn a steam turbine which also generates electricity.

The first archeological evidence of the use of geothermal resources is in North America, dating about 10,000 years ago. The Paleo-Indians used hot springs as a source of heat and cleansing. They also used minerals found near these springs for medicinal purposes. Hot springs were considered a neutral zone to warring Native Americans. Every major hot spring across North America has a history with Native Americans.

The first town to construct a district heating system with the use of geothermal power was in Boise, Idaho in 1892. The Boise Water Works Company pumped water from hot springs for use in homes and businesses. The transferred water was used to heat buildings and bathing. This sparked the beginning of the use of geothermal power within towns around the U.S. Since then, the technology has been developed into an alternative source of electricity used in homes across the U.S.

As technology developed, reservoirs were dug deeper into the surface of the earth to tap steam with- in the surface of the earth to drive turbines that generate electricity. There are three types of power plants in which geothermal energy can be produced: dry steam plants, flash steam plants, and binary-cycle plants.

Dry steam plants use steam directly from reservoirs to turn turbines that generate electricity. This was the first type of geothermal power plants ever built. It was first used at Lardarello, Italy in 1904. Dry steam plants only emit hydrothermal fluids which are mainly steam and a minor amount of gases.
Flash steam plants are the most commonly used power plants today. Water at temperatures of 360º F or higher is used from vents below the surface. It is then pumped under high pressure to the surface. When the hot water reaches generators in the plant, it is then reduced to a lower pressure which will cause the release of “flash” steam that is used to power turbines to generate electricity. Leftover steam in this process can be released again to create more energy. This process emits little steam into the amosphere.

Binary-cycle plants differ from dry and flash steam in that they use hot water or steam to heat another “working fluid.” In the binary system, hot water pumped from the earth is used to heat a “working fluid” which turns generators that produce electricity. The hot water and “working fluid” is contained in its own separated circulating unit to run the system. Neither fluid ever comes in contact with the other. The binary-cycle is a clean way to produce energy because it does not produce air emissions. Many residents of the Big Island currently use this technology to power their homes.

Since 1992, the Puna Geothermal Venture (PGV) has been supplying residents of the Big Island with this “clean” form of energy. The plant supplies the island with 25-30 megawatts, which is 20 percent of the island’s electricity needs. The facility is generating energy exclusively for the island. The contribution of energy saves the island more than 429,600 barrels of oil per year.
PGV is part of a Hawaiian partnership that is regulated by guidelines and laws of the state of Hawai‘i and the Federal Energy Regulatory Commission. It is also under a power purchase agreement with the Hawaiian Electric Company.

PGV is located 21 miles south of Hilo on the Big Island of Hawai‘i. The facility is on a 500-acre plot along the lower-east rift zone of the Kilauea Volcano, and is 13 miles from Pu‘u o‘o, one of the volcano’s vents. This location gives the plant access to hot liquid reservoirs beneath the surface, ideal for the production of energy.

For more information, visit pgvhawaii.com.