Geothermal Energy

Geothermal energy is all around us, a never ending presence that lies under our feet. The challenge of finding ways of harnessing it that is cost effective and not damaging to the environment is what makes using it a challenge. Here we examine the resource, the ways in which it is used in commercial operations and the various types of power plants that are in operation. There is also a list of the top 10 geothermal power projects (in potential capacity) from around the world.

How Is Geothermal Energy Formed?

The formation of geothermal energy is a natural phenomenon that takes place deep within the surface of the earth. The production of heat gives us the potential for creating an energy source.

The majority of geothermal activity is buried deep inside the earth and requires significant effort (and expense) to get to it. However, it is also found close to the earth’s surface in various parts of the world such as the Ring of Fire around the Pacific Ocean, the hot springs of Nevada and hot mud in New Zealand.

Volcanoes, geysers and thermal springs are examples of the geothermal activity reaching the surface. These events can be quite benign, producing hot springs of temperatures that can be used for bathing. They can also be horrifically violent as with the many volcanic eruptions that have taken place throughout history.

While geothermal activity is constantly present in the earth, the creation of geothermal energy is a different matter.

Superheated water is trapped in underground reservoirs and it is identifying its location and tapping the water that is often the challenge.

In some cases the capture and use of geothermal heat is a relatively simple matter. When it is present close to the earth’s surface it is possible to pipe into near to surface water, which maintains a temperature between 50° and 60°F (10° and 16°C). The heat that is generated may be used to directly heat buildings, for example.

Why is Geothermal Energy Considered Renewable?

When geothermal water is tapped it usually requires deep drilling to access the source. The water can be extracted in the form of steam which is used to run a turbine which turns to drive a generator.

When the water has done its job to power the turbine it can be returned to the earth where it will eventually find its way back to the original reservoir to be heated again by the earth. The water will also be replenished by rainfall which will also find its way down into the underground reservoirs.

World’s Top 10 Largest Geothermal Power Plants

Listed below is a list of the top 10 geothermal projects in the world as at 2013. In some cases the listed projects are comprised of a number of separate facilities that are grouped together under a single name. They are joined by their proximity to one another and the feed-in link that they provide.

Power Plant Name

Location

Capacity
(MW)

Date
Commissioned

 Hellisheidi Power Station

Iceland

303

2006

 Malitbog Power Station

Philippines

233

1996

 Wayang Windu Geothermal Power Station

Indonesia

227

1999

 Cerro Prieto II Power Station

Mexico

220

1982

 Cerro Prieto III Power Station

Mexico

220

1983

 Darajat Power Station II & III

Indonesia

200

2007

 Salton Sea Power Station

United States

185

 2010

 Wairakei Power Station

New Zealand

181

1958

 Cerro Prieto I Power Station

Mexico

180

1973

 Mahanagdong Power Station

Philippines

180

1997

 Gunung Salak I, II & III Power Plant

Indonesia

180

1997

 

Types of Geothermal Energy

There are four types of geothermal resources that can be harnessed in some way. They are hydrothermal, geopressured, hot dry rock and magma. The only one of these that is widely in use is hydrothermal. Research and analysis has been performed on geopressure and hot dry rock technology but has yet to be successfully used in a commercial facility.

Geothermal energy is most commonly used in one of three ways: as a means of direct heating through direct use, in the creation of electricity and in geothermal heat pumps.

Geothermal Heating

Direct Heating: it is possible to pipe geothermically heated water through pipes directly into homes, agricultural buildings, greenhouses or baths for a number of different applications. This can be done without the need for power pumps or a heat pump.

Geothermal Power Plant Diagram

Geothermal Electricity: by drilling access wells into underground reservoir it is possible to bring geothermal water to the surface where it can be used to power turbines in a geothermal power plant. There are four commercial types of geothermal power plants currently commissioned: flash power plants; dry steam power plants; binary power plants; and, flash/binary combined power plants.

Geothermal Heat Pump

Geothermal Heat Pumps: the fact that the earth’s temperature is fairly constant at depths from 10 – 300 feet can be used in the supply of heat. The way in which they operate is they can circulate water through the pipes that are buried in a continuous loop. The heat is taken from the earth and is distributed through a conventional duct system. This type of idea also works for cooling by going through the opposite sequence. Warm air is taken from the building and returned to the earth.

Geothermal Electricity Power Plant Types

Flash Power Plants operate by bringing geothermally heated water to the surface under pressure to be separated in a steam separator. The steam from the separation process is then used to operate a turbine which powers a generator. The water is then returned to the reservoir.

Dry Steam Power Plants operate with steam that is produced directly from the reservoir that runs the turbines which powers a generator. This is a more direct process with the steam sourced direct to the turbine without the need of a separator.

Binary Power Plants enable the use of geothermal resources that are lower than 150°C (302°F). The geothermal water is used to heat another liquid which has a boiling point temperature that is lower than water. The liquids are kept separate through the use of a heat exchanger as the heat transference takes place. The gas expansion of the vapor acts like steam that runs the turbine which powers a generator.

Flash/Binary Combined Cycle Power Plants use a combination of the technology that goes into flash and binary technology. In this process the water that is brought to the surface and flashes to steam under reduced pressure is converted to electricity using a backpressure steam turbine. The low-pressure steam existing the backpressure turbine is then condensed and used in the binary system.

Geothermal Energy is a Limitless Resource

The heat that is contained under the earth’s surface is everywhere and it is always flowing to the earth’s surface. It is expected to remain in the same state for billions of years to come and will always provide a limitless supply of energy.