The main forms of renewable energy that most people see and hear about are solar energy and wind power, but there is another major power source that will soon be demanding attention. It has already been used to provide power to 1.2 million homes in the United States. It has far greater potential and to both heat and provide electricity to homes and is yet to be properly utilized. That's about to change.
Geothermal energy comes from a variety of sources of heat within the earth: the planet core, decay of naturally occurring substances within the crust and movement of continental plates as they slide against and underneath each other. Volcanoes, hot springs and steam vents represent the easily accessible points to this energy but most geothermal energy is trapped under the earth’s crust and must be accessed by drilling into the resource and harnessing the energy. The thermal energy in the uppermost 6 miles of the earth’s crust contains 50,000 times the energy of all the world’s gas and oil resources.
What Is Geothermal Energy?
Geothermal energy is the heat stored below the earth’s surface. In some parts of the world where the earth’s surface is cracked or thin, steam and molten rock can escape. These are usually locations of high seismic activity such as earthquakes and volcanoes. If water finds its way into these cracks, it becomes heated and may come to the surface as geysers, fumaroles, hot springs and mud pots.
Parts of USA, New Zealand, Japan and Europe have high geothermal activity. Electricity is generated using high grade geothermal energy such as geysers, mud pots, hot dry rocks and fumaroles. Geothermal energy can also be used as a heating source, for example in Iceland hot water is brought to the surface through a bore , then sent through insulated pipes into homes and radiator panels which provide heat. Over 80% of homes in Iceland are heated this way.
Although geothermal energy doesn’t pollute the air with greenhouse gases, there are other environmental concerns about its use. Scientists are not sure how the long-term use of this resource could affect our underground water supplies. Some geothermal tourist attractions at Rotorua in New Zealand have already suffered a decline in surface activity due to the draw-off of geothermal fluid from the underground reservoir by domestic and commercial uses.
Geothermal energy can be broken down into 4 main types – Geothermal energy can be broken down into 4 main types – hot dry rock, geopressured, hydrothermal and magma.
Hydrothermal
Hydrothermal is the only source used to generate commercially viable energy and is derived from hot water and steam formed in porous or fractured rock at relatively moderate depths from 100 metres to 5 kilometres.
The hot water and steam come from the intrusion of molten magma into the earth’s crust or the deep circulation and heating of groundwater through faults and fractures.
To generate electricity, hot water at temperatures ranging from 180 – 250 degrees Celsius is brought from the underground reservoir to the surface through production wells and is flashed to steam in special vessels by release of pressure. The steam is separated from the liquid and fed into a turbine engine which turns a generator. Ensuring the water levels are not depleted, the used geothermal water is returned to the reservoir.
Geopressured
Geopressured energy is derived from hot, pressurised waters containing dissolved methane, trapped at depths of three to six kilometres in sedimentary formations. The water temperature ranges from 90°C to 200°C.
Energy in 3 forms can be derived from geopressured sources – thermal energy from the hot water, hydraulic energy from the high pressure, and chemical energy from burning the dissolved methane.
Magma
The prospect of using magma directly has still not been exploited. Found at depths from between 3 and 10 kilometers below the earth's surface, magma is molten rock reaching temperatures up to 1200°C. Magma is only accessible where volcanic activity or tectonic plate movement occurs.
Hot Dry Rock
In certain cases granite at a depth of 3 to 5 kilometers under the earth's surface can get to 250°C. Unlike hydrothermal resources, the fractures and faults required to conduct water to the surface are not present, therefore water must be pumped into the rock at high pressure to create an artificial underground reservoir of steam or hot water.
A number of development projects continue into attempting to make use of hot dry rock to create electricity but factors such as cost and questions about resistance of the reservoir to flow, water loss and thermal drawdown remain. As the cost of producing geothermal using hot dry rock technology keeps coming down it will soon be an economically viable option.
The Future Prospect of Geothermal Energy in the US
An exciting new development in the future of geothermal energy in the United States has just been announced by the Department of the Interior who have promised to make 190 million acres of federal land available for geothermal power development. This is good news because the proposed land includes no environmentally sensitive areas such as national parks or designated wilderness areas.
An estimation of something like 5,500 MW of electricity from geothermal power will be generated by 2015. It’s a positive move that will promote a form of renewable energy that has been used for years, but perhaps not to its full potential.
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