Geothermal energy is a renewable energy source from deep within the earth. 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.
There is an enormous level of energy trapped beneath the earth's surface coming from a list of sources: movement of continental plates, the planet core and decay of naturally occurring substances within the crust 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 under the surface of the earth. In some parts of the world where the earth’s surface is thin or cracked, 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 New Zealand, Japan, USA and Europe have high geothermal activity. Electricity is generated using high grade geothermal energy such as geysers, fumaroles, hot dry rocks and mud pots. 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.
While geothermal energy is a renewable resource and the creation of electricity does not pollute the air, the actual process can pose serious environmental problems. 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 – hydrothermal, hot dry rock, geopressured and magma.
Hydrothermal
This is the only type of geothermal energy that is currently producing commercial quantities of electricity 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 are formed 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 then used by being directed 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 comes 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.
Three forms of energy can be captured from geopressured sources – hydraulic energy from the high pressure, chemical energy from burning the dissolved methane and thermal energy from the hot water.
Hot Dry Rock
In certain cases granite at a depth of 3 to 5 kilometers beneath the ground 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.
Obtaining energy from hot dry rock has not been implemented commercially due to the costs, and questions about resistance of the reservoir to flow, water loss and thermal drawdown remain. Costs are coming down though and geothermal technology in general will improve enough to make hot dry rock economically feasible.
Magma
There is still no practical way of extracting the energy potential from magma. Found at depths from between 3 and 10 kilometers under 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.
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.
By the year 2015 it is estimated that electricity from geothermal power production in the United States can reach 5,500 MW thanks to this new initiative. 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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