Geothermal energy is a renewable energy source from deep below the ground. 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 beneath 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 volcanoes and earthquakes. 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. High grade geothermal energy such as mud pots, fumaroles, geysers and hot dry rocks is used to generate electricity. 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 – hydrothermal, hot dry rock, magma and geopressured.

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 steam and hot water 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 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 captured from geopressured sources – chemical energy from burning the dissolved methane, thermal energy from the hot water, and hydraulic energy from the high pressure.

Hot Dry Rock

Hot dry rock is a heated geological formation consisting of dry, impermeable rock, usually granite. Unlike hydrothermal resources, it is necessary to drill bore holes to get to the hot rock formations and then water must be pumped into the rock at high pressure to create an artificial underground reservoir of steam or hot water.

Commercial scale production of electricity has still not been achieved with inhibiting factors such as cost 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 beneath 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.