Geothermal Energy

What is Geothermal Energy?

Geothermal energy is heat energy originating deep in the earth’s molten interior. It is this heat energy that is responsible for tectonic plates, volcanoes and earthquakes. The origin of this heat is from primordial heat (heat generated during the Earth's formation) and heat generated from the decay of radioactive isotopes. The temperature in the earth’s interior is as high as 7000°C, decreasing to 650 - 1200°C at depths of 80 km -100 km (Wright, 1998). Through the deep circulation of groundwater and the intrusion of molten magma into the earth’s crust, to depths of only 1 km-5 km, heat is brought closer to the earth’s surface. The hot molten rock heats the surrounding groundwater, which is forced to the surface in certain areas in the form of hot steam or water (e.g. hot springs and geysers). The heat energy close to, or at the earth’s surface can be utilized as a source of energy, namely geothermal energy.

The total geothermal resource is vast. An estimated 100 PWh (1 x 10¹⁷ W) of heat energy is brought to the earth’s surface each year (World Energy Council 1994). However, geothermal energy can only be utilized in regions where it is suitably concentrated. These regions correspond to areas of earthquake and volcanic activity, which occur at the junctions of the tectonic plates that make up the earth’s crust. It is at these junctions that heat energy is conducted most rapidly from the earth’s interior to the surface, often manifesting itself as hot springs or geysers.

Low-grade geothermal resources are more abundant and widespread. They are located in deep sedimentary basins around the world (e.g. along the Gulf Coast of the United States and in Central and Southern Europe), as well as on the edges of tectonic plates. Western Australia’s Coral Bay sits on top of a very low-grade source, which is nonetheless used (among other things) as a source of water for bathing in tourist centers. 

The Need for Geothermal Power in a Sustainable Energy system

With the concern over anthropogenic climate change (i.e. man-made climate change), there is a growing awareness that we must utilize energy resources that are sustainable. Geothermal power is one such sustainable resource that has the potential to supplement our energy systems and to displace many conventional fuels such as coal. This is due to the inherent stability of the resource. In contrast to many renewable technologies, such as wind or solar, the geothermal resource can be used 24 hours a day, 7 days a week. 

Geothermal Resources

There is currently an estimated 15,000 MW of direct use and over 8,000 MW of generating capacity in geothermal resources worldwide. To put geothermal generation into perspective, this generating capacity is about 0.4% of the world total installed generating capacity. In 2003 there was 8,402 MW of installed geothermal electricity generation capacity worldwide. This total is stabilizing after a growth period due to the over exploitation of the Californian fields in the United States which is decreasing output, with investments from other countries making up for this deficit. The US is the largest producer of geothermal electricity, followed by the Philippines, Mexico, Indonesia, Italy, Japan and New Zealand (International Geothermal Association, 2007).

Based on data from over 3,500 boreholes, conservative estimates of the Australian geothermal resource suggest the energy available for electricity generation is 23 million petajoules, or 7,500 years of Australian energy consumption at the current level. Over 80% of this resource is located in the Eromanga (Great Artesian) Basin. About 11% of this energy resource (2.5 million petajoules), or more than 800 times the current annual demand for electricity in Australia, is thought to be in granite rock, which is the most favored host rock for heat extraction in what is known as Hot Dry Rock (HDR) (Australian National University, 2003).

The Future for Geothermal Energy

In the short term, it is likely that hydrothermal resources will remain the only geothermal resource that is commercially viable. However this resource alone represents an immense source of energy. It is estimated that 80 GW of geothermal electricity could be generated in the short to medium term from known hydrothermal resources worldwide (Wright, 1998).

In the medium to longer term, technological developments will see the utilisation of the geothermal energy in hot dry rocks and geopressured reservoirs. Usable geothermal resources will no longer be limited to the shallow hydrothermal reservoirs. These resources represent a virtually limitless source of energy, and are the future of sustainable geothermal energy. 

Geothermal Challenge

Currently, Geothermal production is hampered due to the combination of pressures and temperatures and the lack of materials that can be used in these environments. Geothermal well drilling is relegated to the shallower depths where tectonic pressures are limited. One day, materials will advance to the degree necessary to make Geothermal production both feasible and economical. 

CorroTube’s Participation

CorroTube will introduce new proprietary materials technology that will meet the challenges of these environments. The clean renewable energy that Geothermal Energy brings will be a part of all of our futures!