Geothermal Energy

The only real base-load capacity alternative of the renewables.

‘Geothermal’ literally means ‘Earth’s heat, which is estimated to be 5,500 degrees centigrade at the Earth’s core – about as hot as the surface of the sun. Geothermal energy is a clean, renewable resource that can be tapped by many countries around the world located in geologically favourable places. Geothermal energy can be harnessed from underground reservoirs, containing hot rocks saturated with water and/or steam. Boreholes of typically two kilometres depth or more are drilled into the reservoirs. The hot water and steam are then piped up to a geothermal power plant, where they are used to drive electric generators to create power for businesses and homes. Geothermal energy is considered a renewable resource because it exploits the Earth’s interior heat, which is considered abundant, and water, once used and cooled, is then piped back to the reservoir.

Glitnir Fact Sheets:

• “Geothermal Energy – An Overview” (pdf), 2 pages fact sheet, text below.
• “Geothermal – The story of Iceland and its implications for other nations” [link to page], pdf version of this 2 pages fact sheet. 

Geothermal energy can be utilized for electricity production and for using geothermal heat directly, e.g. for heating purposes, food processing, fish farming, bathing and other applications that require heat. In this, geothermal is unique compared to other renewables. It not only provides a real base-load capacity for electricity generation, but also presents a real and cleaner alternative to fossil fuels for heat production.

Geothermal energy can be used for various purposes, either using geothermal heat directly for various applications, or indirectly by using steam or heat for electricity generation.

The oldest and probably best known application of geothermal energy is in baths, spas and for heating purposes, used already in Roman times. Applications for this can be found in district heating systems, e.g. with one of the largest geothermal district heating system in Iceland, in baths and spas all over the world, e.g. thermal baths in Hungary and China; in geothermally heated fish farms, e.g. in the United States and for food processing, e.g. food de-hydration in Greece. Furthermore the possibility to utilize ground source (geothermal) heat pumps to either heat homes directly or through energy efficiency programs, allowing savings in energy costs, has vast possibilities for individual or industrial use.

All those "direct use" applications utilize geothermal energy produced from lower temperature water of less than 150 degrees centigrade (< 300°F) that is being derived from wells of 100-1,000 m (330-3,300 feet) deep wells. Today, around 73 nations utilize geothermal energy directly, with an overall energy output of 75.9 TWh thermal per year.  The number of nations using geothermal heat is growing constantly.

The utilization of geothermal energy for the generation of electricity is probably the most prominent form of geothermal energy utilization in the renewable energy debate of today. People tend to forget though that this technology is a mature technology having already been in use in a small power generation installation in Lardarello, Tuscany/ Italy back in 1904. To this day, geothermal energy is used to generate electricity, but also using heat directly for the region around Lardarello.

While the number of nations that generate electricity through geothermal energy is growing, only around 24 nations are producing electricity from geothermal today. The overall installed capacity is around 9,000 MWe with an annual output of 57.0 GWh electric per year.

Electricity is generated from medium and high enthalpy fluids of more than 150 degrees centigrade (> 300°F) derived from wells of around 1,000-3,000m (3,300-9,800 feet) deep wells in hot, permeable rock. The water from those wells is either used directly in a steam turbine or to heat up a secondary working fluid, which has a lower boiling point temperature.

All those applications mentioned above use water as a carrier of geothermal energy in the form of heat. This technology has been proven for hundreds of years, but requires existing water flows in the ground. For electricity production high temperatures are needed, but new technologies using a binary cycle system with fluids boiling at lower temperatures, allow the generation of electricity in lower temperature regions and extend the prospects of geothermal energy utilization for electricity generation even further.

With "a higher capacity factor (a measure of the amount of real time during which a facility is used) than many other power sources" , geothermal has a huge advantage. "Unlike wind and solar resources, which are more dependent upon weather fluctuations and climate changes, geothermal resources are available 24 hours a day, 7 days a week, while e.g. wind and solar have capacity factors of 20-30 percent. In real life terms it means that a 50 MW installation of geothermal provides electricity for around 38,000 U.S. households, while the same installation for wind provides electricity only for around 15,000 and solar photovoltaic only provides enough electricity for 10,000 households.  This gives some indication of the usefulness, but for any industrial user of electricity to receive electricity only when there is enough wind or sunshine simply is no alternative and a 24/7 accessibility to electricity is needed.

New technologies are in various stages of development and could provide further advancements to the geothermal energy industry. Those technologies are e.g. Engineered Geothermal Systems or Hot-Dry-Rock Systems. They are aimed at utilizing heat from non-permeable rocks by creating hot water reservoirs artificially. While those systems are not commercially viable yet, they are potentially extending the geothermal energy utilization dramatically, allowing electricity generation all over the world. Further advancements to drilling technology and the economics of deep(er) drilling are also providing a great hope to further extensive growth in geothermal energy exploration and utilization.

With the industrial proven technology in use today, which is based on hydrothermal, the largest carbon emission reduction potential of geothermal lies in the direct (thermal) use and will thereby probably play the most important role.

For electricity production, further technological developments will have a huge impact on the overall development in this sector.  While the carrier medium for geothermal electricity (water) must be properly managed, the source of geothermal energy, the Earth's heat, will be available indefinitely".

POTENTIAL

The overall prospects for geothermal energy utilization, either for electricity generation or direct use are excellent. While depending heavily on political and financial support, geothermal energy represents the only real base-load capacity alternative to fossil fuels, like coal or oil. The biggest potential and prospects for the short(er) term are in the direct use of geothermal energy, particularly for heating and other applications that use heat directly. With technological developments, e.g. in binary systems and engineered geothermal systems, geothermal could provide all the electricity of this world.