Hot dry rock geothermal energy

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Geothermal power technologies.

Hot Dry Rock Geothermal Energy (HDR) is a type of geothermal power production that uses the very high temperatures (approx 200 Celsius) that can be found in rocks a few kilometers below ground. Electricity is generated by pumping high pressure water down a borehole (injection well) into the heat zone. The water travels through fractures in the rock, capturing the heat of the rock until it is forced out of a second borehole as very hot water, which is converted into electricity using either a steam turbine or a binary power plant system. All of the water, now cooler, is injected back into the ground to heat up again in a closed loop.

HDR wells are expected to have a useful life of 20 to 30 years before the outflow temperature drops about 10 degrees Celsius and the well becomes uneconomic. If left for 50 to 100 years the temperature would probably recover.[citation needed]

HDR and EGS technologies, like hydrothermal geothermal, are expected to be baseload resources which produce power 24 hours a day like a fossil plant. Distinct from hydrothermal (which relies on hot water finding its way to the surface), HDR and EGS are scalable technologies (in that they can be expanded by drilling more wells into deep (hence hot) rock). Good locations are over deep granite covered by a thick (3-5 km) layer of sediments which has kept the heat in [1].

Hot dry rock is the end point for a range of technology for utilizing heat from the Earth that consists of:

  1. Natural geothermal systems, where there are already cracks or pore spaces filled with water hot enough to generate power
  2. Systems where there are some cracks and connected pore spaces
  3. Rocks where there are little to no cracks or connected pore spaces


[edit] Enhanced Geothermal Systems (EGS)

[edit] Enhanced Geothermal Systems, also sometimes called engineered geothermal systems, is to extract heat by creating a subsurface fracture system to which water can be added through injection wells [2].

Natural fractures may provide adequete flow rates, otherwise Enhanced Geothermal Systems (EGS) "enhance" and/or create geothermal systems through hydraulic stimulation. When natural cracks and pores will not allow for economic flow rates, the permeability can be "enhanced" or stimulated by pumping cold water into the rock. These artificially enhanced geothermal systems are called Enhanced Geothermal Systems, or EGS. There are HDR and EGS systems currently being developed and tested in France, Australia, Japan, Germany, the U.S. and Switzerland. The largest EGS project in the world is currently being developed in the Cooper Basin, Australia - with the potential to generate 5,000-10,000 MW.

[edit] CO2 EGS

Research conducted at Los Alamos National Laboratories and Lawrence Berkeley National Laboratories examined the use of supercritical CO2, instead of water, as the geothermal working fluid with favorable results. CO2 has numerous advantages for EGS:

  1. Greater power output
  2. Minimized parasitic losses from pumping and cooling
  3. Carbon sequestration
  4. Minimized water use

The recently established Center for Geothermal Energy Excellence at the University of Queensland, has been awarded $18.3 million (AUS) for EGS research, a large portion of which will be used to develop CO2 EGS technologies.

[edit] HDR/EGS Advantages

  1. Carbonfree and renewable.
  2. Baseload.
  3. Scaleable and Modular.
  4. Massive and distributed resource.

[edit] Risks

  1. Unpredictability of the drilling and rock fracturing economically
  2. May trigger earthquakes

[edit] MIT Report

A 2006 report by MIT [3] conducted the most comprehensive analysis to date on the potential and technical status of EGS. The 18 member panel, chaired by Dr. Jefferson Tester of MIT, reached several significant conclusions.

[edit] Major Findings

1) Resource Size: The MIT report calculated the United States total EGS resources from 3-10 km to be over 13,000 zettajoules, of which over 200 ZJ would be extractable, with the potential to increase this to over 2,000 ZJ with technology improvements - sufficient to provide all the world's current energy needs for several millennia[3]. The report found that total geothermal resources, including hydrothermal and geo-pressured resources, to equal 14,000 ZJ - or roughly 140,000 times total U.S. annual primary energy use.
2) Development Potential: With a modest R&D investment of $1 billion over 15 years (or the cost of one coal power plant), the report estimated that 100 GWe (gigawatts of electricity) or more could be installed by 2050 in the United States. The report further found that the "recoverable" resource (that accessible with today's technology) to be between 1.2-12.2 million MW for the conservative and moderate recovery scenarios respectively.
3) Cost: The report found EGS could be capable of producing electricity for free. EGS costs were found to be sensitive to four main factors: (All of which could be government subsidized) 1) Temperature of the resource 2) Fluid flow through the system measured in liters/second 3) Drilling Costs 4) Power conversion efficiency. This technology has the potential to power the world at little or no cost to the population.

In addition the report has a wealth of data on EGS technology, trial wells and EGS economics.

[edit] EGS Industry

Commercial projects are currently either operational or under development in Australia, the United States, and Germany.

The largest project in the world is being developed in Australia's Cooper Basin by Geodynamics. The Cooper Basin project has the potential to develop 5,000-10,000 MW. Australia now has 33 firms either exploring for, drilling, or developing EGS projects. Australia's industry has been greatly aided by a national Renewable Portfolio Standard of 25% renewables by 2025, a vibrant Green Energy Credit market, and supportive R&D collaboration between government, academia, and industry.

Germany's 23 cent/kWh Feed-In Tariff (FIT) for geothermal energy has led to a surge in geothermal development, despite Germany's relatively poor geothermal resource. The Landau partial EGS project is profitable today under the FIT.

[edit] Current EGS Projects

Project Type Country Size (MW) Plant Type Depth (km) Developer Status
Soultz R&D France (EU) 1.5 Binary 4.2 ENGINE Operational
Desert Peak R&D United States 11-50 Binary DOE, Ormat, GeothermEx Development
Landau Commercial Germany (EU) 3 Binary 3.3  ? Operational
Paralana (Phase 1) Commercial Australia 7-30 Binary Petratherm Drilling
Cooper Basin Commercial Australia 250-500 Kalina 4.3 Geodynamics Drilling

[edit] Research And Development

[edit] Australia

The Australian government has provided research funding for the development of Hot Dry Rock technology. [1][2]

On 30 May 2007, then Australian opposition environmental spokesperson and current Minister for the Environment, Heritage and the Arts Peter Garrett announced that if elected at the 2007 Australian Federal Election, the Australian Labor Party would use taxpayers money to subsidise putting the necessary drilling rigs in place. In an interview, he promised:

"There are some technical difficulties and challenges there, but those people who are keen on getting Australia into geothermal say we've got this great access to resource and one of the things, interestingly, that's held them back is not having the capacity the put the drilling plants in place. And so what we intend this $50 million to go towards is to provide a one for one dollars. Match $1 from us, $1 from the industry so that they can get these drilling rigs on to site and really get the best sites identified and get the industry going."[4]

[edit] United States

The Department of Energy has committed $90 million towards EGS over the next 3 years, only $10.5 of which will be spent in 2008. The research funding, while small when compared to EGS potential and other national programs, is an improvement. The Bush Administration eliminated all geothermal energy research funding in 2007.

The DOE committed $1.6 million towards its EGS R&D project at Desert Peak.

[edit] European Union

The EU's EGS R&D project at Soultz-sous-Forêts, France, has recently connected its 1.5 MW demonstration plant to the grid. The Soultz project has explored the connection of multiple stimulated zones and the performance of triplet well configurations (1 injector/2 producers)]] [5].

Portugal - Portuguese government has awarded, December 2008, an exclusive license to Geovita Ltd, to prospect and explore geothermal energy in one of the best areas in continental Portugal. An area of about 500 square kilometers that is being studied together by Geovita and Coimbra's University - Science and Technology Faculty - Earth Sciences Department, and foresees the installation of an Enhanced Geothermal System (EGS).

[edit] Seismicity

The HDR project in Basel, Switzerland was suspended after it caused an earthquake. On 8 December 2006, only 8 days after water injection started, an event occurred measuring 3.4 on the Richter Scale with the focus at the bottom of the HDR borehole. The event [3] [4]prompted concern from local residents. Water injection was immediately stopped, but minor events continued. Further tremors were recorded on 6 January (measuring 3.1)[5] and 16 January 2007 (3.2).

Basel is in a known earthquake zone (see Basel earthquake) and sits atop a historically active fault. Seismicity associated with hydraulic stimulation can be mitigated and controlled through predictive siting and other techniques. The Basel HDR project is currently under review.

[edit] Modular Enhanced Geothermal Systems (MEGS)

MEGS is a way to use mass produced modules to create electric energy from heat miles below the Earth's surface. Sometimes the flow of heat to a deep well must be enhanced by various methods.

Modular Enhanced Geothermal Systems (MEGS) produce electricity using standard generators that are driven by turbines. They are binary systems in that the heat is carried to the surface by one completely enclosed heat transfer fluid and then a heat exchanger transfers that heat to a second fluid which expands to a gas and drives the turbine. Deep wells are used to bring 90 oC to 300 oC (or more) heated fluid to the surface. These wells can exhaust the heat from an area over time and so techniques are needed to Enhance (E) the flow of heat to the well from the surrounding reservoir of heat. The large number of Geothermal Systems (GS) that are needed to replace current fossil fuel base load plants, and the 100 additional plants needed to provide electric energy for all automobiles and light trucks, demand that mass production techniques be used to provide Modules (M) with the components needed to construct the MEGS generation facilities. The general name for this new way of producing energy from the Earth is Modular Enhanced Geothermal Systems (MEGS).

[edit] See also

[edit] References

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