I would like to start a new thread on this topic because this source of energy will take on increasing importance over the next few decades, and because I have some expertise in conventional geothermal and hence interest (cooling towers in my avatar).
Geothermal energy exploitation can conveniently be divided into three main groups: conventional geothermal, low temperature geothermal and enhanced geothermal. Conventional geothermal energy is extracted from areas mainly around the circum-Pacific along the so-called "ring of fire". Countries that exploit conventional geothermal energy include New Zealand, Indonesia, Philippines, Japan, western Canada, western USA, Mexico, Peru and Chile. There are a few countries in Europe and Africa that can exploit conventional geothermal energy: namely; Iceland, Italy and Turkey (Europe), and Kenya and Ethopia (Africa). Geothermal wells drilled to exploit conventional geothermal energy are typically approximately 3km deep where hot water (>200C) under pressure in permeable rocks can discharge or flash to steam without stimulation.
Low temperature geothermal resources are less than 150C near the ground surface, and are used in direct use applications such as ground-source heat pumps (GSHP) for domestic heating/cooling, greenhouses fisheries and mineral recovery. This sector will take on increasing importance in future as pointed out in
wiki:
Approximately 70 countries made direct use of 270 petajoules (PJ) of geothermal heating in 2004. More than half went for space heating, and another third for heated pools. The remainder supported industrial and agricultural applications. Global installed capacity was 28 GW, but capacity factors tend to be low (30% on average) since heat is mostly needed in winter. The above figures are dominated by 88 PJ of space heating extracted by an estimated 1.3 million geothermal heat pumps with a total capacity of 15 GW.[4] Heat pumps for home heating are the fastest-growing means of exploiting geothermal energy, with a global annual growth rate of 30% in energy production.[29]
Enhanced geothermal energy is typically extracted from impermeable granite reservoir rocks at similar temperatures to conventional geothermal but at greater depth (around 5km). Rather than drilling a single well as in conventional geothermal, enhanced geothermal exploitation requires a two well circuit. One well is a production well while the other is an injection well. Cold water is injected down to the reservoir to fracture the reservoir rock (like fracking but only water is used), then hot water rises up the production well where it flashes to steam near the surface. This steam is then used to power turbines like in conventional geothermal.
Enhanced geothermal system (EGS) energy will also take on increasing importance over the next few decades particularly in USA. The limitations of this method are the costs of drilling deep wells and pumping water down the reservoir as well as demonstrating that heat mining can be sustained over long periods. Conventional geothermal has been operating in NZ for 50 years, whereas the sustainability of enhanced geothermal has yet to be proven.
EGS technologies, like hydrothermal [conventional] geothermal, can function as baseload resources that produce power 24 hours a day, like a fossil fuel plant. Unlike hydrothermal, EGS appears to be feasible anywhere in the world, depending on the economic limits of drill depth. Good locations are over deep granite covered by a 3–5 kilometres (1.9–3.1 mi) layer of insulating sediments that slow heat loss.[5] EGS wells are expected to have a useful life of 20 to 30 years before the outflow temperature drops about 10 c (18 f) and the well becomes uneconomic.
EGS systems are currently being developed and tested in France, Australia, Japan, Germany, the U.S. and Switzerland.
The reason EGS is going to take on increasing importance is because of an excellent
report written and lead by Professor Tester (MIT) in 2007.
A comprehensive assessment of enhanced, or engineered, geothermal systems was carried out by an 18-member panel assembled by the Massachusetts Institute of Technology (MIT) to evaluate the potential of geothermal energy becoming a major energy source for the United States. Geothermal resources span a wide range of heat sources from the Earth, including not only the more
easily developed, currently economic hydrothermal resources; but also the Earth’s deeper, stored thermal energy, which is present anywhere. Although conventional hydrothermal resources are used effectively for both electric and nonelectric applications in the United States, they are somewhat limited in their location and ultimate potential for supplying electricity. Beyond these conventional resources are EGS resources with enormous potential for primary energy recovery using heat-mining technology, which is designed to extract and utilize the earth’s stored thermal energy. In between these two extremes are other unconventional geothermal resources such as coproduced water and
geopressured geothermal resources. EGS methods have been tested at a number of sites around the world and have been improving steadily. Because EGS resources have such a large potential for the long term, we focused our efforts on evaluating what it would take for EGS and other unconventional geothermal resources to provide 100,000 MWe of base-load electric-generating capacity by 2050.
GEA: From DOE’s standpoint, what advancements have been made in EGS since the MIT Report and why is EGS a big part of the portfolio in advancing geothermal technologies?
"Energy Department research in safe, efficient stimulation and monitoring methods has helped advance a number of EGS demonstration projects.
When it comes to harnessing America’s vast geothermal energy resources, knowing where to look is half the battle.
Geothermal energy -- the heat contained within the earth -- represents a growing part of the country’s clean energy mix. Still, for continued growth of this industry, gaining easy access to reliable, comprehensive geothermal data remains a critical barrier.
To help solve this challenge, the
Energy Department is partnering with the Arizona Geological Survey -- among other public and private sector contributors -- to create the National Geothermal Data System at
http://www.geothermaldata.org. This interactive, open source database provides project developers and other industry partners with the critical information they need to cut the time to identify and develop new production areas and reduce upfront discovery costs.
The Department of Energy (
DOE) has just released its 2012 update on the state of geothermal in the U.S. You can download the report here (9.7Mb):
Here is the latest
news on EGS and GSHP in USA.
Sustainable Energy Expert - Geothermal Bill in US Senate Offers Hope for Energy Security“During this time of gridlock in Washington it is very refreshing to see senators Jon Tester of Montana and Mark Begich of Alaska taking a strong leadership position that connects renewable energy deployment to providing both energy security and creating jobs in America.
“If passed, their bill will accelerate our utilization of geothermal energy on a very large scale – including the deployment of geothermal heat pumps and using geothermal heat directly for heating homes. In addition, the bill provides for loan assistance to developers, which directly addresses the higher risks and uncertainties associated with exploration.
“The development of our indigenous geothermal resources is clearly in the best interests of the country as it can provide sustainable base load electric power and heat, complementing efforts to increase other renewable sources such as solar, wind, hydro and biomass.
Further geothermal news will be posted in this thread.
Human history becomes more and more a race between education and catastrophe. H. G. Wells.
Fatih Birol's motto: leave oil before it leaves us.