MIT-led Panel Backs Geothermal as Key U.S. Energy Source
[From MIT via Renewable Energy Access.com:]
A comprehensive new MIT-led study on the potential for geothermal energy within the United States has found that mining the huge amounts of heat that reside as stored thermal energy in the Earth's hard rock crust could supply a substantial portion of the electricity the country will need in the future -- probably at competitive prices and with minimal environmental impact.
An 18-member panel led by MIT prepared the 400-plus page study, titled "The Future of Geothermal Energy." Sponsored by the U.S. Department of Energy, it is the first study in some 30 years to take a new look at geothermal, an energy resource that has been largely ignored.
The goal of the study was to assess the feasibility, potential environmental impacts and economic viability of using enhanced geothermal system (EGS) technology to greatly increase the fraction of the U.S. geothermal resource that could be recovered commercially.
Although geothermal energy is produced commercially today and the United States is the world's biggest producer, existing U.S. plants have focused on the high-grade geothermal systems primarily located in isolated regions of the west. This new study takes a more ambitious look at this resource and evaluates its potential for much larger-scale deployment.
"We've determined that heat mining can be economical in the short term, based on a global analysis of existing geothermal systems, an assessment of the total U.S. resource and continuing improvements in deep-drilling and reservoir stimulation technology," said panel head Jefferson W. Tester, the H. P. Meissner Professor of Chemical Engineering at MIT.
"EGS technology has already been proven to work in the few areas where underground heat has been successfully extracted. And further technological improvements can be expected," he said.
The expert panel offers a number of recommendations to develop geothermal as a major electricity supplier for the nation. These include more detailed and site-specific assessments of the U.S. geothermal resource and a multi-year federal commitment to demonstrate the concept in the field at commercial scale.
The new assessment of geothermal energy by energy experts, geologists, drilling specialists and others is important for several key reasons, Tester said.
First, fossil fuels -- coal, oil and natural gas -- are increasingly expensive and consumed in ever-increasing amounts. Second, oil and gas imports from foreign sources raise concerns over long-term energy security. Third, burning fossil fuels dumps carbon dioxide and other pollutants into the atmosphere. Finally, heat mining has the potential to supply a significant amount of the country's electricity currently being generated by conventional fossil fuel, hydroelectric and nuclear plants.
The study shows that drilling several wells to reach hot rock and connecting them to a fractured rock region that has been stimulated to let water flow through it creates a heat-exchanger that can produce large amounts of hot water or steam to run electric generators at the surface. Unlike conventional fossil-fuel power plants that burn coal, natural gas or oil, no fuel would be required. And unlike wind and solar systems, a geothermal plant works night and day, offering a non-interruptible source of electric power.
Prof. Tester and panel member David Blackwell, professor of geophysics at Southern Methodist University in Texas, also point out that geothermal resources are available nationwide, although the highest-grade sites are in western states, where hot rocks are closer to the surface, requiring less drilling and thus lowering costs.
The panel also evaluated the environmental impacts of geothermal development, concluding that these are "markedly lower than conventional fossil-fuel and nuclear power plants."
"This environmental advantage is due to low emissions and the small overall footprint of the entire geothermal system, which results because energy capture and extraction is contained entirely underground, and the surface equipment needed for conversion to electricity is relatively compact," Tester said.
The report also notes that meeting water requirements for geothermal plants may be an issue, particularly in arid regions. Further, the potential for seismic risk needs to be carefully monitored and managed.
According to panel member M. Nafi Toksoez, professor of geophysics at MIT, "geothermal energy could play an important role in our national energy picture as a non-carbon-based energy source. It's a very large resource and has the potential to be a significant contributor to the energy needs of this country."
Toksoez added that the electricity produced annually by geothermal energy systems now in use in the United States at sites in California, Hawaii, Utah and Nevada is comparable to that produced by solar and wind power combined. And the potential is far greater still, since hot rocks below the surface are available in most parts of the United States.
Even in the most promising areas, however, drilling must reach depths of 5,000 feet or more in the West, and much deeper in the eastern United States. Still, "the possibility of drilling into these rocks, fracturing them and pumping water in to produce steam has already been shown to be feasible," Toksoez said.
Panel member Brian Anderson, an assistant professor at West Virginia University, noted that the drilling and reservoir technologies used to mine heat have many similarities to those used for extracting oil and gas. As a result, the geothermal industry today is well connected technically to two industry giants in the energy arena, oil and gas producers and electric power generators. With increasing demand for technology advances to produce oil and gas more effectively and to generate electricity with minimal carbon and other emissions, an opportunity exists to accelerate the development of EGS by increased investments by these two industries.
Government-funded research into geothermal was very active in the 1970s and early 1980s. As oil prices declined in the mid-1980s, enthusiasm for alternative energy sources waned, and funding for research on renewable energy and energy efficiency (including geothermal) was greatly reduced, making it difficult for geothermal technology to advance.
"Now that energy concerns have resurfaced, an opportunity exists for the U.S. to pursue the EGS option aggressively to meet long-term national needs," Tester observed.
Tester and colleagues emphasize that federally funded engineering research and development must still be done to lower risks and encourage investment by early adopters. Of particular importance is to demonstrate that EGS technology is scalable and transferable to sites in different geologic settings.
In its report, the panel recommends that:
It's great to see a fresh look at geothermal energy. This often overlooked renewable already provides as much clean, renewable energy as the entire wind and solar industries combined and has the relatively unique distinction amongst renewables of offering reliable, baseload power.
The DOE's proposed 2007 budget initially axed all funding for geothermal R&D, arguing that the technology was already well established and didn't warrant future R&D efforts. This attempt was thwarted by geothermal and renewable energy advocates, and this new MIT study should explode the notion that geothermal energy has shown us all it can offer. Clearly, we've only tapped the tip of the iceberg of geothermal heat potential, and there is much more R&D needed to be done to unlock the renewable resources true potential.
The MIT study focuses on the potential of enhanced geothermal energy systems, which sounds like the Hot Dry Rock technology being pioneered by researchers at Australian National University (which I've blogged about before, here).
HDR geothermal power utilizes the hot temperatures (up to 570 C) of underground granite rock layers that are mildly radioactive (the heat source) and are trapped beneath insulating layers of low thermal conductivity sediments. As ANU's hot rock site explains:
Heat is extracted by pumping water through an engineered heat exchanger connecting two or more wells. This heat exchanger is a volume of hot dry rock with enhanced permeability. It is fabricated by hydraulic stimulation. This involves pumping high pressure water into the pre-existing fracture system that is present in all rocks to varying degrees. The high pressure water opens the stressed natural fractures ... The result is a million-fold permanent increase in permeability along the fracture systems and a heat exchanger that can be used to extract energy.Water is then injected into a borehole and circulated through the "heat exchanger". The water is heated through contact with the rock and is then returned to the surface through another borehole where it is used to heat another liquid with a lower boiling point within in a closed loop system. This liquid is flashed into steam which is used to spin turbines and generate electricity. The water is then re-injected into the first borehole to be reheated and used again. The HDR plant thus involves two closed-loop systems, the subsurface water loop and the power plant loop that generally contains organic fluids such as refrigerants and iso-pentane.
This HDR or EGS technology differs from traditional geothermal energy systems which rely on an existing hydrothermal reservior - an underground reservior of superheated water - that can be tapped to spin turbines and generate power. HDR or EGS technologies manufacture such a reservior by enhancing the permeability of hot subterranean rock strata and injecting water into the artificial reservior to flash into steam. Being freed from a reliance on an existing hydrothermal reservior means that HDR/EGS geothermal systems can be deployed over a much greater range of the United States and the technology offers considerably larger energy potential.
In the coming and necessary transition from fossil fuel dependence to sustainable energy independence, we're going to need all of the technologies in our 'toolbox' that we can get. Hot Dry Rock/Enhanced Geothermal Systems technology has considerable potential and warrants a devoted research, development and deployment effort from public and private entities.
Tuesday, January 23, 2007
MIT-led Panel Backs Geothermal as Key U.S. Energy Source