People have been talking about the possibility of clean coal, and carbon capture and storage (CCS), for years. So far, however, real world examples of CCS have remained limited to a few pilot projects. The problem is that it is extremely expensive, and given that a tax on carbon seems politically unfeasible, there is little incentive for power plant operators to invest in reducing their emissions and burying them underground. Some researchers, however, are exploring an interesting premise.
What if we could use carbon capture and storage to enhance our production of clean, geothermal energy?
Radically increasing geothermal capacity
A group of researchers from University of Minnesota, Lawrence Livermore National Laboratory, and Ohio State University believe that by using the CO2 emissions from existing coal or cement manufacturing plants, they can increase the amount of energy produced from geothermal wells by a factor of 10 or more, as detailed over at EnergyPathways.org and Renewable Energy World.
Conventional geothermal plants use water to extract heat from below the Earth's surface, turning it into electricity without emitting CO2. They do, however, require electricity to keep their pumps running. By replacing some of the water with CO2, which flows more easily than water (and plumes naturally to the surface when heated through a process known as thermosiphoning), the plant would be able to reduce or eliminate the need for running pumps. CO2 is also more effective at transferring heat because it expands more when heated — meaning more energy can be produced from the same well.
Here's a video explanation of how the concept works:
Making carbon capture commercially viable?
Because this system would result in tangible increases in energy production (and hence revenue), it makes carbon capture and storage more economically viable. And because it increases the capacity of geothermal wells, it also significantly increases the locations where geothermal power plants are economically feasible to many locations across the Western U.S. The result could be a game changer for both technologies, according to Renewable Energy World:
In computer simulations, a 10-mile-wide system of concentric rings of horizontal wells situated about three miles below ground produced as much as half a gigawatt of electrical power — an amount comparable to a medium-sized coal-fired power plant — and more than 10 times bigger than the 38 megawatts produced by the average geothermal plant in the United States. The simulations also revealed that a plant of this design might sequester as much as 15 million tons of CO2 per year, which is roughly equivalent to the amount produced by three medium-sized coal-fired power plants in that time.
As if these benefits were not enough, researchers also claim that the system could help make renewables more effective too. While wind and solar produce no CO2, their primary drawback is variability — when the sun doesn't shine, solar doesn't produce. When the wind doesn't blow, turbines stop generating. Because a CO2-fed geothermal plant could store heat underground until needed, it could be used to smooth out some of the lapses in production. Such a plant could also utilize surpluses on windy or sunny days to compress CO2 into its liquid form.
It all sounds a bit too good to be true, and according to some renewable energy advocates, it is. Suspicious that CCS is simply a ruse to keep polluting, some commenters over at Renewable Energy World have been voicing their concerns:
Just as any terminal patient's doctor will search frantically and desperately for a cure, these overpaid number-crunching dreamers have the same mindset and goals as they also search for a means of keeping all the current insanity, fueled exclusively by finite fossil fuels, up and running, right up to when they finally figure out what the word finite means.
Others, myself included, are a little more hopeful. Given the monumental challenge of transitioning to a 100 percent low-carbon future, we can't afford to leave any cards on the table. The significant public and private capital invested in fossil-fuel based infrastructure is not likely to be going anywhere anytime soon, so finding ways to mitigate harm should be a top priority. If that mitigation can make clean energy more viable in the process, then I, for one, am all for it.
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