On 11/5/2013 11:39 AM, Nate Vack wrote:
On Tue, Nov 5, 2013 at 11:17 AM, Henry Spencer <henry@xxxxxxxxxxxxxxx> wrote:Now THAT would be revolutionary - drill two ~$10 million fracked dry wells with the right geometry, pump water down one, get steam out of the other to run some number of megawatts of power plant indefinitely.The idea is an old one -- I remember seeing it suggested many years ago -- although fracking technology may make it work better. The main problem in earlier attempts, as I understand it, was establishing a long-lived network of fine cracks connecting the two wells. In particular, erosion had a bad habit of gradually concentrating the flow into a few wider channels, which didn't make nearly as good a heat exchanger.While this is getting really OT even for arocket, ;) there's a fundamental challenge with large-scale geothermal problem. It's discussed in depth here: http://physics.ucsd.edu/do-the-math/2012/01/warm-and-fuzzy-on-geothermal/ but summed up as: "thermal depletion is a dimensional problem. You can draw out energy according to volume, but it is recharged according to area. So the problem is dimensionally stacked to come up short, leading to thermal depletion."
What that implies is that a given geothermal location will have a maximum average power output which can be exceeded for short peaks but not over the long run. As long as that's understood and a given installation still makes economic sense at the max average power available, no problem.
Henry