Geothermal plants such as the world’s largest “The Geysers” in California exist in the rare hot spots near the surface and also need to be near population centers so that the transmission lines don’t end up costing as much or more than the geothermal plant itself. These sites are very uncommon, and are concentrated in California where the best spots have already been developed.
Clearly if we could drill down into the earth anywhere and pour water down the hole for steam turbines, there would be an enormous amount of energy that could be generated. This is what is meant by “enhanced” geothermal systems (EGS).
The drilling process to do this is very similar to fracking, but far more advanced techniques need to be developed for EGS. The deeper the drill bit goes, the more expensive it gets, and the more likely it is to be destroyed from high temperatures or worn down.
Attempts to drill 2 km down or more have been going on since the early 1970s. But the same problems that occurred back then are still occurring now:
- Huge water losses (70 to 90% of the water disappears).
- Permeability issues. Minerals such as silica and lithium precipitate through flow channels, reducing fracture permeability. Removing the minerals is an expensive, time-consuming process that limits the usefulness of enhanced geothermal recovery.
- Short-circuiting between the injection and production wells
- mechanical failures,
- Insufficient connectivity between wells to meet economic requirements for reservoir productivity over its lifetime, etc.
- Some of the few demonstration projects are “cheating” in that they’re on the edges of existing hydrothermal systems.
- “Lessons learned” may not apply to new wells since the geology of each area is unique
- Most of the areas under consideration are the Basin and Range faultlines, where there is very little water to pour down drilled holes.
- In most areas of the country the depths to drill down to, or the kinds of rocks to drill through, or a lack of huge amounts of water to pour down the hole can rule out many areas.
- Lack of models to improve drilling techniques by simulating the movement of fluid through rocks at critical and super-critical conditions
- Objections to these attempts by nearby residents include worries about earthquakes and the chemicals being injected.
The depth to be drilled down to is so deep that it is likely this technology will always be too expensive and use more energy to drill than obtained. Though no one wants to look at EROI since that would prevent investors or research money from flowing.
The EROI of EGS is hard to even guess at since there are no commercial plants, so it’s unknown how (un)productive an imaginary EGS will be. It depends on an unknown reservoir depth, unknown temperature, an unknown temperature decline rate, an unknown amount of energy to correct impermeability issues, an unknown amount of energy to move water from the nearest abundant source to pour it into the bowels of the earth, and so on.
“Australia has much better hot dry rock heat resources than the rest of the world but it is not yet clear how effectively they can be tapped or at what energy-return value. It will require considerable amounts of energy to bore holes 5 km deep through rock, fracture rock at depth, pump water down and force it 500 metres across to the nearest rising hole. It is not known what will be the temperature and rate of flow of the water that comes up, and what generation effi-ciency these will enable. In addition in Australia there will be the dollar and energy costs of constructing very long transmission lines from the deserts where the hot rock is located. The only operating plant in Australia (not at the most promising location) can transform into electricity only 6% of the heat energy in the water, one-sixth the efficiency value for a coal-fired power station” (Trainer).
I don’t want to waste time writing about a technology so far from commercial development, now or ever, with a likely negative EROI. Above all, EGS is useless because it generates electricity, and since transportation can’t be electrified, so what?
Here are a few articles on this technology FYI:
Selvans, Z. Jan 14, 2013. Enhanced Geothermal Systems promise dispatchable zero carbon power. cleanenergyaction.org
Trainer, T., 2012. A critique of Jacobson and Delucchi’s proposals for a world renewable energy supply. Energy Policy 44, 476–481.
Ziagos, J., et al. Feb 11, 2013. A technology roadmap for strategic development of enhanced geothermal systems. proceedings of the 38th workshop on geothermal reservoir engineering, Stanford University, CA.
USDOE. 2008. Geothermal Tomorrow. US Department of Energy.