With the recent failure of geothermal projects in California and Switzerland, where one approach to tapping the earth's heat was found to induce earthquakes, the whole idea of geothermal energy is having some hard knocks. But that doesn't change the essential long-term outlook. Two years ago an MIT study identified huge energy potential in the earth crust's stored heat: By means of enhanced geothermal systems in particular--drilling several wells to reach hot rock and connecting them to a fractured rock region that has been stimulated to let water flow--hot water or steam can be brought to the surface via heat exchangers to drive electricity turbines. Now, in addition, Dutch studies have identified enormous tappable heat reserves found in aquifers at the greater depths where oil and gas companies normally operate.
Holland's Stichting Platform Geothermie finds that after "a spectacular rise in shallow geothermal applications" in the last two decades, now Netherlands "seems set on a similar steep path towards deep geothermal energy use. Exploration license applications have increased from a modest trickle to a torrent of [more than] 50 in the last year, and a major impact is expected from the [government's] new guarantee scheme."
That optimistic prediction is based on part on a report by Holland's TNO estimating the country's deep geothermal potential at 90,000 PetaJoules, and partly on the success of two experimental drillings in the last three years, to depths of 1,700-1,900 meters. Estimates of how much of that geothermal energy could be tapped yearly by 2020 range from TNO's 25 PetaJoules to the Platform's 3 PetaJoules, with the consultancy Ecofys taking an intermediate position. What actually happens, says the Platform report, will depend on whether the Dutch government creates a level playing field by giving geothermal the same feed-in-tariff subsidies that wind and solar get.