Geothermal energy is probably most often associated with Iceland, where around a quarter of electricity demand is met by using volcanic heat. This DOE video summarises the technology.
Globally, the technology is a tiny share of supply and generally sits in the “other” pie piece. As the video mentions, much work is being done to pursue the potential for geothermal as a low life cycle emissions energy source.
In Australia, several potential projects have been under development for some time, as described in the Australian Energy Resource Assessment 2014. The largest pilot plant in the South Australian outback supplies the community of Innamincka with 1 megawatt of power. The remoteness of this location underscores geothermal’s primary constraint. It can only realistically be considered in the immediate vicinity of appreciable underground heat resources, with transmission infrastructure necessary for delivery to load centres.
The Renewables Paradox
Geothermal is classified as renewable energy and is readily included as such in various regions’ energy mixes. So, in the example of Iceland, a combination of geothermal and hydroelectricity is 100% renewables. The same reasoning saw Costa Rica recently claim an impressive run of renewables-only electricity generation: about 12% from geothermal with the remainder almost all from hydro.
This seems to be in spite of the geological reality of geothermal – an average of 70% of the heat is due to subterranean radioactive decay of potassium-40, thorium-232 and both major uranium isotopes (235 and 238). 30% is left over energy from Earth’s formation.
The other important detail is that enhanced geothermal systems technology involves the same method of accessing a desired volume of underground rock as hydraulic fracturing.
While the strawman argument is an undesirable rhetorical approach, it is probably very safe to say that many activists who uncritically reject the use of uranium in nuclear power plants and stand against unconventional fracked gas (regardless of what science might say) also largely support the use of renewable energy – including geothermal.
Furthermore, many activists increasingly bolster the rejection of nuclear energy primarily on grounds of cost. But despite the most recent official Australian levelised cost estimates clearly showing that geothermal is one of the most expensive technologies, it is spared this vocal criticism and exclusion. Indeed, as recently summarised, this is a form of special pleading which has little if anything to do with their true (and even less justifiable) objections.
Just to ensure this list is exhaustive, is it not reasonable to also expect loudly-voiced concerns of groundwater contamination? And considering the many decades of protest surrounding a deep geological repository for radiological waste, activists are dramatically restrained about high pressure fluid being pumped through deep rock heated by radioactive decay.
AERA 2014 states a particularly low average thermal conversion efficiency of 12% as extracted heat is used to drive a turbogenerator. This indicates a substantial loss of thermal energy to the environment. These two considerations are often included in criticisms of conventional nuclear energy, where more like 35% of fission heat is transformed to electricity and the rest lost as steam or into an adjacent river, lake or sea. To be clear, the efficiency of steam-driven turbogenerators is the result of much incredible engineering, and heat rejected to the environment is a relatively trivial concern.
At least we’re all happy that it’s low emissions, right? Well, some motivated commentators seek to exclude nuclear energy on that basis, citing an estimate of the equivalent of no less than 60 grams of carbon dioxide per kilowatt hour generated (gCO2eq/kWh). By this reasoning, geothermal is also out when the US National Renewable Energy Labs estimates a figure of up to 80 gCO2eq/kWh.
By applying basic logic, we should be seeing organised and vocal opposition to geothermal energy. But, of course, we don’t. This isn’t even considering the indefensible perspective of advocates of a radical shift to distributed energy generation – large, distant geothermal renewable energy installations would logically have little or no place in that world.
Myself, I’m excited to see geothermal, as a dispatchable and clean form of energy, flourish and contribute, where practicable, to the challenge of displacing the dominance of coal and gas. In the long run, without misinformed, hypocritical activism ceaselessly opposing it and prohibitively burdensome regulations more than absorbing any economies of scale it can achieve, it may eventually have a good chance.