FOR years, those looking to generate electricity without using fossil fuels have dreamed of tapping the virtually unlimited heat source that lies 8 kilometres or more beneath Earth鈥檚 surface. Prior efforts have been stymied because getting to that heat entails drilling into rock that is too hard for conventional techniques. Now, one tantalising possibility involves repurposing an existing technology to tap into this source and produce electricity at a lower cost than any existing form of power generation.
This isn鈥檛, however, simply a matter of economics. Even if all nations were to meet the pledges that were made under the Paris Agreement on climate change, temperatures are expected to rise by roughly 3掳C by 2100. Tapping into deep geothermal energy has the promise of replacing fossil fuel-powered plants at the scale required to avert this catastrophe.
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The technology that might enable this, which makes use of millimetre-wave beams, was and could provide access to the 400掳C to 500掳C heat that lies several kilometres below Earth鈥檚 surface. Extracted through a borehole, this heat could produce steam for electricity generation as a zero-carbon substitute for fossil fuels.
The opportunity is huge. Coal-fuelled, steam-powered turbines are the . The great majority of these turbines could be retrofitted to use steam from deep geothermal energy, and would produce electricity at less cost than any fossil fuel as a consequence.
Until now, the problem has been that once past the sedimentary rock constituting the first few kilometres of Earth鈥檚 crust, drillers hit granite or basalt that is five to 10 times harder and resistant to standard techniques.
Enter millimetre-wave beams. These are similar to, but vastly more powerful than, the waves used in a microwave oven. Created by a device called a gyrotron, these waves have now been proven to vaporise rock, according to Carlos Araque, CEO of start-up Quaise Energy, which has a licence to commercialise the technology for deep drilling. Combined with conventional drilling, it might be possible to create a borehole reaching reservoirs of deep heat. Araque says he expects Quaise Energy will be able to drill such deep holes in as little as 100 days. Another start-up, GA Drilling, is attempting a similar thing using ultra-high temperature plasmas.
Time is money, so drilling this rapidly greatly reduces costs. Araque estimates that a freshly built, deep geothermal plant will produce electricity at 1 to 3 cents per kilowatt-hour (including capital costs), which is as cheap as, or cheaper than, any electric power generator now operating. Retrofitting an existing coal or gas plant to use steam from deep geothermal energy could produce electricity for less than 1 cent per kilowatt-hour, he says.
That is the genius of this technology: it meshes with existing infrastructure and expertise. As it is just an extension of conventional drilling, it doesn鈥檛 produce the seismic problems associated with fracking. The biggest hurdle will be delivering and focusing the millimetre-wave beams so deep underground.
This challenge can and must be met. Quaise Energy and then construct two deep drill holes in 2024. If its approach proves feasible, deep geothermal energy could be deployed extremely rapidly.
The speed with which a covid-19 vaccine was produced showed what the world can do when faced with an emergency. Deep geothermal energy promises to be the equivalent of a vaccine for the climate emergency.
Eugene Linden鈥檚 latest book is Fire and Flood: A people鈥檚 history of climate change from 1979 to the present
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