“An engineering problem that, when solved, solves energy”
VOX, 10-21-2020, David Roberts
- Geothermal may hold the key to making 100 percent clean electricity available to everyone in the world.
- It is also an opportunity for the struggling oil and gas industry to put its capital and skills to work.
- Fun fact: The molten core of the Earth, about 4,000 miles down, is roughly as hot as the surface of the sun, over 6,000°C, or 10,800°F.
- The heat is continuously replenished by the decay of naturally occurring radioactive elements, at a flow rate of roughly 30 terawatts, almost double all human energy consumption.
- The ARPA-E project AltaRock Energy estimates that “just 0.1% of the heat content of Earth could supply humanity’s total energy needs for 2 million years.”
- There are four basic types of geothermal energy technology
- Conventional Hydrothermal Resources- heated water or steam is trapped under an impermeable caprock which is drilled into with a production well. This is the majority of existing geothermal wells today where heat, water and porosity come together.
- Enhanced Geothermal Systems (EGS)- basically drilling into solid rock, inject water at high pressure through one well, fracture the rock to let the water pass through, and then collect the heated water through another well. EGS benefits from hydraulic fracking with benign fluids, so there is little danger of water pollution.
- Super Hot Rock Geothermal- At the far horizon of EGS is “super hot rock” geothermal, which seeks to tap into extremely deep, extremely hot rock. At extremely high heat, the performance of geothermal doesn’t just rise, it takes a leap. When water exceeds 373°C and 220 bars of pressure, it becomes “supercritical,” a new phase that is neither liquid nor gas. You could get more power out of three wells on a 400°C project than you can out of 42 EGS wells at 200°C, using less fluid and a fraction of the physical footprint.
- Advanced geothermal systems (AGS)- AGS refers to a new generation of “closed loop” systems, in which no fluids are introduced to or extracted from the Earth; there’s no fracking. Instead, fluids circulate underground in sealed pipes and boreholes, picking up heat by conduction and carrying it to the surface, where it can be used for a tunable mix of heat and electricity.
- The main problem facing renewable energy is that the biggest sources, wind and solar, are variable. Whereas fossil fuel power plants that run on coal and gas are “dispatchable” — they can be turned on and off on demand — wind and solar come and go with, well, the wind and sun.
- Geothermal power, if it can be made to reliably and economically work in hotter, drier, and deeper rock, is a perfect complement to wind and solar. It is renewable and inexhaustible. It is available almost everywhere in the world