Shallow geothermal works fine for heating. And you can use the ground as a heat sink. But if you want to generate power, you need to get down to where temperatures can boil water. That's deeper than most oil wells. Fervo Energy claims to have found 270C at 3350 meters well depth. That's progress.
> if you want to generate power, you need to get down to where temperatures can boil water. That's deeper than most oil wells.
That’s going to be very dependant on location.
Here in NZ there are regions where water is boiling at surface level.
According to the below, 18% of our power is produced with it.
https://www.eeca.govt.nz/insights/energy-in-new-zealand/rene...
"New Zealand has an abundant supply of geothermal energy because we are located on the boundary between two tectonic plates. ... Total geothermal electricity capacity in New Zealand stands at over 900 MW, making us the fifth largest generator of geothermal in the world. It has been estimated that there is sufficient geothermal resource for another 1,000 MW of electricity generation."
That's not all that much. That total would be about equal to the 75th largest nuclear plant in the world.
Good sites where high temperatures are near the surface are rare. California has a few, but no promising locations for more.
> That's not all that much
May not be much in world terms but here in NZ national demand maxes out at around 5.5GW so bringing another GW on stream would be quite handy. Most of the geothermal is a lot closer to Auckland* than our hydro is so so that would be another positive aspect.
* Auckland has 25% of the population so a corresponding amount of energy has to be pushed its way.
> That's not all that much.
We don’t have many people. It gets worse’s though, we burn coal and are looking to fund a gas terminal. We have abundant other ways of generating power and subsidise an aluminium smelter for some reason.
Coming up next, data centres.
‘Clean, Green New Zealand.’
Is there any earthquake risk from drilling near tectonic plates?
You brought the conversation in a circle, since the point of this new technology is the geology you speak of is rare.
There are also places in the US with boiling water at the surface. I live near one of those places so always curious about geothermal. There's a spot near my house in a creek bed where snow always melts even in deep winter so apparently I have some potential heat source. Our well water is cold though.
Not near me, but hot water spring, rivers and beaches made for a nice soak every now and again.
Turning them all into power plants would be a shame, but there is plenty of space for both.
> But if you want to generate power, you need to get down to where temperatures can boil water.
Why is that the case? Can't you go down to where it's like 70-80 deg C and close the gap using heat pumps? Yes, you need to put some energy in, but I would expect that the whole process would still be energy-positive at some temperature that's lower than 100C?
I think this looks interesting, but still very early stage. The “150 GW revolution” sounds more like theoretical potential, not something we will see soon in real deployment.
Main problems: drilling is still expensive, managing induced seismic activity is not trivial, permitting can take long time, and you also need transmission infrastructure. Also not yet proven that companies like Fervo can scale this in reliable and low-cost way.
Nope. To efficiently tap geothermal energy, you need to boil something but not necessarily water. Isopentane, for example, boils at 28º at standard pressure, so they pressurize the secondary loop to raise the boiling point close to whatever the primary loop temperature is.
The idea that geothermal only works well at steam temperatures is outdated 20th-century thinking.
But the energy in boiling isopentane would be less right?
Yes, the efficiency is worse, but as is also the case for solar power you need to get used to not caring much about efficiency. It is nuclear energy where the primary side is provided free of charge. The Carnot efficiency is almost without relevance.
In geothermal there is still a lot of interest in efficiency and exploring different working fluids because binary systems now have efficiencies of 10-20%. That is why you see companies like Sage Geosystems working on developing / deploying supercritical CO2 turbines to try and boost practical power densities.