by kragen | 2025-11-18 00:52:09+00:00
I hadn't realized that the IDDP had hit magma! That's very exciting! Obviously I'm very out of date, since that was in 02008.

However, I'm skeptical that geothermal energy can be economically competitive with solar without major innovations in heat engines, no matter how abundant the energy is and how easily you can get that energy to the surface.

https://www.eia.gov/analysis/studies/powerplants/capitalcost... outlines the estimated costs (five years ago) of a 650MW peak ultra-supercritical coal power plant without carbon capture; the total capital cost estimate comes out to US$2.4 billion, which is US$3.70 per peak watt. Of that, I think the only line item that wouldn't be the same in a 650MW peak ultra-supercritical geothermal plant is "Mechanical – Boiler Plant", which is US$905 million, leaving US$1.5 billion, US$2.30 per peak watt. (I'm not even sure you could eliminate even all of that US$905 million in a geothermal plant; some of it might be plumbing you'd also need to pass heat from your downhole heat exchange fluid with the ultra-pure deionized water you use to drive the delicate steam turbine. But let's suppose you could.) Of that US$1.5 billion, US$155.2 million is "Mechanical – Turbine Plant", so the turbine alone costs 24¢/Wp.

But SEIA last year published https://www.seia.org/research-resources/solar-market-insight.... They have a set of cost breakdowns for “turnkey installed price” for power plants, coming in at 98¢ per watt for “utility-scale fixed-tilt”, slightly higher than the previous year and almost half due to about 40¢ for the PV module itself. Residential is at 325¢, with about 20¢ for the PV module. That's even in the US, where the EIA report's estimates were sited, despite the US's prohibitive import tariffs on solar panels from China, which makes most of the world's solar panels.

Mainstream PV modules are now 12.3¢ per peak watt https://www.solarserver.de/photovoltaik-preis-pv-modul-preis... (except in the US), which would drop SEIA's cost estimates from 98¢/Wp to 70¢/Wp, even in the absence of any other cost optimizations in solar farm design.

Now, utility-scale fixed-tilt solar farms typically have a capacity factor of around 20%, depending on latitude, because the sun is below the horizon half the time and somewhat slanted and/or clouded most of the rest of the time, so 70¢/Wp is really about US$3.50 per watt, not counting the batteries. But geothermal typically only has a capacity factor of around 74% in the US https://en.wikipedia.org/wiki/Capacity_factor#Capacity_facto... so US$2.30/Wp is really US$3.10 per watt.

That leaves you 30¢/Wp (74% × ($3.50 - $3.10)) for geothermal exploration and drilling. And if you can reduce the 82% of the solar 70¢/Wp represented by the non-PV-module costs by a little bit, or if you're equatorial enough that your PV capacity factor is 23% or above, that's going to zero or negative. I think the average PV capacity factor in California is something like 29%, though that isn't fixed-tilt and therefore has slightly higher costs.

Also note that the PVXchange page I linked above lists "low-cost" solar panels as having fallen to €0.050/Wp this month, a new historic low, which is 5.9¢/Wp. That's a 50% price decline from two years ago.

Fundamentally I think it's just going to be very hard for 24¢/Wp steam engines to compete against 5.9¢/Wp solar panels. The steam engines have the additional disadvantage that, to get the price even that low, you need enormous degrees of centralization—on the order of a few thousand power plants for the whole population of the US. This requires long-distance electrical transmission lines as well as local distribution lines, which are both substantial costs of their own as well as wasting a double-digit percentage of the energy. Local electrical generation eliminates those costs; you can charge your cellphone or your angle-grinder battery directly from a 5.9¢/Wp solar panel with no more electronics than a couple of protection diodes, not requiring the rest of the 70¢/Wp in the utility-scale solar plant.

This cost analysis is completely indifferent to where the heat to boil the water comes from, so it applies equally well to nuclear power, except for Helion.

The exceptions would be in places where geothermal energy is available and solar energy is either unavailable or very marginal: the surface of Venus, the ocean floor, Antarctica, Svalbard, etc.

Does anyone have a trustworthy estimate of the costs of drilling? Even drilling into cold rocks (for oil) would be a good start, even if hot rocks are more expensive to drill into. The article says that Fervo has raised US$800 million in capital and drilled three appraisal and demonstration wells with it so far, which gives us a ballpark of US$200 million per well. This does not offer much hope that drilling costs will be a minor fraction of the costs of a geothermal plant.

The article unfortunately doesn't enter into this analysis at all.

I am somewhat skeptical of this figure:

> Geothermal energy production in the U.S. at that time [i.e., 02005] was around three or four thousand megawatts.

https://en.wikipedia.org/wiki/Electricity_sector_of_the_Unit... says that geothermal energy production in the US in 02022 was 16.09 billion kWh per year, which is 1825 megawatts. Does that mean that geothermal energy production fell by about half between 02005 and 02022? More likely Rivka Galchen got confused.

It's unfortunate that the article also confuses ground-source heat pumps (thermal energy storage) with geothermal energy sources. It's a common confusion, and it makes conversations about geothermal energy unnecessarily difficult.