Geothermal's path to relevance: cheap drilling
austinvernon.site
austinvernon.site
I don't understand the articles goal of 300C target, though. While some types of geothermal plants do require temperatures that high, binary cycle power plants can use lower temperatures (130C) [1], which seems to open up more area for geothermal development since we expect most gradients between the surface and bottom of the crust to be ~2.5-3.1C / 100M. A lower temperature requirement would in turn allow you to drill less deep, which could consequently also decrease drilling costs.
Another thing the article doesn't mention: another interesting approach (aside from improving the technology, like drill bits) is with financing innovation. There have been / are government programs to de-risk the exploration/drilling cost by reimbursing the costs of drilling (80% for failed wells, for example) which also likely adds well data that could better characterize the underlying geothermal resources in regions (which would allow more accurate future development).
Really glad to see a deeper dive on geothermal though; its non-intermittency is a valuable characteristic separating it from other renewables that we're currently favoring (solar/wind). Because we generally break down energy generation to LCOE, it omits advantages like uptime of the renewable resource.
[1] https://www.energy.gov/eere/geothermal/electricity-generatio...
Power generation is already accomplished with lower heat cycles (e.g., binary plants mentioned earlier would probably use a rankine cycle to deal with the low heat), though we'd expect those power plants to have less nameplate capacity than something like a double flash-steam plant.
I think you're correct you'd get more efficiency with higher gradients, but I don't understand what's limiting about the lower temperatures. Is it economics?
The big breakthrough seems to be making drill bits out of a composite material formed from diamond and tungsten carbide.[1] One of their bits lasted through 25km of drilling. (Not one hole, re-used for multiple shallow holes.) That's encouraging. The geothermal people only need to go down 10km. Being able to do much of the job without backing out the drill string, one pipe section at a time, to change the bit is what seems to yield the cost estimates in the original article.
The next problem is to get everything at the down-hole end up to that level of reliability. Which is why the author talks about seal problems in mud-powered drilling motors. For the geothermal application, they just want to drill straight down, so they don't need all the fancy stuff used for slant and horizontal drilling.
So there remain some grungy, hard, and important problems to solve, like a seal material that will work better at high temperatures. Such things exist.[2]
This is encouraging.
The article points out that this isn't like hunting for oil and gas pockets; if you have roughly the correct overall geology, there will be hot rock down there anywhere you drill. This upsets some financial models, where drilling the first well in a new area is more like a VC-funded high-risk high return project. You're really drilling for the valuable info that oil or gas is there, not for the oil or gas from the exploration well. Deep geothermal is going to be dull, boring (literally), usually successful, and profitable over a long period but not in the short term. Great for regulated utilities.
Heat exchange pumps work with much lower temperature gradients which is great for heating a building or some water since you don't need to drill that deep. But it's not very efficient for generating electricity. There actually are some companies that can use heated water in your boiler as a battery and generate electricity from it but that is more from the point of view of using the energy you are storing anyway instead of letting it cool down. So a lower efficiency is acceptable for that.
The open question mark for geothermal is if the cost of drilling will ever be low enough to compete with solar and wind + batteries. Solar and wind are a lot cheaper per kwh but of course intermittent. There are various ways of fixing that that basically involve using some form of battery. You can think of geothermal as a battery where the fully charged battery simply is our planet. Nice if you can get to it but not necessarily cheap enough compared to other ways to store energy. Getting to it involves expensive drilling projects and operating a lot of plumbing to get energy out of it.
An example of a battery that is pretty cheap is a thermal mass based batteries. It is basically the same material (i.e. rocks) plus some insulator. Given enough mass, you can store quite large amounts of energy for very long and there are some companies starting to do exactly that. Several companies are working on those. It's all going to boil down to cost per kwh in the end. wind and solar converging on about a cent per kwh. Batteries tend to be more expensive but still cheaper than burning gas/coal. Geothermal sits somewhere in between. It could be cheaper in some places long term. But then batteries are also getting cheaper.
Its much less sexy than a giant plant connected to a magma stream, but if we made these routine for all new suburban constructions, alongside passivhaus standards, we could eliminate residential fossil fuel connections for huge sections of the Western world.
Like another commenter mentioned, we could even have communal systems for individual streets, drilled beneath roads, to service townhouses and apartment blocks.
You can run the ground-source for heating and cooling, alongside a single wall-mounted air conditioner for dehumidification in the summer.
https://www.dlsc.ca/borehole.htm
It gets up to nearly 80C, but took a few years of operation to get there.
The website covers it really well and I'd recommend checking it out.
They heat it with solar energy, and pull out heat during the winter. I wonder how well this would work to provide both AC/cooling during the summer and heating during the winter in climates that experience both, like the midwest US. Perhaps using the pumped water as a stable, biased thermal source for a reversible heat pump.
Check out this guy, he grows oranges in Nebraska in thermal heated greenhouses. As I recall he talks about cooling as well. He has tubes around 8 feet under the ground running around the yard.
If there is a difference in the temperature, then the heat can be moved around. However, that doesn't mean you can run the entirety of the heating for the house in the winter off of the heat battery.
https://dnr.wisconsin.gov/topic/Wells/Geothermal.html
> Geothermal works on the principal of using the earth's natural underground temperature and a geothermal heat pump unit to provide heating in the late fall, winter and early spring and cooling in the late spring, summer and early fall. In Wisconsin, the average underground temperatures range from about 52 degrees in the south to 42 degrees in the north. Below about 20 feet in depth, the influence of surface temperature variations begins to dissipate rapidly and becomes the average of all surface temperature values.
Note the heating in the late fall and early spring and cooling in late spring to early fall. The Canadian one is stuffing more heat into the battery which gets it above where it is efficient for cooling in the summer.
Aside - the wikipedia article for the Canadian one - https://en.wikipedia.org/wiki/Drake_Landing_Solar_Community
> On October 5, 2012 the DLSC set a new world record by covering 97% of space heating needs with solar thermal energy. In the 2015-2016 heating season, 100% of space heating needs were met with solar energy.
The location is just a bit south of Calgary ( https://www.google.com/maps/place/Drake+Landing,+Okotoks,+AB... )
For 2020, Calgary had 4835 heating degree days based on 18°C and 72 cooling degree days (2021 has had 174 cooling degree days)
https://calgary.weatherstats.ca/charts/cdd-yearly.html and https://calgary.weatherstats.ca/charts/hdd-yearly.html or https://portfoliomanager.energystar.gov/pm/degreeDaysCalcula...
Using that last one It's provided in °F too. hdd: 8780 °F and cdd: 117 °F
Going back to Wisconsin for the midwest datapoint... https://www.aos.wisc.edu/~sco/clim-history/7cities/madison.h... - though this data is in °F. The ten year average for heating degree days is 7200 in °F. The ten year average for cooling degree days is 620 in °F.
So... Calgary compared to Madison:
* 8780 vs 7200 hdd (65 °F)
* 117 vs 620 cdd (65 °F)
Based on this, and that there is still a lot more hdd than cdd - it would probably be more worthwhile to try to offset the heating costs on the heating degree days than the air conditioning costs on cooling degree days.
And just for comparison, Houston, TX is has 1000 hdd 65°F and 3444 cdd 65°F. San Francisco is hdd 2467 °F and 190 °F for cdd.
As another note that heating and cooling costs don't scale linearly with heating or cooling degree days.
https://www.researchgate.net/publication/326121453_Drake_Lan...
They get around 2000 GJ/year out of the storage, so 555 MWh, so 10.7 MWh/home.
Estimated current price of the system 4 millions USD (excluding one off 3 millions USD R&D costs) so 77000 USD/home.
7.2 USD/kWh of yearly thermal storage.
LFP battery is probably currently below 100 USD/kWh, so for this use the thermal battery is 10x cheaper.
The existing housing stock needs solutions too, and installing heat pumps in older terrace housing is far from ideal due to noise pollution, cost, lack of space, and a limit to what can be done in terms of insulation. Geothermal plants can be used to provide district heating, which is a much better fit for certain types of houses.
The problem is that you need to a dig up a large area of possible natural vegetation to do it.
That said, my residential options for energy are rich. I have the Chesapeake Bay 80ft from my current heat pump. So I could theoretically implement a plethora of heat exchange mechanisms taking advantage of that. Wind power is feasible except for the footprint. Yesterdays 35kt gust may have been a bit much tho. Have waves that could power things also. And mostly unobstructed roof which could host solar. Tidal range is not very large, and current is greatly reduced near shore.
The principle difference, as others have pointed out, is that when converting heat to mechanical energy, or for electrical generation (mechanical + a generator), efficiency greatly increases as the temperature gradient between the hot and cold ends of the process increases.
There's still a lot of utility from lower-grade heat, for space heating (to about 24C/75F), water (about 60C/140F), and cooking (175C/350F). Even a partial boost can assist with other heating methods.
But for large-scale electrical generation, high temperatures, well above boiling point, are what are needed.
Community thermal energy storage is a thing. That can use either geological formations or specially-constructed insulated structures. Thermal potential may be stored as a hot or cold medium, for heating or cooling.
A ground-source heat pump is a heat pump: a machine which consumes usable energy in order to move heat from a LOW-temperature heat source to a HIGH-temperature heat sink (a process which would not occur naturally without energy input due to the 2nd law of thermodynamics).
The goal is to pump water down one, and extract it from the other borehole and then use a heat exchanger to pull the anticipated 160F to 180F temperature to provide heat to the entirety of the campus.
It's similar to the University's Lake Source Cooling system, which they use the naturally cold water temperature of the local Cayuga lake. At the 250' depth they draw the water in, it's a constant 39F year-round. The cooling system is used to provide chilled water to all the buildings, and a few thousand homes, removing the need for standard air conditioners.
The Lake Source Cooling system has saved the university 20 million Kwh a year, an 85% reduction in power usage, since it was made in 2000. It's hoped that the Earth Source Heat project will have the same kind of impact on the energy necessary for heating.
There are a lot of unknowns. Nobody has drilled a borehole so deep in this area before because there hasn't been a reason to do it before.
[1] https://earthsourceheat.cornell.edu [2] https://fcs.cornell.edu/departments/energy-sustainability/ut... [3] https://fcs.cornell.edu/departments/energy-sustainability/ut...
So, a 1km geothermal well? Break even, and you are limited to only a few places in the world.
A 5km geothermal well (needed for broad power availability)? 25x the cost...
So, sure, if you can get a 25x cost reduction in an already cutthroat industry, all power to you (no pun intended).
It is possible that drilling 30,000' of granite has conditions that make the estimation model irrelevant. 5 km isn't really deep enough, anyway. My next post will cover the thermo. It is pretty dang hard to get down to anything approaching $50/MWh. Definitely need more than cheap drilling.
As an example Solar energy as it exists now would have been ridiculed in the late 80s as something that would never be cost effective.
It was the massive subsidies/tax rebate schemes in Germany and later on in other EU countries that open the window for manufacturers to produce at scale and make it the cost competitive source of energy that we see now.
I mentioned this in a previous comment on a biomass thread. We would be better off with EU funds allocated to solving the massification of geo-thermal or the massification of small vessel nuclear reactors, than to continue to pour money into converting coal plants into natural gas plants and opening up new biomass furnaces.
Natural gas and biomass are just a means for governments to play with statistics on 'renewable' pie-charts. Until we solve the problem of mass energy storage of intermitent renewables or a far away nuclear fussion we need to start _now_ deploying non-carbon emitting non-intermitent energy generation.
We have to be realistic and accept that we need to find a means of replacing coal and not all regions have the resources for hydro-generation, geo-thermal is the next best bet considering the time and friction it would take to roll out more nuclear for example.
Florida geothermal systems pull cool water from the aquifer, use it for A/C and return it via a 2nd well. They're about the only wells that water management districts will rubberstamp.
Geothermal cooling (in FL) becomes cost efficient above 15k-20k sq ft (based on my 2010s exp). That led me to an idea that neighborhoods could be cooled by small geothermal utilities. I wonder about increased heat energy down the line but I've seen a doz+ chillers work efficiently, from one 4" well. On a larger scale, downstream heat buildup might be mitigated via a more distributed water system.
Do Floridians at least install heat-pump pool heater systems indoors so the cold goes indoors?
We always bought big blocks of ice to throw in the pool in the summer to cool it off.
Also, I think a lot of wells add concrete casing (or metal, as indicated in the article) around portions of the well, which would prevent extraction around those zones of the well.
caveat: thinking like a physicist, not an engineer :-)
For your example: A 1/2 acre home is 2023 m2, 1kg of rock is ~2000j/degrees Celsius, 1 cubic meter of rock is ~2500 kg, down 1k = ~2000 j * 2500 * 2023 * 1000 / 60 / 60 / 1000 ~= 2,800,000 kWh per degC. If you’re talking 1kw of heat on average from that rock you only drop 1 degree after 300 years.
Of course 1km is a fairly deep, but if you’re using a heat pump chances are you’re averaging much less than 1kw over the entire year.
Much higher ground temperatures are of course useful to create electricity, but such systems are best centralized not used for single family homes. Also, as a centralized system it’s volume is arbitrary. In the north that 6-25C can still make heat pumps vastly more efficient, but you’re extracting energy and cooling that down over time. Which is why it is relevant to the discussion.
Though usually you’re pumping more heat out of the ground than in. There must be a perfect place for these systems where it’s well balanced.
The energy flow from the Earth's core is small in a percentage sense, but keep in mind that humanity's energy use is actually tiny when measured on planetary or cosmic scales. Here's the total solar surface area we'd need, for scale:
https://www.axionpower.com/knowledge/power-world-with-solar/
Cover much of New Mexico with solar PV and you could power all of global industrial civilization (ignoring storage).
Here's a few answers:
https://earthscience.stackexchange.com/questions/2302/can-th...
i.e. "Is Geothermal Really Going to be a Thing?" https://austinvernon.site/blog/geothermal.html