Anecdotally, I looked into this when building our house, and can confirm - the bulk of costs was drilling, and it was expensive. When I did the math at the time, the cost of ground source heat pump over air source heat pump was several times more. Energy bills would be much less, but the payoff was around 20 years, assuming the unit lasted that long.
Geothermal's path to relevance: cheap drilling
41–50 of 77 posts
Re: Geothermal's path to relevance: cheap drilling
#42From the article: Traditional geothermal wells target rare hydrothermal resources 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…
What I always find dumb is when I see a swimming pool and an air conditioner without the two being one system. Do Floridians at least install heat-pump pool heater systems indoors so the cold goes indoors?
It'd be somewhat custom, but there is a commercial heat exchanger (https://www.hotspotenergy.com/pool-heater/) that an HVAC tech should be able to install
Re: Geothermal's path to relevance: cheap drilling
#43Could there be a completely novel way of digging ? Maybe with Laser ? maybe a chemical process ? or a high pressure water cutter ? what if you could cut small block of stone in the hole without using so much energy reducing it to sand ?
Re: Geothermal's path to relevance: cheap drilling
#44Could there be a completely novel way of digging ? Maybe with Laser ? maybe a chemical process ? or a high pressure water cutter ? what if you could cut small block of stone in the hole without using so much energy reducing it to sand ?
I imagine part of the challenge would be undercutting the resulting cylindrical rock (still attached to bedrock at the bottom). Also there's the significant issue of removing the cut rock from 10k feet below ground. This is much easier to do with sand which gets picked up in a mud slurry.
Re: Geothermal's path to relevance: cheap drilling
#45Earlier quoted context omitted.
I think the 300C target is to support the article's assertion that geothermal could replace e.g. nuclear plants. Geothermal for heating can work well with a lower approach temp, but industrial processes/power generation needs a higher differential.
Could I get your help understanding your statement "industrial processes/power generation needs a higher differential"? Why does geothermal need a higher differential for power generation? 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 capa…
The higher the differential the higher the efficiency of heat to electricity transformation. If I remember correctly it's a big efficiency gain between 200C and 300C. From economic side of things, more bang for the buck.
Re: Geothermal's path to relevance: cheap drilling
#46Earlier quoted context omitted.
There's a 52-home community in Alberta that provides ~all of their winter heating by storing heat in the ground throughout 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.
Wow that's amazing! Basically a community-sized thermal battery. I find the design curious; they use insulation around the outside, but still bored 144 holes on the inside, I guess the bottom is just left alone as solid rock. 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…
Yes I think that would work.
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.
Re: Geothermal's path to relevance: cheap drilling
#47Could there be a completely novel way of digging ? Maybe with Laser ? maybe a chemical process ? or a high pressure water cutter ? what if you could cut small block of stone in the hole without using so much energy reducing it to sand ?
They've tried a lot of these things, if not all of them. A colleague of mine in grad school was working on optimally using flame jets to crack the rock ("thermal spallation drilling").
Re: Geothermal's path to relevance: cheap drilling
#48Earlier quoted context omitted.
There's a 52-home community in Alberta that provides ~all of their winter heating by storing heat in the ground throughout 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.
Wow that's amazing! Basically a community-sized thermal battery. I find the design curious; they use insulation around the outside, but still bored 144 holes on the inside, I guess the bottom is just left alone as solid rock. 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…
> 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.
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.
Re: Geothermal's path to relevance: cheap drilling
#49Are ground-source heatpumps considered 'geothermal'? 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 beneat…
No, this is totally irrelevant to anything in the article, except in the sense that both pertain to thermal energy and the earth. They have nothing else in common. The difference is not just a matter of sexiness; you can't run a factory, a computer, or a car off a ground-source heat pump, because heat pumps consume energy; they don't produce it.
Re: Geothermal's path to relevance: cheap drilling
#50From the article: Traditional geothermal wells target rare hydrothermal resources 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…
This is totally irrelevant to anything in the article, except in the sense that both pertain to thermal energy and the earth. They have nothing else in common. You can't run a factory, a computer, or a car off a ground-source heat pump, because heat pumps consume energy; they don't produce it. A seasonal thermal store like what you're talking about is only slightly less irrelevant, because while in theory it could be an energy source, the energy available is orders of magnitude too small.