[HN Gopher] Geothermal's path to relevance: cheap drilling
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Geothermal's path to relevance: cheap drilling
Author : drocer88
Score : 95 points
Date : 2021-10-26 16:52 UTC (6 hours ago)
(HTM) web link (austinvernon.site)
(TXT) w3m dump (austinvernon.site)
| shireboy wrote:
| 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.
| chris_va wrote:
| Drilling cost is usually estimated as ~depth^2.
|
| 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).
| animal_spirits wrote:
| It's okay to intend a pun every now and then. Take credit for
| your poetry ;)
| avernon wrote:
| Drilling cost is usually estimated for drilling in sedimentary
| rock with assumptions about how casing is run ;)
|
| 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.
| phreeza wrote:
| I am always a bit bearish on geothermal, because the energy flow
| through the earths crust is just so damn low. Per surface area,
| it is about 3 orders of magnitude less than solar irradiation,
| which means that the circumstances in which it really makes sense
| to exploit geothermal are those where you can effectively harvest
| flows from a much larger area, most likely due to convection of
| water or magma. My understanding is that it will never make sense
| for e.g. every house in a suburban setting to have their own heat
| probe and pull energy from that, they will be competing with
| their neighbors and effective energy gained will be negligible.
| Retric wrote:
| It's often less about the heat flow than simply the amount of
| heat contained in that volume of rock.
|
| 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.
| phreeza wrote:
| Thanks that is a great point I hadn't considered. I suppose
| strictly speaking it is not renewable when you use it like
| that, but still pretty clean.
| streamofdigits wrote:
| is surface area a fair comparison? A deep well should be able
| to extract all along its length
| cdeonier wrote:
| How does a deep well extract all along its length? My belief
| was the production well will experience a gradient (so the
| bottom of the well will have the temperature you need), and
| the temperature will drop as you get closer to the surface
| (which also contributes to the calcite scaling problem
| geothermal can experience).
|
| 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.
| streamofdigits wrote:
| assuming you can reach a working temperature differential
| why not continue deeper with the well? From that threshold
| depth onwards you can extract heat along a line segment
| that extends to the ultimate depth (which is pressumably
| dictated by engineering limitations)
|
| caveat: thinking like a physicist, not an engineer :-)
| Scoundreller wrote:
| Sounds like the systems would work best where you have both
| heating and cooling loads throughout the year.
|
| 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.
| api wrote:
| The great thing about geothermal is that it's 24/7 dispatchable
| without expensive added storage. That would make it a great
| companion to solar and wind energy in place of natural gas.
| Even 5-10% of total power on an absolute basis from geothermal
| could be more valuable than it appears by adding stability to
| the grid without fossil fuels. Drilling into geothermal would
| make sense if it were cheaper than adding grid-scale battery
| storage for nighttime use.
|
| 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).
| goldenshale wrote:
| Yeah, per-house is probably never going to make sense, but
| larger scale operations where they can use hydraulic fracturing
| techniques to expand the surface area could be the solution.
| They call these Enhanced Geothermal Systems, and basically they
| frack the rock between two well bores to try to maximize
| connectivity and surface area.
| brtkdotse wrote:
| I'd say more than half of single family houses in Sweden are
| heated by geothermal heat pumps, so it's _very_ viable.
| WarOnPrivacy wrote:
| From 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 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.
| Scoundreller wrote:
| 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?
| energ8 wrote:
| 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
| WarOnPrivacy wrote:
| I've only seen winter water heating in geothermally cooled
| homes.
| cmrdporcupine wrote:
| I looked into this here, and couldn't find a company to do a
| heat exchanger hookup for my pool, but also... at least here
| in the great lakes area, when you want to heat your pool the
| most is the time when your AC isn't really running (spring /
| fall), and you don't care about heating your pool as much
| when the AC is blasting. So while the pool may offer some
| efficiency gains to the AC, the waste heat from the AC
| doesn't help much with the pool.
| beerandt wrote:
| Swimming pool temperatures in the south easily get over 85,
| and sometimes 90 degrees in the summer.
|
| We always bought big blocks of ice to throw in the pool in
| the summer to cool it off.
| goda90 wrote:
| I'm reminded of this video talking about cooling the London
| Underground. Since it's running through clay, it's very well
| insulated and the ground around it is warming year over year.
|
| https://www.youtube.com/watch?v=hQo6_GkITe0
| cdeonier wrote:
| Cheap drilling would be a large boon for geothermal, considering
| the cost of surveying/exploring/drilling is > 50% of the cost of
| the development of a geothermal 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...
| [deleted]
| Accujack wrote:
| 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.
| cdeonier wrote:
| 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 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?
| briffle wrote:
| My old University powers, heats, and cools itself with
| Geothermal wells that are at 195F, not sure about the 300C
| either. (and clears snow/ice from sidewalks and outdoor
| staaircases) The college also sells extra power to the hospital
| next door. (it makes around 2MW with a binary cycle plant)
| https://urbanecologycmu.wordpress.com/2016/11/01/geothermal-...
| aaron695 wrote:
| The USA is the geothermal king, top of the world, so it'd be
| exciting for them to up their game, no one else is.
|
| The depths they are talking about here would be in the top 10
| deepest holes _and_ they need to go sideways, unheard of, so it
| 's pushing technology which is also exciting.
|
| Geothermal doesn't rely on supply chains for fuel so the military
| might help with funding.
|
| I expect it's not economical, but it's a cool thing to try, bring
| back 50's science, we need to continue fighting the Woke.
|
| This is just a 'study' which generally is code for won't happen,
| but it would be good if it did, good on Texas -
| https://www.thinkgeoenergy.com/sage-geosystems-to-explore-ge...
| fouc wrote:
| This seems to be a sequel to
| https://news.ycombinator.com/item?id=27775927
|
| i.e. "Is Geothermal Really Going to be a Thing?"
| https://austinvernon.site/blog/geothermal.html
| Factorium wrote:
| Are 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 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.
| generalizations wrote:
| I'd be more interested in residential heat pumps if there were
| also heat engines that were feasible at that scale. Seems like
| it needs to scale up by at least an order of magnitude though,
| before electricity can be generated efficiently.
| uuddlrlr wrote:
| 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.
| infogulch wrote:
| 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 experience both, like the midwest US. Perhaps
| using the pumped water as a stable, biased thermal source for
| a reversible heat pump.
| Freak_NL wrote:
| This is already being done in some countries (e.g., the
| Netherlands), but it is just a (necessary) part of the puzzle.
|
| 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.
| turtlebits wrote:
| Yes, ground source/loop is considered geothermal.
|
| The problem is that you need to a dig up a large area of
| possible natural vegetation to do it.
| serpix wrote:
| I had my borehole going straight down about ~150m deep from
| right next to the side of my house. I moved the lawn right
| next to the pipes.
| [deleted]
| rudedogg wrote:
| You can go vertical instead of horizontal
| wkearney99 wrote:
| We have two 350' wells for loops at our house in Maryland.
| Tripled square footage in the new house and energy costs
| stayed the same. Moved from natural gas for heat, but still
| have it fir backup (which in a decade has never been
| needed).
| brtkdotse wrote:
| Geothermal heat pumps are very common in the Nordics. It's a
| one day operation, they come in, drill a 150M hole and run a
| brine loop hooked up to a heat pump. Sorts the heating and hot
| water for a 180 m2 house above the attic circle with less than
| 7000 kWh per year.
| serpix wrote:
| that is a ground-source heat pump as the heat energy is
| mostly from ambient solar. But yes very common and I used to
| have one in my home before I moved away. It cost practically
| nothing to keep the house at t-shirt temperature during -25c
| cold weather snaps.
| larsalmen wrote:
| No it's not. The bore-hole is lined with a outer steel pipe
| until the drill hits bedrock, keeping it very much
| insulated from the ground. And the upper-most part of the
| energy-well that's lined is considered inactive, and is not
| counted in the "150 m deep energy well".
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