Does the article describe how the heat gets from the mound to the houses or buildings it plans to heat, or factor in the cost of that?
Naively, I'd assume that would like 90% of the cost.
I know that physics is under no obligation to be intuitive, but it's also surprising to me that it's so easy to heat and keep dirt this temperature (600C / 1100F) throughout Winter, and I didn't see how that piece worked either, though I'm willing to assume that part is figured out and factored in.
Dirt keeps a constant temperature year round quite close to the surface that’s a ~60 degree difference between summer and winter in many areas. So 600c would just be a tradeoff between depth, heat loss, and thermal efficiency. However, what they aren’t saying is electricity > heat > electricity is quite lossy and even just using the heat directly is far less efficient than a winter heat pump.
More realistic end to end numbers are likely in the 30% range which means summer electricity needs to be vastly less valuable than winter energy before you nominally break even and start repaying the investment. Further you instantly lose all the electricity required to heat the mound up to working temperatures. IE: If you can only operate between 550C and 650C then going from 20C to 550C needs to happen before you can extract any energy and you don’t get that investment back. On the other hand if you’re a chemical plant that needs 200C things start looking a lot better.
A 10 ft pile of dirt (assuming 10 ft between heat exchanging pipes and the outside air) has an R value of 24 to 96, which is extremely significant.
I expect there would still be notable losses trying to keep it at 1100F indefinitely, but 10 ft of dirt will have insulation values approximating many feet of fiberglass insulation.
You’d want a very large mass to heat however, scaling matters a lot. You’d want the ratio of surface area to mass to be as small as possible, and that means as large a volume with as thermally dense a material as possible inside. Surface areas increases by the square, while volume increases by the cube.
Also, no matter what you do, you would eventually cook whatever was at the surface or underground, so don’t do this where you want trees - or where there are underground coal seams
Heat loss inside of dirt is so incredibly slow it's hard to wrap your head around. One fact that I find helps is the fact that after an entire winter of extremely cold temperatures, you only need to go down 10 ft or so before you hit the average annual temperature. 4 months of winter buffered by 10 ft of ground!
Obviously there is incredible potential to this even if you just keep the energy as heat. The amount of electricity we use on heating and air conditioning is huge. If we could just create hot and cold piles or underground wells or something that we could tap into 4 months later when the temperature has changed, you would have completely solved heating and cooling.
Really excited by companies looking into this and wish them the best of luck!
Is this because of geothermal energy leaking upwards? If so, it's not the dirt, it's the geothermal energy.
There are 2 gradients: The surface gradient is what I mentioned about and its quite steep(only a few meters to drop tens of degrees). After that, you reach approximately the average annual surface temperature, but do continue to get small drops due to the geothermal gradient. The geothermal gradient is relatively shallow - you need to go down a thousand meters to see tens of degrees drop.
No. The heat energy comes from the sun. Power flux from geothermal is measured in milliwatts per square meter, while the sun can provide more than a kilowatt during the day. So real geothermal heating is negligible at the surface. That's why the temperature a few feet down equals the average annual temperature at the surface.
The only reason people call this "geothermal" is because marketing people realized that this sounds more impressive than "ground source heat pump". It really should not be called "geothermal", because that's something very different. Real geothermal involves extremely deep drilling (not feasible for residential use) or unusual geology.
Geothermal heating > Extraction (GCHE, GHX) || Ground source heat pump (GSHP) https://en.wikipedia.org/wiki/Geothermal_heating
GSHP: Ground source heat pump: https://en.wikipedia.org/wiki/Ground_source_heat_pump
Heat pump: https://en.wikipedia.org/wiki/Heat_pump #Types :
> Air source heat pumps are the most common models, while other types include ground source heat pumps, water source heat pumps and exhaust air heat pumps.
Heat pump > Types:
- SAHP: Solar-assisted heat pump; w/ PV
- acronym for a heat pump with TPV thermophotovoltaic heat to electricity:
- acronym for a heat pump with thermoelectric heat to electricity:
- TAHP: Thermoacoustic heat pump
- ECHP: Electrocaloric heat pump
Electrocaloric effect > Electrocaloric cooling device studies: https://en.wikipedia.org/wiki/Electrocaloric_effect#Electroc...
GCHE, GHX: Ground-coupled heat exchanger: https://en.wikipedia.org/wiki/Ground-coupled_heat_exchanger
Acronyms! From https://www.google.com/search?q=Ground-coupled+heat+exchange... :
HGHE: Horizontal Ground Heat Exchanger: a GCHE installed horizontally e.g. in trenches
VGHE: Vertical Ground Heat Exchanger: GCHE installed vertically e.g. in boreholes or piles.
PGHE: Pile Ground Heat Exchanger: A specific type of GCHE that is integrated into the structural foundation piles of a building.
Solar chimney or Thermal chimney: https://en.wikipedia.org/wiki/Solar_chimney
OTEC: Ocean Thermal Energy Conversion: https://en.wikipedia.org/wiki/Ocean_thermal_energy_conversio... and the ecological salinity gradient:
FWIU archimedes spiral turbines power some irrigation pumps in Holland at least. Is there an advantage to double/helical archimedes spirals in heat pumps if/as there is in agricultural irrigation?
Screw turbine: https://en.wikipedia.org/wiki/Screw_turbine
Noiseless double-helical Achimedes spiral wind turbine on a pivot like a pinwheel: Liam F1 average output with 5m/s wind: 1500 kWh/yr (4.11 kWh/day); Weight: ~100 kg / ~220 lbs; Diameter: 1.5 m / 4.92 ft
What about CO2 and heat pumps? Would a CO2 heat pump make sense?
Absorption Heat pump (AHP) https://en.wikipedia.org/wiki/Absorption_heat_pump
Adsorption Heat pump (AHP)
CO2-Sorption Heat Pump: a Adsorption Heat pump (AHP) that uses CO2 as the adsorbate.
NISH: Nano-Ionic Sorption Heat Pump; with e.g. sustainable hydrogels
Is it better to just recover waste heat from other processes; in a different loop?
LDES heat pump
Supercritical CO2 heat pump
Aerogels don't require supercritical drying anymore,
There's also buoyancy. The pyramid builders may have used buoyancy in a column of heated bubbly water to avoid gravity, in constructing the pyramids as a solar thermohydrodynamic system with water pressure.
That’s not entirely insulation. Some of the heat flows upward toward the surface during winter and some warmth flows downward during summer.
> If we could just create hot and cold piles or underground wells or something that we could tap into 4 months later when the temperature has changed, you would have completely solved heating and cooling.
Geothermal heating and cooling already exists. It’s semi-popular in some areas. It can be expensive to install depending on your geology and the energy savings might not compensate for that cost for many years. Modern heat pumps are very efficient even if the other side is exposed to normal outdoor air, so digging deep into the earth and risking leaks in the underground system isn’t an easy win.
Start getting into permafrost though where the cold is more constant and that cold layer gets deeper.
I can imagine that there's a lot of total energy in the dirt 10 feet down. But once you've tapped the energy near your well, how long does it take to replenish? How long until the immediate vicinity reaches equilibrium with the surface?
He is talking about storing the heat in the dirt and he gives good economic reasons for that.
Environmental exchange would be limited to the interface between the storage tank and the surrounding soil.
It should be orders of magninitude more efficient to transfer energy intentionally than what would be lost to the environment.
You put pvc pipes into a hill of dirt that is covered by a plastic sheet or other waterproof membrane; during hot summer months you use a small fan to put heat into the pile; during winter the heat moves from the dirt to the house.
He is talking about electrically heating very large amounts of dirt to temperatures of 600C or more. Your PVC tubing approach is talking about 50 times smaller swings.
But depending on your definition of this, it's been around for hundreds if not thousands of years. People used to cut ice out of frozen lakes and store it in underground basements for year-round cooling. And in arid climates they have windcatchers [1] and other techniques where they store the nighttime cool for usage during the day, or these [2] to store or even create ice, all without using electricity.
[0] https://en.wikipedia.org/wiki/Seasonal_thermal_energy_storag...
We already do, in a way: septic tanks
The application here is big, slow annual oscillations. Slow charge, slow discharge.
I'm sorry, but you write this as if that's nothing. Making a 10 foot hole is a massive amount of energy being spent. It's a massive amount of weight as 1 cubic yard of dirt is roughly one ton. In 10 cubic feet, that's roughly 3.5 tons. I say this as someone that moved 6 cubic feet of dirt by myself with a shovel and a wheelbarrow.
So to think of 10 feet of dirt as a slow insulator would have to be one of the worst insulators out there.
https://en.wikipedia.org/wiki/Drake_Landing_Solar_Community
We (USA) could have 80% of our Northern homes off fossil fuel and electric heat for less cost if we were a little more forward thinking and willing to work together.
But after nearly two decades they're decommissioning because the one-off components needed too much NRE to refurbish. If we all adopted this it'd be cheaper than what we pay today and zero greenhouse gas emissions. It'd finally make living in the temperate climates more climate-friendly than the warmer latitudes.
it's really depressing to read this and deep down immediately know: well so that's never going to happen then.
This is literally what ground-loop heatpumps are doing. The ground loop is used as an energy source in winter, and since water is always at 0C, the heat pump efficiency can always be around 500%. And vice versa in summer.
Surprisingly, that's only equivalent to about 10" of polyiso rigid foam.
What this project is really taking advantage of is the super cheap thermal mass. Dirt has about a quarter of the specific heat of water, but it is, literally, dirt cheap, and much easier to keep in place than a liquid.
The net is dirt wins by a factor of 2.5.
> There is an efficiency penalty converting back to electricity; round-trip efficiency is 40%-45%, but sometimes the steady supply of electricity is worth it.
I wonder if it has to be the same kind of sand, or could be some that we neither have another use for, nor would damage any ecosystem (too much).
Sand batteries don't need sharp sand.
In a situation where you have a lot of energy generation that would go to waste, storing it in a system with low round trip efficiency could be better than losing it.
For planned installations where the generation cost is nontrivial (like a solar install) then increasing the generation to compensate for poor battery efficiency isn’t as easy of a decision.
The power to gas is also carbon neutral, even negative depending on what you decide to do with the natural gas (if you don't burn it for power but use it for industrial chemistry, you get some sequestration out of it).
Meanwhile multiple grids are now paying renewable to curtail, because guess what, the variability is correlated (it's the exact same damn mathematics we used to fuck up the entire global economy in 2008, which is why I'm so surprised people are handwaving that too, but whatever). If you want to minimise cost without relying on gas to save you on dark still days, you want a cheap use for the surplus, round-trip be damned.
Batteries are already economical in most grids where they can arbitrage daily prices of 0-10c during the day to 10-30c during the night, with the occasional outlier event contributing dollars per kwh.
They will never load-shift across seasons, agreed, but for daily loadshifting they are already economical, and being 90%+ efficient (and very simple/easy to deploy and scale) is part of why they're popular. It opens up power shifting opportunities that aren't just daytime solar too.
And when electricity is in essence too cheap like with solar and wind it can be, losing half in efficiency actually doesn't matter too much.
Practically speaking, you're probably not going to get 1000s of years out of any storage method. There's just too much stuff that breaks down.
Heck - a lot of historic dams are in the low hundreds of years old and are experiencing serious problems.
IMO, the shorter lifespan of batteries isn't that big of a downside as long as the "bad" batteries can be mined for raw materials eventually.
Heat pumps do magic by changing the pressure at which a working fluid changes phase, so you can boil the fluid over here, have it absorb an enormous amount of energy then compress it back to a fluid elsewhere and push that heat back out -- this works pretty well because you're just moving the heat and only pushing the temperature on the "hot" side up a relatively small amount. I don't think, for instance, you could make an oven with heat pumps.
To do useful work you need a _substantial_ energy gradient -- it's hard to live in the sun even though its got lots of free energy floating around. The sun is very useful to the earth because the energy it provides is so much more energetic than the ambient environment.
Edited to add:
There are discussions of using exotic working fluids like compressed CO2 -- that'd allow you to manage the phase change maybe to a region where you could concentrate the energy in the fluid then expand it elsewhere at "room temperature" temperatures -- but I think things like compressed (to a _fluid_) CO2 are really hard to work with.
Could an PV system energise an existing GSHP steel bore and warm up the earth and rock a bit around the bore? This heat would then be tapped in the winter.
https://www.sciencedirect.com/science/article/pii/S266711312...
For it to be worth spending more time and effort on, I would need a closed system thermodynamic calculation. The technical term for this is a "heat balance diagram". This is the first thing any technical consultant would request.
At home, it's suitable in warm climates but is more challenging in snowy / very cold regions. Generally speaking, converting to electricity then using an electric water heater is more efficient because there's much less insulating, heat loss, and piping that can leak and cause water damage.
Why not building it under already wasted dead space like parking lot and have snow-free parking lot as extra bonus.
For home use, it seems like you could rig up some heavy stones on pulleys to do the same thing could be fun because you’d get to physically see your batteries filling up. Back of the envelope calculations suggest that an array of ten 10-ton concrete blocks lifted 10m in the air could power a house for a day (ignoring generator inefficiencies)
It's a silly scenario anyway, but I was doing a bit of guesswork about typical "home" lot sizes.
Anyway I agree it's silly, definitely not a realistic idea
I have trees in my back yard I'm kind of worried about, which is why this immediately came to mind.
Pumped hydro storage and flywheels are cool but ultimately battery storage, distributed everywhere, will win.
There is no magic solution. I'm happy to see all those efforts, but am missing a mention of saving energy. In the age of record-setting data centers for AI training, that's not a popular aspect to mention. Though at least we get higher res more realistic artificial cat videos out of it.
A Tesla Powerwall contains about 13.5kwH (about 4,000 times as much)
So you can either raise 100 tons 10m above your house, or you can have 1/13 of a Tesla Powerwall.
https://www.energyvault.com/products/g-vault-gravity-energy-...
I like the picture, but the the size of the construction is enormous, especially if you're considering a tank for some kind of pumped hydro. Hydroelectric power is practical because a dam in a strategic location can back up much more than 1000x of its volume in water. If you had to build all those walls forget about it.
I am giving that one a 0% chance of long term success.
Edit: no seriously. Do some back of the napkin maths. The amount of energy stored is too small. Way too small. And then the infrastructure to haul hige blocks of concrete around.
It 100% works, but it's a system that has very specific applications and doesn't scale up well. And the best systems use a magical property of some fairly heavy materials called "being liquid" to simplify the logistics of getting millions of tonnes of weight to the lifting mechanism.
If you'd want to store 1kWh at 10m height, assuming no loss at all from heat, friction, etc, you'd need about 4 of those blocks block weighing 10 tons (according to ChatGPT). So you'd need a lot of those blocks to power a house for a day, unless you're very efficient.
In perfect conditions assuming no loss through drag, you're looking at the kinetic energy formula which is ½mv² = E (in joules).
E = 1 kWh = 3,600 kilojoules, velocity v at 10 meters is 14 m/s, so we need to calculate m for v = 14 and E = 3600k, which is just under 36735 kg. "about four of those blocks" is "about" correct.
E = mgh
m = E/gh
m = 3.6 * 10^6 J / (9.8 m/s^2 * 10m) = 3.6735 * 10^4 kg
The same is true for batteries of course, but at the very least there are protections and checks for failures in most consumer accessible home solutions (and decades of engineering at this point). Worst case you at least have smoke detectors... not sure if there's a "cable is wearing thin and might snap and decapitate you" warning system.
Water based systems work better because water is easy to move, plentiful, and there's natural basins to pump into / flow out of that can contain billions of liters.
Of course it's probably not the simplest engineering effort...
No, that's only 2.7 kWh. Most homes use 10-20 kWh/day. A battery of that size is easily under $1k. Good luck building your ridiculous concrete block system for that.
Batteries are really good. Gravity, not so much. It only works when you can lift & store a tremendous amount of stuff "for free" because nature has done most of the work, e.g. in valleys, mountains, aquifers, caves, etc. If you have to build the whole thing it will never be viable.
Nevertheless, you can get a 16 kWh battery (which is enough for most days of a typical house) for only £2k, which is kind of insane really: https://www.fogstar.co.uk/products/fogstar-energy-16kwh-48v-...
here in Switzerland 1kWh is 1k CHF.
The issue here is: the "stored energy" isn't electricity, but heat. Converting heat into electricity is quite wasteful.
And if it’s very cheap, does it matter if the conversion is wasteful?
The question is about conversion is, is it still cheap if you add a powerplant (i.e. converting heat into electricity) and have to maintain it (moving parts, in contrast to batteries).
When it comes to this article, I doubt the 500x cheaper statement, we would see these already everywhere if that were the case.
> Two economists are walking down the street. One of them says “Look, there’s a twenty-dollar bill on the sidewalk!” The other economist says “No there’s not. If there was, someone would have picked it up already.”
A battery that cycles daily makes revenue on its capacity about 350 times in a year. A seasonal energy store makes revenue on its capacity about once in a year.
A battery arbitrages between the most expensive and least expensive energy generators in the system. A seasonal energy store arbitrages between seasonal price averages.
A battery smoothing out solar production is operating on the difference between how much sun there is in the day, and how much sun there is at night. A seasonal energy store in the same role averages between summer and winter.
A factor 500 cheaper plus a significant quantity of solar energy production is about where you'd expect this kind of thermal storage to start making economic sense.
And being capable of seasonal storage doesn't stop you from using it for daily storage. It's less efficient than batteries, but you can overcome that.
Let's say you can make a 24 hour power source with $10M in solar panels and $20M in batteries, including the other equipment and costs. $30M total. If we need twice as much solar for thermal storage, but the storage only costs $1M, then that's $21M for an equivalent system.
What stops systems like that from being built right now? I was under the impression that batteries were most of the cost if you want them to last more than a few hours.
Surely you can write a short model of the system at the level of undergraduate thermo. If you have a pile of dirt this big (say about a thousand times the size of a spherical cow) with these pipes running through it, then at a storage temperature T your capacity is X, your leakage is Y, and your recovery rate is Z. Fill in the blanks.
It is a flimsy mental bubble of three stages.
'Battery storage' has no scalable reason to exist as a topic except for a millionaire's survival enclave. Natural disasters span days and weeks NOT hours. Probably a lot of millionaires are trying to trick you into this kind of thinking so you do their work for them. And in the end it won't solve the problem for them either.
The first stage is, how much would this have to scale to provide for me and my family? And countless shadows of 'others' in the background work to make this a reality.
The second stage is merely to include the 'others' who helped to make it reality in a grandiose gesture. Though it could never scale so far in real life. And even if it did, it would be such as massive and Earth and land=destroying endeavor that the 'others' could not accomplish it either, they would have to be joined by a magnitude greater complement of other-others who could not be compelled to accomplish such a project (that would not benefit them in the end) that you're toying with slavery, threat of violence and broken promises to make it work.
Stage three is imagining energy poverty as a bad solution, but the only workable plan in the end is to reduce the number of people in the world, by lots. It's only logical. Start with other peoples' children. That's stage three.
People who cannot or will not do the math and promote irrelaible or unworkable energy sources are dangerous people. You can sell them anything, and some Pol Pot or Chairman Mao will always step forward to offer help with the human part of the equation in the end. Nuclear now, it's the only thing on the table. Or get ready for a world so ugly it will eclipse history in ugliness.
Go ahead, flag this message so it will disappear and no other persons will be ever know it existed. That's the HN way.
Commentary like this is a reason to flag posts in and of itself.
But the rest of your post presents far more rhetoric and conspiratorial thinking (including bringing in entirely unrelated policies that nobody ITT is arguing for) than analysis, evidence or even logical reasoning.
> 'Battery storage' has no scalable reason to exist as a topic except for a millionaire's survival enclave. Natural disasters span days and weeks NOT hours.
An experiment to try: fully charge your cell phone or some other similar device, then turn it off and leave it off. How long into the future do you expect you'll be able to turn it on again without another recharge? You might be surprised.
Larger scale batteries can store enough energy for seasonal storage. The larger the size, the better the insulation can keep the heat losses to a minimum. Basically you have a smaller surface area relative to the volume and mass. But even with a small unit, you can keep it hot for quite long.
Stuff like this is easier in areas that are already on some sort of district heating or have some kind of water based central heating. For those systems it's pretty much plug and play. You don't really need to modify the houses.
I think Helsinki has a few larger scale units already operational and a few more under planning / construction. I think the largest one will store 90ghw of heat. Which is quite a lot.
The beauty with thermal storage is that almost any kind of mass with enough heat capacity works. Water, rocks, sand, etc. All fine.
It reminded me about another geothermal energy idea: dig about 3 or so miles straight down and harvest the heat that is there already. I guess that's a lot harder than making a dirt pile. But maybe it could become practical if there was enough commercial effort and large scale manufacturing of the equipment.
Kind of brings it around full bore though. Why do that kind of project when you can just harvest actual fuel like oil or gas?
I think this stuff can become practical with more scale and wide manufacturing of equipment and development of efficient techniques. But it requires you to do a lot of upfront work based on principal rather than the bottom line.
So anyway again great idea because it eliminates a lot of challenges and costs that come with concepts like "Journey to the Center of the Earth" etc.
How can that still be a question in this day and age? Unless somebody doesn't "believe" in climate change caused by greenhouse gas emissions.
For the US, the best reason is sustainable energy. Gas, oil and coal are not renewable, so you eventually need to adapt a new form of energy. Just transporting it is problematic, with most communities rejecting pipelines. In the meantime you're polluting your local environment and putting workers at risk. Whereas if your energy plan is largely "the sun shines", "the wind blows", and "dirt holds heat", that is ridiculously more sustainable.
The biggest problem we have is we demand too much energy. AI has made this problem way worse. Nuclear is the only thing that's going to fill the gaping chasm of demand.
Deep geothermal ought to work. Deep drilling is hard, but it's been done. Eavor-Deep got down to where they got 250C water. [1] That was back in 2023. Not much new since. The problem seems to be that when you drill into really hot rock, most drilling techniques run into trouble. Rock becomes plastic and clogs things up. The drilling tools have problems with the heat. Progress continues, slowly.
There's these guys, trying to drill with microwaves: [1] On September 4, they're going to do a public demo and try to drill a 100 meter hole.
This concept appears immediately flawed. Heat will definitely escape the "dirt pile" at some point between summer and winter.
However, if that's the case you would think that you can cut out the PV step as well and use direct heat from the sun to heat the dirt, by running water hoses though the dirt and through solar water heaters. Should be cheaper and more efficient than the sun -> PV -> heat coils cycle.
Solar panels and heating elements are cheap, simple and easily replaceable.
the problem is scale. the dirt is free but heaters, piping, controls, permits, and contractors are not. balance of system costs creep up fast and thats where most cheap energy ideas collapse.
the market fit is narrow too. industrial heat or maybe district heating could work. coal plant conversion sounds good in headlines but takes forever to line up politics and utilities. daily cycling wont compete with batteries, only long slow seasonal storage makes sense.
execution decides if this survives. if they can keep real projects near the claimed cost then it has a shot, otherwise it stays as a cool demo.
For reference, point-in-time energy market rates usually swing by 2x-3x per day - meaning if you charged during the cheapest market rate and discharged during peak you'd net about 2.5x return on that cycle) - even more so during extreme temperature events like heat waves or cold freezes - those are ultimately what you're riding here in terms of validating the system's viability from a financial perspective. If you reduce that scale from hours to months, and if draw-down speed is slow (ie: you can't sustain 50MW of steam with 500,000 tons of dirt even at 600'C) then you're looking at even more complicated returns.
By my simple, assumption-laden math, a 50MW "system" (capable of providing up to 50MWe peak output and requiring a requisite (assuming since it's not mentioned in the article - that at 200'C a 1,000,000 ton dirt pile would only be able to sustain 40MW of thermal output/20MW of electrical output and 240MW thermal/120MW electrical output at 600'C) would be:
PV system (20MW system would require ~30 days of charging to provide 50MWe output for 1 day, ~1200MWhe), alternatively, per day, you could discharge 50MWe for ~48 minutes. 1,000,000tons of dirt storage at 600C should hold a theoretical ~28 days of 50MW electrical supply. (also worth noting, getting the dirt pile heat up to "steam" temp would likely eat up a considerable number of months charging, which is also capex)
$1,000,000 for dirt
$5,000,000 for balance of system (heater elements and wiring + ASME tubing - as an aside this seems very opportunistic for 20MW of heaters and tubing to supply 100MWt of steam)
$12,000,000 for Solar Panels ($0.60/w bulk)
$8,000,000 for Solar Supporting systems and installation (assuming heaters can run on DC power and no inverters are required and there is no grid tie, minimal permitting and simplified ground install)
$25,000,000 for a 50MW steam generator turbine and transformer yard, provisioning etc
land use: ~25 acres for dirt pile, ~100 acres for solar, 10 acres for steam/aux, call it $300,000 assuming US averages for cleared land.
----------
Assuming north-eastern US (~20% solar efficiency with subzero winters where you also have high off-solar peak demands)
If you only charge/discharge this twice per year you're looking at some pretty paltry economics - you could only really fill about 18k MWh of thermal energy during half of the year for a ~7,400MWhe discharge - $592,000 gross electricity revenue per discharge cycle at an opportunistic 7-day "peak" market rate of $80/mWh which is about $1,184,000/yr gross margin. If you did it once per day (40MWhe per day at peak average intra-day market rate -$68/mWh) you're looking at ~$2,720/day or $992,800/yr gross margin.
$51M capex would be difficult to justify margins of only $1.1M/yr, and that's before any operating costs of which there would be several.
If you just sold the same solar at market rate (~$36/MWhe) throughout the year you'd net out at $1,261,440. Capex would be ~$40M and grid-tie solar is very cost effective in OPEX.
Likewise, if you just connected the system to the grid and skipped solar altogether (powering the heaters with grid energy like battery storage would): 50MW in for 12 hours on cheap time-of-day rates (typically overnight ~$18-20/MWh) and sold for 5 hours during daily peak rates ($55) you'd cut your capex considerably without the solar component and you'd be able to net, even with round-trip energy efficiency around 41%, (600MWe in @ $11,400, 248MWe out @ $13,640 = $2,240/day ~$817,600/yr gross margin) for a capex of $31.3M.
So in the end, the best solution seems to be collocating this on an existing coal/gas plant, where the capex is already sunk in the transformers, grid interconnect, steam turbine, land and permits and you're only adding the earth battery - you could run the model with the above margins with a capex of only $6-7M, which is very viable and even more favorable than the economics of spinning up a new gas/coal plant.
The economics of battery energy storage (BES) systems are much better known (ROIs of <4 years in extreme-swing energy markets doing intra-day peak arbitrage is very possible) since your round-trip efficiency is closer to 91%. A 250MWh BES plant with 1-hour charge/discharge window would be~ $40M installed and could arb twice per day - at 2x (low end averages - buying at $26 and selling at $52 twice per day = $14,285 cost for $26,000 revenue) $11,715 margin per day, $4,275,975/yr on $41M capex is still better economics than all the above models except those where the steam generator and grid infrastructure is already sunk.
Imagine 1,000,000 Drake Landing installations per year in Canada, pre-heating with the excess electricity. In 30 years Canada would need zero fossil fuels for buildings.
which... is only 13% of their GHG emissions? Oh we're fucked. The planet's so fucked.
Why not sell something in tbis vein to households and then let them use cheap daytime electricity to charge it up and and then heat their homes at night.
(Or it could store “cold” during the summer)
Electricity is easy to move. Heat isn’t.
https://eepower.com/news/engineers-repurpose-oil-wells-as-so...
California has thousands of abandoned (orphaned) oil and gas wells, with more than 5,500 identified as "likely orphaned" in 2023, and an additional 70,000 economically marginal and idle wells that could become orphaned in the future.
Kern County, California has 75% of the state oil wells, and the largest solar farms. Even after the 70,000 wells are idled, Kern County will continue to produce enough oil to meet all internal demands in California, although the state no longer has the refining capacity or anywhere to lay off the oil.
https://www.latimes.com/environment/story/2025-08-06/major-c...
Or is there like a practical maintenance window each year at the end of the winter when you’d do this?
This is a steam boiler. Those are well understood. They have well understood problems. Leaky boiler tubes. Crud in the tubes. Cleaning. The problem here is that you can't easily turn the heat source off.
It's possible to build a long-life boiler for a heat source you can't fully turn off. Every nuclear reactor has one. Heavy stainless steel tubes, precision welding, distilled water. Works fine, but not cheap.
This paper is very hand-wavey about the details of getting the energy out. They're all about the side that puts the energy in, which is the easy part.
Then we talk round-trip efficiency.
PV panels are dirt cheap and dead simple. They're also portable. Wire a bunch of panels to a heating element and dunk it in sand/water/etc.
pfdietz•7h ago
EDIT: dupe, darn it.