Standard Thermal: Energy Storage 500x Cheaper Than Batteries
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!
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!
Thatβs 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. Itβs 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 isnβt an easy win.
Based on some guesses and uninformed searches if a house spends 200MJ on cooling and there is a 20 C delta between winter temperatures and desired cooling temperature and assuming a specific heat capacity of ~800 J/(kg*K) you would need 12.5 tons of rock as battery which would be around 6~8 mΒ³ which sound very small.
I am sure that there are hundreds of complex factors at plays (eg rain water and aquifers reheating the battery during spring) but it came out to be a far smaller number than I would have guessed.
Google:
An AC unit's electricity usage varies by type, with window units using around 500β1,500 watts and central air systems using 3,000β5,000 watts, though usage can range from 2,000 to over 6,000 kWh annually for central units
Also, how much you use it during the year can vary hugely from 0 (when I lived near the coast) to like 10 hours a day for months in hot or cold places. There's not a standard, but 55kwh for a year means you live someplace that doesn't really need AC / heating.
If that wasn't true, you'd need to keep moving the underground passageways of buried passive cooling systems.
dirt isn't very insulative
Whether it is sufficiently insulative depends on the scale of the system. The thermal time constant of a 3D mass is proportional to (thermal conductivity)^-1 (heat capacity per volume) (radius)^2. So if the thermal conductivity is too high, just increase the size.
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.
The {...} is the counter intuitive step of solar -> electric -> heat storage for six months -> electricity for later.
The secret sauce is increased heat deltas, not just heating dirt directly using sunny daytime temperatures but really cranking up the heat of an underground mass to 500C + (IIRC - I skimmed the article some hours ago).
Just thermodynamic pumping of heat, from the article:
Electricity from the solar arrays flows to heating elements in the earthen mound, building up heat. The storage temperature is 600 Β°C or higher. The outer mass of the mound, plus a favorable volume-to-area ratio, insulates and minimizes heat loss. Pipes embedded in the mound carry fluid that delivers heat to users.
I'm guessing you caught but ignored the part that is moving heat?
A heat pump is a specific kind of thermodynamic device that moves heat energy from lower to higher temperature.
The system that is described in the OP link does not use a heat pump. Electrical energy is used to make heat, but it does so with a resistive heater, not a heat pump.
Has anyone looked at the subsurface ground temperatures after days, weeks, months, even years of heat pump operation?
I do seem to remember seeing one article on the subject showing that after one winter the subsurface temperature had declined enough to materially affect the heat pump's COP. But the timescale didn't extend to multiple years.
edit: found this one: https://pangea.stanford.edu/ERE/db/GeoConf/papers/SGW/2024/M...
In one of eight cases studied where heat flow is unidirectional (cooling load only) over a 20 year timescale the authors find:
"the mean ground temperature ... increased from 21.87 Β°C to 26.18 Β°C, ... . This significant rise could have a potential impact on the performance of the system in the later years of its operational life."
An additional graph shows COP variation over 15 years and the worst case shows a decline of perhaps 10% (just eyeballing it).
Surprisingly, some cases showed a long term improvement in heating COP - presumably the injection of summer heat into the soil made for warmer soil than just sunshine and natural diffusion?
So my takeaway: "it depends." :-)
For example, I spent a bunch of money to install solar panels, house insulation, and soon a heat pump. They each have, respectively, about 9 year, 30 year and probably 15 year payback time at today's energy prices, so depending on lifespan and future energy prices it's an open question if it would've been cheaper just to stay as I was.
But there's the comfort factor (heat pump should regularize house temps) and security factor (still warm & cosy during a power cut). I'll allow myself a little feel-good factor of carbon emission reduction too. Maybe these can also apply to the question of using a heat-pump in the dirt-as-thermal-storage scenario here.
I suppose overall I'm of the mind we should be collectively treating carbon emissions as the highest priority and using a heat pump here might aid that?
However, the cost incurred in building the storage system is independent of the number of charge/discharge cycles.
So: in comparing diurnal (daily) storage systems, with seasonal (up to yearly) storage systems, the relative importance of efficiency and capex are radically different. In the latter, capex can be 365 times more important than in the former.
For seasonal storage, one is strongly driven to minimize capex, even at the cost of making round trip efficiency worse.
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.
Start getting into permafrost though where the cold is more constant and that cold layer gets deeper.
you only need to go down 10 ft or so before you hit the average annual temperature
Is this because of geothermal energy leaking upwards? If so, it's not the dirt, it's the geothermal energy.
Is this because of geothermal energy leaking upwards
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.
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.
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.
4 months of winter buffered by 10 ft of ground!
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.
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.
When 5 of the 6 semiaxes of possible heat flow have no temperature gradient, the temperature becomes much more stable.
Insulation would be if a 10 ft radius dirt ball maintained a stable temperature all year round - which would surprise me, although dirt does have some insulative value. However, wet dirt is really not very insulative - try sleeping on the ground sometime.
The dirt here will not be wet in most of its volume -- the initial charging will bake out all volatiles. The hottest part of the pile will become something like dry brick. It's like storing energy in ziggurats.
The application here is big, slow annual oscillations. Slow charge, slow discharge.
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.
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.
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...
For home use, it seems like you could rig up some heavy stones on pulleys to do the same thing could be fun because youβd 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)
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.
It just seems so awfully wasteful.
If someone can find some real costs I would be more than happy.
Now, I know reservoirs are ecologically pretty iffy, expensive and obviously geographically sensitive, so you can't slap them around everywhere. But all these mechanical schemes have big "look what they need to mimic a fraction of our power" vibes!
I could imagine that steel-on-steel block movements could actually be quite efficient and effective in limited scenarios, but logistically it just seems like a lot of squeeze for not a lot of juice considering how much power is required to be stored for utility-scale projects. I would like to say that that they're just delusional people truly hoping it'll work, but I think there's a core of hard-nosed scammers who smell money for a shiny PPT and a plausible-to-non-engineers Wile E. Coyote/Troll Physics contraption with big numbers in the brochure: 7000 blocks! 25 tonnes per block! Megajoules! Efficiencies! Scale! Repurposed coal mining infrastructure! They even have AI in the spiel now: https://www.energyvault.com/solutions/software
Or maybe it'll work and I'll look stupid in 30 years when there are huge fields of hundreds of kilometre-deep boreholes with 100 kilotonne masses moving up and down in them. But somehow it seems quite unlikely on a practical level considering the cost of boring gigantic holes that you'd have to do to make it scale. Onsies-twosie installations in a few mines here and there may work for lucky outlying towns, but they aren't civilisational scale solutions.
an array of ten 10-ton concrete blocks lifted 10m in the air could power a house for a day
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 Β£2k, which is kind of insane really: https://www.fogstar.co.uk/products/fogstar-energy-16kwh-48v-...
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.
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 Β½mvΒ² = 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
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.
But PHES can be placed far from any river, even in a desert.
https://www.whitepinepumpedstorage.com/
I suspect this project may not happen, what with batteries getting so cheap.
Pumped hydro storage and flywheels are cool but ultimately battery storage, distributed everywhere, will win.
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.
Of course it's probably not the simplest engineering effort...
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.
This scheme is probably superior though, with lower capex and working at smaller scale, especially if one doesn't have deep salt formations to solution mine for hydrogen storage caverns.
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.
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).
Direct air capture is out, so it'll have to be recovered from the combustion of the synfuel. Using the Allam cycle has been explored to do this (you also have to store the oxygen from electrolysis for later use in this oxyfuel combustion cycle) but it ends up being more expensive than just burning hydrogen, if there's reasonable geology for hydrogen storage.
So, if this thermal storage scheme is cheaper than hydrogen, as it appears it will be, then these alternative synfuel schemes are ruled out.
But, if you read the wikipedia article, you can see there are prototype plants using ambient air capture. It's probably a bit less efficient, but since it's actually reducing carbon levels, it's even better than just a battery.
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).
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.
But chemical batteries cost a lot more and don't have lifespans of hundreds or thousands of years in seasonal storage scenarios.
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.
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 isnβt as easy of a decision.
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.
When it comes to this article, I doubt the 500x cheaper statement, we would see these already everywhere if that were the case.
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 $21M for an equivalent system.
What stops systems like that from being built right now? I was under the impression that batteries were most of the cost if you want them to last more than a few hours.
Imo, the current system of solar energy etc. might be more carbon emissions than even coal because of the way of using batteries and how they are extracted and the whole process and batteries limitations and not solar panels themselves (I think)
Like, please pardon me but I think that there might be batteries that overall are cheap/economical/less carbon emissions and they can store energy for a night cycle right? Then using those batteries in your system and I don't know the price point, but I am definitely sure that they might be orders of magnitude cheaper
So in your 21M$ example lets say that we can add such night time cheap batteries to counter solar panels not generating light at night and use this 1M$ to generate energy when its either rain or solar production is less or when winters come
I still feel like, this might be more economical than the current state of batteries + solar panels.
Okay, I just realized that the night time issue can be solved by the grid but still if that's the case, then why have batteries in the first case if lets say every community builds something like this (if this is economical) and people could just pull up energy from it 100% solar in rainy times etc.
Like maybe my mind is perfectionist or I genuinely don't know about green energy but to me I wish to know if there is a way that we can transition (almost) 100% to the green (solar) without the drawbacks that I saw in the michael's moore documentary in the sense that it produces more carbon emissions net overall theoretically (which hurts my heart :< but the logic was sound imo)
The problem with using this approach for daily cycled loads is that it relies on passive heat transfer to distribute heat through substantial regions of dirt. This simply doesn't work for daily storage.
You can overbuild, but then your energy losses are going to be immense, because you never saturate or drain the bulk of the material, and are just losing energy to it.
You could build faster cycling systems instead, and active systems especially can cycle reasonably fast, but then your dominant costs no longer reduce down to a pile of dirt with a few rods stuck into it.
I don't think losses would be immense. You'll spend a few months warming up the neighboring dirt, but after that the amount of heat escaping per day will look about the same as the seasonal system.
While that's not going to increase the cost by 350x directly, it is going to change the character of the pile from a bunch of dirt to a bunch of dirty pipes. This makes a lot of the simplifying assumptions no longer work; like you can no longer ignore the heat losses through the rods, or the lower thermal mass of the rods.
And to be clear, you can do this. There are faster-cycling thermal storage solutions out there. It's just not implied from the claim that these solutions would be so much better than batteries.
Two economists are walking down the street. One of them says βLook, thereβs a twenty-dollar bill on the sidewalk!β The other economist says βNo thereβs not. If there was, someone would have picked it up already.β
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.
another geothermal energy idea: dig about 3 or so miles straight down and harvest the heat that is there already
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.
Why do that kind of project when you can just harvest actual fuel like oil or gas?
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.
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.
Despite the simplicity of a solar water heater the even greater simplicity is often part of the argument for PV being better, but the higher grade of energy that you only optionally have to use for heat and relative price changes are the key driver
See, I was a huge solar fan/renewable fan except but then I watched the infamous michael moore video and I had sort of concluded that either we need to focus on nuclear since I have this only grudge against the documentary that it didn't depict nuclear energy.
But overall, the conclusion of that documentary was that solar might not be the right approach given its storage mechanism and that batteries might be net negative overall the way they might be used right now
And that it might lead to more net negative emission even compared to Coal etc. (or comparable)
Seeing this, I feel like this can atleast be a very huge boost into not using batteries and building systems that only require land with less maintanence overall. Like, I can imagine a solar farm with solar panels and communities can build them in vacant land and then they build the system proposed in the article and then basically have more solar panels than the consumption or just enough to store them into such a system and then lets say that a stormy weather comes or rainy seasons comes or something or winter comes and then we might be able to push the energy from the reservoir.
This might be more efficient compared to using batteries or having more solar panels in the first place and "wasting" excess solar energy in the summers if lets say that we overprepare ourselves with a lot more solar panels (which seems to be the current approach) without using batteries.
Now to be fair, the author does propose that he likes batteries. I wonder if I can change that but I myself can be wrong too (I usually am), and so maybe we can discuss it! I wonder, how this system without batteries might work though.. like how are we gonna prepare for night without batteries completely, like maybe we can have a system where we can shift to the grid in the night?
Now although I will be honest, I feel like using the grid at night doesn't make sense but I am assuming here that michael's moore's video is right (which it is) and that the current way that batteries are used is more carbon emissions in the context of solar right now
Then this system that I was talking about doesn't include batteries and such might be atleast definitely better for the environment overall.
But that being said, I am still not a big fan of solar compared to nuclear. I feel like nuclear is one of the best things.
I wonder if we can actually have a nuclear reactor which can create energy and then send it to such communties and then they can store it in their ground and (its efficiency seems to be 50%) which might be actually good considering how atleast to me nuclear genuinely feels like unlimited energy and thus I was genuinely thinking of a cheap way to store energy, this isn't definitely portable but I feel like that communities can build it economically and so maybe countries with nuclear energy can setup lines with other countries and all that nuclear energy straight up goes to the community which stores it in such land and then they might actually use solar too and rely on this too and just store a ton of energy as much as it makes sense economically and then maybe combine this with solar and then use that nuclear energy at winters or if it turns out to be economical even at nights.
Now why I am saying this? Because this feels like a completely clean method. Now although I like nuclear energy a lot, I feel like a lot of countries can't access nuclear energy as they can't build it because if they can, they would've made bombs and its hard and they can't rely on other countries which have unlocked it for their power because that's a geopolitical disadvantage
but just using it for storing energy at scale might make true sense since it isn't that big of a priority and even if some nuclear power lets say denies them, then maybe they can go back or go to other nuclear power without their infrastucture being completely reliant or essentially melting because of some other countries decision and they still have autonomy which can make it a lot more viable
Overall a net win win situation imo. Makes me a little bit more optimistic.
But that being said, I am still not a big fan of solar compared to nuclear.
This technology, if it works, is a bullet in the head for any remaining chance for nuclear. It provides heat at a cost competitive with natural gas, and natural gas is what destroyed the nuclear renaissance here in the US.
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.
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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.
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.
Pipes run through the pile, and fluid flowing through them removes heat to supply the customer.
Dirt keeps a constant temperature year round quite close to the surface thatβs 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 arenβt 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 donβt get that investment back. On the other hand if youβre 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.
Youβd want a very large mass to heat however, scaling matters a lot. Youβd 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 donβt do this where you want trees - or where there are underground coal seams
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.
Do the numbers. Making the top of the heliostat isn't what matters. What matters is making the inside of a pile of dirt that hot.
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.
The issue here is: the "stored energy" isn't electricity, but heat. Converting heat into electricity is quite wasteful.
And if itβs 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).
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.
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.
Overall it's a good idea but I'm skeptical that random "dirt" will reliably withstand the temperatures required for
the stored heat creates steam on demand for the turbines instead of burning coal
but mostly-quartz sand without any calcite and crushed granite surely can, and those are widely available for barely more than the cost of driving a truck to your construction site, because those are the main ingredients in concrete. (As he says in his white paper https://findingspress.org/article/141340-thermal-energy-stor..., US$20β50 per tonne.)
From perusing https://www.eia.gov/analysis/studies/powerplants/capitalcost... I'm also skeptical that the turbines (especially steam turbines rather than gas turbines) will have a low enough cost to make this worthwhile.
If your random dirt is good enough I'd think you'd want to trench into the existing dirt to lay pipe, the way most ground-source heat pumps are done, rather than hiring a bulldozer. But I haven't done it; maybe the cost structure is different than what I imagine.
I wonder why he says
Surrounding the earthen mound will be high-density, low-profile solar arrays.
What's stopping you from putting the solar arrays on top of the earthen mound (or sandpile) too?
Sand or feolite thermal "batteries" on the daily rather than seasonal timescale are eminently economical for even household thermal storage for heating. With TCES energy storage, which I expect to be barely more expensive at the household scale, you can get cooling too. TCES also scales down to small systems and long storage times in a way that sensible and phase-change thermal energy storage can't, while also bettering them on density.
https://fortune.com/2025/08/14/data-centers-china-grid-us-in... β#AI experts [#Rui-Ma] return from #China stunned: The U.S. grid is so weak, the race may already be over. (...) In the U.S., surging AI demand is colliding with a fragile power grid, the kind of extreme bottleneck that Goldman Sachs warns could severely choke the industryβs growth. ΒΆ In China, Ma continued, itβs considered a βsolved problem.ββ because βChina has an oversupply of electricty [sic]β. βIn China, renewables are framed as a cornerstone of the economy because they make sense economically and strategically, not because they carry moral weight. Coal use isnβt cast as a sign of villainy, as it would be among some circles in the U.S. Itβs simply seen as outdated.β #energy #USA
https://xcancel.com/ruima/status/1955040979259650267 #Rui-Maβs account of her trip to #China to go to the World #AI Conference (#WAIC) and see investors and renewable #energy. "We met with companies ranging from Baidu, Alibaba, and Tencent (BAT) to unicorns, as well as young startups founded less than a year ago. (...) Energy is considered a solved problem. The Chinese governmentβs investment in sustainable energy β from advanced hydropower to next-generation nuclear β means that, relative to many other markets, electricity supply is secure and inexpensive. Everywhere we went, people treated energy availability as a given. This is a stark contrast to the U.S., where AI growth is increasingly tied to debates over data center power consumption and grid limitations."
https://xcancel.com/ruima/status/1955372325970514161 #Rui-Ma on #energy in #China: βChina: Electricity generation jumped from roughly ~5.6 PWh (2015) to ~10.1 PWh (2024), which is +80% in less than a decade. And 2024 alone grew ~7%, accounting for ~HALF of the worldβs increase. China now produces ~1/3 of global electricity. Thatβs what βsupply went up a lotβ looks like, so yeah even if coal as a % of total went down, the total will still increase but the increase is QUICKLY PLATEAUING (...) Multiple independent analyses now show Chinaβs COβ fell yearβonβyear across the last 12 months (and in Q1β25), driven by the cleanβpower surge rather than an economic slump.β
the resistor material itself is $1-$2/kilowatt. (...) There are only a few materials that are even acceptable as resistors.
This depends strongly on your target temperature and conditions. Nichrome may cost US$2/kW but galvanized barbed wire doesn't. It can kill you with the fumes, and in oxidizing conditions it won't last long above 200Β°, but zinc fumes inside a dirt pile won't hurt anybody, and you can probably maintain reducing conditions by mixing some humus into your dirt initially and keeping the pile dry. If process heat or climate control is your objective, you don't need temperatures high enough to oxidize iron rapidly even in an oxidizing environment.
(Incidentally, reducing conditions will destroy nichrome at the temperatures people use nichrome for. Maintaining oxidizing conditions inside your dirt pile over the years is going to be a lot more challenging, I suspect.)
I suspect keeping the pile dry is the reason for not just trenching in existing soil. Dryness is essential for maintaining temperature over 100Β°.
My intuition is that you could probably scale the seasonal-sensible-TES-in-dirt approach further down from the few megawatts he's talking about if you can use real insulation instead of dirt. But insulation is expensive at this scale, even things like perlite and vermiculite.
Spitballing, suppose we want to withdraw 100kW energy for 4 months (1TJ) and can deal with a time constant of 8 months, so leakage is ballpark 50kW. Suppose we have 1J/g/K sand and ΞT = 200K. Then we need 5300 tonnes of sand; at US$20/kg that's US$100k, a dollar a watt, cheaper than power from a coal plant but not really competitive. A larger ΞT can save you but might shorten the life of your barbed wire. But at those low temperatures you pretty much can use any old dirt, US$5300 of it by Vernon's embankment figure.
But that's about 2000mΒ³, whose minimum insulated surface area would be as a 7.8m sphere with 800mΒ² of surface area. 50kW of leakage over that area would be 70W/mΒ², or 0.3W/mΒ²/K, or 3KΒ·mΒ²/W.
Or is there like a practical maintenance window each year at the end of the winter when youβd 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.
Why not building it under already wasted dead space like parking lot and have snow-free parking lot as extra bonus.
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 βcoldβ during the summer)
Electricity is easy to move. Heat isnβt.
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...
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.
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...
Our system can store the summer excess production for winter thermal demand.
This concept appears immediately flawed. Heat will definitely escape the "dirt pile" at some point between summer and winter.
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.