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Standard Thermal: Energy Storage 500x Cheaper Than Batteries
- pfdietz 1y agoA fascinating energy storage startup just emerged from stealth mode. The concept involves DC coupled PV feeding resistive heaters buried in dirt, providing heat at 600 C for a capex of $.10/kWh-th of storage capacity. Storage is seasonal, from summer to winter. EDIT: dupe, darn it.
- deleted 1y ago[deleted]
- onlyrealcuzzo 1y agoI have more questions than answers. 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.
- Retric 1y ago> 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 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.
- teiferer 1y agoThey mention end-to-end efficiency of 40-45%...
- Retric 1y agoThat’s just for heat to thermal and quite optimistic not end to end. “Conversion back into electricity is 40%-45%” 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.
- pfdietz 1y agoThat's for round trip electricity->heat->electricity.
- newyankee 1y agothey mention that demand source should be close by to reduce losses in transportation
- lazide 1y agoApparently the insulation value (R value) of dirt and soil is between .25 and .8 per inch (depending on moisture content). That wouldn’t be great if it was a material like fiberglass, but since it’s dirt cheap (ba-dum-tssh) and easy to pile up in large quantities with little to no ongoing maintenance in this kind of context, it matters. 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
- simplicio 1y agoI think there have been about 5 different contexts over the years where I've been surprised by how good an insulator a pile of dirt is.
- thelastgallon 1y agoDupe: Building Ultra Cheap Energy Storage for Solar PV https://news.ycombinator.com/item?id=44998441 https://news.ycombinator.com/item?id=44998441
- adolph 1y agoInteresting how this turns the standard cogeneration plant strategy on its head. Instead of creating chilled water overnight and using that for cooling buildings, heat up the center of a large mass and use that for heating buildings or making steam to run turbines.
- adverbly 1y agoLong-term thermal storage is something I've been fascinated with the last year or so. 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!
- profsummergig 1y ago> 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.
- vasco 1y agoHad the same thought, we'd have to put a thermometer inside a 10ft cube full of dirt for science.
- profsummergig 1y ago> a 10ft cube full of dirt suspended in air
- werdnapk 1y agoYes, the you can put "thick" insulation over top of any buried plumbing and the exposed bottom will gain geothermal heat from the below and it can prevent freezing.
- adverbly 1y agoIts a bit of both, but its primarily due to the high insulation. 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.
- elil17 1y agoOne thing they neglect to mention (which is by no means a deal-breaker) is that you waste a good portion (about half) of the electricity in the process of charging and discharging the pile of dirt. Chemical batteries are much more efficient in this regard.
- eplawless 1y agoThey mention it: > 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.
- carlos_rpn 1y agoI didn't have time to read the whole thing so I don't know if they mention it, but another article about about using sand as heat storage pointed out one of the advantages is that the material isn't toxic, unlike chemical batteries.
- pbhjpbhj 1y agoThere were reports last year, IIRC, of "sand shortages". Presumably a logistics infrastructure problem that could be relatively easily overcome?
- carlos_rpn 1y agoI remember those reports. 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).
- coryrc 1y agoThat's of "sharp sand". Sand batteries don't need sharp sand.
- Aurornis 1y agoThey do mention it, but it’s downplayed relative to how much of a problem it can be. 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.
- profsummergig 1y agoI do like how well and concisely they've explained not only the technology, but the exact use case, on their landing page.
- BiteCode_dev 1y agoI always wondered if, instead of using solar panels in the deserts, we could use very long and black pipes running water, heated by the sun. Then the heat is moved to the ground for storage, and once there is enough heat, we use a turbine to generate electricity.
- cduzz 1y agoI don't think you ever get enough of a temperature difference just by having a passive black pipe in the sun, to do any useful work besides potentially keeping someone warm in the winter. You could do useful work if you concentrate the energy from the sun somehow, like with mirrors. 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.
- throwway120385 1y agoIt's done a bunch, all over the place: https://en.wikipedia.org/wiki/Solar_thermal_energy https://en.wikipedia.org/wiki/Solar_thermal_energy. Most commonly people use them either for batch pre-heating of hot water or for full heating. I looked in to getting something like that for the hydronic heat in my house because currently it's propane-fueled and the deliveries are quite expensive in the winter.
- endoblast 1y ago>the heat is moved to the ground for storage ..or into a giant sand-filled barge which transports the thermal energy up north for the winter.
- Mistletoe 1y agoHow hot do they get the piles of dirt? They are making steam from it?
- tgtweak 1y ago600'C at the high end seems to be the cited number. Steam or other heat extraction method such as air.
- willvarfar 1y agoGround-source heat pumps are really common in the nordic countries. 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.
- bartco 1y agoThere are simpler solutions using thermal solar panels which don't require converting solar energy into electricity first: https://www.sciencedirect.com/science/article/pii/S2667113123000189 https://www.sciencedirect.com/science/article/pii/S266711312... https://youtu.be/OdyrF96q2TQ?si=GT7ar0yoS6jR0mZe https://youtu.be/OdyrF96q2TQ?si=GT7ar0yoS6jR0mZe
- smartmic 1y agoThis is a blog article outlining a rough concept idea. As others have commented, many questions remain unanswered, and speculation about isolated physical properties and technical ideas is unhelpful. 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.
- deleted 1y ago[deleted]
- jongjong 1y agoInteresting because I've been thinking about mechanical energy storage recently. I feel like these concepts hold a lot of promise on a small scale, per-house; coupled with solar panels. Although mechanical batteries they are not as efficient as electric batteries (and lose some energy), they can be both cheap to make and durable; these characteristics are much more important than raw efficiency when dealing with a single house.
- dwallin 1y agoSeems like a case where directly going from sunlight to heat would be a better approach for this, instead of converting to electricity first.
- zdragnar 1y agoIt's been done, but not without controversy. https://en.wikipedia.org/wiki/Ivanpah_Solar_Power_Facility https://en.wikipedia.org/wiki/Ivanpah_Solar_Power_Facility 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.
- orev 1y agoHow would you move the solar energy into the piles of dirt? You’d need something like an array of mirrors focusing the rays, which has definitely been done already but has drawbacks. Electricity can easily be moved to where it’s needed.
- quickthrowman 1y agoYou could heat up a metal heat exchanger that you circulate a working fluid through. Probably easier to just convert sunlight to electricity to heat via resistive heating, less maintenance.
- tgtweak 1y agoIf you look at "evacuated solar" panels this is as close as you could get, and they don't get anywhere near the temperature you need to generate consistent steam. Concentrated solar is closer, but cost impracticalities make it unattractive here as well.
- darkwater 1y agoAnother question I don't see answered in the article: is there any risk for existing life by heating a huge amount of dirt? Will at some point surface and possibly influence local weather / thermal winds? Or should I just get my tin hat off?
- febusravenga 1y agoIs there bigger harm to env than building parking lot? We've got plenty of these. Why not building it under already wasted dead space like parking lot and have snow-free parking lot as extra bonus.
- tgtweak 1y agosnow-free means you're losing heat to the environment vs keeping it contained. I would imagine if properly designed you could stand on top of the completed dirt pile without feeling any temperature delta with the air.
- userulluipeste 1y agoIf the underlying stored heat leaks to the surface then it may indeed melt the snow and you'll have "snow-free" parking, but that won't be the end of the story, as all that resulted water will most likely turn your parking lot into an ice rink.
- parpfish 1y agoI visited a pumped storage facility a while back that stored electricity by pumping water uphill to store it and then draining it past a turbine to reclaim it. Ever since I’ve been intrigued by using gravity instead of batteries. 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)
- empyrrhicist 1y agoHoisting 100 tons of stuff high into the air, and then efficiently converting that into the high RPM needed to drive a generator seems like it would take a truly staggering construction effort. Suspending that amount of weight high above your house also has some... interesting potential failure modes.
- sfn42 1y agoWhy would you put it above your house? Just construct a sort of battery tower nearby.
- zozbot234 1y agoWhy not just build a water tower? Easier to manage, it's a proven technology and it has well-known ancillary uses beyond energy storage.
- sfn42 1y agoI don't even think the gravity battery thing is viable for individual residential power storage at all. I was just wondering why you'd assume that the 100 ton weight would be placed directly above your house given the obvious problems with that approach, and the obvious way to avoid those problems.
- empyrrhicist 1y ago
- tomp 1y agoThese are cool ideas but there's always an asterisk. The issue here is: the "stored energy" isn't electricity, but heat. Converting heat into electricity is quite wasteful.
- orev 1y agoThey’re using the stored heat energy as heat, not converting it back to electricity. And if it’s very cheap, does it matter if the conversion is wasteful?
- tomp 1y agoI'm not saying it's bad, but it's clearly not a replacement for batteries, given its applicability is quite limited. 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).
- pfdietz 1y agoIt's explicitly not a replacement for batteries. Did you not read the article? It's a crucial complement for batteries. Batteries suck for seasonal storage.
- zahlman 1y agoAs I understand it, this is meant as a supplement to batteries, so that batteries can do most of the intraday load shifting while thermal can store energy over longer durations.
- epistasis 1y agoIt's not really an asterisk if it's right in the title and the name of the company, is it?
- Ciantic 1y agoFinland has an operational "sand battery", which primary purpose is heating. That was discussed in HN few months ago [1]. When it comes to this article, I doubt the 500x cheaper statement, we would see these already everywhere if that were the case. [1]: https://news.ycombinator.com/item?id=44295132 https://news.ycombinator.com/item?id=44295132
- metalman 1y agothe reason that thermal storage is becoming very atractive is that electrical power from PV, wind, and other sources has become increadably cheap, and there is litteraly no where to put it, so prices go negative now, which is a new thing. so 500x cheaper may be an understatement, considering the nature of how cheap, mature and availible the technology to build a thermal storage battery is, any municicipal civil engineering team can build one from off the shelf and localy sourced materials, and the basic battery "housing" could be a re purposed industrial building, cheap does not begin to describe it.
- nyeah 1y agoBut it's easy to build & easy to read about, so "why isn't it everywhere already" still feels like an open question.
- DangitBobby 1y agoIt's a good question. But still... > 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.”
- nyeah 1y agoYeah, valid point.
- Dylan16807 1y agoIf it's a relatively busy sidewalk and you know the object has been there for several hours, that gets to be a pretty good argument.
- defraudbah 1y agoBest landing website! Keep pushing it
- moondistance 1y agoHow does this compare with Exowatt? Assume fresnel lenses are more efficient.
- timerol 1y agoExowatt requires rethinking the solar energy system entirely. This is meant to be bolted onto an existing solar panel field that is mostly selling energy to the grid, but gets curtailed sometimes
- maxbaines 1y agoThere are plenty of slag heaps (spoil tips) near coal plants, wonder how it could work with those? I guess the specific heat capacity is greater..
- scythe 1y agoThere's not enough comparison with the conventional ground-source heat pump here. There's not enough modeling of the expected system dynamics. I don't have a physics argument against it (right now at least) but I think that the author is trying way too hard to sell me on the idea of energy storage and not hard enough on why this proposal can work. And I don't think it's just me. Anyone reading the pitch for an energy storage startup in 2025 is probably aware of the basic goals, and more importantly is fatigued and suspicious after watching several dozen clever ideas go nowhere. 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.
- tgtweak 1y agoGSHP/ASHP can't get to steam-generating temperatures on the hot side unfortunately - you're looking at a "heat concentrator" which doesn't really exist in the form of a commercially available heat pump today - possibly not even in the theoretical.
- pfdietz 1y agoHeat pumps are a nonstarter here, because the goal here is minimizing capex, not maximizing efficiency.
- scythe 1y agoSorry, that comparison to heat pumps wasn't meant to imply that heat pumps would be used in this system. Rather, the focus was on the pipes that transfer heat from the system to the ground and back. That component remains basically the same — the heat pump components of a GSHP are above ground. My thought was that experience installing GSHP would allow you to bracket out the cost of the interred heat exchanger and make a comparison to the title proposal.
- HocusLocus 1y ago[flagged]
- deleted 1y ago[deleted]
- zahlman 1y ago> 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.
- tgtweak 1y agoI'm sure you meant it to be edgy and offensive but it's quite flat in substance - you can't reasonably reduce the population and any means you'd employ to do so would be equally destructive to the environment - you can't change the capitalistic paradigm of energy generation and consumption, without some effort and resources drastically beyond what you've demonstrated here, and you can't ignore economy of scale that is demonstrated particularly with energy generation to insinuate that these solutions must be collocated on premise for them to be viable.
- g-b-r 1y agoWhen did it become fashionable to say "PV" instead of photovoltaic, without ever saying what that stands for?
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- jmpman 1y agoAt what scale does this become efficient? I may have 1000 sqft to dedicate to this type of system on my lot. Feels like that’s at least an order of magnitude too small to maintain the energy through the seasons. Could we build one of these slightly larger systems for every square mile (~1000 homes), or does this only work at a 10,000 home scale? The article is showing a pile of dirt on the ground. Could this just be an area of the subsurface which is heated, or does ground water become too much of a problem?
- jillesvangurp 1y agoThere are some companies making heat batteries that you can install inside your house. They won't last very long but it's a great way to store excess energy from your rooftop solar and use it for heating and warm water. Also it allows you to timeshift when you draw power from the grid (i.e. when it's cheap rather than when you need hot water). 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.
- Scaevolus 1y agoYou can scale this down to be reasonable for homes, yes, but they're specifically trying to make it usable for large industrial processes: https://en.wikipedia.org/wiki/Seasonal_thermal_energy_storage https://en.wikipedia.org/wiki/Seasonal_thermal_energy_storag...
- 4b11b4 1y ago... and then build a 4 season greenhouse nearby...?
- tgtweak 1y agoYou can do that with normal pipes buried 5+ft underground that pull air into the greenhouse - the earth's temperature regulates the cold in the cooler months and the heat in the warmer months. There are similar calculations for how much piping you need to sustain a certain volume of air at earth temperature (typically 15'C in most places). This is shallow geothermal.
- ilaksh 1y agoSeems like a great concept. Hope they are commercially successful. 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.
- teiferer 1y ago> 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.
- 0xbadcafebee 1y agoForget climate change, the best reason is national security. Russia's war plummeted Europe into gas shortages and price hikes. Many countries would love to not be dependent on them. And since WW2, all war requires vast quantities of oil; maybe drones will reduce that a bit, but you still need to move stuff (and people) around a lot. So you need a reliable source of energy both in peacetime and wartime. 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.
- arnoooooo 1y agoWhy use photovoltaic panels instead of direct solar thermal ?
- pfdietz 1y agoDirect solar thermal that would produce 600 C would require expensive tracking concentrators. These lose a lot of energy to reradiation, don't use diffuse sunlight, and now you have very hot fluid you have to convey to your storage mass. With PV, you can just send electricity to resistive heaters in the storage mass.
- gigel82 1y ago> 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.
- tgtweak 1y agoHonestly not bad if there's enough earth between the heater element and the air - you'd only lose about 1% per month with a thick dirt wall.
- sophacles 1y agoSome yes. But there's a flaw in your reasoning: It ignores the concept called "rate of change". Because of this concept there will be more energy put into the pile than escapes, leaving some to be extracted and not just "escaping".
- speleding 1y agoI'm surprised that they use the PV power for heating coils instead of using heat pumps. I'm sure they've run the numbers and considered it too expensive or too much maintenance hassle. 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.
- wrsh07 1y agoI just read Project Hail Mary which suggests a use of solar thermal energy and I thought "ha too bad solar PV is so cheap in the real world this would almost certainly never happen" and yet, solar thermal energy plus heat pumps does seem extremely simple and cheap for this company
- maxmcd 1y agoDoes this become much trickier because they're trying to heat to 600c?
- leiroigh 1y agoPumping heat from 300K to 900K is not a big gain over heating -- the entire thing is premised on using extremely cheap intermittent electricity during the summer, and your savings are capped at 30%.
- turtlebits 1y agoSolar water heaters are expensive, complicated, fragile, and generally immobile. Solar panels and heating elements are cheap, simple and easily replaceable.
- speleding 1y agoA solar water heater is just a black box with a tube running through it. Many houses here have one, because they're much cheaper than PV panels to generate similar kW heat. But a sibling comment pointed out they want to go up to 900 °K, you can't do that with those, of course.
- jjangkke 1y agothis works in principle. heating dirt to store energy is cheap, the material costs almost nothing and the physics are solid. if the output needed is heat then it can beat batteries by a mile on cost. 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.
- tgtweak 1y agoIt begs the question - why use solar if the storage mechanic is sufficient to cover peak/off-peak storage of any surplus electricity in a significant way? Hydro Quebec has significant ($500M+/yr) electricity surpluses on a given year in the form of underutilized hydro during spring/fall months where energy demand is very low and export possibility is limited. These seem like ideal candidates for this vs something like a (relatively) small-scale solar setup. The slow-charge slow-release is also a considerable factor here since most battery energy storage solutions are designed for charge/discharge events multiple times per day to arbitrage energy rates - their ROI (which is currently very aggressive, sometimes less than 4-5 years) is a function of how many charge-cheap/discharge-expensive cycles they can perform per year. That is something that this doesn't seem equipped to do which is a negative multiplier on the ROI these systems can yield. If you can charge/discharge a battery 500 times per year, and the cost is 500x more, this is only at parity with a much slower charge/discharge schedule (charge during the summer, discharge during the winter - or vice versa). The other reality here is the steam turbine required to generate electricity (assuming electricity storage and not heat storage model) is a significant capex - roughly $300-400/kW (and some considerable OPEX in the form of maintenance and regulation/compliance). In this reality it only makes sense to retrofit an existing sunken-cost turbine and grid transmission system vs purchasing and co-locating a generating turbine along with the storage solution. 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.
- bilsbie 1y agoThe biggest problem is it has to be located near things that can use the heat. 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.
- Hilift 1y agoCalifornia is converting thousands of abandoned oil wells to thermal storage for electrical generation. https://eepower.com/news/engineers-repurpose-oil-wells-as-solar-storage/ 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-clean-power-plant-fully-online-in-kern-county https://www.latimes.com/environment/story/2025-08-06/major-c...
- zharknado 1y agoMy lingering question is how do you service a leaky pipe surrounded by dirt that’s 600C? Do you just have to forfeit a good chunk of your energy savings for the year? Or is there like a practical maintenance window each year at the end of the winter when you’d do this?
- pfdietz 1y agoYou probably don't; you just cap it and accept gradual degradation of the system. If needed, you build another system and connect them in series.
- Animats 1y agoThat's not a lingering question. It's the question. 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.
- Animats 1y agoWasn't this covered yesterday on HN? [1] [1] https://news.ycombinator.com/item?id=44998441 https://news.ycombinator.com/item?id=44998441
- Straw 1y agoIf you want heat, why bother converting sunlight to electricity first? You lose 80%. Is it that much more expensive to use mirrors to concentrate sunlight and capture near-100% of the energy as heat?
- turtlebits 1y agoMirrors require heliostats. 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 1y agoAnd PV panels work with diffused sunlight; high concentration solar only works with direct sunlight.
- kragen 1y agoI don't understand how, but apparently solar photovoltaic panels are indeed cheaper than thermal solar collectors now.
- apexalpha 1y agoIf you 'bother' with converting it to electricity first you can sell the electricity for profit and only convert the excess to heat.
- ted_dunning 1y agoBecause with a heliostat you have to move the energy as heat and that isn't as efficient and definitely not as easy or cheap as moving it as electricity. 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.
- Straw 1y agoThey are pitching co-located PV, and they already have a system to move the heat inside the pile of dirt!
- Imustaskforhelp 1y agoThis seems really cool if this can be done at scale 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.
- tsoukase 1y agoMy basement without any heating/cooling. External/Basement temp in C: -10/12, 40/24
- kragen 1y agoOh hey, this is the Energy Superabundance guy. 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-storage-in-dirt-for-repowering-decommissioned-coal-plants https://findingspress.org/article/141340-thermal-energy-stor..., US$20–50 per tonne.) From perusing https://www.eia.gov/analysis/studies/powerplants/capitalcost/pdf/capital_cost_AEO2020.pdf 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.
- kragen 1y agoIncidentally, energy superabundance is apparently becoming a reality in the PRC, and CO₂ emissions are falling: https://fortune.com/2025/08/14/data-centers-china-grid-us-infrastructure/ https://fortune.com/2025/08/14/data-centers-china-grid-us-in... “#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 industry’s growth. ¶ In China, Ma continued, it’s considered a “solved problem.”” because “China has an oversupply of electricty [sic]”. “In 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 isn’t cast as a sign of villainy, as it would be among some circles in the U.S. It’s simply seen as outdated.” #energy #USA https://xcancel.com/ruima/status/1955040979259650267 https://xcancel.com/ruima/status/1955040979259650267 #Rui-Ma’s 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 government’s investment in sustainable energy — from advanced hydropower to next-generation nuclear — 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 https://xcancel.com/ruima/status/1955372325970514161 #Rui-Ma on #energy in #China: “China: 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 world’s increase. China now produces ~1/3 of global electricity. That’s what “supply went up a lot” 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 China’s CO₂ fell year‑on‑year across the last 12 months (and in Q1’25), driven by the clean‑power surge rather than an economic slump.”
- smeeger 1y agoive been obsessed with passive heating recently. one thing that is really interesting that i only heard of until recently is pumping heat into the ground beneath a dwelling… far enough depth into the dirt so that by the time the heat rises and reaches the house the seasons have changed and its cold outside. the ultimate passive thermal