A 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.
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.
Interesting 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.
Long-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!
You are confusing the concepts of insulation and reservoirs.
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 thermal time constant of a 3d object scales as the square of the linear dimensions of the object, so time constants measured in years are quite achievable.
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.
One 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.
However, for long term storage, the "cost of inefficiency" is swamped by the amortized capex of the batteries. The goal is to minimize capex, not maximize efficiency. This becomes even more true as the cost of the input energy declines.
I 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.
Ground-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.
This 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.
Interesting 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.
Another 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?
I 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)
There'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.
At 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?
51 comments
[ 4.2 ms ] story [ 54.5 ms ] threadEDIT: dupe, darn it.
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.
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!
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.
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.
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.
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)
The issue here is: the "stored energy" isn't electricity, but heat. Converting heat into electricity is quite wasteful.
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
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.