US Government funds pilot project for heated sand energy storage(pv-magazine.com)
pv-magazine.com
US Government funds pilot project for heated sand energy storage
https://www.pv-magazine.com/2024/04/04/us-government-funds-pilot-project-for-heated-sand-energy-storage/
130 comments
> better than most rechargeable battery technologies
you can't compare heat storage to electricity, because you can't directly use heat for anything else other than for heating, where as electricity can be used to perform motion.
If you used heat storage as a battery, there's an additional loss when converting to electricity.
However, if the heat is cheap/free during summer, storing it for winter is a no brainer.
you can't compare heat storage to electricity, because you can't directly use heat for anything else other than for heating, where as electricity can be used to perform motion.
If you used heat storage as a battery, there's an additional loss when converting to electricity.
However, if the heat is cheap/free during summer, storing it for winter is a no brainer.
But that doesn't really matter before all heating demand is served from storage. Sure, heat will never be the be all end all of energy storage, but there's a lot of demand in places that have winter. On top of this, when the conversion to heat is done by heat pumps, you not only get the benefit of a warmer baseline during the conversion, you also get some free cooling while charging.
The sand is gravity-fed into a heat exchanger which transfers the heat to a fluid that drives a combined cycle turbine, in this case. I'm curious what the conversion loss is here.
To add to that, what is the energy expenditure of building the battery compared to sand containment plus heat exchanger and turbine - i.e. mining, refining, transport, manufacture, delivery?
To add to that, what is the energy expenditure of building the battery compared to sand containment plus heat exchanger and turbine - i.e. mining, refining, transport, manufacture, delivery?
Gas turbine efficiency targets for combined cycle are targeting 65%, so loss is at least 35%. To me I the loss sucks, but if it can be cheap to build and maintain it matters less. If solar is the energy source and that gets driven cheap enough then that loss could be acceptable.
IIUC there is a physical limit from thermodynamics in converting back, based on the temperature. So when efficiencies are quoted, it could be either the proportion of input energy retrieved, or the proportion of the theoretical max efficiency achieved. I'm guessing you're quoting the former?
No way you'll get 65%. This sand won't be stored at the same temperature as a natgas generator's combustion chamber. Efficiency depends on delta T.
I'd guess 20%
I'd guess 20%
They're estimating over 50%, apparently. The sand is stored at over 1000 degrees. Not combustion temperatures, true, but also nothing to sniff at.
Nope.
The report says that the sand will be heated up to 1200 Celsius degrees.
This is much higher than the maximum temperature for steam turbines and equal to the temperature of the gas in the best gas turbines.
Therefore they will use a combined cycle, first a gas turbine will use hot air passed through the sand and the exhaust from the gas turbine will produce steam for a chain of steam turbines with decreasing working temperatures.
There should have been no problem in reaching a 65% efficiency for the conversion from heat to electricity, except that between hot sand and a gas burner there is the same difference as between an electric capacitor and a battery, while heat is extracted from the sand, it cools down.
Presumably, when the sand becomes too cold, the gas turbine is bypassed and the hot air just produces steam. When it becomes even colder, I suppose that the first steam turbine is also bypassed and only the low-temperature steam turbines are used.
This will lower the average efficiency, probably to around 50%. If the residual heat (after the steam turbines) had been used for heating or for cooling (i.e. heat-powered air conditioning), the efficiency could have been higher, e.g. over 80% in the beginning, while the sand is still very hot.
The report says that the sand will be heated up to 1200 Celsius degrees.
This is much higher than the maximum temperature for steam turbines and equal to the temperature of the gas in the best gas turbines.
Therefore they will use a combined cycle, first a gas turbine will use hot air passed through the sand and the exhaust from the gas turbine will produce steam for a chain of steam turbines with decreasing working temperatures.
There should have been no problem in reaching a 65% efficiency for the conversion from heat to electricity, except that between hot sand and a gas burner there is the same difference as between an electric capacitor and a battery, while heat is extracted from the sand, it cools down.
Presumably, when the sand becomes too cold, the gas turbine is bypassed and the hot air just produces steam. When it becomes even colder, I suppose that the first steam turbine is also bypassed and only the low-temperature steam turbines are used.
This will lower the average efficiency, probably to around 50%. If the residual heat (after the steam turbines) had been used for heating or for cooling (i.e. heat-powered air conditioning), the efficiency could have been higher, e.g. over 80% in the beginning, while the sand is still very hot.
I did not read the report, but one way you can improve the round trip efficiency is to not let the sand cool below, let's say 1000 °C. You pay a one-time penalty of heating the sand to this temperature and then you operate the storage only between 1000 and 1200 °C. This reduces the capacity of the "sand battery", roughly by a factor of 6. But sand is (reasonably) cheap.
I have seen another proposal where instead of sand the material would be graphite, which can be heated to more than 2000 °C. Graphite also has a huge heat conductivity. But it's more expensive.
I have seen another proposal where instead of sand the material would be graphite, which can be heated to more than 2000 °C. Graphite also has a huge heat conductivity. But it's more expensive.
because you can't directly use heat for anything else other than for heating
There's Stirling Engines. If the solar collection is pure thermal, and if that collection and the storage can be made dirt cheap, then the 37% or so efficiency of conversion to electricity stops being a problem. But what are currently problems with Stirling Engines -- Hardly any of the industrial optimization has been applied to them Re: Wright's Law. So they are quite costly! Heat pipe solar thermal could be made dirt cheap through economies of scale, and it works very well, even in climates like England's.
I could envision house construction changing to include sub-basements which are just polystyrene insulated boxes filled with sand. By over-provisioning storage by 4X, houses in cold climates could have huge electrical power stores, especially in summer. (Especially if the house uses heat exchangers which can draw directly from the thermal store.)
There's Stirling Engines. If the solar collection is pure thermal, and if that collection and the storage can be made dirt cheap, then the 37% or so efficiency of conversion to electricity stops being a problem. But what are currently problems with Stirling Engines -- Hardly any of the industrial optimization has been applied to them Re: Wright's Law. So they are quite costly! Heat pipe solar thermal could be made dirt cheap through economies of scale, and it works very well, even in climates like England's.
I could envision house construction changing to include sub-basements which are just polystyrene insulated boxes filled with sand. By over-provisioning storage by 4X, houses in cold climates could have huge electrical power stores, especially in summer. (Especially if the house uses heat exchangers which can draw directly from the thermal store.)
Doesn’t even need to be seasonal.
Plenty of times+places where you only need heating at night and still have some net electrical draw (because the sun isn’t shining at night).
Also, cold fronts move in with a lot of wind, but then it can stay cold a few days with calm winds until a warm-front moves in.
Plenty of times+places where you only need heating at night and still have some net electrical draw (because the sun isn’t shining at night).
Also, cold fronts move in with a lot of wind, but then it can stay cold a few days with calm winds until a warm-front moves in.
Half of all primary energy usage is for heating purposes. Heat is the best format to displace, as well, since a significant chunk of all that primary energy use is direct fossil fuel combustion right now.
Especially since you can use heat to drive a heat pump, which ends up actually achieving above unity efficiency effectively since the heat input is used to move additional heat from the environment. Even if it's inefficient, if the heat would otherwise have been wasted, it's a net benefit.
Especially since you can use heat to drive a heat pump, which ends up actually achieving above unity efficiency effectively since the heat input is used to move additional heat from the environment. Even if it's inefficient, if the heat would otherwise have been wasted, it's a net benefit.
The Pernell with heat compared to electricity is portability. It is easy and efficient to transmit electricity but heat is not
Heat can be used directly not only for heating, but also for cooling.
There are air conditioning systems that are powered by heat, not by electricity.
There are places where the power plants use the residual heat from the generation of electricity not only for heating during the winter, but also for cooling during the summer, by producing chilled water.
There are air conditioning systems that are powered by heat, not by electricity.
There are places where the power plants use the residual heat from the generation of electricity not only for heating during the winter, but also for cooling during the summer, by producing chilled water.
> There are air conditioning systems that are powered by heat, not by electricity.
How does that work?
How does that work?
Either absorption refrigeration or a steam turbine that compresses the working fluid.
> you can't compare heat storage to electricity, because you can't directly use heat for anything else other than for heating
You can use heat to generate steam that can spin turbines to perform work. But, I am not sure if it’s practical to generate steam from a sand battery, my background is in electrical construction. I’m guessing the sand battery isn’t nearly as hot as a natural gas steam boiler’s combustion chamber.
https://www.johnsoncontrols.com/en_sg/hvac-equipment/chiller...
You can use heat to generate steam that can spin turbines to perform work. But, I am not sure if it’s practical to generate steam from a sand battery, my background is in electrical construction. I’m guessing the sand battery isn’t nearly as hot as a natural gas steam boiler’s combustion chamber.
https://www.johnsoncontrols.com/en_sg/hvac-equipment/chiller...
Thermovoltiacs, converting heat dirctly to electricity. IIRC, At least one of the "box of rocks" thermal battery startups (interviewed on the Volts podcast) intends to have both a two way heat exchanger and electricity play.
> you can't directly use heat for anything else other than for heating, where as electricity can be used to perform motion.
Maybe today. But NASA has some interesting metal tires [0][1] which might change your mind for the future.
[0]: NASA info https://technology.nasa.gov/patent/LEW-TOPS-99
[1]: Neat youtube vid: https://www.youtube.com/watch?v=vSNtifE0Z2Q
Maybe today. But NASA has some interesting metal tires [0][1] which might change your mind for the future.
[0]: NASA info https://technology.nasa.gov/patent/LEW-TOPS-99
[1]: Neat youtube vid: https://www.youtube.com/watch?v=vSNtifE0Z2Q
Is a battery electricity or is it a chemical reaction?
Is absorption refrigeration bad enough to be permanently non-viable here? Or is it "just" a matter of scaling a niche technology?
Define "bad enough" in more specific terms.
I believe it largely depends on the application. If you have a lot of waste heat, it's potentially a way to get "free" refrigeration. (e.g., a paper plant that uses a lot of steam can use absorption chillers to make use of waste heat.) If fuel is much cheaper than electricity, it can be economically viable. Peak shaving can save lots of money. etc. But it's probably not competitive purely in terms of energy efficiency or GHG emissions.
I believe it largely depends on the application. If you have a lot of waste heat, it's potentially a way to get "free" refrigeration. (e.g., a paper plant that uses a lot of steam can use absorption chillers to make use of waste heat.) If fuel is much cheaper than electricity, it can be economically viable. Peak shaving can save lots of money. etc. But it's probably not competitive purely in terms of energy efficiency or GHG emissions.
If I had exact figures, I wouldn't need to ask for anyone's intuition. Thankfully, ChatGPT was willing to work with me, and I will summarize the results here.
Typical refrigeration COP (Coefficients of Performance):
Absorption refrigerator: 0.6-1.2
Compressor refrigerator: 1.5-4.0
Estimated TES economic advantage: 1.1-2.5x
Conclusion: yes, absorption refrigeration is probably inefficient enough to make it a long shot in this application. The only way I can see it becoming viable is if extremely hot TES can completely change the efficiency game, and then only just.
Typical refrigeration COP (Coefficients of Performance):
Absorption refrigerator: 0.6-1.2
Compressor refrigerator: 1.5-4.0
Estimated TES economic advantage: 1.1-2.5x
Conclusion: yes, absorption refrigeration is probably inefficient enough to make it a long shot in this application. The only way I can see it becoming viable is if extremely hot TES can completely change the efficiency game, and then only just.
The temperature in TFA are outside the range of most commercial absorption chillers, so this is more about making cheap electricity. I would imagine absorption would be more applicable if the same tech was used to generate lower-quality heat that's not suitable for a combined-cycle generator.
> outside the range of most commercial absorption chillers
"Off the shelf" isn't a constraint here, sort of the opposite: I'm trying to imagine the space of things that are physically possible but not yet commercially mature. Theoretically, higher temperatures mean more possible efficiency. That's the one ray of hope in otherwise dismal efficiency figures that are currently only viable, as you point out, if the heat is ~free.
"Off the shelf" isn't a constraint here, sort of the opposite: I'm trying to imagine the space of things that are physically possible but not yet commercially mature. Theoretically, higher temperatures mean more possible efficiency. That's the one ray of hope in otherwise dismal efficiency figures that are currently only viable, as you point out, if the heat is ~free.
>Theoretically, higher temperatures mean more possible efficiency.
I think you might be conflating a few things here. For a cycle to produce electricity, that's correct. But the mechanism of absorption chillers is fundamentally different. The chemistry of the materials and their phase change temperatures are definitely a constraining factor. Could you, in theory, develop some other absorbent/refrigerant that works at those higher temperatures? I suppose, but I would suspect there are much easier ways to get efficiency gains.
I think you might be conflating a few things here. For a cycle to produce electricity, that's correct. But the mechanism of absorption chillers is fundamentally different. The chemistry of the materials and their phase change temperatures are definitely a constraining factor. Could you, in theory, develop some other absorbent/refrigerant that works at those higher temperatures? I suppose, but I would suspect there are much easier ways to get efficiency gains.
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Nit: Rechargeable batteries have a loss when converting the chemical energy stored inside to electricity. There’s no free lunch.
Yes, but for Lithium and sodium batteries you are looking at 90+ efficiency.
you kinda can with sterling generators I think
An extrapolation directly to heat transfer is the Biot number
https://en.m.wikipedia.org/wiki/Biot_number#:~:text=The%20Bi....
https://en.m.wikipedia.org/wiki/Biot_number#:~:text=The%20Bi....
Gravity seems much more natural to me than heat; eg pumping water up a dam and releasing it again when you need the energy.
It strikes me that heat has the problem that it always loses energy in its “stable state” because the surrounding environment absorbs the heat, and gravity doesn’t have this problem.
It strikes me that heat has the problem that it always loses energy in its “stable state” because the surrounding environment absorbs the heat, and gravity doesn’t have this problem.
The issue of finding a location that has dramatic elevation change, a basin capable of storing vast amounts of water, and a suitable source/sink for pumping make pumped hydro difficult to deploy. Then there are additional logistics challenges such as environmental damage and proximity to human settlements for maintenance and engineering teams (prior challenges mean you don't really get to select the locations).
Heat sinks meanwhile can be built wherever you have a big rock by drilling some holes. Additionally, gravity definitely does lose stored energy in its "stable state", through evaporation and water entering the water table. Losses depend on geology and local climate, but it's not negligible.
Not to say that pumped hydro is a bad technology, it's just got it's own challenges and uses. It's most applicable in the form of electrical grid storage. But specifically on the scale of keeping towns and cities warm, heatsinks outperform almost across the board.
Heat sinks meanwhile can be built wherever you have a big rock by drilling some holes. Additionally, gravity definitely does lose stored energy in its "stable state", through evaporation and water entering the water table. Losses depend on geology and local climate, but it's not negligible.
Not to say that pumped hydro is a bad technology, it's just got it's own challenges and uses. It's most applicable in the form of electrical grid storage. But specifically on the scale of keeping towns and cities warm, heatsinks outperform almost across the board.
And, if you inundate an area of wilderness to create reservoir you have to also count the lost carbon capture of the growing plants, and the significant methane emissions of the now dead and rotting plant matter under the water. In dry deserts this may be negligible, but the mountains where people most want to install hydro projects are generally very forested.
The "vast basin" part of that is an exaggeration.
Look at https://www.whitepinepumpedstorage.com/ and the sizes of the upper and lower reservoirs there. This is to be a 8 GWh, 1 GW facility.
Look at https://www.whitepinepumpedstorage.com/ and the sizes of the upper and lower reservoirs there. This is to be a 8 GWh, 1 GW facility.
"vast" is a pretty non specific word so I can maybe see why you would think that? I feel like it's pretty obvious from context I'm not talking about an inland sea here. The quoted 5000 "acre-feet" in that project is a considerable amount of water for a man-made structure!
Either way, the details page[1] supports all of my above points. It even comments on the page how rare it is to find a suitable site like the one they've chosen.
[1]https://www.whitepinepumpedstorage.com/project-details
Either way, the details page[1] supports all of my above points. It even comments on the page how rare it is to find a suitable site like the one they've chosen.
[1]https://www.whitepinepumpedstorage.com/project-details
Pumped hydro is great, but the potential energy from gravity is actually really low. Stacking blocks will probably never work, and pumped hydro only works due to scale and existing geography. It’s also not modular and can’t be co-located with generation or loads unless the geography works out.
Terrament is working on a modular gravity storage solution that uses deep mine shafts to gain 20x more height than stacking blocks above ground. So you don’t need water or mountains. And since gravity storage uses ballast that is really just dumb weight, it could even be economical to make that ballast a secondary storage like thermal storage.
Pumped hydro is great, but only in certain areas where you already have the elevation gain available.
Compressed air storage is another one that's pretty good, but it's only particularly good if you can store it in underground caverns or unused mines, so it's also geography dependent.
For longer term storage, producing hydrogen can be a good one.
And batteries are actually fast becoming competitive with some of these options from the other end, generally better for shorter term storage but getting better at longer term. Even shorter term, flywheels can be a good option.
There's room for several different types of grid-scale energy storage, based on how efficient they are at different energy storage periods and numbers of charge-discharge cycles, and also in some cases on local conditions, like the availability of terrain and water sources for pumped hydro.
There's a good paper here which shows what the most efficient energy storage systems are for various combinations of length of storage (hours per discharge) against number of discharges per year, and for each one shows the current cost, and a predicted cost based on trends in technological advancements: https://www.sciencedirect.com/science/article/pii/S254243511...
There's a lot of the chart that is dominated by pumped hydro currently, but plenty of other storage technologies that are more cost effective on different timescales and numbers of discharges. But it looks like it's predicted for prices of battery storage and hydrogen storage to fall relative to the others, causing a different predicted landscape in 20 years.
And some of these, like pumped hydro, are dependent on geographic features, or access to certain resources, so even when one dominates overall, there can be others that dominate in particular geographical regions.
Compressed air storage is another one that's pretty good, but it's only particularly good if you can store it in underground caverns or unused mines, so it's also geography dependent.
For longer term storage, producing hydrogen can be a good one.
And batteries are actually fast becoming competitive with some of these options from the other end, generally better for shorter term storage but getting better at longer term. Even shorter term, flywheels can be a good option.
There's room for several different types of grid-scale energy storage, based on how efficient they are at different energy storage periods and numbers of charge-discharge cycles, and also in some cases on local conditions, like the availability of terrain and water sources for pumped hydro.
There's a good paper here which shows what the most efficient energy storage systems are for various combinations of length of storage (hours per discharge) against number of discharges per year, and for each one shows the current cost, and a predicted cost based on trends in technological advancements: https://www.sciencedirect.com/science/article/pii/S254243511...
There's a lot of the chart that is dominated by pumped hydro currently, but plenty of other storage technologies that are more cost effective on different timescales and numbers of discharges. But it looks like it's predicted for prices of battery storage and hydrogen storage to fall relative to the others, causing a different predicted landscape in 20 years.
And some of these, like pumped hydro, are dependent on geographic features, or access to certain resources, so even when one dominates overall, there can be others that dominate in particular geographical regions.
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With water you lose some due to evaporation.
That was my first thought too. But lakes lose ~20% / year to evaporation, and with the use of shade balls that is cut by ~90%, so we are at 2% / year - which is about the same as very efficient daily loss from heat storage.
If the heat is being turned back to electricity, a heat sink is needed and if this is done by evaporation the water loss will greatly exceed that of natural evaporation from a PHES facility.
It's not the evaporation per se that matters in the pumped hydro, it is the evaporation loss of water you already invested in pumping, so it is just an efficiency loss. The vapor loss for the heat sink is indirect, you usually just calculate the turbine efficiency. I don't know if the (generally much smaller) pumping requirements for turbines is already included in their efficiency calculations, but it would need to be of course.
Either way, it just goes to show further that pumped hydro would be more efficient, when and where it is feasible.
Either way, it just goes to show further that pumped hydro would be more efficient, when and where it is feasible.
With a mineshaft gravity storage you could actually try to spin up a convective loop powered by geothermal that dries the sand over time, allowing you to lift dry sand when charging and abseil heavier wet sand when discharging.
When you can store electricity more directly instead of the (inefficient) conversion to and from heat it is just crazy to not do so. With electricity, thanks to heat pumps you can "move" heat instead of producing it, which makes heating a lot less expensive since the "efficiency" can often reach 300-400%. For that reason you want to keep using electricity for as long as possible in most cases.
Of course, if you have a huge source of cheap heat the equation might change. In such cases you might still want to use some of the heat to get higher temperature heat. (https://en.wikipedia.org/wiki/Absorption_heat_pump)
And no, it will not help too much if you use a heat pump before storing the energy in this facility. You still have huge conversion losses, the volume for low-temperature heat storage will be huge. If you want high temperature storage your heat pumps will need more stages and run less efficient.
And no, it will not help too much if you use a heat pump before storing the energy in this facility. You still have huge conversion losses, the volume for low-temperature heat storage will be huge. If you want high temperature storage your heat pumps will need more stages and run less efficient.
> the ratio of the volume to surface area decreases the larger you make a container
Did you mean to write the reverse? i.e the ratio of the surface area to volume decreases the larger you make a container.
Did you mean to write the reverse? i.e the ratio of the surface area to volume decreases the larger you make a container.
Yes.
I also think this is a very interesting approach to take. This might be a pipe dream but it would be really cool if we could just turn a big chunk of desert into a battery by plumbing some heat exchangers through it.
Or maybe just putting a gigantic Fresnel lens in the desert and pointing it at the ground. I almost wish someone would try this just to see what would happen.
Or maybe just putting a gigantic Fresnel lens in the desert and pointing it at the ground. I almost wish someone would try this just to see what would happen.
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> The sand used in the thermal energy storage (TES) system could be heated to the range of 1,100 C using low-cost renewable power. [...] when electricity is needed, the system will feed hot sand by gravity into a heat exchanger, which heats a working fluid, which drives a combined-cycle generator.
So this is definitely not a "bury your heating coils in a sand dune, then connect..." technology.
Quartz melts (per Wikipedia) at 1,713 C. Hotter would obviously be more efficient (basic thermodynamics) - but from the linked govt. report, it sounds like getting usefully hotter would lead to excessive technical problems.
Beyond sourcing the sand (a real issue in many places), this tech sounds incredibly benign, environmentally. Zero-ish rare elements / nasty chemicals / emissions. And the worst-case "melt-down" leaves just a pile of burning-hot sand.
Edit: IANAME (not a Mech. Engineer), but that govt. technical report looks like great stuff if you're seriously into energy storage tech, or just an amateur gearhead. Direct link: https://www.nrel.gov/docs/fy23osti/84728.pdf
So this is definitely not a "bury your heating coils in a sand dune, then connect..." technology.
Quartz melts (per Wikipedia) at 1,713 C. Hotter would obviously be more efficient (basic thermodynamics) - but from the linked govt. report, it sounds like getting usefully hotter would lead to excessive technical problems.
Beyond sourcing the sand (a real issue in many places), this tech sounds incredibly benign, environmentally. Zero-ish rare elements / nasty chemicals / emissions. And the worst-case "melt-down" leaves just a pile of burning-hot sand.
Edit: IANAME (not a Mech. Engineer), but that govt. technical report looks like great stuff if you're seriously into energy storage tech, or just an amateur gearhead. Direct link: https://www.nrel.gov/docs/fy23osti/84728.pdf
Huh, it intuitively seems like piping working fluid to the sand ought to be easier than moving the sand to the working fluid. Is the moving-sand approach fundamentally desirable thing (I can't imagine why) or is it just a simplification for the proof of concept?
>> Is the moving-sand approach fundamentally desirable thing (I can't imagine why) or is it just a simplification for the proof of concept?
I suspect this is about operating temperatures. If you run pipes through the thermal mass then you will be slowly heating/cooling the entire mass. That means the temp will be constantly changing and would basically never be at optimum. But by withdrawing small amounts of sand to be cooled/heated separately, the bulk can remain at an optimum. Only the removed sand is cooled. So your tank of "hot" sand remains at the same temperature until the last bit of hot sand is gone, rather than it slowly cooling as you withdraw heat from the bulk. That no doubt makes thermal transfer more efficient and predictable.
I suspect this is about operating temperatures. If you run pipes through the thermal mass then you will be slowly heating/cooling the entire mass. That means the temp will be constantly changing and would basically never be at optimum. But by withdrawing small amounts of sand to be cooled/heated separately, the bulk can remain at an optimum. Only the removed sand is cooled. So your tank of "hot" sand remains at the same temperature until the last bit of hot sand is gone, rather than it slowly cooling as you withdraw heat from the bulk. That no doubt makes thermal transfer more efficient and predictable.
I suspect it's because the thermal conductivity of sand isn't that great. If you've got your working fluid running through pipes embedded in hot sand, the system is likely bottlenecked on getting the heat energy from the main body of the mass through the cooler sand closest to the pipes.
Do it the other way and the enormous surface area is working for you, so you can presumably get the energy out arbitrarily fast (or, at least, that's no longer the bottleneck).
Do it the other way and the enormous surface area is working for you, so you can presumably get the energy out arbitrarily fast (or, at least, that's no longer the bottleneck).
The thought occurs that if that is indeed the problem, you could attack it by mixing a metal in with the sand. You'd still get the thermal mass, but conductivity would no longer be a problem as long as it had been in a liquid phase at least once.
The problem isn't so much the sand, it's all the air gaps between the grains of sand.
Adding metal won't help any- once it gets to a liquid phase, it'll sink down, or if it doesn't stay liquid long enough, will just trap most of the air in it.
Edit: you'll also want to keep oxygen out of the environment in the liquid phase. Depending on the metal you use and the exact makeup of the sand, you'll wind up with some materials that are often used in refractory cement- aluminum, oxygen, and silicon will do the trick and absolutely ruin the effectiveness of your heat battery.
Adding metal won't help any- once it gets to a liquid phase, it'll sink down, or if it doesn't stay liquid long enough, will just trap most of the air in it.
Edit: you'll also want to keep oxygen out of the environment in the liquid phase. Depending on the metal you use and the exact makeup of the sand, you'll wind up with some materials that are often used in refractory cement- aluminum, oxygen, and silicon will do the trick and absolutely ruin the effectiveness of your heat battery.
That's what I was getting at. Fill the air gaps with metal.
Piping the working fluid to the sand means your pipes have to increase in size and cost as you add more sand. Dropping the sand into a heat exchanger means the heat exchanger doesn't increase in cost with the volume of sand.
Nah it's nuts to mobilise the sand as a working fluid. The more mature design option seems to be refractory brick for heat energy storage, with piping running through it where you can raise steam. Running a steam turbine generator is generally seen as uneconomic due to the very low round-trip efficiency, and heat storage usually follows the principle of "if you store it as heat, use it as heat".
Sand-sourcing issues are typically related to types of sand required for special applications, such as in concrete or silicon wafer production that needs very specific types or shapes of the grains. This kind of application would probably work with “regular” sand that’s unsuitable for those special purposes, and also happens to be the most common type of sand.
This seems like a really cool technology that also doesn't need much engineering to make it viable. Why isn't it already widespread?
there is a DIY community around it and because it is so simple to make I just dont see any need to rely on commercial solutions. Literally store sand somewhere and heat it, use it for days or months depending on the setup.
I am really intrigued by using sand for energy storage - what I don't get (not my field) is given a typical 2000sf house, located in the colder part of the country as an example, how much heat could be stored for how long? i.e. is it even feasible to use solar panels to power resistance heaters all spring/summer/fall, to save up enough heat to keep a house warm for the entire winter? if so, how many panels would you need and how big a sand battery would it take.
I am not planning on doing this, but explaining it on a scale that I can relate to would be helpful, because I know, for example, that said house can store a winter's worth of heat in a 1000 gallon oil tank, or small woodshed big enough for 6 cords of wood.
I am not planning on doing this, but explaining it on a scale that I can relate to would be helpful, because I know, for example, that said house can store a winter's worth of heat in a 1000 gallon oil tank, or small woodshed big enough for 6 cords of wood.
https://en.wikipedia.org/wiki/Seasonal_thermal_energy_storag...
> In Alberta, Canada, the homes of the Drake Landing Solar Community (in operation since 2007), get 97% of their year-round heat from a district heat system that is supplied by solar heat from solar-thermal panels on garage roofs. This feat – a world record – is enabled by interseasonal heat storage in a large mass of native rock that is under a central park. The thermal exchange occurs via a cluster of 144 boreholes, drilled 37 metres (121 ft) into the earth. Each borehole is 155 mm (6.1 in) in diameter and contains a simple heat exchanger made of small diameter plastic pipe, through which water is circulated. No heat pumps are involved.
That development is 52 homes. They are presumably engineered to be highly energy efficient and it's not a perfect comparison to sand, but it's less than I'd have imagined.
> In Alberta, Canada, the homes of the Drake Landing Solar Community (in operation since 2007), get 97% of their year-round heat from a district heat system that is supplied by solar heat from solar-thermal panels on garage roofs. This feat – a world record – is enabled by interseasonal heat storage in a large mass of native rock that is under a central park. The thermal exchange occurs via a cluster of 144 boreholes, drilled 37 metres (121 ft) into the earth. Each borehole is 155 mm (6.1 in) in diameter and contains a simple heat exchanger made of small diameter plastic pipe, through which water is circulated. No heat pumps are involved.
That development is 52 homes. They are presumably engineered to be highly energy efficient and it's not a perfect comparison to sand, but it's less than I'd have imagined.
Storing heat in bedrock sounds like a good idea, but there are risks, e.g. https://www.thelocal.de/20170818/this-historic-german-town-i...
https://www.cbc.ca/player/play/1.7155409
I live in Calgary and have seen a few articles about Drake Landing recently.
I live in Calgary and have seen a few articles about Drake Landing recently.
A very low key variation of heat storage is using a ground-source heat pump in winter and then in the summer using the same heat pump for cooling the house and replenishing the ground source while doing so.
Small ground sources, or ground sources with neighbors too close who do the same, will actually accumulate noticeable ground cooldown from season to season if they are not replenished. Free air conditioning comfort from the replenishing effort, or free replenishing from the air conditioning, you can spin it however you like. It's very low gradient and certainly won't get you through winter without a another power source, but it absolutely is seasonal heat storage.
Small ground sources, or ground sources with neighbors too close who do the same, will actually accumulate noticeable ground cooldown from season to season if they are not replenished. Free air conditioning comfort from the replenishing effort, or free replenishing from the air conditioning, you can spin it however you like. It's very low gradient and certainly won't get you through winter without a another power source, but it absolutely is seasonal heat storage.
I don't think that the sand units you can install in your home have the ability to store energy across seasons. They are more like hot water heaters; heat when you have solar, but you can use some hot water at night when electricity is more expensive.
So this would be like, in a mild climate, the sun is going to keep your house warm during the day and you are generating some solar. You use the solar to heat up the sand, and then overnight, you recover some of that energy to use for heat. (I think you can get electricity back out of the heated sand as well, but it's like 70% efficient compared to >90% for a lithium battery. So I think the big application is in heating, less for charging your car after you get home from work.)
So this would be like, in a mild climate, the sun is going to keep your house warm during the day and you are generating some solar. You use the solar to heat up the sand, and then overnight, you recover some of that energy to use for heat. (I think you can get electricity back out of the heated sand as well, but it's like 70% efficient compared to >90% for a lithium battery. So I think the big application is in heating, less for charging your car after you get home from work.)
A single house is too small to make that work. I can't see how you could insulate such a small volume for more than a few hours. It can start to work at district scale, but the Finns are just targeting a few days.
https://www.euronews.com/green/2024/03/10/sand-batteries-cou...
https://en.wikipedia.org/wiki/Drake_Landing_Solar_Community
https://www.euronews.com/green/2024/03/10/sand-batteries-cou...
https://en.wikipedia.org/wiki/Drake_Landing_Solar_Community
I think this is a surface area/volume problem. A smaller installation is going to have a larger relative surface area given the amount of stored heat, so your losses/insulation requirements are going to be much worse.
https://www.renewableenergymagazine.com/storage/first-commer...
This is 8MWh (of heat), the 1000 gallon oil tank is about 40MWh.
Something like a two story basement filled with sand at the maximum temperature of a home oven is probably in the ballpark.
This is 8MWh (of heat), the 1000 gallon oil tank is about 40MWh.
Something like a two story basement filled with sand at the maximum temperature of a home oven is probably in the ballpark.
The temperatures we’re talking about (1000C) would be incredibly dangerous in residential applications, plus a small installation would lose too much energy to the environment due to the ratio of surface area to volume. More practical IMO is to use a daily cycle like what Harvest Thermal is doing: store energy in your water heater tank during the daytime and release it at night.
> winter's worth of heat in a 1000 gallon oil tank
That's a massive fire risk because it is combustible fuel. A pile of hot sand in an auxilary, non-flammable structure isn't going to catch fire.
That's a massive fire risk because it is combustible fuel. A pile of hot sand in an auxilary, non-flammable structure isn't going to catch fire.
A 1000 gallon tank stores about 146 gigajoules of energy (diesel motor fuel = 138,700 BTU/gallon, "138700 BTU * 1000 in gigajoules").
1000 gallons of sand (about 6000 kg) heated 1000 °C above ambient stores about 1000 K * 6000 kg * 1.1 kJ/kg-K (from the paper, on page 9) = 6.6 gigajoules.
So to match a fuel tank for energy storage, it needs to be at least 22x the volume, have extremely good insulation (even more volume), a heat-exchanger, and sand-handling augers. Additionally, the sand needed to be heated in the first place, which means a good electrical connection, but if you have that power in the first place, just use that during the winter? The nice part about fuel is that a man and a truck can move a few thousand gallons of hydrocarbons several hundred miles out to the middle of nowhere and transfer that energy at megawatt speed with a hose.
1000 gallons of sand (about 6000 kg) heated 1000 °C above ambient stores about 1000 K * 6000 kg * 1.1 kJ/kg-K (from the paper, on page 9) = 6.6 gigajoules.
So to match a fuel tank for energy storage, it needs to be at least 22x the volume, have extremely good insulation (even more volume), a heat-exchanger, and sand-handling augers. Additionally, the sand needed to be heated in the first place, which means a good electrical connection, but if you have that power in the first place, just use that during the winter? The nice part about fuel is that a man and a truck can move a few thousand gallons of hydrocarbons several hundred miles out to the middle of nowhere and transfer that energy at megawatt speed with a hose.
Huge amount of the rural population already have an oil or propane tank sitting within a hundred yards of their house. Being even slightly remote means you require backup heating options for when things fail.
Undecided did a couple of videos on this technology. It seems quite useful for heat storage - as other commenters have noted, it isn't that efficient for pure electric <-> electric storage.
* How a Sand Battery Could Change the Energy Game - https://www.youtube.com/watch?v=G6ZrM-IZlTE
* Sand Batteries for Home Usage - https://www.youtube.com/watch?v=KVqHYNE2QwE
* How a Sand Battery Could Change the Energy Game - https://www.youtube.com/watch?v=G6ZrM-IZlTE
* Sand Batteries for Home Usage - https://www.youtube.com/watch?v=KVqHYNE2QwE
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I like this one too https://youtu.be/KVqHYNE2QwE?si=GM80NBsE_Ms8oT-n
I love this idea
I have been following the progress of sand batteries.
So much so that I actaully made one at home.
https://hackaday.com/2022/11/21/making-a-do-it-yourself-sand...
I made some changes to this idea. I used a 12V supply from an old PC power supply to run the heat element in the sand. I used some course pool filter sand that I use for my aquariums.
I have a very chilly hallway with no radiator between my lounge and main entrance door.
It did work. Raised the temperature from 62F to a modest 70F. It took a few days to warm through and remain constant.
I see there are developments in Scandinavia to heat entire towns.
This is the good science I like to see.
I have been following the progress of sand batteries.
So much so that I actaully made one at home.
https://hackaday.com/2022/11/21/making-a-do-it-yourself-sand...
I made some changes to this idea. I used a 12V supply from an old PC power supply to run the heat element in the sand. I used some course pool filter sand that I use for my aquariums.
I have a very chilly hallway with no radiator between my lounge and main entrance door.
It did work. Raised the temperature from 62F to a modest 70F. It took a few days to warm through and remain constant.
I see there are developments in Scandinavia to heat entire towns.
This is the good science I like to see.
Does this differ in design from the Finish sand battery from 2 years ago: https://news.ycombinator.com/item?id=32006791
The Finnish system is just heat->heat. They generate heat when the wind is blowing, and inject heat back into the district system when it isn't. Super simple - resistive heating, and passive heat transfer.
This system produces electricity. Exciting, but much fancier.
This system produces electricity. Exciting, but much fancier.
A stirling engine can generate heat from electricity, such as those used in MicroCHP, you can burn wood, produce heat, and generate electricity from that heat. You could do the same with a pile of sand.
You just need to pipe liquid through the sand, and a supply of cooler water.
You just need to pipe liquid through the sand, and a supply of cooler water.
Yes, this involves higher temperature (the sand is stable up to ~1200 C) and transfer of heat from the sand to a working gas by means of Babcock & Wilcox's fluidized bed heat exchanger technology. This is a neat idea that intimately mixes the gas and sand for very rapid and compact heat transfer.
Using resistive heaters, round trip efficiency (back to electricity) is estimated to be around 52%.
Using resistive heaters, round trip efficiency (back to electricity) is estimated to be around 52%.
Love the idea. Hate the acronym...ENDURING, short for "Economic loNg-DURation electrIcity storage by using low-cost thermal energy storage aNd hiGh-efficiency power cycle"? ELDESbULCTESaHEPC.
Thermal storage works nicely with solar thermal plants. Not so good for direct electricity storage though.
Pretty inefficient, yes. Thermodynamics is a harsh mistress.
But if the other choice is "throttle down the wind farm, because the grid doesn't need that much power" - then a really cheap/simple/safe (but inefficient) storage tech could prove pretty useful.
But if the other choice is "throttle down the wind farm, because the grid doesn't need that much power" - then a really cheap/simple/safe (but inefficient) storage tech could prove pretty useful.
One can get higher round trip efficiency (practically, perhaps 65%) using pumped thermal storage. Here, one uses some thermal cycle in reverse to separate "cold" and "hot", then reverse that to discharge. This also reduces the maximum temperature needed to maybe 500 C, below the creep limit for cheap steel. The cold end would be maybe -100 C, stored in something like liquid hexane.
True. But the govt. report on this idea seems confident of 50% RTE, or 55% if they used a more-complex turbine system.
For limited & short-term use, the plant with vastly-more-expensive storage masses might make sense.
But as soon as you were faced with NIMBYs or environmentalists (hexane's MSDS is far closer to hydrogen fluoride's MSDS than it is to sand's), or if you are working in a less-prosperous part of the world...sand is great stuff.
For limited & short-term use, the plant with vastly-more-expensive storage masses might make sense.
But as soon as you were faced with NIMBYs or environmentalists (hexane's MSDS is far closer to hydrogen fluoride's MSDS than it is to sand's), or if you are working in a less-prosperous part of the world...sand is great stuff.
How does this compared to pumped storage?
You can pump sand by bubbling compressed air through it.
1. https://www.youtube.com/watch?v=My4RA5I0FKs
1. https://www.youtube.com/watch?v=My4RA5I0FKs
seems to me that this would result in heat-loss as the air is heated quickly then ejected from the mass. perhaps the bubbled gas doesn't hold a significant amount of heat though? (but if it did, it could be used to extract the heat without pumping the sand...)
Modern pumped hydro might have a RTE of 80%.
I was going to chime in to second this. In a former life I worked on power towers and we had designs for air receivers that would potentially work really well with this type of system:
- High temperatures - Intermittent solar input not a problem - tall central structure (?? maybe a plus given the paper's tall storage vessels)
But high temperature air receivers have their own problems, mostly around receiver material properties (thermal cycling / stress) and heat loss. It's really hard to focus a lot of light from the sun into a tiny aperture, because the sun isn't really a point source, and no mirror is perfectly shaped.
- High temperatures - Intermittent solar input not a problem - tall central structure (?? maybe a plus given the paper's tall storage vessels)
But high temperature air receivers have their own problems, mostly around receiver material properties (thermal cycling / stress) and heat loss. It's really hard to focus a lot of light from the sun into a tiny aperture, because the sun isn't really a point source, and no mirror is perfectly shaped.
And highly concentrating mirrors only work with direct sunlight, while PV works with diffuse sunlight scattered off clouds, dust, or the air itself. Bifacial PV cells even capture light hitting the back of the panel.
It could be interesting to burry heating coils in the ground under the house and maybe dig deep, insulated petimeter foundation to better keep the heat inside. Power them with solar of course at times of negative prices.
Or dig out a deep cellar, insulate on the sides and a the bottom against heat loss and moisture and put back the earth you dug out with heating element in the center. You don't even have to insulate wires that go through earth to the heating element because electricity passing through earth will get turned to heat as well.
It might be nice additional heating for cooler climates.
If you dug deep enough to have actual cellar on top of that you'd have a very warm cellar, you could put underground swiming pool there.
Or dig out a deep cellar, insulate on the sides and a the bottom against heat loss and moisture and put back the earth you dug out with heating element in the center. You don't even have to insulate wires that go through earth to the heating element because electricity passing through earth will get turned to heat as well.
It might be nice additional heating for cooler climates.
If you dug deep enough to have actual cellar on top of that you'd have a very warm cellar, you could put underground swiming pool there.
I'm dubious about all long duration energy storage systems (LDES).
I feel their addressable market gets squashed between a) simply building more renewables and short term battery storage, both of which are reducing in cost due to massive buildout, b) making chemicals from renewable energy (i.e. green hydrogen, that then gets used as a building block for Ammonia or hydrocarbons).
As long as the former is able to cheaply eat marketshare then you can just use the fossil fuels it displaces in the hard to decarbonise markets and still come out ahead financially and in terms of carbon.
The latter can be used in jumbo jets or whatever, but also in fairly standard turbines for electricity production if needed, but emphasis on "if" because if you need it just as insurance against unpredictable demand/weather, then it's a plus point if you can just sell it to farmers, airlines or factories once you get to spring, and the physical storage already exists on a large scale for those purposes.
I think this already makes pumped hydro financially dubious, never mind more theoretical ideas.
The timeshifting of electrical heat demand for industry is another market nibbling away at this, and might be another use for the fluidized bed and sand storage part though.
I feel their addressable market gets squashed between a) simply building more renewables and short term battery storage, both of which are reducing in cost due to massive buildout, b) making chemicals from renewable energy (i.e. green hydrogen, that then gets used as a building block for Ammonia or hydrocarbons).
As long as the former is able to cheaply eat marketshare then you can just use the fossil fuels it displaces in the hard to decarbonise markets and still come out ahead financially and in terms of carbon.
The latter can be used in jumbo jets or whatever, but also in fairly standard turbines for electricity production if needed, but emphasis on "if" because if you need it just as insurance against unpredictable demand/weather, then it's a plus point if you can just sell it to farmers, airlines or factories once you get to spring, and the physical storage already exists on a large scale for those purposes.
I think this already makes pumped hydro financially dubious, never mind more theoretical ideas.
The timeshifting of electrical heat demand for industry is another market nibbling away at this, and might be another use for the fluidized bed and sand storage part though.
Here are some informative slides on the technology from 2021:
https://arpa-e.energy.gov/sites/default/files/2021-03/07%20D...
Previously linked at https://news.ycombinator.com/item?id=28451131
https://arpa-e.energy.gov/sites/default/files/2021-03/07%20D...
Previously linked at https://news.ycombinator.com/item?id=28451131
it seems the primary benefit for sand over water, is a 1:10 operating temp vs. 5:1 specific heat. So it depends on whether the added complexity of working with a hotter, solid is worth not having to build a facility that is 2x bigger. Are there other benefits I'm missing, or is this concrete block gravity storage vs pumped water storage, all over again?
Comparing water's 4.18 kJ/kg-K * ~75 K (25 °C -> 100 °C) to the sand's 1.1 kJ/kg-K * 900 K?
I think you can (or it's easier) get more useful work out of a lesser amount of hotter stuff, even if the thermal energy or total heat is the same. Unsure of that, I don't know what the specific principle is. I'd vaguely gesture at the 2nd law of thermo as if I poured a cup of boiling water into a pot of room-temperature water, the total heat leaving the pot would wind up being the same as the heat leaving the cup, but less useful?
I think you can (or it's easier) get more useful work out of a lesser amount of hotter stuff, even if the thermal energy or total heat is the same. Unsure of that, I don't know what the specific principle is. I'd vaguely gesture at the 2nd law of thermo as if I poured a cup of boiling water into a pot of room-temperature water, the total heat leaving the pot would wind up being the same as the heat leaving the cup, but less useful?
Sand doesn't leak down or up (via evaporation) nearly as much.
It's also far less of a precious resource and non-corrosive, compared to the most common version of water.
It's also far less of a precious resource and non-corrosive, compared to the most common version of water.
If the goal is conversion back to electrical energy, the high temperature is a huge advantage.
I have wondered if this technology could be used in open loop mode where the sand is replaced with some material that you want to thermally process. For example, olivine particles that become more reactive with CO2 (for mineral carbonation for CO2 sequestration) after being heat treated. Run the particles though once and use them afterwards.
Feed in calcium carbonate, heat it up and sequester the CO2, and use the hot calcium oxide once then ship it off to the cement plant.
Or, how about taking an existing cement plant and have it use the air heat-exchanger/turbine/generator setup described in this project to recover the energy in the red-hot clinker? I assume they'd have some sort of heat exchanger system already to preheat feedstock using the outflow, however?
Or, how about taking an existing cement plant and have it use the air heat-exchanger/turbine/generator setup described in this project to recover the energy in the red-hot clinker? I assume they'd have some sort of heat exchanger system already to preheat feedstock using the outflow, however?
What if we grind asteroids and send bags of sand from orbit? Sand will overheat while falling giving us free energy and sand. Sand is valuable.
Whatever you are on, I need some of it. It must be good.
Also an unstoppable onslaught of kinetic weapons
With such cheap solar panels soaking up summer sun combined with this storage, winter heating could get really efficient.
Seems to me that direct battery storage research is a much much much MUCH better use of government research funding. Sure if you want to use sand heat holders for heating houses, fine.. but for conversion to electricity? bleh
Batteries are likely better for diurnal storage, but the per-energy capital cost of the sand silos ($2/kWh(th))) would be really hard to beat with batteries, so for longer periods this could be superior.
Using heat for energy storage and then converting back to electricity are ok if you don't care about cost of electricity, the facility or the maintenance. In basically all other cases they are some of the worst ideas. We have much better technologies that are known for the last ~50 years. They are simple, they do work and have volumetric energy density within striking distance of fossil fuels however don't include carbon. Just reading the expired US patents would reveal that.
I guess there are worse things to invest into but come on, we teach the physics needed to comprehend why this is a bad idea in high school.
I guess there are worse things to invest into but come on, we teach the physics needed to comprehend why this is a bad idea in high school.
Like a giant Turkish coffee stove?
I go to the beach fill up 50 gallon drums with it and then pipe hot water through it so that you can enjoy heat without electricity or gas.
im obsessed with it. i love the way it feels on my body. i take warm sand baths with it. i have cold feet so i use nylon socks, fill it with sand providing endless massage and keeping it warm.
ive yet to try different types of sand from other regions but Canadian beach sand does the job.
im obsessed with it. i love the way it feels on my body. i take warm sand baths with it. i have cold feet so i use nylon socks, fill it with sand providing endless massage and keeping it warm.
ive yet to try different types of sand from other regions but Canadian beach sand does the job.
i can't tell if you are trolling or not
why would i be trolling?
so maybe someone will try putting sand in their socks
i dont understand it feels really good
[1] https://commons.wikimedia.org/wiki/File:Comparison_of_surfac...