US Government funds pilot project for heated sand energy storage
pv-magazine.com
pv-magazine.com
[1] https://commons.wikimedia.org/wiki/File:Comparison_of_surfac...
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.
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?
I'd guess 20%
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 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.
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.
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
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...
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.
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.
"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.
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.
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 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.
How does that work?
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.
Did you mean to type "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.
Either way, it just goes to show further that pumped hydro would be more efficient, when and where it is feasible.
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.
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.
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.
That is big for time-shifting daily energy usage, but way too small for seasonal energy storage
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.
https://en.m.wikipedia.org/wiki/Biot_number#:~:text=The%20Bi....
Did you mean to write the reverse? i.e the ratio of the surface area to volume decreases the larger you make a container.
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.
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.
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
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).
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.
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 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.
> 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.
I live in Calgary and have seen a few articles about Drake Landing recently.
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.)
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.
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.
https://www.euronews.com/green/2024/03/10/sand-batteries-cou...
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.
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.
* 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
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.
Using resistive heaters, round trip efficiency (back to electricity) is estimated to be around 52%.
This system produces electricity. Exciting, but much fancier.
You just need to pipe liquid through the sand, and a supply of cooler water.
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.
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.
- 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.
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 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.
https://arpa-e.energy.gov/sites/default/files/2021-03/07%20D...
Previously linked at https://news.ycombinator.com/item?id=28451131
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?
It's also far less of a precious resource and non-corrosive, compared to the most common version of water.
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?
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.
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.