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US Government funds pilot project for heated sand energy storage

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Re: US Government funds pilot project for heated sand energy storage

#41

Post by mecsred »

stingraycharles wrote: post #34
retrac wrote: post #28

Heat storage has an aspect that was counterintuitive to me, but follows from basic geometry. It benefits greatly from large scale, since the ratio of the volume to surface area [1] decreases the larger you make a container. Accordingly, if a heat tank is large enough, the surface area becomes negligible relative to its volume, and it, in effect, becomes well-insulated by its own mass. For really big tanks, like might…

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.

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.

Re: US Government funds pilot project for heated sand energy storage

#42

Post by standeven »

stingraycharles wrote: post #34
retrac wrote: post #28

Heat storage has an aspect that was counterintuitive to me, but follows from basic geometry. It benefits greatly from large scale, since the ratio of the volume to surface area [1] decreases the larger you make a container. Accordingly, if a heat tank is large enough, the surface area becomes negligible relative to its volume, and it, in effect, becomes well-insulated by its own mass. For really big tanks, like might…

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.

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.

Re: US Government funds pilot project for heated sand energy storage

#43

Post by robviren »

datameta wrote: post #38
chii wrote: post #33

Earlier quoted context omitted.

> 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.

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?

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.

Re: US Government funds pilot project for heated sand energy storage

#44

Post by nick238 »

dheera wrote: post #27
ejb999 wrote: post #7

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…

> 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.

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.

Re: US Government funds pilot project for heated sand energy storage

#45

Post by scotty79 »

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.

Re: US Government funds pilot project for heated sand energy storage

#46

Post by syllablehq »

stingraycharles wrote: post #34
retrac wrote: post #28

Heat storage has an aspect that was counterintuitive to me, but follows from basic geometry. It benefits greatly from large scale, since the ratio of the volume to surface area [1] decreases the larger you make a container. Accordingly, if a heat tank is large enough, the surface area becomes negligible relative to its volume, and it, in effect, becomes well-insulated by its own mass. For really big tanks, like might…

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.

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.

Re: US Government funds pilot project for heated sand energy storage

#47

Post by Scoundreller »

chii wrote: post #33
retrac wrote: post #28

Heat storage has an aspect that was counterintuitive to me, but follows from basic geometry. It benefits greatly from large scale, since the ratio of the volume to surface area [1] decreases the larger you make a container. Accordingly, if a heat tank is large enough, the surface area becomes negligible relative to its volume, and it, in effect, becomes well-insulated by its own mass. For really big tanks, like might…

> 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.

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.

Re: US Government funds pilot project for heated sand energy storage

#48

Post by NavinF »

robviren wrote: post #43
datameta wrote: post #38

Earlier quoted context omitted.

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?

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.

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%

Re: US Government funds pilot project for heated sand energy storage

#50

Post by ndonnellan »

HPsquared wrote: post #3

Thermal storage works nicely with solar thermal plants. Not so good for direct electricity storage though.

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.

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