https://newatlas.com/energy/sand-battery-finland/
A new industrial-scale 'sand battery' has been announced for Finland, which packs 1 MW of power and a capacity of up to 100 MWh of thermal energy for use during those cold polar winters. The new battery will be about 10 times bigger than a pilot plant that's been running since 2022.
The sand battery, developed by Polar Night Energy, is a clever concept. Basically, it's a big steel silo of sand (or a similar solid material) that's warmed up through a heat exchanger buried in the center, using excess electricity from the grid – say, that generated during a spike from renewable sources, when it's cheap.
That energy can then be stored for months at a time, with reportedly very little loss, before being extracted as heat on demand. This could theoretically be converted back into electricity, although with some energy loss. But Polar Night says that the most efficient method is to just use the heat itself.
In a chilly place like Finland, that means feeding it into the local district heating system, which shares heat produced from industry or energy production through the community. Networks of pipes carry this heat as hot water or steam to warm up houses, buildings, even swimming pools. In this case, the new sand battery would be trialed in the district heating system of the Finnish municipality of Pornainen, run by a company called Loviisan Lämpö.
This new sand battery is expected to stand 13 m (42.7 ft) tall and 15 m (49.2 ft) wide, providing an output power of 1 MW and a capacity of 100 MWh. That, the companies claim, equates to a week's worth of Pornainen's heat demands in winter, or a month's worth in summer. By comparison, Polar Night's previous sand battery stands 4 x 7 m (13 x 23 ft), for a nominal power rating of 100 kW and a capacity of 8 MWh.
(Score: 2) by Adam on Friday March 15, @01:23AM (7 children)
There is something to be said for having some extra generating capacity. Big batteries smooth over peaks and valleys in supply and demand and let the power grid move ever closer to 1:1 demand and capacity. Saves money until demand goes up or capacity goes down for more than a few days, then shortage.
I am curious how hot they're getting this sand if they're expecting to using it to generate steam for several days.
(Score: 4, Informative) by janrinok on Friday March 15, @01:53AM (1 child)
https://en.wikipedia.org/wiki/Soapstone [wikipedia.org]
It is not a sand that you or I might recognise as such. It is also a waste product that is found locally to this experiment. I could not find any data that specified the actual temperature attained during the heating process.
(Score: 2, Interesting) by Anonymous Coward on Friday March 15, @02:02AM
From https://en.wikipedia.org/wiki/Soapstone#Americas [wikipedia.org] (part of your link):
Older relative b.1910 grew up in small town central Maine and told stories of using a soapstone to warm up his bed on cold nights.
(Score: 3, Interesting) by RS3 on Friday March 15, @02:12AM (4 children)
I glanced at TFA and I'm not sure if steam or electricity generation is the present goal. TFA talks more about "local district heating system":
TFA also says: "This could theoretically be converted back into electricity, although with some energy loss."
Steam used to be a more prevalent way to heat buildings, and is still used some, but many houses that had steam have been converted to hot water. Point is, you don't necessarily need steam or high enough temperatures to generate steam to heat buildings. I'm visiting in a house right now that has big steam pipes and radiators for heating, but long ago the steam boiler was replaced with hot water and circulating pump.
And maybe that's why steam had been so common- you didn't need a pump- the steam would rise up into the radiators, and the condensed water would drain back by gravity into the boiler.
(Score: 0) by Anonymous Coward on Friday March 15, @03:22AM (3 children)
The "drain back" part sounds tricky in certain houses... With pumps you have more options and flexibility when placing radiators and pipes.
(Score: 2, Interesting) by Anonymous Coward on Friday March 15, @03:35AM (1 child)
> The "drain back" part sounds tricky ...
In the 1970s I lived in a c.1900 apartment building that was heated by single pipe steam. While I don't claim to really understand the system, it worked OK when the heat was really pouring off the radiators. If the valve on the steam pipe was closed part-way to provide less heat, the radiators started to bang and clang, loudly. I guessed that water was condensing in the bottom of the radiator and not draining out fast enough...and the incoming steam was bubbling through.
My attempt at a solution was to leave the valve open and when less heat was needed, insulate the radiator from the room with various kinds of covers. This shut it up, but the radiator got really hot. No idea if this high temp could cause damage in the long term, I wasn't there long enough to experience any damage.
(Score: 2) by RS3 on Friday March 15, @05:02AM
Your thoughts re. valve and banging sound correct. I've had some experience with some steam systems and there's no gurgling- it's very loud bang and clang.
Also, very good understanding of thermodynamics by insulating the radiator. Sometimes the simplest solution really is the best one. I've seen idiots open windows when the system was too hot.
Yes, there are 2-pipe and 1-pipe steam systems. Obviously the condensed water drains back down the same pipe. It should be obvious that the condensate takes up far less room in the pipes.
Many people still love and swear by steam heat systems. I know several who still have steam heating systems, including a couple of 1-pipe systems.
One downside of steam systems: the water level in the boiler must be fairly well controlled. Those water level control valves get pretty trashed, as with many other things in steam systems.
(Score: 2) by RS3 on Friday March 15, @05:06AM
You misunderstood my post, which I admit, I didn't have time to edit. The point I was trying to make was that they did convection-driven steam heat systems because they didn't have pumps available like we do now. So yes, they had to consider heights and slopes, etc. when installing steam heat systems. I've seen some where the drain-back condensate pipes were significantly smaller than the large steam-carrying pipes.
(Score: 2, Informative) by Anonymous Coward on Friday March 15, @01:51AM (7 children)
"some energy loss" is putting it mildly. You will lose more than half of it, although that could still be OK if the alternative is losing all of it because you otherwise can't use all your power generation capacity.
I assume this is a cylinder, so it has a volume of about 2300 cubic metres, which would be about 7000 tonnes of sand. 100 MWh / 7000 tonnes is ~50 kJ / kg (14 Wh / kg). Sand has a specific heat capacity of about 800 J / kg / K [engineeringtoolbox.com], which means the temperature of the sand inside the vessel is about 65°C higher than the outside temperature.
If you heated the same volume of ordinary water (which would be about 2300 tonnes of water) by 65°C, you would store about 170MWh in the same space, almost twice as much thermal energy, and it seems like it would be much easier to use hot water than hot sand if the goal is to heat buildings with it.
(Score: 5, Interesting) by janrinok on Friday March 15, @01:59AM (1 child)
See my link in https://soylentnews.org/comments.pl?noupdate=1&sid=60200&page=1&cid=1348840#commentwrap [soylentnews.org]
"Soapstone is easy to carve; it is also durable, heat-resistant and has a high heat storage capacity. It has therefore been used for cooking and heating equipment for thousands of years."
(Score: 3, Interesting) by Anonymous Coward on Friday March 15, @03:35AM
Whereas soapstone can be heated far past 100C[1] without changing the design as much. Yes getting the heat out may also involve water/steam but maybe fixing that stuff would be a problem of a different magnitude.
[1] I'm no thermodynamics expert, but things might be more efficient the hotter the hot stuff is compared to the cold stuff.
(Score: 4, Interesting) by VLM on Friday March 15, @12:15PM (1 child)
I find that strange, why not heat it up by 650C or 1300C? Sand will melt around 1700C. I'm sure there are annoying to deal with impurities in the sand, but storing 20x the energy sounds like fun. I'm guessing its the usual "pilot plant" "experimental process" issues and if this is version 2.0, version 3.0 will go up to 1300C.
A barrel of sand at 100C is a lot less energy than a barrel of room pressure steam at 100C, but the sand can get up above 1500C at zero added pressure whereas steam pressure is a real PITA above 300C or so. One of those engineering-rules-of-thumb for back-of-the-envelope calculations is 300C steam would be about 90 bar. Its non-linear, 200C steam is only about 15 bar, not the "45" you'd guess. These engineering-rules-of-thumb only being good to maybe one sig fig, maybe 20%. But good enough for estimates.
I don't know that I've ever seen a theoretical steam table that goes up to 1300C. Sand would be fine at room temp. I would guesstimate steam at 1300C would be "around millions" bar pressure. I'm sure there's some bored material scientist with a diamond-anvil lab who knows...
(Score: 2, Informative) by Anonymous Coward on Friday March 15, @05:50PM
The short answer is that a high mass at a low temperature can store thermal energy more effectively than low mass at a high temperature because the energy lost via thermal conduction (or the amount of insulation required) will be a lot less.
Quadrupling the temperature difference between the inside and outside of the vessel quadruples the amount of energy stored, but also quadruples the rate you are losing energy due to thermal conduction to the outside. So to keep the losses the same your insulation needs to be four times as effective as before.
But you can also quadruple the energy stored by quadrupling the mass, and the square-cube law means you can do this while only doubling the vessel's surface area, so to keep the losses the same your insulation only needs to be twice as effective as before.
(Score: 3, Interesting) by anotherblackhat on Friday March 15, @02:32PM (2 children)
Generally speaking, they try to optimize $/J, not L/J or kg/J.
Water is probably cheaper than sand, but water tanks are a different story.
Water boils at 100ºC, a temperature that could reasonably occur, and thus your tank needs to be a pressure vessel.
(Or you need a pressure valve and a way to re-fill the tank)
You could leave an opening, but then the water tends to evaporate and you'd need to deal with that.
Even very tiny holes can cause problems.
Sand on the other hand, just sits there.
It can get a lot hotter (~1700ºC) — a temperature hot enough that it's not (reasonably) going to occur.
It doesn't melt, it certainly doesn't boil, and even if it did, it wouldn't cause a catastrophic explosion.
Tiny holes are undesirable, but don't ruin the tank.
(Score: 3, Interesting) by SomeRandomGeek on Friday March 15, @09:10PM (1 child)
This project is making me think of thermal energy storage in a whole different way. You can essentially get the entire thermal storage medium for free, and only pay for the insulation that you wrap around it. And since capacity increases with volume while insulation cost increases with surface area, if you make a big enough battery the cost of insulation will be very cheap. On the other hand, the bigger you make the thing, the more energy you need just to get it up to an effective operating temperature.
It seems like this will produce energy storage with the properties:
1. Really large capacities
2. Really low price per unit of capacity
3. Really inefficient. You might only get 10 or 20% of the energy you put in back out.
That could be a game changer when paired with a lot of cheap wind power and really cheap solar power. Most of the time, your needs are fulfilled by either the wind or the solar, with some left over to charge the batteries. And on the rare occasions when there is not enough wind or sun, there is enough in storage for an extended period.
(Score: 0) by Anonymous Coward on Tuesday March 19, @05:29PM
If the goal is to extract the stored energy as electrical power, mechanical systems are so vastly much more efficient that I don't think there's any reason to consider thermal storage. Pumped storage hydroelectricity is already in wide use today and you can actually get the vast majority of the electrical energy input back as electrical energy out because no part of the system involves fundamentally inefficient processes like heat engines. Flywheels are also pretty great, especially in high-power applications.
Thermal storage will probably only ever make sense for thermal-related applications (presumably why TFA suggests using it for heating buildings).