Sand 'Battery'... well, thermal store - Page 1
Forum section: electronics / general

author: Gyro
author_rank: Super Contributor
timestamp: July 05, 2022, 08:04:30 pm
content: I just came across this story on the BBC News Site...https://www.bbc.co.uk/news/science-environment-61996520QuoteThoughs:1. They've actually installed one, so it must work to some useable extent.2. Using builders sand is cheap and lets them reach to 500'C. Presumably it has heating elements directly embedded in it.3. I wonder what sort of insulation they use to efficiently isolate high temperature sand from the cold Norwegian winter climate.4. How do they harvest the heat at that temperature? Air ducts are the only thing that immediately comes to mind, combined with a heat exchanger to heat the water. [Edit: Yes, it's in the article].5. They are relying entirely on thermal mass - not taking advantage of a phase change of the storage medium.6. It sounds really simple (compared to other 'energy' storage systems). I guess storing energy in its lowest grade form is always going to be simplest.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 06, 2022, 02:00:56 pm
content: World is literally full of these "World's first sand batteries". For some reason, it seems to be trendy for startups to store thermal energy in sand.Sand has poor thermal capacity compared to water. This means larger temperature differences need to be used. Which is of course fine because sand can easily survive high temperatures. Cheap insulation materials like mineral wools can too.The problem with high temperature storage is the inability to use heatpumps to charge it. With lower temperature systems, heatpumps provide an excellent way to extract even more renewable energy from the environment; not just the PV/wind generation itself, but also thermal energy extracted from air. How much free energy is available depends on the temperature difference. So in effect, it will be a compromise between efficiency vs. storage energy density. The choice can be dynamic. Average COP around 2 would be quite realistic, which is a pretty big deal.Water also greatly simplifies distribution as it can be pumped. Everything is low cost and off-the-shelf because this is something that has been done for over a century. So if sand sounds simple to you, water is even simpler.A much more interesting project IMHO, in Finland too, is this:https://www.vantaanenergia.fi/en/fossil-free-2026/worlds-largest-cavern-thermal-energy-storage-to-be-built-in-vantaa/It's a much much bigger project, and it will actually be something more than just a small test. But you won't hear about it in mass media because media loves stupid startup stories (compare to solar roadways).Regarding thermal storage, there is this extremely interesting relationship of volume (^3) per surface area (^2). This is the ratio between storage capacity and heat loss, and it is linear. Meaning, make storage 10x bigger, and the relative loss goes down to 1/10th. Taken at extreme, no insulation is needed at all.If you make a large cavern in bedrock, the few first meters of the rock itself participates in thermal storage, but slowly transitions into thermal insulation. Nothing needs to be done; it just has to be large enough. A million cubic meters sounds about right to me. At peak temperature of 140degC, average temperature will be lower and I would guess heatpumps will be used.

author: madires
author_rank: Super Contributor
timestamp: July 06, 2022, 02:10:44 pm
content: Thermal storage using molten salt is known for more than 20 years. Please see 'Thermal energy storage' (https://en.wikipedia.org/wiki/Thermal_energy_storage).

author: tszaboo
author_rank: Super Contributor
timestamp: July 06, 2022, 03:46:44 pm
content: In other news, there is a global shortage of good quality sand, which is impacting the construction industry.You know what is available in massive quantity, stores a lot of power with small footprint, and a working technology? CO2 + H2O => CH4.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 06, 2022, 04:34:12 pm
content: Quote from: tszaboo on July 06, 2022, 03:46:44 pmIn case you did not notice, it is global shortage of everything.Such artificial and hopefully temporary situation should not lead our decision making. And if it does, then we indeed can't do anything right now.World is literally full of sand, and it is utterly trivial to make it "good quality" in large masses. Shortage of sand is not because of shortage of sand itself; it's just an indicator of failed processing and logistics. The same problem why everything's in crisis now.

author: tszaboo
author_rank: Super Contributor
timestamp: July 06, 2022, 04:39:00 pm
content: Quote from: Siwastaja on July 06, 2022, 04:34:12 pmIt's not a recent shortage, it has been going on for a while now, here is an article from 2017:https://www.businessinsider.com/global-sand-shortage-2017-9?international=true&r=US&IR=TIt's also not trivial which sand can be used. Saudi Arabia imports sand from here, because theirs cannot be used for construction, and this specifically uses construction grade sand.

author: pcprogrammer
author_rank: Super Contributor
timestamp: July 06, 2022, 04:50:41 pm
content: Dutch TNO developed a heat storage battery using salt. Probably also know to most of you.https://www.tno.nl/nl/over-tno/nieuws/2020/9/doorbraak-in-ontwikkeling-warmtebatterij-voor-woningen/The article is in Dutch, but the principle is that with drying the salt energy is being stored, which can be released again by adding water. It is a development for houses to be heated in the winter when it is needed and recharged in the summer when there is an excess in energy.The advantage of this system is that there is no need for insulation because the energy is not stored as heat.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 06, 2022, 05:03:41 pm
content: Note that all storage mechanisms mentioned in this thread (sand heat, water heat, salt exo/endothermic desiccation; I don't know enough about synthetic methane but I assume tszaboo is right) are completely practical and viable ideas that have been demonstrated numerous times and do not require high tech or massive investments. They hold a lot of potential in solving the "energy crisis".The only reason these are not seen in wild very much is that the "energy crisis" is still just a bubble. Oil and Putin's fart gas are still very cheap and plentiful. There is no motivation to make even simple and relatively small investments, because we can just keep buying dirt cheap fossil fuel. Even if the cost increases by 50%, that will lead to everything else, including our wages, to inflate by at least 25%. We will then cry about "expensive" fossils but still keep using them because we can't and won't make even trivial 10k€/citizen investments to have sustainably heated houses during winter, when we can just pay 1k€ per year to do it in unsustainable way.I don't like the way it is, but it is what it is. Personally I'm making all the practical investments I can to reduce energy, specifically fossil use.

author: themadhippy
author_rank: Super Contributor
timestamp: July 06, 2022, 05:30:44 pm
content: so they reinvented the night storage heater

author: Siwastaja
author_rank: Super Contributor
timestamp: July 06, 2022, 06:42:35 pm
content: Quote from: themadhippy on July 06, 2022, 05:30:44 pmYes. It's a scale-up. As I mentioned, thermal storage scales up really well, because insulation only getseasierthe bigger it is. A tiny mouse needs a lot of energy to just keep warm because of poor volume to surface area ratio. A large bear is capable of eating a lot once and then hibernate for months.

author: Gyro
author_rank: Super Contributor
timestamp: July 06, 2022, 08:00:53 pm
content: Quote from: madires on July 06, 2022, 02:10:44 pmI did wonder whether anyone was using salt as a phase change medium, it did seem the logical choice. I would think that it is a technology more suited to use at a larger scale than a solid medium for storage though ( albeit having a much better thermal storage capacity). For small community installations, though, it sounds a bit corrosive if things go wrong.I think I can see a case for relatively small community scale thermal reservoirs of this type, certainly where heat pumps are not possible, desirable, or efficient due to the size of the temperature differential (thinking air sourced here). Certainly, in the UK, something with a small ground footprint and sensible height would be very desirable for keeping heating bills down by providing a pumped supply of low grade heat. Most houses have radiator central heating which will require significant enhancement to work with lower water temperatures from heat pumps.Yes, it is reinventing the night storage radiator, but hopefully on an annual, rather than nightly, basis. You have the whole summer to slowly pump it up from solar energy when everyone has their central heating turned off anyway, ready for the comimg winter.In terms of the storage working medium. No, sand doesn't have the greatest thermal conductivity but I'm not sure how much that matters when you are heating it slowly over a long period and drawing heat off at a slow rate. Im not sure about the sand shortage. I know desert encroachment is a problem in a number of countries, maybe it is too fine grained for building use, where sharp sand is needed but it would be no problem, maybe a positive benefit, for thermal storage.There are probably other alternatives, finely ground waste concrete? ash and slag left over from coal fired power stations (again finely ground)? Powdered Alumina would probably be the best for thermal conductivity and specific heat capacity of the powdered solid media, but sounds expensive in significant quantities(?)I can certainly see a place for smallish comumnity scale thermal stores for leveling the domestic heating load on the grid / gas network. There are already many community schemes using waste heat from various processes, so maybe this is just a logical extension. The reduction in heating bills would be welcome, if nothing else.

author: tszaboo
author_rank: Super Contributor
timestamp: July 06, 2022, 10:42:47 pm
content: Quote from: Siwastaja on July 06, 2022, 05:03:41 pmGermany is investing Billions into P2G, I think they want something like 5GW capacity in the next 5 years.These sort of projects are "cute" but they don't really solve problems, and just divert our attention from technologies that actually can solve the issue.At this point, I think the EU made up their mind, and the process is only going to accelerate. The political reasons were probably the last straw.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 07, 2022, 06:18:23 am
content: Quote from: tszaboo on July 06, 2022, 10:42:47 pmAnd you would be wrong here. Thermal storage (sand or water) is not just cute, it's a real solution to a real problem. It is because fundamentally, the life on Earth exists because our climate is suitable for human population,on average. Large part of our energy goes into locally manipulating this climate, temporarily heating or cooling our spaces to our desires. All we actually need is a heat "capacitor"."The average annual temperature in the Netherlands in 2020 was 11.7 degrees Celsius" nice, yeah?Thermal storage is one of the least risky approaches because it has been used for over a century (in some forms, over millennia), it is known to be scalable, all building blocks are easily available, no special materials are needed, and finally, it is very simple to model and calculate. But this also means no massive amounts of money is poured at it, because there is no need. But it seems you measure the viability by looking at how much government is investing into research. This is the wrong metric.For example, price difference to lithium ion energy storage is around two orders of magnitude (total cost of ownership). Of course, electric energy is a more valuable form of energy, and thermal energy can only respond to thermal energy needs, but those needs are still a huge part of our total energy demand.Seasonal thermal energy storage can't be built just anywhere because the volumetric and gravimetric energy density is in the same order of magnitude with lead acid battery, significantly worse than li-ion let alone pressurized gas. That does not mean it is not viable. It's a part of the total solution. Same solution does not apply everywhere.Thermal energy storage with shorter time constant, say a few days, would be integratable into buildings, and to some degree already is. Working systems are being dismantled as we speak because there is no incentive to store energy as long as hourly energy prices are optional pricing model and there are no rolling blackouts.The problem is with the market: we desperatelyneedenergy storage, and we can already easily store energy with existing technology, but this is just not being done because no one pays you to do that. It has to become a full-blown crisis before anything happens. Meanwhile, "cute" research projects are being done, some more viable than others.Demand control is a big thing, orthogonal to seasonal storage of course, but it can significantly clean up our grid emissions and improve reliability by shifting energy use to happen more evenly throughout the day, or matching renewable production; at best, completely avoid bringing up production reserves which are most expensive and most dirty. I can already choose the hours during which I heat my house because I have 1.2m^3 of water-based thermal storage which is good for nearly 24hrs. This just needs to be scaled up. And we will need some incentives to run those systems. I'd prefer free market mechanisms because politicians notoriously get things wrong.As far as I understand it, power-to-gas solutions suffer from poor efficiency. Solution to this is waste heat collection. It might just happen that optimal solution would be a combination of P2G and thermal storage: this means P2G equipment investments would be smaller as there is no need to scale it to full power, and waste heat collection would bring the efficiency near 100%. Total energy density would still be better than thermal storage alone. Thermal energy could be distributed where it is most viable (with existing district heating pipes, or new areas where it can be built), and gas could be distributed to different places, where gas is more viable; for example existing natural gas pipes.

author: dmills
author_rank: Super Contributor
timestamp: July 15, 2022, 08:02:48 pm
content: As memory serves one of the railways back in the day experimented somewhat successfully with a fireless loco that used the heat released by NaOH (conc Aq) -> NaOH (aq) to power a train, recharge consisted of evaporating the water to concentrate the hydroxide brine.Some sort of cycle like that might even be able to power a UK style radiator heating system, and driving off the water should mostly be doable with low grade heat.

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 16, 2022, 04:00:46 am
content: Quote from: Siwastaja on July 07, 2022, 06:18:23 amLack of incentives to invest is indeed the biggest problem with thermal storage right now. For air conditioning, one could make use of the phase change of water and end up with an energy density competitive with lithium batteries.