Sand battery article

[UndercoverElephant]

https://www.bbc.co.uk/news/science-environment-61996520

Finnish researchers have installed the world's first fully working "sand battery" which can store green power for months at a time.

[adam2]

Not as revolutionary as is suggested. There is nothing very new about thermal storage.
Water is more commonly used in the interests of simplicity.
Sand or rocks have the merit that much higher temperatures can be used. Probably also safer, if the container breaks a large pile of very hot sand is only a very local danger, whereas a flood of scalding water is dangerous for some distance.

Storing heat is a lot simpler than storing electricity.

New homes should be so well insulated that they need very little heating. Bulk thermal storage might be more applicable to places with a large hot water demand, hotels, hospitals, industrial laundries and the like.

We have no need for this sort of thermal storage AT PRESENT since we have no regular surplus of renewable energy with which to fill the stores. That situation will change quite soon though. If we build enough wind and solar capacity to meet a much larger proportion of our needs, then a surplus at times of low demand or high production will become unavoidable.

[PS_RalphW]

The headline is a little misleading. It is using a large (presumably insulated) silo of sand as a high temperature long term thermal store for a district heating scheme. The sand is heated to 500C by simple resistive heating using excess renewable electricity during the summer months to be a heat source for a district heating system in winter. It is not an electric battery as its output is relatively low grade heat.

It may have applications in some urban environments, but district heating has not been a great success in the UK with its low grade of housing stock and socialist undertones.

It's main advantages over smaller domestic thermal stores are that it's energy density is higher, meaning it is easier to insulate sufficiently for low losses over the longer timescales, and the low tech and cheap nature of its design. However, it only makes sense in a country that has excess supply of renewable electricity that cannot be put to more efficient uses. For example, heat pumps.

For now, a higher priority in the UK is better house insulation (and education of the public on how not to waste energy).

[BritDownUnder]

Seems a good idea but for district heating you would be better off using water as a storage media I think. However for other uses of heat then I think it has merits. 500C heat is quite high grade heat and can be used for a number of industrial processes. Water has a heat capacity about five times the value of sand so only needs to be heated to 95C to store a similar amount of heat in.

I agree about the safety things regarding sand and the fact it is quite inert. About 70% of the UK domestic energy use is as heat and storage heaters have been used for years. Perhaps this is a larger scale and longer duration version of that.

I could not help doing some calculations on this but I wont bore you with the details.

Assuming a cylinder with height 6 metres and diameter 4 metres the sand inside will weigh 113 tons and be able to store 12,870 kWh if heated from 0C to 500C. If not insulated it will cool fairly quickly over a matter of days so I presume it is well insulated in real life.
Interestingly I make the storage capacity at about 0.11kWh per kg which is about the same a Tesla lithium ion battery although not as flexible in its uses.

[clv101]

Interestingly I make the storage capacity at about 0.11kWh per kg which is about the same a Tesla lithium ion battery although not as flexible in its uses.

For static application, energy per volume is probably more useful than per weight. Here I expect sand to outperform lithium... but could be scuppered by insulation requirements. Given domestic heat only requires around 60C, I still expect water - even at the 100 tonne scale is a more straightforward energy store.

[BritDownUnder]

There's more sand than lithium that's for sure and less difficulty in extraction.

I wonder if there has been a study done on how many and what resources that the renewable transition is going to need and how they can be best allocated?

[adam2]

Water is a lot simpler, and the lower maximum temperature is partly offset by the greater specific heat capacity of water.
Any very large hot water stores should be below ground to avoid danger from the tank breaking.

There is also the potential for storing "cold" in chilled or frozen water. For use in air conditioning.

[clv101]

There's more sand than lithium that's for sure and less difficulty in extraction.

I wonder if there has been a study done on how many and what resources that the renewable transition is going to need and how they can be best allocated?

This video discusses copper and lithium:
https://youtu.be/nCbWYoKoRww

[adam2]

I do not expect shortages of lithium or of copper.
Lithium is present in seawater and could be extracted therefrom if other supplies run short.
In Ghana there are said to be huge reserves of low grade copper ore. Not economic to mine at present, but will be if prices increase much more. The same rocks also contain traces of gold, very small traces, but worth extracting as a sideline to copper refining.

[adam2]

I could not help doing some calculations on this but I wont bore you with the details.

Assuming a cylinder with height 6 metres and diameter 4 metres the sand inside will weigh 113 tons and be able to store 12,870 kWh if heated from 0C to 500C. If not insulated it will cool fairly quickly over a matter of days so I presume it is well insulated in real life.
Interestingly I make the storage capacity at about 0.11kWh per kg which is about the same a Tesla lithium ion battery although not as flexible in its uses.

12,000 kwh is probably more realistic, since if the output is to be used for space heating, you cant "discharge" the store to freezing point, it has to remain above room temperature. 50 degrees is probably about the lower limit so as to give a reasonable heat flow into a space at 22 degrees.

At times of surplus renewable energy, this wont be free since it costs money to transmit and distribute the electricity. 10 pence a unit might be reasonable.
At 10 pence a unit it will cost about £1,200 to fill the store. Emptying the store at times of peak demand might yield about 11,000 kwh after losses. If we presume that the 11,000 kwh obtained from discharge is displacing peak rate electricity worth 50 pence a unit, then it is worth about £5,500.
This suggests a net saving of about £4,300 per cycle. If cycled say ten times each winter than about £43,000 has been saved per winter. Probably worthwhile. If only cycled seasonally, i.e. once per year then unlikely to be viable.

If cycled say 30 times a year, perhaps for hot water in a large facility then almost certainly worthwhile.

Grid upgrade costs extra. Remember that the local network will need to charge the 12 MW store in a few hours AND ALSO to supply the heating demand directly.

[BritDownUnder]

Most of that I agree with but the use may not be limited to domestic space heating of 50C. There are various temperatures required for process heat, for instance drying of wood needs 100C to 150C and a commercial bakery may require up to 220C. Some chemical processes may need higher than that and cement or metals need more than 500C. Obviously the higher the temperatures needed then the less fraction of the battery that can be used to get these temperatures before it goes below the minimum temperature required.

I think that charging the sand 'battery' in a few hours is not practicable and given the vagaries of wind and solar especially in the UK there should an expected 'dunkelflaut' (which I believe is German for periods of darkness and low winds) period of 2 to 5 days and therefore the sand battery should be expected to carry the heat requirements over that time interval and when wind and solar are in abundance should be able to recharge over a similar time interval.
therefore I think a recharging electrical input of around 2 to 3 times of normal heating demand might be more realistic and taking into account the wind capacity factors of around 30-40% in the UK.

The above assumptions are based on a process being continuous. If processes electrical requirements can be interrupted (load shed) for a short time without any consequences then a smaller heat battery may make sense.

I can see these being useful in a future world of limited or expensive lithium batteries and non-despatchable renewables.
low grade ores or even extraction from seawater would I expect require larger energy inputs to get the same quantity of metal. There could be a limiting factor same as EROEI is for oil and gas reserves that prevents very low grades of ores being extracted. I heard a report saying that lower grades require more intense crushing of rock to get to the smaller particles of the correct minerals that contain the metals. There have been some research publications saying that seawater can be concentrated by some kind of ion exchange or limiting barrier process that allows lithium ions to be extracted from seawater but the more plentiful and chemically related sodium ions to be blocked.

Maybe in the future we will be using sodium batteries and have aluminium doing much of the role that copper now does in things like motors and transformers?

[BritDownUnder]

Quite an interesting study on the theory of this from someone's blog.