Sand battery first!

[Adsibob]

This is pretty insane, storing heat at 500C in sand for months at a time:

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

 

[JohnMo]

Third thread today on sand batteries 

[G3dfatboy]

Saw this thread on here and was wondering if anyone had perused this line of energy storage.  I saw the Finish guys on youtube and polarnightenergy.fi who are doing this in a big way.  It looks like reasonably simple concept for a small scale project.

So, I am currently designing a solar/wind charged IBC based sand battery system which can be daisy chained with multiple units. The hot air would be run through a converted commercial boiler coil exchanging the heat into the water. No pressure, open system, no risk of explosions..
If anyone has made something work, I would be interested to hear of any pitfalls.

 

[SteamyTea]

5 hours ago, G3dfatboy said:

So, I am currently designing a solar/wind charged IBC based sand battery system

What are you using to insulate the orange juice containers and how are you going to stop them melting?

[Gus Potter]

The concept is great. For example there are folk on BH that have large plots.. access to excavators as part of their day job, space to dump the muck away and so on and this could make things cost efective.

 

On a small scale I have UF in a structural concrete slab on a well insulated perimeter wall. I know I'm heating the dumpling of clay soil in the middle of the house.. like a battery.. I notice it as going into winter we need to pump in a bit of heat to dry out the concrete slab above the insulation.. and warm the dumpling below.. it takes about a month to settle and after that all things being equal the energy input drops off.

 

As on clay there is no ground water flow that carries the heat away.

 

I'm sure I have some kind of low temperature battery / heat store .. just can't prove it.

[SteamyTea]

A bit of arithmetic can help here.

 

Let us start with a box, 1 m on each side.

So 1 m³, that will hold around 2,700 kg of sand, which has a specific heat capacity of around 0.8 kJ/kg.K, so 2,160 kJ/K or, 0.6 kWh/K

If we add 0.5 m of insulation around it, we then have a cube that is 2 m on each side, and a volume of 8 m³. so a volumetric capacity (AKA Heat Capacity) of 0.075 kWh/m².K.

Why so much insulation you may well ask.  Well the sand will have to be kept at a high temperature, so the thermal losses will be quite high without it.

If we choose a phenolic insulation with a thermal conductivity of 0.02 W/m.K we can work out the losses.

The total surface area will be 12 m², and let us say that the ground is, during winter, at 1 m depth 5°C and we store the sand at 70°C, a temperature delta of 65 K and an initial energy storage of 39 kWh.

Converting the thermal conductivity to a U-Value give us 0.042 W/m².K (about half what a Passivhaus uses).

0.042 [W/m².K] x 12 [m²] x 65 [ΔT] = 33 W [2 significant figures).

 

After a day, 0.8 kWh will have leaked out, leaving 38.2 kWh, the temperature will have dropped by 1.3K, to 68.7°C, day two, there will be 37.4 kWh of storage and the temperature will be 67.4°C.

After 15 days of losses, the energy stored will be 27.3 kWh and the temperature will be at 50.5°C, about as low as to be useful.

Now you can top up to counteract the losses with relatively small amounts of energy, 0.8 kWh/day, but that just covers the losses, not usage.

If you run the heat store down to 50.5°C every day, then you need to replenish it with 11.7 kWh for usage, plus the 0.8 kWh for losses, 12.5 kWh/day.

Now I have a small storage heater in my kitchen, a 10.5 kWh model. It is 0.56 m wide, 0.18 m deep from the wall and sits 0.71 m high from the floor.  That gives a volume of 0.072 m³.

A volumetric capacity of 146 kWh/m³.  Compare that to the sand storage of 4.9 kWh/m².

Now my storage heater does not have anything like the insulation levels of an intersessional storage system, but then it does not need to, as all the thermal losses end up heating the room, which is what heaters are meant to do.

So for less space, less price and thermal losses where they are wanted, my storage heater is better, by a factor of 30.

 

If intersessional storage was so brilliant, all our houses would be built on them.

 

(as usual, quickly calculation things can introduce errors, so I may have made one that could turn the whole thing on its head)

 

Just had a thought, GSHP would be easier and cheaper, it effectively works the same.

 

Done a chart.

 

 

After 50 days, the losses have depleted the store.

It is 45 days till Christmas day.

 

Edited November 10, 2023 by SteamyTea

[Alan Ambrose]

>>> A volumetric capacity of 146 kWh/m³.  Compare that to the sand storage of 4.9 kWh/m².

 

I would have guessed that the sand would be about the same as brick thingys they usually put in storage heaters?

[SteamyTea]

15 minutes ago, Alan Ambrose said:

I would have guessed that the sand would be about the same as brick thingys they usually put in storage heaters

I seem to remember that storage heater bricks (Feolite) are about double the capacity of sand/stone/brick/concrete/earth.

They are properly designed not only to store extra energy, but not degrade when in contact with a electrical element at 800°C+.

 

Just found this on Stackexchange about Feolite

• specific heat = 920.0 J·kg⁻¹·°C⁻¹,
• density = 3,900 kg·m⁻³,
• thermal conductivity = 2.1 W·m⁻¹·°C⁻¹.
• maximum operating temperature 1000 °C

So a bit better than brick on the SHC, but due to the much higher density than sand, the volumetric capacity is higher, about 1 kWh/m³.K  Just a bit better than sand at 0.6 kWh/m³.K.

I think I may have made an error in the conversion, but not in favour of sand.

The reason storage heaters can store more energy is that the bricks are very hot >200°C.

Commercial sand systems also also stored at higher temperatures, but a domestic system in an polypropylene/polyethylene container is limited to about 70°C.

 

 

[Adsibob]

On 10/11/2023 at 08:34, SteamyTea said:

After a day, 0.8 kWh will have leaked out, leaving 38.2 kWh, the temperature will have dropped by 1.3K, to 68.7°C, day two, there will be 37.4 kWh of storage and the temperature will be 67.4°C.

After 15 days of losses, the energy stored will be 27.3 kWh and the temperature will be at 50.5°C, about as low as to be useful.

Don’t you need to do some differential equation to model the fact that the heat leaks out continuously not incrementally.

[Marvin]

HaHa! I first brought this up in a thread on the second of January this year.  

 

The design that would work for an individual home involves the thermal store under the floor in the ground, with Mineral wool as insulation, thermal protection from rising heat in the summer, as much PV as possible, as wide an area of sand as possible to reduce the high temperature required, a waterproof structure, rust proof tubes in the sand, a blower and an electrical element above ground, thermostats and some sort of valve control for input and output of heat to the sand and to the building.  The main cost would be the excavation, disposal and basement type foundations.

 

Soon realised that an above ground external store would not work for winter heating....

 

 

Edited November 11, 2023 by Marvin
further thought

[SteamyTea]

2 hours ago, Adsibob said:

Don’t you need to do some differential equation to model the fact that the heat leaks out continuously not incrementally

Ideally yes. But as it is not a practical idea, rather a moot point 

See what @Marvin said.

 

GSHPs are taking advantage of stored energy. As are ASHP and WSHP.

[SteamyTea]

Here is an idea, all be an old one.

The use if heat pumps could make it more viable.

Biggest problem I see, apart from environmental risks, is distribution.  It would probably be cheaper to distribute the electricity than start a new underground infrastructure project.

 

Abandoned coal mines could store wind energy

Surplus wind power can be used to heat up water in flooded mines – a test of the idea is being planned in Scotland in 2024

By James Dinneen

23 November 2023

 

 

 

The Barony Colliery in Scotland is one proposed site to test storing wind energy in old coal mines

Ayrshire UAV Images/Alamy

 

Flooded mines across the UK could store large amounts of wind energy that would otherwise go to waste by heating up the water within them. The heat could then be extracted to warm homes in winter.

In 2022, enough wind energy to power more than a million homes was wasted in the UK, according to the think tank Carbon Tracker. That is largely because infrastructure for wind energy transmission and storage has not kept pace with the boom in wind turbine installations, forcing suppliers to pause production when demand falls below supply.

That has spurred experts to search for new ways to store this energy for long periods in order to maximise how much can be captured when the wind is blowing.

“The UK is peppered with mine shafts from the days of coal mining – we want to turn these holes in the ground into thermal stores to help balance the electrical grid and to decarbonise homes and businesses,” says a group of researchers led by Zoe Shipton at the University of Strathclyde in the UK in a proposal to explore this idea.

 

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The group – which includes representatives from several energy companies, as well as the UK’s Coal Authority – is now studying the feasibility of the idea, with plans to run tests in a mine in Scotland by mid-2024.

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Shipton tells New Scientist this will involve warming the top 20 metres of the water in a mine shaft with loops of steel tubing carrying a heated fluid. The researchers will use the experiment to answer a slew of questions about the safety of such systems, from how the heat affects the water’s convection in the shaft to how it impacts the integrity of the concrete walls of the mine.

Shipton says they have not yet settled on a site for the experiment, but are considering the Monktonhall Colliery near Edinburgh and the Barony Colliery south of Glasgow, which are among the deepest mines in Scotland.

“The thing that I really like about this idea is that they’re trying to take all the infrastructure that has been abandoned and do something useful with it today,” says Lorenzo Sani at Carbon Tracker.

There are around 170,000 mine entrances in the country. Shipton estimates that if just 1 per cent of those were used to store heat, they could provide enough energy to warm 10 per cent of UK homes for a week, even in a worst-case scenario of cold weather and low energy production.

 

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If heated to at least 55°C (131°F), Shipton says the mine water could be used directly in district heating networks or industries that use low-grade heat. She says mine shafts are ideal for storing heat because they are well insulated, and the water in them is already kept relatively warm by geothermal energy and chemical processes.

There are more than 40 sites in the country that already use heat extracted from naturally warmed mine water, says Jon Gluyas at Durham University in the UK. The Dutch town of Heerlen also uses industrial heat to recharge mine water for supplying warmth to the town in winter. But he says Shipton’s plan to use surplus renewable electricity to heat the water is new and interesting. He thinks the idea could be particularly valuable for communities that lost livelihoods from the closure of the mines. “We can rebuild communities around a shared heat facility,” he says.

Gluyas adds that finding ways to reuse heat is a very efficient application of surplus energy. “You can’t beat the second law of thermodynamics. But you can snuggle up pretty close to it,” he says.