Inter seasonal store

[JohnMo]

Recent topics on sand thermal storage and a mention of inter seasonal store on another topic has got me thinking.

 

I live on an old sand dune (sea now 6 miles away).  So have more sand than you shake a stick at.

 

So my thoughts are

 

1. Dig big hole.

2. Line with 200mm PIR, or 300mm polystyrene.

3. Insert big tube coil, use same coil for charging in summer and extract heat in winter.  Add suitable valves.

4. Back fill hole with sand, cap with more insulation.

5. With a spare solar thermal panel charge over summer.

6. Pump through same coil in winter to extract heat.

 

Use heat stored to provide some heating load to UFH.  UFH only needs a mean flow temp of 26/27 degrees for coldest day.

 

Is it practical or would need to huge and not cost effective?

 

Any thoughts 

[Nickfromwales]

I think everyone on here should sponsor you with £1 to fund it, and see what happens 👍. 

Edited July 10, 2022 by Nickfromwales

[JohnMo]

That sound like a good plan, hope there many hundreds

[Radian]

I'd Instrument the heck out of it first. Drive a scaf. pole as deep as you can with a temperature probe attached and log it over a year to see what it does naturally.

[Miek]

It's been tried many many times. And won't work . The time constant of several months just kills it. You can store heat for a week or two, but not months. 

[SteamyTea]

I think you will find that it has been done, and failed big time.

There was an Irishman, that some will remember well from the Other Place, that got a customer to pay for it.

He also got another customer to buy into a domestic AD unit.  When I met the Australian 'Inventor' my 'con man' flag went up immediately.

 

“extraordinary claims require extraordinary evidence” (ECREE)

Carl Sagan 1979

[RobLe]

Ooooo maths!

 

If it's a cube of insulation, each side of size X (metres), with a U-value called Y(W/m^2/degC), full of water DT(degC) above surroundings(it makes the maths easy, and you'll not do better than water):

Area = 6.X^2

Losses = 6.X^2.Y.DT/1000 (kW)

Volume = X^3

Energy storage = DT.X^3 (kWh) - just so happens that 1T of water stores 1kWh/degC 🙂

 

So the time constant = energy / losses = DT.X^3 * 1000 / (6.X^2 . Y . DT) = 180 X / Y (in hours)

Lets say Y = 0.1W/m^2/degC, so the time constant = 1800X.

So if X is 2metres, using a U of 0.1, we can get to 3600hours, a time constant of around 5 months - just enough.  If we have water in it.  Sand won't be quite as good I think. 

Agree with last post .... it needs to be big!

 

[Iceverge]

Our resident @tonyshouse did this. 

 

As far as I can remembered it shortened the winter but didn't cover the coldest months. 

 

Probably better off using the insulation to make some insulated shutters I reckon. 

[Nickfromwales]

3 hours ago, Miek said:

It's been tried many many times. And won't work . The time constant of several months just kills it. You can store heat for a week or two, but not months. 

Yanks and Aussie off-grinders bury decommissioned fuel tanker trailers as thermal stores for summer harvest / winter yield, so absolutely can and is being done. 
 

Would need to be massive to succeed, but temps of countries that have done this must be of relevance? 

[Miek]

1 hour ago, Nickfromwales said:

but temps of countries that have done this must be of relevance? 

No doubt about that.  Would work well in a country where you don't need heating. Dubai maybe 😉

 

Your better off in the UK using wind to generate heat in the winter, rather than trying to store summer sun. 

 

[SimonD]

18 hours ago, JohnMo said:

Any thoughts 

 

13 hours ago, Nickfromwales said:

but temps of countries that have done this must be of relevance? 

 

I have a copy of Solar Houses for a Cold Climate from the 1970s/early 80s that demonstrates it is possible. Many of the cases studies are in worse climates that the UK - but there are significant climate differences related to annual insolation that play a factor for the UK. Here's a link to archive.org where you can read it after registration: https://archive.org/details/solarhousesforco0000carr/mode/2up With a large enough solar array, it is certainly possible. I once had a reference about a house built in the UK that has a roof designed as a large solar collector  - can't find it now. I also came across a recent paper through google scholar on a study looking at total roof area required to do this in the UK and it wasn't silly amounts - again can't find the link right now due to switch over of laptops a little while ago.

Edited July 11, 2022 by SimonD

[SteamyTea]

If a solar house, or an interseasonal store were viable in the UK, there would be lots of working examples.

Fact is, there isn't.

If my memory is correct from when I studied this, we have a mean insolation of 135 W/m2 down here.

The very best PV modules will, over a day, give you 15% efficiency. So around 20W/m2.

Just not enough.

Even ST, at 80%, only gives you, on average, 110W/m2, of low entropy energy.

It is that low entropy that is the problem. You need a machine, or a Maxwell Daemon to make it useful.

Redo all your thermal calculations on Kelvin scale and it highlights the problem nicely.

 

Edited July 11, 2022 by SteamyTea

[Nickfromwales]

How long a pipe do I need to access volcanic heat from the earths core? 

 

Just asking for a friend…..

[Radian]

[Radian]

A more helpful example of geothermal gradient perhaps?

 

[MikeSharp01]

44 minutes ago, Radian said:

A more helpful example of geothermal gradient perhaps

So best part of 1000m for a decent shower @Nickfromwales I hope your friend has deep pockets cos he will have deep holes.🤔

Edited July 11, 2022 by MikeSharp01
Added a bit

[SteamyTea]

1 hour ago, Nickfromwales said:

Just asking for a friend

I pretended to be that friend.

Here is what it costs to heat a small section of pool.

https://jubileepool.co.uk/pool-info/geothermal/

It was meant to be all GT, but as they were over enthusiastic amateurs, it all went wrong and they fitted a HP.

So really just a GSHP.

Odd choice as they have one if the world's largest bodies of seawater, that they pump in anyway, a few meters away.

It is 34°C today, they are proud to say it is too warm.

So they have no thermostat on it.

They also have the phones switched off 'because it is Monday, we don't open Mondays'. They do, (expletive deleted)ing amateurs spending my money.

 

Edited July 11, 2022 by SteamyTea

[SimonD]

3 hours ago, SteamyTea said:

If a solar house, or an interseasonal store were viable in the UK, there would be lots of working examples.

Fact is, there isn't.

 

The fact that there are few UK examples is not a testament as to viability but to lack of trial and experimentation, but certainly not non-existent. There are several ways to skin a cat not all using PV. Cost is seen as one of the major problems. 

 

UK Energy Research Centre looking a typically larger installations highlights cost as per below but also as always with any UK based implementation, that of poor quality housing stock https://d2e1qxpsswcpgz.cloudfront.net/uploads/2020/03/the-future-role-of-thermal-energy-storage-in-the-uk-energy-system.pdf : 

 

Large inter-seasonal stores are only sized for
a maximum of a few hundred buildings for
reasons of cost and financial return. A strong
relationship exists between store size and
cost, ranging from about £390/m3 for small
tank-based systems (volume around 300m3 ),
to about £25/m 3 for large pit-based systems
(volume around 75,000m3 ).

 

This paper looks at viability for the domestic sector with smaller stores which I mentioned earlier: https://reader.elsevier.com/reader/sd/pii/S0038092X18300227?token=5BD4A1BEF09BBCA25643BC6D4E463AF9F4E62D5E237FA1297528B54D444AC895E251123C4D173A481F64C939A73E7ADF&originRegion=eu-west-1&originCreation=20220711123502 I'm sure you'll relish in the numbers 😉😁

 

[SteamyTea]

22 minutes ago, SimonD said:

The fact that there are few UK examples is not a testament as to viability but to lack of trial and experimentation,

Most failled experiment don't get published.

[JackofAll]

 

[Onoff]

1 hour ago, SteamyTea said:

Most failled experiment don't get published.

 

Mine do, well on here anyway.

 

 

[Onoff]

Less inter seasonal but more out of hours but there were some projects over in the now defunct US solar forum (can't remember the name but a "Gary" ran it).

 

A few people were using bfo, homemade ST panels to heat large, insulated volumes of sand or I think gravel under their house or in their basement. They then released this overnight i.e when the Sun wasn't shining. 

[Temp]

23 hours ago, RobLe said:

Ooooo maths!

 

If it's a cube of insulation, each side of size X (metres), with a U-value called Y(W/m^2/degC), full of water DT(degC) above surroundings(it makes the maths easy, and you'll not do better than water):

Area = 6.X^2

Losses = 6.X^2.Y.DT/1000 (kW)

Volume = X^3

Energy storage = DT.X^3 (kWh) - just so happens that 1T of water stores 1kWh/degC 🙂

 

So the time constant = energy / losses = DT.X^3 * 1000 / (6.X^2 . Y . DT) = 180 X / Y (in hours)

Lets say Y = 0.1W/m^2/degC, so the time constant = 1800X.

So if X is 2metres, using a U of 0.1, we can get to 3600hours, a time constant of around 5 months - just enough.  If we have water in it.  Sand won't be quite as good I think. 

Agree with last post .... it needs to be big!

 

 

Lets see how big...

 

Let's say your house needs an average of just 1kW to maintain temperature over the four winter months Nov, Dec, Jan, Feb....

 

That would mean you need it to store energy of..

 

4 x 30 x 24 x 60 x 60 x 1000 = approx 10^9 Joules

 

To be useful the store probably needs to have a minimum temperature of say 20C (unless a heat pump is used) and the max temperature would need to be just below boiling say 90C? So a swing of about dt = 70C.

 

E = mass x dt x shc

Mass = E/(dt x shc)

= 10^9/(70*4182)

= 34,000 kg 

 

So 34 cubic meters per kW not taking into account losses from the store.

 

 

 

 

 

[SteamyTea]

10 minutes ago, Temp said:

So 34 cubic meters per kW

My house needs about 500W.

It has a volume of 160m3.

So about a tenth of the house size.

But as you say.

10 minutes ago, Temp said:

not taking into account losses from the store

 

Just realised that is about the size of my shed.

Edited July 11, 2022 by SteamyTea

[SimonD]

44 minutes ago, Temp said:

So 34 cubic meters per kW not taking into account losses from the store.

 Or as per the above linked paper:

 

3.4. Critical storage volume

The critical storage volume to satisfy 100% solar fraction using different thermal energy storage technologies can be estimated based on the energy densities given by literature (Hadorn, 2008), which estimated the storage volumes required for a storage capacity of 1850 kWh with 25% heat loss were 1 m³, 10 m³, 20 m³ and 34 m³ respectively for chemical reaction storage, sorption storage, phase change material storage and water sensible heat storage.

Take the moderate overall heat loss coefficient at 150 W/K as an example, the critical storage volume using sorption storage is 31.5–44.3 m³ in all studied cities. Critical values of using other storage technologies can be proportionally calculated according to the data provided by literature (Hadorn, 2008), for example, if using water as the storage material, this storage volume should be in the range of 107.1–150.62 m³. Nevertheless, in reality, the energy density of SSTES system depends on the system structure and scale, some experimentally tested energy densities of SSTES prototype and corresponding critical storage volume are shown in Fig. 5.

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Fig. 5. (a) Energy densities of SSTES prototypes, the number besides the dot symbol is the prototype system scale in unit of kWh; (b) corresponding critical storage volumes. β = 45°, γ = 0°,

 = 150 W/K. Storage technology: 1. Hot water in pebble-bed storage (Hahne, 2000); 2. Na₂HPO₄·12H₂O supercooling latent heat storage (Hirano and Saitoh, 2007); 3. Closed SrBr₂-water sorption (Mauran et al., 2008); 4. Open SrBr₂-water sorption (Michel et al., 2014); 5. Closed LiBr-water sorption (Zhang et al., 2014); 6–8: Closed LiCl-water sorption (Zhao et al., 2016, Bales, 2008); 9: Open MgCl₂-water sorption (Zondag et al., 2013); 10: Open vermiculite-CaCl₂-water sorption (Aydin et al., 2016); 11–14: Closed zeolite-water sorption (Bales, 2008, Finck et al., 2014, Hauer, 2002); 15–17: Open zeolite-water sorption (Bales, 2008, Weber et al., 2016); 18–19: Closed silica gel-water sorption (Bales, 2008); 20–21: Closed NaOH-water sorption (Bales, 2008).

Current results are based on the situation of 100% solar fraction for domestic heating with 21 °C room temperature all through a year, which might not be practical; however, these results can be used as baselines or fundamental database, then the SSTES system performance with lower solar fraction or shorter space heating period can be reasonably estimated.