Calculating for the use of sand for a thermal store.

[Onoff]

Insulate and fill a basement with sand?

 

Or put down 300mm of insulation, x tonnes of sand, another 300mm of insulation then your slab? You'd get the area required under a house perhaps?

[SteamyTea]

1 minute ago, Onoff said:

Or put down 300mm of insulation, x tonnes of sand

What sort of insulation and how many x's.

 

We consider a U-Value of 0.1 W/m².K pretty good.

But if we increase the K to a delta of 80, rather than 10, losses become significant.

[jack]

2 minutes ago, Onoff said:

Insulate and fill a basement with sand?

 

Or put down 300mm of insulation, x tonnes of sand, another 300mm of insulation then your slab? You'd get the area required under a house perhaps?

 

I looked into adding an insulating "skirt" hanging down from the insulation under our slab, and heating underneath that as a sort of thermal store. Far too much excavation required to make it feasible.

 

I did wonder about whether you could calculate the rate of heat movement and bury pipes at a depth sufficient to provide a ~6 month time offset. Add heat during the summer months, and have the heat "pulse" arrive at the slab during winter. Again though, expensive to do, experimental to say the least, probably huge round-trip losses, plus at best all you're doing is stopping/reducing heat loss through the floor.

[Marvin]

Continuing on with the theory of a sand thermal store...

 

Assuming a theoretical one square meter of surface for thermal loss from inside to outside:

 

510C temp inside  one meter thick sand, (ignoring tank resistance), 400 mm mineral insulation, (ignoring external weather protection) outside temperature -10C.

 

The question is In one hour how much heat would be lost.

 

[Roger440]

20 minutes ago, SteamyTea said:

Shall we look at that.

 

So between the 1^st October and 1^st Jan 2023, out low CO₂ generation was higher than out fossil fuel generation.

The reality is that we are changing the generation type, and it is working reliably.

As I said, it will not happen over night, and there are challenges to over come, but making a wild claim that cannot be backed up with data just panders to prejudice.

 

Follow the green and red lines, the columns are my usage and irrelevant in this context.

The missing 6% is imports, as I don't know the generation type and biomass, as I don't consider it low CO₂.

 

 

Im not sure of the relevance of the graph? Its just showing the split? If its 100% wind and we never have shortages, great.

 

Its working reliably. So far. But we did have to issue a warning prior to christmas that there may be a shortage. To me, thats living on the edge. Going from memory that night, wind was down at 3%. We just didnt have the ability to generate more. As it happened, it passed without incident.

 

You have to believe that the government wont allow us to have power outages to reley 100% on the grid, even leaving aside ever increasing costs.

 

Sadly, i dont believe it at all and fully expect us to have shortages. That could be incompetence or otherwise. Doesnt really matter which, Shortages are shortages. I dont want to be a victim.

 

I guess you believe the challenges will be overcome?

 

 

[Roger440]

3 minutes ago, Marvin said:

Continuing on with the theory of a sand thermal store...

 

Assuming a theoretical one square meter of surface for thermal loss from inside to outside:

 

510C temp inside  one meter thick sand, (ignoring tank resistance), 400 mm mineral insulation, (ignoring external weather protection) outside temperature -10C.

 

The question is In one hour how much heat would be lost.

 

 

How would you get it to 510 degrees though?

[Marvin]

8 minutes ago, Roger440 said:

 

How would you get it to 510 degrees though?

by blowing air along a tube that runs into the sand and heating the air using an electrical resistance element at the start of the tube and circulating the air in the tube around the element and sand(simplified version omitting controls)

Edited January 3, 2023 by Marvin
further thought

[Roger440]

1 minute ago, Marvin said:

by blowing air along a tube that runs into the sand and heating the air using an electrical resistance element at the start of the tube (simplified version omitting controls)

 

Hmmm. But surely that means the air needs to hotter than that?

[Marvin]

Just now, Roger440 said:

 

Hmmm. But surely that means the air needs to hotter than that?

Yes. mineral wool will take up to about 600C without problem, steel pipe, steel container, sand will go a lot higher.

[Kelvin]

I like the Ripple Energy approach in principle. They are also doing some thermal storage proof of concept designs with Sunamp and will be looking for 100 houses to trial it. I also like what Octopus are doing. They’ve taken the fight to big energy dinosaurs and will force them to change in time. 
 

We’ve had an interesting social experiment over the Christmas period. We’ve had a lot of folk stay with us over the last 10 days. They all live in modern houses compared to this old farmhouse we rent. I don’t have any gizmos in the house so no Alexa, Ring doorbells, cameras, etc. The house is poorly insulated so while you can heat it up quite quickly, as it has large radiators everywhere, it doesn’t retain the heat. What everyone has said is that they run their houses too hot. 
 

 

[Marvin]

Assuming the theoretical set up as listed in my third posting above, my calculation is:

 

Thermal conductivity of sand 0.25 

 

https://www.geothermal-energy.org/pdf/IGAstandard/WGC/2010/2952.pdf

 

Thermal conductivity of Mineral wool 0.035 W/mK

https://www.google.com/search?q=thermal+conductivity+of+mineral+wool&sxsrf=ALiCzsZ55VU1Hax1EltJUgwhzjwpX2LASw%3A1672745639975&ei=pxK0Y9iSO9OThbIPt-6M6AU&ved=0ahUKEwiYgq6Np6v8AhXTSUEAHTc3A10Q4dUDCA8&uact=5&oq=thermal+conductivity+of+mineral+wool&gs_lcp=Cgxnd3Mtd2l6LXNlcnAQAzIFCAAQgAQyBggAEBYQHjIGCAAQFhAeMgYIABAWEB4yBQgAEIYDMgUIABCGAzIFCAAQhgMyBQgAEIYDOgQIABBDOggIABAWEB4QD0oECEEYAEoECEYYAFAAWL8RYIUUaABwAXgAgAFpiAGlB5IBBDExLjGYAQCgAQHAAQE&sclient=gws-wiz-serp

 

500 degrees temp change, one meter thick Sand, 400mm thick Mineral wool. My calculation suggests the loss to be about 5 Watts per hour. 

 

Where have I gone wrong??

[SteamyTea]

30 minutes ago, Roger440 said:

But we did have to issue a warning prior to christmas that there may be a shortage

We get them every year. It is part of the usual reporting. Just this year, people are taking an interest.

 

30 minutes ago, Roger440 said:

I guess you believe the challenges will be overcome

Yes. The technical ones are, the rest is socio economic. They are the hard ones. But I keep telling people it is possible, and backing it up with data. So the message is sinking in. Not as quick as a power cut mind.

32 minutes ago, Roger440 said:

not sure of the relevance of the graph? Its just showing the split? If its 100% wind and we never have shortages, great

The relevance was to dismiss your assumption that over 3 months we had very little RE generation. In reality we had lots.

RE is much more than just wind generation. 

[Roger440]

43 minutes ago, Marvin said:

Yes. mineral wool will take up to about 600C without problem, steel pipe, steel container, sand will go a lot higher.

Sorry, I meant how do you get the air to 600?

[Roger440]

24 minutes ago, SteamyTea said:

We get them every year. It is part of the usual reporting. Just this year, people are taking an interest.

 

Yes. The technical ones are, the rest is socio economic. They are the hard ones. But I keep telling people it is possible, and backing it up with data. So the message is sinking in. Not as quick as a power cut mind.

The relevance was to dismiss your assumption that over 3 months we had very little RE generation. In reality we had lots.

RE is much more than just wind generation. 

 More interest is unsurprising given what's going on.

 

I don't doubt for a minute there are technical solutions. That's not what I'm worried about. It's the ability of our government to make the right decisions, well, any decisions really. No amount of data will solve that.

 

Of course RE is more than wind. But it forms the biggest part of it. And you graph is nicely smoothed. Like the day when wind was at 3%.  The graph says all was well. But the reality was, had we not fired up every fossil fuel burning contraption we had available, there would have been a shortage. Again, can technical solutions be found? Sure. Will they be, not a chance. Not to a level that gives us a reliable supply at a sensible stable cost.

 

[Marvin]

9 minutes ago, Marvin said:

Assuming the theoretical set up as listed in my third posting above, my calculation is:

 

Thermal conductivity of sand 0.25 

 

https://www.geothermal-energy.org/pdf/IGAstandard/WGC/2010/2952.pdf

 

Thermal conductivity of Mineral wool 0.035 W/mK

https://www.google.com/search?q=thermal+conductivity+of+mineral+wool&sxsrf=ALiCzsZ55VU1Hax1EltJUgwhzjwpX2LASw%3A1672745639975&ei=pxK0Y9iSO9OThbIPt-6M6AU&ved=0ahUKEwiYgq6Np6v8AhXTSUEAHTc3A10Q4dUDCA8&uact=5&oq=thermal+conductivity+of+mineral+wool&gs_lcp=Cgxnd3Mtd2l6LXNlcnAQAzIFCAAQgAQyBggAEBYQHjIGCAAQFhAeMgYIABAWEB4yBQgAEIYDMgUIABCGAzIFCAAQhgMyBQgAEIYDOgQIABBDOggIABAWEB4QD0oECEEYAEoECEYYAFAAWL8RYIUUaABwAXgAgAFpiAGlB5IBBDExLjGYAQCgAQHAAQE&sclient=gws-wiz-serp

 

500 degrees temp change, one meter thick Sand, 400mm thick Mineral wool. My calculation suggests the loss to be about 5 Watts per hour. 

 

Where have I gone wrong??

 

[Onoff]

It would be interesting to do this with an old swimming pool.

 

[SteamyTea]

15 minutes ago, Roger440 said:

But the reality was, had we not fired up every fossil fuel burning contraption we had available, there would have been a shortage

I don't think so.

We have about 50‰ extra on capacity.

You have to remember that some old thermal plants were ready to be decommissioned, but not actually shut down. Keeping these going a few hours longer makes much more sense than waiting until a new solar farm, or hydro plant is built.

As I keep saying, and shall say again. 

IT DOES NOT HAPPEN OVER NIGHT.

 

While I don't have much faith in any individual government, I do have quite a bit of faith in the National Grid to guide the Civil Service into presenting the right options to the appropriate Ministers.

Again, those decisions are not acted on right away, but they do get acted on.

 

This debate about what happens when the wind does not blow and the sun does not shine has been going on for 30 years at least.

In that time we have gone from virtually no RE generation to 50‰ generation. And we have had a reliable supply.

So your arguement that it can't happen/won't happen is rather wrong.

When I was at university studying RE, there was an assumption that more than 30% renewables on the grid would cause massive instability.

Well, thanks to behind the scenes investment, decent planning and very clever engineers, along with statisticians, we now frequently have 60%+ RE loading, and still get a reliable supply.

And that is before large scale storage has happened. 

Storage is the next phase in this journey.

Storage systems are going to cause more arguements than on shore wind turbines, and a lot more misinformation.

You will be told, by someone, that storage uses more energy to make than it will ever deliver.  It is up to you to find out if that is true or not, me telling you will not work.

 

[SteamyTea]

18 minutes ago, Onoff said:

It would be interesting to do this with an old swimming pool.

 

Does swimming pool have a silent P in it?

[Roger440]

3 minutes ago, SteamyTea said:

I don't think so.

We have about 50‰ extra on capacity.

You have to remember that some old thermal plants were ready to be decommissioned, but not actually shut down. Keeping these going a few hours longer makes much more sense than waiting until a new solar farm, or hydro plant is built.

As I keep saying, and shall say again. 

IT DOES NOT HAPPEN OVER NIGHT.

 

While I don't have much faith in any individual government, I do have quite a bit of faith in the National Grid to guide the Civil Service into presenting the right options to the appropriate Ministers.

Again, those decisions are not acted on right away, but they do get acted on.

 

This debate about what happens when the wind does not blow and the sun does not shine has been going on for 30 years at least.

In that time we have gone from virtually no RE generation to 50‰ generation. And we have had a reliable supply.

So your arguement that it can't happen/won't happen is rather wrong.

When I was at university studying RE, there was an assumption that more than 30% renewables on the grid would cause massive instability.

Well, thanks to behind the scenes investment, decent planning and very clever engineers, along with statisticians, we now frequently have 60%+ RE loading, and still get a reliable supply.

And that is before large scale storage has happened. 

Storage is the next phase in this journey.

Storage systems are going to cause more arguements than on shore wind turbines, and a lot more misinformation.

You will be told, by someone, that storage uses more energy to make than it will ever deliver.  It is up to you to find out if that is true or not, me telling you will not work.

 

 

Well, I was looking at gridwatch. Ok it's all a dumbed down dashboard, but still a reasonable indicator I would have thought?

 

As I said, I don't doubt technical solutions exist. Of course they do. A

nd will continue to be developed. Where we differ, is that you believe stuff will get done to ensure we don't have shortages. I don't believe it at all. The days of government essentially doing their best for the country are in the past.

 

I don't believe it and will do what I have to do, to ensure I don't suffer as a consequence. Or at least limit that suffering to a minimum.

 

Many will disagree with that position, but me doing it won't impact anyone else, other than some possible small scale fossil fuel burning.

 

Meanwhile, yes, energy storage would be a game changer, which is what we are supposed to be discussing 🙂

[SteamyTea]

38 minutes ago, Roger440 said:

Where we differ, is that you believe stuff will get done to ensure we don't have shortages. I don't believe it at all. The days of government essentially doing their best for the country are in the past.

Not really down to 'the government' though.  They have told the industry what has to be done i.e. supply power reliably, then left it up to the industry.

It is only then that the public horse trading and mudsling starts.

The alternative is a system where governments micro-manage everything, that has not ended well for those countries.

In my life (in the UK), apart from the scheduled power cuts caused by industrial action, I doubt if I have had 48 hours in total of power cuts.  And not one of them has been caused by lack of production.

Now I know some people have had longer power cuts, usually caused by exceptional weather pulling down power lines, not power stations failing to generate, there was the exception where a wind farm and a power station went off line together on the 9^th August 2019.  Lessons where learnt.

 

Quite simply, if you want to isolate yourself from power outages, get a generator, going to be the cheapest option by far, and it will not use hardly any fuel as we just don't have multi day outages in the civilised parts of Buckinghamshire, or Cornwall.

 

[Kelvin]

I disagree. Government’s role is to not just tell industry what to do but to make it straightforward and quick to make the investment and create legislation that supports the goals. The oil industry could never have got off the ground without significant Government support. 

[Roger440]

37 minutes ago, SteamyTea said:

Not really down to 'the government' though.  They have told the industry what has to be done i.e. supply power reliably, then left it up to the industry.

It is only then that the public horse trading and mudsling starts.

The alternative is a system where governments micro-manage everything, that has not ended well for those countries.

In my life (in the UK), apart from the scheduled power cuts caused by industrial action, I doubt if I have had 48 hours in total of power cuts.  And not one of them has been caused by lack of production.

Now I know some people have had longer power cuts, usually caused by exceptional weather pulling down power lines, not power stations failing to generate, there was the exception where a wind farm and a power station went off line together on the 9^th August 2019.  Lessons where learnt.

 

Quite simply, if you want to isolate yourself from power outages, get a generator, going to be the cheapest option by far, and it will not use hardly any fuel as we just don't have multi day outages in the civilised parts of Buckinghamshire, or Cornwall.

 

 

But it is. Nobody is going to build a muclear power station, for example, without direct say so from government and gurantees about prices. Understandably as government is prone to move the goal posts on mere whims.

 

If my only concern was outages, then yes, have a generator (which i do, a nice disel 5KVA affair) but as we discussed earlier there is the price element too. That got lost in the debate. Again, i dont trust them not to allow, through supply and demand, or otherwise deliberately, to drive up the cost of electricity. eg, Starmer says no more gas (or oil) for homes  after 2030. This is your next PM. Probably. What do you reckon will happen to electricity demand when that happens? And the corresponding effect on prices? Given as you yourself say, the lead times on infrastructure.

 

We both know there is zero possibility of converting 30 million homes from gas to heat pumps in that time frame no matter what he says. The national grid nor the civil service can save us from this level of stupid. As i said, im not going to be a victim.

[pdf27]

21 hours ago, Roger440 said:

Interesting. But i note they dont answer the question, what if they go bust? Which they probably will.

 

I think investing in the stock market would be much safer.

If I've understood their business model correctly, they're unlikely to go bust - all of their capital comes from shareholders, and the business model is essentially to sell the electricity they produce to their customers at close to cost price rather than market price. Unless market prices go below the cost of production (very unlikely for a wind farm!) they're unlikely to go bust. Returns might however be very poor.

 

21 hours ago, SteamyTea said:

There may be a reason they are chasing small investors rather than the large institutional investors who know the industry very well.

Plenty of large institutional investors doing exactly the same thing. I get the feeling Ripple was set up because someone wanted to buy shares in a wind turbine and couldn't do it easily, and decided there was a gap in the market to sell these shares. Given the rate of take up, that appears to be true.

 

20 hours ago, MikeSharp01 said:

That's an interesting read - 23T of  water and you cannot make it pay.

Energy is very cheap, and most forms of storage have very low energy density. It's a particular problem if you only recharge and use it once a year.

 

19 hours ago, Roger440 said:

Good point on the storage size. Hadnt considered that. I was considering large in case i wanted to add a gasification log boiler which would generate a lot of heat quickly (as per previous discussions). Need to ponder how that would work with smaller multiple tanks. A complicated control system i suspect. I dont like complicated. complication = unreliability.

Whatever you do a gasification boiler is going to add a lot of complexity. If it's just PV then you can just wire all the immersion heaters up with DPDT relays to replace the SPDT. That way once the first immersion reaches temperature and the relay fires, the current is connected to the next immersion, and so on. 

 

19 hours ago, Roger440 said:

But in this scenario, water needs diverting, that means valves. And that means valve control. Which means sensors and electronics. Electronics = unreliability. And a level of understanding to fix when it goes wrong that i dont possess. Back to where we started.

Exactly how long would it take for a plumber to get to where you live, 6 weeks? This is supplementing the existing heating system I assume, in which case reliability really isn't that big a deal. Valves, etc. are reliable enough that they're rarely the cause of problems in domestic systems.

 

18 hours ago, Nickfromwales said:

A crane to lift an immensely heavy weight a very short distance seems a good idea. That stored energy will last until you release the brake.

 

Am I a Boffin yet?

Problem is to get a decent amount of energy stored you really need a heavy weight a long distance, and there aren't many options for that. Gravitricity seem to be the least hopeless of the lot - using disused mine shafts so the hole is already there - but they don't seem to be able to make it work economically either and are pivoting to hydrogen storage underground.

 

18 hours ago, Marvin said:

Any idea how much a Sunamp system is per 100kWh? 

No published data for the big systems, retail price for the smaller ones is in the region of £250/kWh so you'd be looking at £25k or so for a 100kWh system. Capable of storing about £10 worth of heat!

 

9 hours ago, Roger440 said:

Do we not think that adding 30 million households to electric heating when starmer turns off gas in 2030, and the longer term addtion of 30 million electric cars wont have an effect on prices, given that, in simplistic terms, generation capacity isnt increasing significantly?

• 2035 is the current date for fitting no new gas boilers - realistically that means that there will still be gas boilers on the grid in 2050. The transition time is getting up there with the life of a power station, so the capacity really isn't an issue - and I can't find any Labour policies to change this.
• Electric cars overwhelmingly charge at night when demand is maybe half that during the day anyway. Little or no new capacity needed there.

 

6 hours ago, Marvin said:

Assuming the theoretical set up as listed in my third posting above, my calculation is:

 

Thermal conductivity of sand 0.25 

Thermal conductivity of Mineral wool 0.035 W/mK

 

500 degrees temp change, one meter thick Sand, 400mm thick Mineral wool. My calculation suggests the loss to be about 5 Watts per hour. 

 

Where have I gone wrong??

Hard to say when you don't show any calculation!

• Surface area of the insulation box is ~6m². To make the maths easier, flatten it out and act as if everything is one-dimensional.
• To steal from Wiki, 
  • In this case, q has units of W/m² - it's a heat flux not a power.
  • k is 0.035 W/m.K
  • T₂-T₁ is 500 K
  • L is 0.4m
  • This means q is 43.75 W/m² and so total losses are 262W (multiply by 6).
• This means losses are 6.3 kWh/day at full temperature.
• Sand weighs about 1600 kg/m³ and specific heat capacity is 290 J/kg.K. This means that the heat capacity of 1m³ of sand is 464 kJ/K. 1 kWh is 3600 kJ, so each m3 of sand holds 0.13 kWh/K.
• This means the temperature in the store would initially drop by 50°C/day - obviously the rate of decay will slow down quickly as the temperature drops, and you really need to solve the integral to plot the behaviour with time (repeating this calculation in excel with time steps is fine).

Conclusion: a 1m³ cube of sand is hopelessly small for this application, and 400mm of mineral wool is grossly insufficient as insulation at these temperatures.

[SteamyTea]

7 minutes ago, pdf27 said:

sell the electricity they produce to their customers at close to cost price rather than market price

But are they relying on the old subsidies? FiTs and so forth.

Do they have a list if installations, and the deals they are on.

From that it should be possible to see how long the income stream will last, and at what level.

[pdf27]

1 hour ago, SteamyTea said:

But are they relying on the old subsidies? FiTs and so forth.

Do they have a list if installations, and the deals they are on.

From that it should be possible to see how long the income stream will last, and at what level.

No subsidies, and all the risk on level of returns (up and down-side) is passed on to shareholders/members/whatever you want to call them. Basically you're buying a share in the profits of a wind farm, which you can only redeem via your electricity bill with a small number of suppliers (possibly for tax reasons).

Quote

With Ripple, your energy supplier buys your electricity from your wind farm at its low and stable operating cost. The difference between this price and the volatile market price is passed onto your electricity bill , every month, for the 25 year lifespan of the wind farm. We estimate you should save about 23% on your electricity bill.