A rather impractical shape - but if the box were a cylinder instead the surface area would be a lot smaller, built underground at least the base could be hemispherical even if the top would be flat to allow the gubbins to be put in and maintained.
How do you exchange the heat stored in a Sand Battery into a water heating system.
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slimshady
Established Member
Hi.
Could you sell / exchange the power to neighbour(s). Heat their Swimming pool, charge their car, etc.
Alex.
Could you sell / exchange the power to neighbour(s). Heat their Swimming pool, charge their car, etc.
Alex.
Terry - Somerset
Established Member
As the heat is discharged from the sand "battery" the temperature will fall.
How heat stored is released and used will be different at different temperatures - possibly starting at 600C slowly falling to just above ambient at which point it is exhausted (discharged/flat).
Fancy oils and chemicals which work at higher temperatures may cease to function. Control gear designed to avoid personal injury at 600C and provide hot water at 50C is costly and may be inappropriate at 100C.
Perhaps the simple solution is mixing air flow from the sand (at whatever temperature) with ambient to give a constant which could be used for space heating and hot water. This should be controllable by simple thermostatic controls (a bit like a shower with hot and cold feed).
Or am I being overly simplistic.
How heat stored is released and used will be different at different temperatures - possibly starting at 600C slowly falling to just above ambient at which point it is exhausted (discharged/flat).
Fancy oils and chemicals which work at higher temperatures may cease to function. Control gear designed to avoid personal injury at 600C and provide hot water at 50C is costly and may be inappropriate at 100C.
Perhaps the simple solution is mixing air flow from the sand (at whatever temperature) with ambient to give a constant which could be used for space heating and hot water. This should be controllable by simple thermostatic controls (a bit like a shower with hot and cold feed).
Or am I being overly simplistic.
I’m thinking an in ground system with a green house positioned on top would be a good use of the heat leakage.
PlumBZone Plumbing
New member
Hi...here goes...I've filled a 200L geyser with mainly sea sand and a bag of riversand on the top. I've put 1 x 3kw and 1 x 4 kw element on either side of the geyser towards the top...my copper pipes run down thru the gasket plate down into the geyser say 60cm down into the sand...the elements are straight from the PV panels...3 in series but I'm not getting the soil hot enough. The element gets to 170* but when I run the pump from geyser down into the sand battery, I'm not getting the temperature I need...the geyser only goes up 2 - 4 degrees...any ideas what I can do? Thanks. Geyser is situated outside closest to the geyser location down below from the geyser in the roof.
Jameshow
Established Member
Is your geyser / tank insulated perhaps you gave heat leakage. Do you have sufficient solar panels?
I had a play with a big jam pan full of silver sand. One full 20kg bag.
For my heating element I used a spare, new 3kW fan oven ring element, buried in the centre of the sand. I pushed a thermocouple in close to the heating element to monitor it. The concern is that sand has low conductivity and no convection so running the element at rated power in air will make it overheat in sand.
I looked at tubular heating element specifications and figured that they should be safe upto 300, 350C.
I fed the element from a 10 amp rated variac autotransformer
The sand heats quite slowly.
It takes a long time for heat to move through the sand.
I found a steady state where I was powering the element at about 1/3 rated power and it was maintaining a steady temp in the 300's.
At first I could place my hand flat on the surface of the sand just 60mm above it after a good while, the heat began to conduct through and eventually the whole lot became too hot to touch.
At that point I unplugged and moved it outside for safety. It took some hours to cool down.
My thought was that I should try again bigger at some point. Wiring 3x 3kW heating elements in series would be an easy way to derate them so that they didn't overheat.
The heat exchanger pipes will need to be plentiful and the water will need to flow slowly to extract the heat I think. I still don't know the answer to how to stop water becoming steam when there isn't a steady and adequate flow.
My project has gone on the back burner while I upgrade my hot water tank to a bigger, better insulated one witb better placed immersion heaters. That should absorb 13kWh of surplus electricity. Much less than a sand battery but immediately useful and it'll get cycled almost every day when the sun's shining.
For my heating element I used a spare, new 3kW fan oven ring element, buried in the centre of the sand. I pushed a thermocouple in close to the heating element to monitor it. The concern is that sand has low conductivity and no convection so running the element at rated power in air will make it overheat in sand.
I looked at tubular heating element specifications and figured that they should be safe upto 300, 350C.
I fed the element from a 10 amp rated variac autotransformer
The sand heats quite slowly.
It takes a long time for heat to move through the sand.
I found a steady state where I was powering the element at about 1/3 rated power and it was maintaining a steady temp in the 300's.
At first I could place my hand flat on the surface of the sand just 60mm above it after a good while, the heat began to conduct through and eventually the whole lot became too hot to touch.
At that point I unplugged and moved it outside for safety. It took some hours to cool down.
My thought was that I should try again bigger at some point. Wiring 3x 3kW heating elements in series would be an easy way to derate them so that they didn't overheat.
The heat exchanger pipes will need to be plentiful and the water will need to flow slowly to extract the heat I think. I still don't know the answer to how to stop water becoming steam when there isn't a steady and adequate flow.
My project has gone on the back burner while I upgrade my hot water tank to a bigger, better insulated one witb better placed immersion heaters. That should absorb 13kWh of surplus electricity. Much less than a sand battery but immediately useful and it'll get cycled almost every day when the sun's shining.
A nice idea but not easy to get it right. When I replaced some wooden steps outside my house I installed some pipes under the treads. I can circulate water around the pipes, heated by my (thermal) solar panels. My idea was to keep the steps clear of snow.
In reality it doesn't work. It does have some effect but not much. It is better if I have the water circulating before the snow starts, but normally I don't. If I start the circulation after the snow has settled on the steps the heat is not enough to clear the snow. It is so poor that I don't even run the circulation any more. To get it to work I would need a lot more pipes under the steps and the energy input would have to be a lot higher.
The water wouldn’t turn to steam if it’s a sealed system as the boiling point is raised like in a car radiator. If you fitted a relief valve then it could blow off as steam depending on the pressure setting and water temperature.
Have you looked at those hot air blowers that were used to get your fire going, Grenadier Electric Firelighter - The Easy Way To Light Your Fire or BBQ
This is a modern version and the one I remember as a kid had a gold crackle finish but it was a super weapon to destroy the enemy army of toy plastic soldiers.
Chris Harris
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I added a metal tube to a hot air paint stripper to light the Aga. Perhaps an experiment around this would be worthwhile (and a lot cheaper than the commercial version).
In 1975 a colleague played with a massive heat store in the cellar of his old house. It was filled with common salt. It worked, but when energy prices dropped dramatically, he abandoned the project. Sand is clearly cheaper and less corrosive, but I've no idea of his sources..
Do you need those high temperatures? The greater the mass (size of battery) the more heat you can store and 200C is easier and safer to handle than 400/700 as well as being adequate for water and space heating. In your circumstances could you just go for a bigger battery?
In 1975 a colleague played with a massive heat store in the cellar of his old house. It was filled with common salt. It worked, but when energy prices dropped dramatically, he abandoned the project. Sand is clearly cheaper and less corrosive, but I've no idea of his sources..
Do you need those high temperatures? The greater the mass (size of battery) the more heat you can store and 200C is easier and safer to handle than 400/700 as well as being adequate for water and space heating. In your circumstances could you just go for a bigger battery?
The only advantages that sand has and why they are being explored are
1. The sand is very cheap
2. You can heat it much hotter than water (450C I believe in commercial sand batteries)
Water stores much more heat energy than sand kilo for kilo but is limited to 90 ish degrees in practice
Unless you can run the sand battery at high temperatures then there isn't much point. What most of us don't have in our flats, semi's and small homes is the space for a big tank.
The concept of something the size of a single fridge that can store 30kWh is quite appealing but the commercialisation is in it's infancy and and prices are way above where they will end up.
1. The sand is very cheap
2. You can heat it much hotter than water (450C I believe in commercial sand batteries)
Water stores much more heat energy than sand kilo for kilo but is limited to 90 ish degrees in practice
Unless you can run the sand battery at high temperatures then there isn't much point. What most of us don't have in our flats, semi's and small homes is the space for a big tank.
The concept of something the size of a single fridge that can store 30kWh is quite appealing but the commercialisation is in it's infancy and and prices are way above where they will end up.
Jacob
New Luddism. Wake up and resist.
Looks like communal systems could be the future. How a sand battery could transform clean energy.
Presumably any masonry would do but sand is a convenient way of handling stone. Or do some stones/sand have higher calorific values?
https://temperaturemaster.com/does-sand-hold-heat/
Presumably any masonry would do but sand is a convenient way of handling stone. Or do some stones/sand have higher calorific values?
https://temperaturemaster.com/does-sand-hold-heat/
That would blow sand all over my living room !
The big district heating sand battery in Finland uses hot air blown through pipes in the sand. Great idea because the element and blower are external and easy to replace, but cumbersome and maybe not so easy to scale down to something small and quiet enough to sit in the kitchen.
I believe Tepeo use not a pure sand core but something more like the old storage radiator bricks. It has slightly, only slightly, better thermal properties and the heating elements are placed in it.
I don't know but I can't see a domestic appliance having a pressurised steam circuit for the energy extraction.
There was enough controversy when they introduced the sealed hot water cylinder and all sorts of assumptions that they will explode so having a steam circuit, even low pressure would cause alarm but think of the training needed, old joe turns up and uses plastic push fit !!
Terry - Somerset
Established Member
This is a very interesting intellectual/academic debate about how to engineer and optimise sand storage. However reality intrudes for most folk.
PV systems generate more energy in summer than winter due to greater daylight hours and sunshine by a factor of ~4. Consumption is higher in winter than summer due to lower daylight hours and lower temperatures requiring more heating - perhaps by a factor of ~2.
A system with the capacity to meet peak winter demand is high cost and will generate surpluses in summer for which the only real option is sale at a low price back to the grid. Conversely a system built to match summer demand will need grid back up in winter.
A somewhat heretical thought given much of this debate is driven by a desire to minimise environmental impacts is a diesel generators to make up any energy shortfall.
A system sized to meet total demand over the year will require storage for the surpluses generated in the summer months to be used in winter.
A sand battery seems an effective method of storing heat for future use. I am not clear it can generate electricity for lighting and appliance (steam turbine generator??).
Heat loss means the energy cannot be stored indefinitely, although I suspect the time can be extended at cost through better insulation.
If the goal is self sufficiency, then perhaps the cost and space issues do not intrude. Otherwise it seems a complex balance between the cost and and performance of different approaches.
PV systems generate more energy in summer than winter due to greater daylight hours and sunshine by a factor of ~4. Consumption is higher in winter than summer due to lower daylight hours and lower temperatures requiring more heating - perhaps by a factor of ~2.
A system with the capacity to meet peak winter demand is high cost and will generate surpluses in summer for which the only real option is sale at a low price back to the grid. Conversely a system built to match summer demand will need grid back up in winter.
A somewhat heretical thought given much of this debate is driven by a desire to minimise environmental impacts is a diesel generators to make up any energy shortfall.
A system sized to meet total demand over the year will require storage for the surpluses generated in the summer months to be used in winter.
A sand battery seems an effective method of storing heat for future use. I am not clear it can generate electricity for lighting and appliance (steam turbine generator??).
Heat loss means the energy cannot be stored indefinitely, although I suspect the time can be extended at cost through better insulation.
If the goal is self sufficiency, then perhaps the cost and space issues do not intrude. Otherwise it seems a complex balance between the cost and and performance of different approaches.
Agent_zed
Established Member
As mentioned most things have already been done in some form or another and what we are talking about in real terms is just a night storage heater. The only difference being that it uses sand rather than special blocks.
My parents house has a central air unit that is the size of a wardrobe and has a fan that pushes hot air out to each room. They installed the first one 40+ years ago and have had one replacement about 10 years ago.
From my limited understanding 400c is not that hot for a night storage heater. This paper http://www.ibpsa.org/\proceedings\BS1997\BS97_P038.pdf says 650c at max power in the core.
I'm certainly not against the idea of using sand though as it requires far less energy to use than the manufacture of bricks etc, should be cheaper, and is more diy friendly.
The other thing to throw into the mix is the thought that we don't just have to use solar. A small wind turbine could be added to the system and would potentially be more important over the winter months.
Another thing i've been wondering about is building a solar chimney Solar/Thermal Chimney which is mostly passive, only requiring a few motorised vents to direct the air.
My parents house has a central air unit that is the size of a wardrobe and has a fan that pushes hot air out to each room. They installed the first one 40+ years ago and have had one replacement about 10 years ago.
From my limited understanding 400c is not that hot for a night storage heater. This paper http://www.ibpsa.org/\proceedings\BS1997\BS97_P038.pdf says 650c at max power in the core.
I'm certainly not against the idea of using sand though as it requires far less energy to use than the manufacture of bricks etc, should be cheaper, and is more diy friendly.
The other thing to throw into the mix is the thought that we don't just have to use solar. A small wind turbine could be added to the system and would potentially be more important over the winter months.
Another thing i've been wondering about is building a solar chimney Solar/Thermal Chimney which is mostly passive, only requiring a few motorised vents to direct the air.
Jameshow
Established Member
How much energy would a ibc container of water hold at 90c if you insulated it with 100mm celotex?
Cheap as chips to buy. You could partially fill with rocks to give better heat output?
Would surely carry you over still / cloudy days??
Cheap as chips to buy. You could partially fill with rocks to give better heat output?
Would surely carry you over still / cloudy days??
artie
Sawdust manufacturer.
Very interesting topic. but possibly only applicable to off grid installations.
I like the majority, I imagine, can't really see a way to go totally off grid. At least not in the near future.
Currently Powerni buys at 17.66p per unit and sells at just under 28p per unit.
Lets call it a 10p difference.
A 5k battery won't be able to store all the surplus in mid summer and it probably won't have much to store in mid winter.
What it does store there will always be a loss, how much or little I don't know.
I would/have opted to sell the surplus as I think the rate of return wouldn't justify the outlay.
I like the majority, I imagine, can't really see a way to go totally off grid. At least not in the near future.
Currently Powerni buys at 17.66p per unit and sells at just under 28p per unit.
Lets call it a 10p difference.
A 5k battery won't be able to store all the surplus in mid summer and it probably won't have much to store in mid winter.
What it does store there will always be a loss, how much or little I don't know.
I would/have opted to sell the surplus as I think the rate of return wouldn't justify the outlay.
Agent_zed
Established Member
about 3 x more than a standardish hot water tank. Mine is about 300litres.
My brother has a 3000litre hot water tank though! So 3 x bigger than an ibc. That is used as a thermal store which is heated with biomass and thermal solar. His expansion tank is the same 300l size as my actual tank.
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