>I don't wanna deal with water, >changes state after 100C
That's why it's one of the best thermal storage materials. When gas condenses, it releases thermal energy.
Stupid, this whole idea is stupidly inefficient. The only way this is beneficial is if you are trying to locate the storage medium far from the source of power. Even at that point water is the best solution. You need to up the solar panel quantity and just put a relay on the heating element to shut off at 95° C to keep the tank from exploding. At that point you should be using the power to circulate the water through a heat exchanger that shuts off when the space has reached the desired temperature.
>Stupid, this whole idea is stupidly inefficient. The only way this is beneficial is if you are trying to locate the storage medium far from the source of power. Even at that point water is the best solution. You need to up the solar panel quantity and just put a relay on the heating element to shut off at 95° C to keep the tank from exploding. At that point you should be using the power to circulate the water through a heat exchanger that shuts off when the space has reached the desired temperature.
this is all incredibly wrong.
wow.
water is a terrible medium for storing heat. >b b but, i kept it under 100 C!
yeah, but why? >b b because the pressure will rise when it converts steam!
so, you're going to intentionally limit the heat capacity of your heat battery to use water, which you even acknowledge causes problems above 100 C, for... reasons?
are you moronic?
you want to capture as much heat as possible, and limiting the heat capacity of your thermal mass--just so you can use water--is just about the dumbest thing you could do.
the next time you think of commenting on something which you have no knowledge about,
maybe just keep your mouth shut?
1 year ago
Anonymous
If OP is capturing as much heat as possible he would be using something that starts out at better than at best 20% efficiency. So what should OP be using to store his heat?
Water has a specific heat capacity of 4.1813J/(g*K), so suppose you use a 10l pot you have 10kg of water at room temperature, let's say 20°C, so 80K to get to 100°C so you need 3345kJ. 1W is 1J/s so at 100W assuming no losses whatsoever it'll take you 9 hours and 17 minutes to reach that 100°C.
I'm gonna go with "not an issue."
Also, why the hell are you using a photovoltaic panel with at best 30% efficiency to capture heat when an evacuated tube solar heater costs a fraction as much and has like 95+% efficiency?
>10l pot
Personally I'd go with a 220l hobo barrel I I decided to actually build this. So even more of a non-issue.
Just wrap it in some rockwool or something.
[...]
I don't wanna deal with water, changes state after 100C
Water has an insanely high heat capacity. It is the reason why the Earth doesn't burn in the day and freeze at night, and is why deserts are so cold at night.
People do indeed use water as thermal batteries for keeping their warm climate plants alive in cold climate nights. All you do is stick a wall of water bottles behind them. Even something as simple as that will keep your home slightly warmer at night. Since I don't imagine you don't want to heat your home above the boiling point of water, I can guarantee with a sufficiently large battery, water is absolutely usable here. Even boiling by accident isn't an issue since you can quite easily install a thermostat to cut power supply once your battery surpasses a dangerous temperature, add chemicals like salt to increase the boiling point and/or seal your battery to keep it pressurized (you should be able to find a pressure cutoff switch to keep it safe) which also increases the boiling point
You can't easily turn the energy in a sand battery back into electricity. They are only used for heating.
>Can the sand store enough heat?
Yes. OP's plan is way the frick to small though. They are also ignoring the thermal insulation needed for the "battery".
I'm pretty sure water is far better.
And you can just pump it through a radiator like everyone else, no need for corrugated pipes and whatnot.
Water has a max heat of 100 C. Sand has a max heat of 1700 C.
Can your heating element withstand 1700°C?
Or the wiring insulation?
Do you honestly think you'll ever heat it up to 1700°C with a 100W solar panel?
Water is fine because going higher than 100°C gets you over the glass transition temperature of most plastics and the temperature rating of consumer grade electronics anyways, and it's easily scalable. Just add more water.
When I had cats at my shop, I made a winter house for them by taking a large portable cooler and cutting a hole in the side of it and sticking a cat door flap in it. Then I got a self-regulated water pipe heat cable, coiled that up in the bottom, and put a piece of carpet on top of it. The heat cable doesn't use much power and never gets any hotter than around 80-100 fahrenheit so there's no risk of it starting a fire or making it too hot inside.
you're going to want to put insulation around the outside of your pot.
you will also want a path to blow in air that you want to heat (like from inside your house) and use a blower to move the air.
it's not a bad idea for cheap heat.
Two pots inside of one another with insulation or better yet just a straight up vaccum would work better. Water holds heat pretty well already, but it does boil and could cause a pressure bomb if you don't know wtf ur doing. Silica sand is ok so long as you can keep the heat IN; hence the insulation or vaccum layer. Tbh, the capacity youd get out of a pot is so fricking tiny that it probably wouldnt be worth it. Additionally, using a solar panel is ass. I would use one of those old magnifying pieces in tube tvs to focus sunlight directly into the sand or the heating element somehow. The more direct the better.
get rid of the solar panel and replace the sand with thermite. Your room will be toasty in no time. Also might want to consider putting a bed of graphite underneath so it doesn't melt through the pot, the floor, and several feet of ground.
>summoning some butthole who glows in the dark and thinks he's important.
That's why you get several dogs stuffed with tannerite and put them around your property
OP Here
okay guys, I have a new idea, instead of using pipe to transfer hot air, I'm going to use an insulated (fiber glass insulation wrap) set of copper wires and bury one end into the sand bucket, and just hope the heat transfers 1 meter efficiently over to a set of bricks that I can put the other end of the wire under. The bricks will heat up, and the bricks will be around the cat house.
Put a water heating element inside a barrel full of water sitting in the space you want heated. Wrap barrel in insulation. At night, remove lid and let heat escape to heat the space. Your tiny ass solar panel isn't going to raise 50 gallons of water to 100c. And even you upgraded to more solar, Just remove some insulation to let more heat escape sooner.
Alternatively, skip the electric inefficiencies and build a solar water heater. Either a batch or panel heater.
when coal and nuclear were running at constant output there is more energy during the night than the day.
so power company installed switching meters, in the night you turned on the storage oven while the energy was at a lower tariff.
the oven is made from stones containing Chromium 6 and are insulated with asbestos. so there often on Craigslist for free.
Water is the only material that really works for storing heat.
The problem with other materials being heated to hundreds of degrees is that the loss of heat through air convection and radiation is too big.
Even if you try to insulate with mineral wool or expanded perlite, the thermal loses are too great because the thermal coefficient of an insulator goes drastically up with temperature.
So in the end if you want to store enough heat to do something useful with it you have to use water that has a very high thermal capacity and is cheap.
You're going to need an air inlet so that cooler air flows in, gets heated up, and then flows out. Otherwise you just built a radiator without any fins and a useless hose coming out the top. Presumably an intake on the bottom and an exhsut on top would let convection do its thing.
But here's the trick. A hose run through a pile of sand isn't a terribly great heat exchanger (you want to use a metal hose obviously, rather than something that would insulate the air in the hose from the warm sand. So basically you need a heat exchanger inside the pot to do the same job that fins on the outside of the pot did if you were using external convection instead of internal convection. Now, you might or might get decent results just coiling the tube all around in there. A typical, say, gas fired forced air furnace uses something much more like a car's radiator full of lots of channels and fins so that the air moving through the furnace has maximum surface area exposure to the heat of the flame. So if you have an old car radiator or intercooler or whatever then that might be a a substantial upgrade. I would also suggest keeping the diameter of the hose not very big so that once the convection gets going you'll have a reasonable velocity of air to act in a siphon-like fashion, since air, unlike water, is compressable and won't siphon as intensely based on a low pressure differential. A fan could cure this, but you can experiment with that as a later step.
In theory it should work, but you might need to mess around to get it to work well. I suspect you might have better results with water, since it stores and conducts heat relatively well, and all you'd need to do is put a pressure relief valve on top in case you start boiling it. But there's no harm in trying sand (or even wet sand!) and not worry about venting pressure just to see. Substantially venting vapor then you know you have an inefficient heat exchange and need more velocity or surface area
Dear lord the bad info in this thread is astounding.
Water can hold a lot of heat but conducts that heat too easily. It also conducts electricity, which is an obstacle.
Aluminum is used as an insulator because while it conducts heat efficiently, it also repels radiated heat extremely well.
Build it out of solid porous ceramic insulated with tetrapak or cardboard with aluminum foil glued to both sides. Exclude the aluminum if the device will be located outside or anywhere without stagnant air.
Use a ceramic heater embedded in the porous ceramic, but make sure it's rated for significantly higher temps than its operating temp. DO NOT use a TEC thermoelectric device because they are extremely inefficient and have special design requirements you dont want to deal with.
DO understand that 100w isn't much so don't expect to heat a large area unless you build it with a large volume and have plenty of time to "charge" it.
Fire is going to outperform solar by a wide margin and cost significantly less so be sure you actually NEED the sustainability you're after.
Can the sand store enough heat?
I thought sand had a small thermal mass.
I forgot to draw some aluminum foil for insulation, but a sufficiently large sand store will last a whole night for sure
>I forgot to draw some aluminum foil for insulation
aluminum conducts heat very well and is a terrible insulation.
what about tin? idk
I don't wanna deal with water, changes state after 100C
Well it's not like a 100W panel is going to make a barrel of water boil anytime soon.
Especially with no real insulation (LOL)
Try rock wool or fiberglass.
all metals conduct heat the worst one is stainless steel. nobody uses metal as an insulator.
the best insulator is a stainless steel double pot with a vacuum in the middle. like in thermos.
>I don't wanna deal with water,
>changes state after 100C
That's why it's one of the best thermal storage materials. When gas condenses, it releases thermal energy.
energy that you have to put in there to begin with its not free. state change makes sense in aircon where you benefit a huge energy differential
I don't like high pressure things that explode
Stupid, this whole idea is stupidly inefficient. The only way this is beneficial is if you are trying to locate the storage medium far from the source of power. Even at that point water is the best solution. You need to up the solar panel quantity and just put a relay on the heating element to shut off at 95° C to keep the tank from exploding. At that point you should be using the power to circulate the water through a heat exchanger that shuts off when the space has reached the desired temperature.
>Stupid, this whole idea is stupidly inefficient. The only way this is beneficial is if you are trying to locate the storage medium far from the source of power. Even at that point water is the best solution. You need to up the solar panel quantity and just put a relay on the heating element to shut off at 95° C to keep the tank from exploding. At that point you should be using the power to circulate the water through a heat exchanger that shuts off when the space has reached the desired temperature.
this is all incredibly wrong.
wow.
water is a terrible medium for storing heat.
>b b but, i kept it under 100 C!
yeah, but why?
>b b because the pressure will rise when it converts steam!
so, you're going to intentionally limit the heat capacity of your heat battery to use water, which you even acknowledge causes problems above 100 C, for... reasons?
are you moronic?
you want to capture as much heat as possible, and limiting the heat capacity of your thermal mass--just so you can use water--is just about the dumbest thing you could do.
the next time you think of commenting on something which you have no knowledge about,
maybe just keep your mouth shut?
If OP is capturing as much heat as possible he would be using something that starts out at better than at best 20% efficiency. So what should OP be using to store his heat?
Water has a specific heat capacity of 4.1813J/(g*K), so suppose you use a 10l pot you have 10kg of water at room temperature, let's say 20°C, so 80K to get to 100°C so you need 3345kJ. 1W is 1J/s so at 100W assuming no losses whatsoever it'll take you 9 hours and 17 minutes to reach that 100°C.
I'm gonna go with "not an issue."
Also, why the hell are you using a photovoltaic panel with at best 30% efficiency to capture heat when an evacuated tube solar heater costs a fraction as much and has like 95+% efficiency?
>10l pot
Personally I'd go with a 220l hobo barrel I I decided to actually build this. So even more of a non-issue.
Just wrap it in some rockwool or something.
why do we wrap warm food in it
Radiation isn't the only means of heat transfer
Because it blocks light, moisture, and bacteria. Not heat.
I'm pretty sure water is far better.
And you can just pump it through a radiator like everyone else, no need for corrugated pipes and whatnot.
here, op.
these will help you.
you are pretty wrong. water starts to boil at 100 C.
Water has an insanely high heat capacity. It is the reason why the Earth doesn't burn in the day and freeze at night, and is why deserts are so cold at night.
People do indeed use water as thermal batteries for keeping their warm climate plants alive in cold climate nights. All you do is stick a wall of water bottles behind them. Even something as simple as that will keep your home slightly warmer at night. Since I don't imagine you don't want to heat your home above the boiling point of water, I can guarantee with a sufficiently large battery, water is absolutely usable here. Even boiling by accident isn't an issue since you can quite easily install a thermostat to cut power supply once your battery surpasses a dangerous temperature, add chemicals like salt to increase the boiling point and/or seal your battery to keep it pressurized (you should be able to find a pressure cutoff switch to keep it safe) which also increases the boiling point
You can't easily turn the energy in a sand battery back into electricity. They are only used for heating.
>Can the sand store enough heat?
Yes. OP's plan is way the frick to small though. They are also ignoring the thermal insulation needed for the "battery".
Water has a max heat of 100 C. Sand has a max heat of 1700 C.
Can your heating element withstand 1700°C?
Or the wiring insulation?
Do you honestly think you'll ever heat it up to 1700°C with a 100W solar panel?
Water is fine because going higher than 100°C gets you over the glass transition temperature of most plastics and the temperature rating of consumer grade electronics anyways, and it's easily scalable. Just add more water.
pretty dumb really.
I'm just going to use it to heat my outdoor cat house without electricity since no fires plz
Insulate it and put a chicken coop heater in it
Can't you just power a heat lamp wired straight to the solar?
Seems viable for keeping a small room warm if you can put upwards of 200w into the system and keep it properly insulated while its outside.
Consider suicide, thanks for wasting my time being stupid
thermal energy -> electric energy -> thermal energy
Not very efficient tbh
This OP. Just use some mirrors/lenses to heat the barrel of sand directly with solar heat rather than running a solar panel to it
I plan to put the pot under shade
sand doesn't conduct it insulates - you are just going to destroy the element
just make a skylight
When I had cats at my shop, I made a winter house for them by taking a large portable cooler and cutting a hole in the side of it and sticking a cat door flap in it. Then I got a self-regulated water pipe heat cable, coiled that up in the bottom, and put a piece of carpet on top of it. The heat cable doesn't use much power and never gets any hotter than around 80-100 fahrenheit so there's no risk of it starting a fire or making it too hot inside.
you're going to want to put insulation around the outside of your pot.
you will also want a path to blow in air that you want to heat (like from inside your house) and use a blower to move the air.
it's not a bad idea for cheap heat.
It's not total rubbish OP I think you can salvage it. Looks like the wires are plenty long enough to have a nice day.
wtf is a sand battery?
just put the heating element directly in your colon, it will be most efficient this way
Two pots inside of one another with insulation or better yet just a straight up vaccum would work better. Water holds heat pretty well already, but it does boil and could cause a pressure bomb if you don't know wtf ur doing. Silica sand is ok so long as you can keep the heat IN; hence the insulation or vaccum layer. Tbh, the capacity youd get out of a pot is so fricking tiny that it probably wouldnt be worth it. Additionally, using a solar panel is ass. I would use one of those old magnifying pieces in tube tvs to focus sunlight directly into the sand or the heating element somehow. The more direct the better.
get rid of the solar panel and replace the sand with thermite. Your room will be toasty in no time. Also might want to consider putting a bed of graphite underneath so it doesn't melt through the pot, the floor, and several feet of ground.
But you have to replace the thermite after every use, and there's a risk of summoning some butthole who glows in the dark and thinks he's important.
>summoning some butthole who glows in the dark and thinks he's important.
That's why you get several dogs stuffed with tannerite and put them around your property
OP Here
okay guys, I have a new idea, instead of using pipe to transfer hot air, I'm going to use an insulated (fiber glass insulation wrap) set of copper wires and bury one end into the sand bucket, and just hope the heat transfers 1 meter efficiently over to a set of bricks that I can put the other end of the wire under. The bricks will heat up, and the bricks will be around the cat house.
Nice, that idea is even better than the original. Good job.
Mass heat capacity of building materials
Substance Phase cP
J⋅g−1⋅K−1
Water liquid 4.1813
Wood solid 1.7 (1.2 to 2.9)
Gypsum solid 1.090
Asphalt solid 0.920
Concrete solid 0.880
Marble, mica solid 0.880
Brick solid 0.840
Glass, silica liquid 0.840
Sand solid 0.835
Soil solid 0.800
Granite solid 0.790
Glass, borosilicate liquid 0.753
Glass, crown liquid 0.670
Glass, flint liquid 0.503
how about salt and a ceramic container?
>implying not just directly capturing head from the sun using a radiator and heat pipes or something
Imagine being this stupid
This. Your solar>electricity>heating element idea is massively moronic. Why not an old style heat generating solar panel?
Put a water heating element inside a barrel full of water sitting in the space you want heated. Wrap barrel in insulation. At night, remove lid and let heat escape to heat the space. Your tiny ass solar panel isn't going to raise 50 gallons of water to 100c. And even you upgraded to more solar, Just remove some insulation to let more heat escape sooner.
Alternatively, skip the electric inefficiencies and build a solar water heater. Either a batch or panel heater.
wow looks like a waste of effort
Don't use a solar can heater for hot water unless you want free HRT
its 60s technology,
when coal and nuclear were running at constant output there is more energy during the night than the day.
so power company installed switching meters, in the night you turned on the storage oven while the energy was at a lower tariff.
the oven is made from stones containing Chromium 6 and are insulated with asbestos. so there often on Craigslist for free.
I studied this concept time ago.
Water is the only material that really works for storing heat.
The problem with other materials being heated to hundreds of degrees is that the loss of heat through air convection and radiation is too big.
Even if you try to insulate with mineral wool or expanded perlite, the thermal loses are too great because the thermal coefficient of an insulator goes drastically up with temperature.
So in the end if you want to store enough heat to do something useful with it you have to use water that has a very high thermal capacity and is cheap.
You're going to need an air inlet so that cooler air flows in, gets heated up, and then flows out. Otherwise you just built a radiator without any fins and a useless hose coming out the top. Presumably an intake on the bottom and an exhsut on top would let convection do its thing.
But here's the trick. A hose run through a pile of sand isn't a terribly great heat exchanger (you want to use a metal hose obviously, rather than something that would insulate the air in the hose from the warm sand. So basically you need a heat exchanger inside the pot to do the same job that fins on the outside of the pot did if you were using external convection instead of internal convection. Now, you might or might get decent results just coiling the tube all around in there. A typical, say, gas fired forced air furnace uses something much more like a car's radiator full of lots of channels and fins so that the air moving through the furnace has maximum surface area exposure to the heat of the flame. So if you have an old car radiator or intercooler or whatever then that might be a a substantial upgrade. I would also suggest keeping the diameter of the hose not very big so that once the convection gets going you'll have a reasonable velocity of air to act in a siphon-like fashion, since air, unlike water, is compressable and won't siphon as intensely based on a low pressure differential. A fan could cure this, but you can experiment with that as a later step.
In theory it should work, but you might need to mess around to get it to work well. I suspect you might have better results with water, since it stores and conducts heat relatively well, and all you'd need to do is put a pressure relief valve on top in case you start boiling it. But there's no harm in trying sand (or even wet sand!) and not worry about venting pressure just to see. Substantially venting vapor then you know you have an inefficient heat exchange and need more velocity or surface area
Dear lord the bad info in this thread is astounding.
Water can hold a lot of heat but conducts that heat too easily. It also conducts electricity, which is an obstacle.
Aluminum is used as an insulator because while it conducts heat efficiently, it also repels radiated heat extremely well.
Build it out of solid porous ceramic insulated with tetrapak or cardboard with aluminum foil glued to both sides. Exclude the aluminum if the device will be located outside or anywhere without stagnant air.
Use a ceramic heater embedded in the porous ceramic, but make sure it's rated for significantly higher temps than its operating temp. DO NOT use a TEC thermoelectric device because they are extremely inefficient and have special design requirements you dont want to deal with.
DO understand that 100w isn't much so don't expect to heat a large area unless you build it with a large volume and have plenty of time to "charge" it.
Fire is going to outperform solar by a wide margin and cost significantly less so be sure you actually NEED the sustainability you're after.