Hot sand battery charges up
The first commercial, sand-based, high-temperature, heat storage system is now operating in Western Finland.
www.iom3.org
Storing heat in sand?
- Thread starter Guda
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www.iom3.org
What is a sand battery? — Polar Night Energy
A “sand battery” is a high temperature thermal energy storage that uses sand or sand-like materials as its storage medium. It stores energy in sand as heat.
polarnightenergy.fi
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I'm trying to adhere to the KISS principle with this. Otherwise it is not worth doing IMHO.
Ceefiveceefive
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I for one appreciate things explained out to simple terms!I'm trying to adhere to the KISS principle with this. Otherwise it is not worth doing IMHO.
Stupid people like me need things explained on a low level. ??
Gold Country Russ
New Member
A simple system would be a metal tank filled with 3"-5" round river rocks heated internally with electric resistance heat elements powered directly from PV panels. No active control would be necessary if the power input somewhat matches the heat extracted. The easiest way to extract heat would be to blow air into the bottom of the tank and extract hot air from the top. If the tank is well insulated temperatures inside the tank could easily reach 1,000F. That said, the tank must be well sealed because any water inside the tank would instantly flash into steam and could result in a massive explosion. A properly sealed tank with adequate emergency pressure relief even with very high internal temperature would be safe to operate as long as no liquid is allowed to enter. The high differential temperature and high specific gravity of rock well compensates for the low specific heat of the rock so very large quantities of heat can potentially be stored.
Have you personally used 3”+ river rock with an electric element? That just seems very unwise…
Sand is difficult enough to remain in contact with an element enough to prevent element failure… rock that large seems impossible to do so.
Also… river rock when heated kinda explodes… so…
Gold Country Russ
New Member
Typically tank heating elements are enclosed in stainless steel pipes with external flanged ends placed horizontal thru the tank. The element is isolated from the pipe, the element heats the pipe internally and the element is fully serviceable. In this case the rocks would be heated by direct contact, convection, and radiant heat. Air would distribute thru-out the tank. The mostly round shape of suitably sized river rock would provide adequate space for high volumes of air flow with minimal backpressure. Rocks can contain water but if initially heated slowly few will be damaged even at 1,000F. Once dry, no problem.
I actually have a lot of hands-on experience designing and installing electrically heated tanks from 5,000 to 35,000 gallons. Sure, rocks are a bit different than the corn syrup, fructose, honey, coconut oil, beef fat, and other edible oils I have worked with, but the concept is the same, just at higher temperatures. Kanthal, (formerly Sandvik) makes suitable high temp heating elements for use making glass and metals, so no problem to operate an element at 1,200F.
Just throwing this out there, so don't roast me please..
How about heating the sand directly with the sun? One tricky part on my design would be back filling the section above ground. Maybe some portland cement mixed with your black sand to shape it at the collector? Maybe a reflector of some sort gathering and directing more energy?
If it were me, I would follow polarnightenergy's lead and bury 6 inch stove pipe in the sand and recirculate air.
Again, just throwing this out there..
Attachments
OffGridForGood
Catch, make or grow everything you can.
Heating rock sand soil water...
pulling heat out during winter.
Sounds an aweful lot like geothermal to me. Like an engineered constructed geothermal site.
Some places have good local conditions for this, some do not. (like where I live).
We had three truck loads of 'bark' delivered years ago, to use as mulch in planting beds. A neighbour asked if I would put a bucket of the bark in his pick up for them to use, even though it was March (-20C) the bark pile was not frozen, and when I dug into the pile with the loader, it was steaming and quite warm to the touch. Some forestry processing plants around have had fires start spontanously from bark piles that are allowed to build up too thick.
Before we moved here 22 years ago, we had a place on a large ravine, the bottom of the ravine was 6 feet of peat bog 'hot swamp' - it would bearly build up any snow and never froze, since the organics were generating sufficient heat to subliminate the snow to the air. If we had stayed at that property I was going to trench in ground loops in that bog to run heat pump systems for the shop and house, but we moved instead. No such bog on our current property, too bad really since I have often thought that would have been a fun project to try out.
pulling heat out during winter.
Sounds an aweful lot like geothermal to me. Like an engineered constructed geothermal site.
Some places have good local conditions for this, some do not. (like where I live).
We had three truck loads of 'bark' delivered years ago, to use as mulch in planting beds. A neighbour asked if I would put a bucket of the bark in his pick up for them to use, even though it was March (-20C) the bark pile was not frozen, and when I dug into the pile with the loader, it was steaming and quite warm to the touch. Some forestry processing plants around have had fires start spontanously from bark piles that are allowed to build up too thick.
Before we moved here 22 years ago, we had a place on a large ravine, the bottom of the ravine was 6 feet of peat bog 'hot swamp' - it would bearly build up any snow and never froze, since the organics were generating sufficient heat to subliminate the snow to the air. If we had stayed at that property I was going to trench in ground loops in that bog to run heat pump systems for the shop and house, but we moved instead. No such bog on our current property, too bad really since I have often thought that would have been a fun project to try out.
Mart Hale
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I have been testing this by using a hot water heater combined with pex pipe to + pump to heat the sand. It is much better to use a restive coil combined with a solar panels..... I switched over to using the solar panels direct to my hot water heater coil, now I have free hot water via the sun and solar panels. That said I am also looking to improve my sand thermal mass project...
Your setup uses PV and water, and saying your testing directly heating the sand with the sun like in my drawing is a stretch. If I had a backhoe, I have plenty of clear unobstructed sun and I wouldn't need to dig as much as for a geothermal loop. My guess, about 1/4 of the excavating..
From the air heating collectors Ive seen on youtube reaching 300 °F, the black sand should easily reach 300 °F directly behind the glazing, but how far down this heat would travel is a guess. Many passive solar homes with large southerly facing glazing have insulated curtains to retain heat when the sun isn't shinning, or you need to open and close windows etc. You could cover my sand heater glazing's at night too, or have it automated. This would be a attempt to retain heat until the sun was out again.. Not months.
Gold Country Russ
New Member
The advantage of using sand or rock is that the material is cheap, readily available, will withstand very high temperatures, and there are no problems with fire or pressure. Considering the low specific heat of these materials, very high temperature differentials are required to store enough heat to make it worthwhile. I'm thinking internal storage temperatures of 500-1,000F will be required for worthwhile efficiency.
Mart Hale
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I agree I am not heating the sand as you suggest. The problem with your suggestion is that dry sand is an insulator It may heat the first few inches like on a beach but unless you had good insulation the heat would be loss. Both of our methods use the sun... I do agree yoru method is different. Perhaps to test your method one could fill a Sun Oven solar cooker with sand and see what the results would be.
Gold Country Russ
New Member
Exactly why I think river rocks (round) with air circulation as the heat transfer and as heat extraction medium makes the most sense.
Warpspeed
Solar Wizard
The problem with rock bed heat storage is that over time dust, bacteria, fungus and other crap builds up on your rocks, and the circulated air can then become a real health hazard.
This problem also exists with ducted heating and airconditioning, its commonly called "sick building syndrome".
Its usually more economic to demolish and rebuild an older building than to completely strip and replace the entire heating and ventilation ducting system.
I only know personally of one Government funded experimental solar/rock bed heat storage project in a domestic home. A large pit was dug and filled with loose rock below the concrete slab on which the home was built. Hot air from solar collectors was used to heat the rock storage during the day, and at night circulated air air was warmed by the stored heat.
It did not work very well in spring or autumn, and not at all during winter. After about five years (I think it was) people started to come down with various illnesses that were finally traced to bacteria in the air.
This problem also exists with ducted heating and airconditioning, its commonly called "sick building syndrome".
Its usually more economic to demolish and rebuild an older building than to completely strip and replace the entire heating and ventilation ducting system.
I only know personally of one Government funded experimental solar/rock bed heat storage project in a domestic home. A large pit was dug and filled with loose rock below the concrete slab on which the home was built. Hot air from solar collectors was used to heat the rock storage during the day, and at night circulated air air was warmed by the stored heat.
It did not work very well in spring or autumn, and not at all during winter. After about five years (I think it was) people started to come down with various illnesses that were finally traced to bacteria in the air.
Sand on a beach or uninsulated will lose its heat to the earth fast. I read someone mention "its cool just a few inch's below", well yeah.. Most of the US has soil temperatures about 50 so heat will travel to cold. I don't think there is a larger heat sink, so you cant compare it to sand in a highly insulated vessel. .
Wow. To bad this situation wasn't well documented to prevent it from happening again. Do you have any more details?
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Warpspeed
Solar Wizard
Back in the mid 1980's I worked for a State Government department that funded and became involved in many different kinds of alternative energy projects. My job as Technical Officer was doing maintenance and data collection, as well as assisting at the original planning stage.
It was one of the most interesting jobs I ever had, and I learned a lot about grand plans that turned out to be less than wonderful. Or put another way, how to spend large amounts of Government money on projects that do not actually work.
Politicians love this stuff. They like the publicity and being seen on TV and in the newspapers as being green, and making the world a better place.
Making long speeches, and cutting ribbons, is great public relations for them.
Anyhow, this particular rock bed heat storage project was old, even back in the mid 1980's, long before my time. So I heard a bit about it, and once visited the site. By then it had all been shut down. The home was still there and occupied, but the rock bed was sealed off, and the solar collectors removed from the roof.
I suppose in retrospect, some mechanism could be built into it to flush and disinfect the rock bed heat storage, maybe annually. But the truth is, any type of practical solar heating through mid winter is just not possible. When its frosty cold and the sky is solid grey for several days in a row, it obviously cannot keep your whole house toasty warm. At least not if running off 100% solar. The whole concept is completely impractical.
If it had worked better (or at all) no doubt some system to overcome the health issues could have been tried in another project.
But the sad truth is, it was a very expensive failure, swept under the carpet and forgotten about.
Warpspeed
Solar Wizard
Did an internet search, and found reference to a research paper, which is very likely about this particular project.
The date and place seem about right, Melbourne around 1964.
https://publications.csiro.au/rpr/pub?pid=procite:9312ff70-7fa7-4f73-aee1-2279d37117a1
https://en.wikipedia.org/wiki/CSIRO
If you are still interested, there are 1,800 pages of a report available which probably contain quite a lot of info, although I doubt it will be free.
The date and place seem about right, Melbourne around 1964.
https://publications.csiro.au/rpr/pub?pid=procite:9312ff70-7fa7-4f73-aee1-2279d37117a1
https://en.wikipedia.org/wiki/CSIRO
If you are still interested, there are 1,800 pages of a report available which probably contain quite a lot of info, although I doubt it will be free.
Gold Country Russ
New Member
That is certainly an issue at low temperatures. However, in a well insulated tank at high temperatures of say 500F or more no mold or bacteria could survive and if being used for domestic heating any residual solid would easily be filtered out of the tempered final air thru conventional furnace filters prior to discharging into the rooms. Other options would be to just recirculate air thru the tank in a closed loop that has an air x liquid heat exchanger. Or maybe directly to a high temperature Sterling motor to produce useful energy.
