Homemade sand battery

Yesterday my sand battery with the dutch oven, insulated with fiberglass hit over 600 F! This morning the next day the lowest temp it was at was 234 F!

The temp is going up again, looks like I will have this well over 200 F for over 24 hours!

This is with 3 solar panels 220 watts each… I have about 1 5 gal bucket of sand in the mix.

I am now thinking about what if I used an aluminum puck in the dutch oven so that I could pull it out and cook on it…

These temps are with partially cloudy days, next week they are calling for clear sunny days…

Now I am thinking of moving forward with building a sand battery the size of a IBC container 250 gal…

I would then use the power I am not using after my batteries are charged to dump into that to store heat…

The present setup should give me a good idea of how to scale up…


With 5 gal bucket of sand, this is the temps my thermo coupler is getting. It looks like I will be staying over 200 + deg F for over 24 hours. 600 deg F is HOT!


Is this the 1st post on your Sand Battery? How are you heating the sand with the three solar panels? I have a string of three 250 watt panels connected directly to the bottom 240 volt element in a 60 gallon water heater tank. Last Summer, the water hovered around 130 F. In my solar oven, I used large iron pieces to retain the heat for cooking. ( aluminum has about twice the heat capacity of steel (per unit weight). But steel is about 3 times as dense, so heat capacity PER UNIT VOLUME is 1.5 times that of aluminum." I have been melting down scrap aluminum and casting them in muffin tins…


Not a sand battery, but similar… what l worked on for the last few days.

Its a greenhouse heater/hot bed. About a tone of usefull material, stone and concreete. Roughh calculations say it shuld output about 350w constant output of heat over a 12h period, if delta T is at 20 degrees. Shuld be enaugh to keep the greenhouse from freezing, and those values are wery conservative…


Hi Ray,

This is why I love this group, everyone here thinks outside the box :wink:

I posted one other post on sand battery in this group, but it was not my creation.

I have been trying various methods of heating the sand, I have used a solo stove, and I am not testing out used nichrome wire in the form of hot water elements, and stove heating elements…

Like you last year I figured out that after my battery is charged I could take the solar energy and dump that power ( direct DC ) from my solar panels into my hot water tank. I am now getting solar powered hot showers with propane instant hot water heater as backup. Using this system I set the propane on the lowest heating as possible because even on cloudy days I get enough heating to make luke warm hot water, which the propane heater does not have to work hard to heat, saving me propane. When I get a few sunny days in a row, I take very long hot showers with no guilt :slight_smile:

I also play with solar ovens, sounds like you are a brother from a different mother :wink: I have a sun oven, vacuum glass oven, and I have played around with making a Pex hot water heater which did not work out very well for me…

At present I went to the dollar store and bought a $20.00 single stove top burner. I took this and then I used 2 1/2 gal stainless steel pots to hold sand inside a trash can, inside a 55 gal barrel. I found the heat was too intense and melted thru the stainless pots. So, I have moved to a dutch oven design with fiber glass insulation around the dutch oven and a stainless pot below filled with sand.

With this setup, I have dried wood ( before I used insulation ) that I use for starter material for my rocket stove, temps were 200 - 320 degrees F before I added fiberglass insulation…

I have been searching for better types of insulation, I would like to get some rockwool, have been watching craigslist close…

What I have been doing is preparing for the next step, which is to make one far larger than this with additional insulation of perhaps styrocrete which uses cement with chopped up styrofoam for insulation. I have this all ready chopped, but in my research I am considering using chopped up cardboard instead, or dust crete which is cement mixed with sawdust.

I bought thermometers to guide me as to what would give me the best results. I have also been looking at used kilns as I am considering making a solar kiln, or a rocket stove kiln to move up to the next level of working with metals, as I would like to do casting with my 3d printer for moulds.

After watching a documentary of special made bricks they use graphite combined with metal to store heat, I am considering putting a bucket of old bolts I have into the dutch oven to see how it retains heat and at what rate it would give it out.

I also follow a solar project called ISEC where they take 100 watt panels and modify them to cook with.

I have been scaling up their ideas…

For me to be at this point of now having over 200 degrees for over 24 hours is earth shattering for me. :wink: I was looking into heat retention cooking but moved into much more.

I want to be able to store heat chemically. So far quicklime looks to be the most reasonable option, but there are other chemical reactions I am looking at. I want a reaction that I can simply store the heat chemically and then pull it out years later.

Love to chat about this stuff as I am seeing real world results from all of my efforts.


I think you would enjoy this video. Great minds around the world think alike :slight_smile:

Nice project, I have a friend who built a cob oven out of sand and firebricks…

Use of sand in stove… I found this interesting + the use of bricks.


This is what I have been looking at for heat storage… Storing heat for years…

I guess this is why people cut firewood :wink:


Mart, this video inspired me on my build. They complicated it a bit and theirs sure is preetyer thain mine but hope the functiality is good :smile:


Very interesting and inspiring videos, thank you.
It will be interesting to see what you guys are making :smiley:


Good to hear we all need to be inspired.

I run a group on Gab for building rocket mass heaters. So far the design I like the most is Peter Van batch box design. Load it and walk away.

In watching the video above I saw they did have creosote build up inside that stove so the fire is not getting hot enough to burn the secondary gasses, thus the need for clean out as they show in the video.

I am a big believer in using refractory boards in the burn tunnel and insulating with Morgan wool for a cleaner burn and for more energy pulled out of the wood. But what they have is a work of art, and thermal mass both in terms of sand, and blocks… I bet their stove cooks like a crock pot.

Love ideas and testing them, and looking back at others to see what works.


Insulating concrete can be made with vermiculite. Vermiculite is available in a number of versions - some very fine where others - such as attic insulation - are more coarse. I sold vermiculite as masonry insulation under the name Zonolite. I had a customer who made low density “concrete” with vermiculite that was used as a mold for prosthetic limbs. It was technically able to be shaped after curing. I suspect they used setting type drywall compound or plaster of paris as a bonding agent.

Perlite beads also works for a heat resistant filler. Styrofoam beads are messy to work with due to the static electric charge they create which makes them cling to everything. Fragmented polystyrene foam does work as an insulator.

Of course - the last thing you want for thermal mass for heat storage is light weight concrete. You want as much mass as possible. Some stamping press byproducts can be size and shape compatible for making high density concrete. I used to have a company near me who made replacement cutting edges for road graders and snow plows. The bolt holes in the blades were punched using a press. Those punchings would work as a high density aggregate in concrete or even for a system that passed hot air through the loose aggregate.


Yeah, perlite works as insulation used in rocket stoves and cob ovens. Light weight concrete like air crete is made for insulation, not for thermal mass, for that I intend to use sand, bricks, aluminum, steel.

So the light weight concrete would go around the outside shell, with the thermal mass on the inside.

As of now I am very impressed with the fiberglass insulation.


Today hit the highest temp ever, over 803 deg F…

It was a bright sunny day, I had replaced the wire with silicon covered wire…

Also I removed some of the sand and I put a 12 inch long rail road rail in the dutch oven with some sand inside.

I believe if I opened this up and put a pot on the top with water it would instantly boil…

I am most curious how long this will take to cool off…


I, too, have the Sun Oven, which seems to be a bit “low powered” compared to my large oven which uses 54 bathroom mirror squares (12" X 12") all focused down to a 4" spot (+ or -). Supposed to be 3000 peak watts and 950 C. I believe there is a photo somewhere on this site. I TIG welded spiders to force each mirror into a very slight parabolic shape, and mounted six rows of 9 mirrors on a boat trailer with a dolly at the front. The mirrors focus on the oven (if you pay attention) and the trailer dolly needs to be moved every ten minutes or so, wearing a pair of welding goggles.
We roasted chicken, made angel food cake, pizzas, and breads. It will light a 2 X 4 on fire if you stick it in the beam. (My wife’s favorite thing.) If unattended, it could melt plastic car bumpers, etc.
I have also experimented with AirCrete as an insulator, and used plenty of charcoal fines, and even some broken glass powder. I have been saving Styrofoam pieces, but have yet to make a grinder. (One guy uses an electric lawnmower to chop it up and blow it into bags.) I did experiment with chopped cardboard and printer paper sliced very small.
This year I installed a solar powered Mini-split that runs off of 8 used 250 watt solar panels. We just leave it on, and in the winter, it provides heat when the sun is shining, and the rest of the year it is in the cooling mode. (Only when the sun shines, of course.)
Most of my recent effort has been with the installation of over 80 used solar panels that feed into the grid, and power our house and barn, and keep two EVs charged. The panels are available for about $50 each from Santansolar.
I recycled all my solar water heating hoses and schemes for heating water directly with the sun and pumping it to a large tank in favor of heating the water with the 3 used solar panels, and sending the electricity to the heating element in the water tank. I have a valve to turn off the water so it does not thermally moved up and down the pipes. Also, heavy insulation all around the tank, so it will store the hot water for many days.


Search on “Helios” on this site for a photo of my concentrator.


Ray, how many bags of charcoal do you have now in your barn?


Have you been reading my diary?

LOL I have 30 Santan solar panels and with them I run 2 window mini splits with solar, using EV batteries. I am off the electrical grid with this system.

I have been saving mirrors and watching youtube videos on how to cut glass so I could make a solar mirror. Now that you mention it, I like your idea of leaving them whole and then focus them all onto a spot…

I was thinking with the boat trailer that one could create a “path” for the front of the trailer to move in an arc with winches moving the front of the boat.

I made the lawnmower setup to chop up the styrofoam… But I am now starting to think that using nichrome wire to cut the styrofoam into shape might be even better.

I was thinking another option we could try is to re-mold the styrofoam into blocks using steam… not sure if it would work… Also thought about pressing the styrofoam into a mold shape.

Heavy insulation does look to be the next stage in my expirments… I am thinking putting this trash can that is in this 55 gal barrel into an IBC and filling that IBC with the styrofoam that I made or chop up some cardboard…

I am now looking at buying a used Kiln… I would really love to melt aluminum and use my 3d printer to make moulds.

I am curious what insulation you use on your hot water tank…
Thanks for your sharing your adventures, I will look up your solar heating beast :wink:


Link to Hellos Mirrors…


Bags everywhere! Some of those white plastic horse feed bags have been decomposing, which makes a mess. Several months ago, I gave Martin Payne a load of charcoal, and I have been adding it to my 5 compost piles. (Mix it into the pile with a front-end loader.) I moved some of the charcoal to other outbuildings.
I was going “great guns” on melting aluminum cans with a Gingery charcoal furnace which has air blowing in at the bottom via a pipe L. A stainless steel can I was using as a crucible melted and dumped a liter of melted Aluminum down the air hole. I went online and bought a VEVOR propane furnace and some real crucibles, but I like doing it with the charcoal.
I’ve been cleaning some fence lines, and making even more charcoal, which I have been leaving in piles outdoors. Also make a small stainless steel kettle of it inside my woodstove, which is really high-grade stuff. I am saving that in old sealed coffee cans, with labels (Bamboo, Willow, Oak, Red Cedar, Mesquite, Huisache, etc.) Charcoal is so easy to make. I have had very little success convincing neighbors NOT to burn slash piles to a white ash. I have been attempting to organize and clean out the barn, but its something I’ll be doing until my clock runs out.


My water tanks use a Home Depot water tank insulator, covered with wall type fiberglass, which is all covered with a cover blanket from a double bed. There are two tanks, side by side, because the best one is 45 years old, and came with a heat pump water heating system I bought in the eighties. It takes many aluminum cans to make a muffin tin full of aluminum. The cans have paint and a plastic liner which burns off and leaves lots of slag. Old pistons, aluminum motor windings, old ladders, and computer heat sinks are easier. I label the ingots as “cans” or “Cast”.