Storing heat in sand?

[Mart Hale]

I made a video of my progress.... I have been tied up with gardening I may have more time this winter to move forward.

This video is quality about sand battery storage ->

This is my progress I have made with my sand battery.

Testing different types of sand batteries.. Results of testing I have done.

My progress and videos I have gained info from: Overview of the sand battery: 1752 A DIY Sand Battery - The Theory, Practice And Use https://www.youtube.com/watch?v=Icai6OOIh2M Using the waste heat of

rumble.com

On my thread on Permies on this subject I ran into a guy who uses this to cook food for a school in Kenya.

 

[orangezero]

Watched your video, thank you for sharing. I like the idea of using your sand to get water out of wood or to make quick lime.

Cleaning out the garage today, and found two bags of sand. At the very least I should do an "experiment" where I heat the sand enough to dry it out...

I know this is the "sand thread" but a serious disadvantage of sand compared to water; sand doesn't magically get pumped into my house when I turn a faucet handle.

 

[Mart Hale]

Watched your video, thank you for sharing. I like the idea of using your sand to get water out of wood or to make quick lime.

Cleaning out the garage today, and found two bags of sand. At the very least I should do an "experiment" where I heat the sand enough to dry it out...

I know this is the "sand thread" but a serious disadvantage of sand compared to water; sand doesn't magically get pumped into my house when I turn a faucet handle.

Yeah, that is why I do both... After my batteries are charged from my solar panels, my system auto magically flips a relay to my hot water heater and it heats my hot water. I have had to only use propane for back up for a few days.... Storing heat in water is indeed the way to go.

 

[Michelle Konzack]

I'm quite sure it's physically impossible to achieve a heater greater than the source..without more work input, say, from a compressor or something. This is a fundamental limit if you're using hot water as the heat source. If it was a steel bucket of sand, you could of course just place it over a fire and it will get hotter than that.


Hmmm.. if you can seal an engine, there will be sealing materials out there that can withstand very high temperatures. But you are right that heat is a concern and does deserve some engineering attention. You would have to make your vessel out of uniform material, so that it all expands evenly.


Is there any need for a pressurised vessel? It could be vented, unless I'm missing the glaringly obvious? I had in mind something like a steel drum? You can get some that secure the top on with a band clamp, allowing you to remove the lid to add fittings to it easily and place items on the inside.

Regarding mold, you would have the option of treating the water of course - though many cooler towers do just dump the water periodically as far as I know. The addition of chlorine, or keeping a low pH, to prevent stuff growing are options is potentially damaging to process equipment - certainly the mild steel drum as above would not fare well in either of those situations.

Simply add Glycole to it (minimal 20%) to prevent mold and reduce rusting of the barrel

 

[Michelle Konzack]

Sounds like you are off by about factor of five.
Specific heat of Water is 1 btu/lbs/F but sand is only 1/5 of that. https://www.engineeringtoolbox.com/specific-heat-capacity-d_391.html

Water is hard to beat as heat storage medium. Easily available, easy to heat and extract the heat from and excellent heat capacity per weight and volume.

This was my first idea too,

But it would require under my Greenhouse 5 bunker cells 4,0x6,8m, insulated with 50mm EPS and then a bag of HDPE or EDPM, which can be even ordered from Chinaman for a resonable price. Heated up to 70degC, you can store per Meter hight roughly 1.250kWh of energy. The make it 2m high and you have already 2.500kWh. My Greenhouse is 21,5m long and I can have 5 cells...

1.250kWh at a temperatur difference of 40degC (70-30 because of the underfloor heating system)

12,5MWh of Energy.

On top of it put 10cm of EPS and 50cm of sand as insulator.

This should be enough to keep the Greenhouse over the winter nicely warm and additional you can heat your house.

Hahaha, I need roughly 50kWh a day to heat my house at -20degC and the Water Storrage would keep my house 250days warm MINUS losses for the Greenhouse.

And there is another option, by using washed Gravel together with the water.

Mixing Sand with Oil give a nice problem with the authorities.

 

[maddonny]

I built a sand battery out of a used 20 gallon hot water tank. I have eight 100 watt 12VDC panels set up for 24VDC output. I'm using a 600 watt 24 VDC heater. The only use for it will be a pre-heat for my studio/hobby room LG heat pump. So far my test run has shown promise. I live in Michigan and the winters get pretty tough around these parts. It takes quite some time to get to the 80 degree temp, but stays pretty even during the night with the batteries in the circuit. I know there is some argument between sand and water, but these were items that I had on hand and most of the panels were free anyway. I'm only into it for the temp relays and cost of sand and little things. What else to do when its to cold to be outside. Nice experimental project!

 

[Mart Hale]

I was thinking we could get more out of the system in terms of heat if we were to use a heat pump to pull heat from the environment and put it into storage.

Looks like someone already had my idea and made their own DIY system....

In my experimenting with a 1 gal vacuum sealed container filled with boiling water, I found it made a great substitute for a hot water bottle as the top of the container released heat all thru the night....

As I think about it, I imagine if this was mixed with cold water, one could have a hot shower with a mixing valve..... I have found some turn their hot water tanks up to a higher temp, then use a mixing valve to cool down the water....

 

[DEVLP]

Mart Hale If you have the time I'd like some answers for some questions. I'm new here but I see you're doing what I'm currently building (or trying to). I'll dig a 2 meter cube pit lined w/ 3" styrofoam insulation and pond liner. Then fill w/ sand, interspersed w/ electric stove heat elements, 2 PEX coils and at least 1 temperature limiter. Hook up the PV panels (@ 200 watts new) and run to my current radiant floor and domestic hot water system. My questions: what volume of sand are you using? How many elements? Do you need any electrical components between the PV and elements? How long do your elements last? Any expert advice to give me? Thank you, Mart.​

 

[Hedges]

Approaching it from a theoretical perspective ...

Once you've heated that sand, what temperature will the styrofoam be exposed to? (the point of sand is very high temperature storage.)
Now engineer a solution to that ...

 

[DEVLP]

Approaching it from a theoretical perspective ...

Once you've heated that sand, what temperature will the styrofoam be exposed to? (the point of sand is very high temperature storage.)
Now engineer a solution to that ...

140-160 degrees. I paln for the styrofoam to be outside of the EDPM membrene which houses the sand. I assume that order is the best for this project.

 

[DEVLP]

Approaching it from a theoretical perspective ...

Once you've heated that sand, what temperature will the styrofoam be exposed to? (the point of sand is very high temperature storage.)
Now engineer a solution to that ...

Sand is the absolute cheapest, safest and easiest storage method I have seen. My already installed hydroponic floor system will only handle a maximum of 85 degrees (laminate's max), and my domestic hot water requirement max is 120 degrees. So in my thinking sand will handle both with one or two temperature limiters between PV panels and sand.

 

[upnorthandpersonal]

I was thinking we could get more out of the system in terms of heat if we were to use a heat pump to pull heat from the environment and put it into storage.

Like what I do, explained in #231

 

[efficientPV]

Like what I do, explained in #231

Did you ever get that Loadmaster working?

 

[upnorthandpersonal]

Did you ever get that Loadmaster working?

Yeah, that's working fine at the in-laws.

 

[Mart Hale]

Like what I do, explained in #231

Yeah, you are further ahead of me in my journey to wrap my brain around this.

I keep hearing the chant "thermal mass" from many, my experiments with the sand battery has taught me the value of

Insulation in the right place, of the right type.

Using different types of thermal mass from sand to metal.

Being able to have the right amount of thermal mass for the job, too much thermal mass is bad and too little also bad to get the job done.

I being in the south, am looking to attempt to stay cool more than I am trying to keep warm, I really like the idea of taking that heat from the air and heating water in my hot water tank for showers..... As of now I am doing that with a resistive heating coil of the hot water heater, but now seeing how efficient mini splits are to harvest heat or cold from the environment, I would like to save those watts I am using for the resisitive coil for my mini split to give me hot water.

As of now my system works, I only have to kick in the propane on cloudy days..... But I have so many solar panels that I have been looking at various ways to store that energy..... I believe the next path I want to venture down is to vacuum distill alcohol, creating alcohol would give me a means of storing the energy I am not using to run engines or heat.... Energy that could be stored for long term, longer than most batteries could hold.

Another idea is I could make alcohol using waste motor oil as the fuel to distill the alcohol, exchanging waste product for a pure one.

 

[upnorthandpersonal]

Another idea is I could make alcohol using waste motor oil as the fuel to distill the alcohol

Just turn it into diesel. I do that with waste vegetable oil. Much simpler in my opinion than creating and storing alcohol, and much less dangerous in large quantities. Alcohol fires are invisible.

 

[Hedges]

 

[DEVLP]

Open question: Has anyone developed a formula about how much voltage (or how many electric heating elements ) requred to bring sand up to a certain temperature? I'll be (still working on it) using about 1 1/2 cubic yards.

 

[Hedges]

Wrong question.
Or you need a bunch of component specs.

Various elements operate at various voltage.
Calculate watts dissipated.

Multiply by thermal resistance of insulation around sand (insulation could be just cinderblock enclosure, or just sand itself if simply a pile (but air could drift through.)

Sand will have a heat capacity, degrees C / kg, from which you can determine rate of temperature rise.

Make sure heating element and wire insulation can handle the temperature.