diy solar

diy solar

Storing heat in sand?

Cover the tank in biomass. Make an Anaerobic Combustion wood chip pile or other biomass Heat Source

Simplest way is wire the hotwater to 120 volts for 1100 watt draw and or wire the 2 elements in series to get a 550 watt load. We do it all the time when on generator.
 
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This isnt true.

A slab with too much mass will react very slowly. Running really hot water is a way to get it to react faster but you will end up overshooting every time. If you get a huge swing in outdoor temperature, if the mass of the slab is too high, you will be too warm or cold for several days while it is cooling down or you are pouring heat into it waiting for it to actually warm up and freezing in the meantime.

Huge mass is very nice but you have to set the temperature of the mass for the warmest (outside) temperature you expect and then use a direct to air heater or water to air heat exchanger to manage the short term temperature swings. You have to watch the weather forcast a couple days (or more depending on mass) out.

If it looks like it is warming up, turn the slab heat off and run all your DHW through it if its an open system or through a heat exhanger to help start cooling it down. If its cooling down, start pouring heat in. It really isnt hard but each system has its own nuances and you have to live with them for a little while.
Can personally confirm what you are saying: we have floor heating that goes berserk 2-3 times per year when outdoor temperature changes drastically.
I actually considered building a weather forecast control to our slab heating: small linux computer to fetch the 3-day forecast and adjust the heating based on that.

As an added insult our water-to-air heat exchanger is in the same loop with slab heat and it is bit marginal to heat the incoming fresh air.
 
As an added insult our water-to-air heat exchanger is in the same loop with slab heat and it is bit marginal to heat the incoming fresh air.
just add another pex loop in the ground in your garden few thousand feet.
Use that as a heat dump. It's probably not enough to cool building, but should help with swings.
Don't even need a heat exchange - it's just another "room-loop"

Our Slab heating system rarely gets too cold - but sometimes too warm. No issues when you got 2 days warm two days cold - daily swings from freezing to 80 - degrees no problem. The insulation and mass is just buffering those.

Since our delay is about 3 days - when the weather oscillates from warm to cool days in a 3 day interval - the system is not happy. So when you get 3+ days of cold - followed by 3+ days of hot weather - on the 3rd day it feels kind warm inside the house. since the slab is still radiating heat when the walls are getting warm.
 
just add another pex loop in the ground in your garden few thousand feet.
Use that as a heat dump. It's probably not enough to cool building, but should help with swings.
Don't even need a heat exchange - it's just another "room-loop"

Our Slab heating system rarely gets too cold - but sometimes too warm. No issues when you got 2 days warm two days cold - daily swings from freezing to 80 - degrees no problem. The insulation and mass is just buffering those.

Since our delay is about 3 days - when the weather oscillates from warm to cool days in a 3 day interval - the system is not happy. So when you get 3+ days of cold - followed by 3+ days of hot weather - on the 3rd day it feels kind warm inside the house. since the slab is still radiating heat when the walls are getting warm.
Normally we don't have any problem with too hot weather. No need for cooling loops. :ROFLMAO:
And no point of dumping the energy to ground in middle of the winter even if indoor temp happens to get to +25Cel/+77F
(last summer was sort of exeption)
 
The entire point of a sand battery is to store more heat than liquid water can in a smaller amount of space. If you want to use water (or water/glycol) for the medium to transfer heat from one place to another, you may as well store the heat in water. Storing hot water will not get you through the winter, if you live in a cool climate.

It is my understanding that to get sand beyond 212°F (100°C), you’ll need to use electric heating elements. Another way to get heat into a sand battery would be to heat up oil like they do with parabolic solar troughs.
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3D2038CC-F0E5-432A-8791-E455284DA2F6.jpeg

Although hot air and hot water rise,
I hope to have almost none of either in my sand battery. This heat will migrate through the sand via conduction, not convection. So I should try to put my electric heating elements throughout the sand, not at the bottom. Hmm, I could put them at the top for easier accessibility and maintenance.

To get heat out of the sand battery, you would need to be able to survive in heat that exceeds 300°C, maybe as much as 600°C. Sand will not melt until 1700°C. Dammit! We’re back to oil as a medium in the pipes. Water will flash to steam at 100°C, and steam takes up 1000x the space as liquid water. Kaboom!

You could also blow air over the hot sand, but you may end up with mold issues and silica dust in the ductwork. Silica dust is microscopic glass shards that end up in your lungs — you can imagine why I’m not a fan of that plan.

I’m looking into creating a sand battery by building an insulated box under my driveway. If I can get it hotter than 100°C, the sides of the box will be made of 3 layers of Corrugated steel (Melting point 1200°C), with peaks and valleys offset to make a honeycomb structure; mineral wool (melting point over 1100°C) between the layers of corrugated steel that are screwed together.

If I cannot go higher than 100°C, I will use 2” thick Owens-Corning FOAMULAR rigid insulation panels (softens at 104°C and decomposes at 316°C).

I THINK either will maintain its structural integrity because the sand is dense enough to keep the surrounding dirt from crushing or displacing it. (Yes, I am planning to compact the sand in 1-foot lifts.). An alternative is to buy a prefabricated concrete septic tank (or something similar) but they only come in certain sizes and it would still need to be insulated.
 
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Guda (what a “cheesy” name #DadJoke)
The entire point of a sand battery is to store more heat than liquid water can in a smaller amount of space. If you want to use water (or water/glycol) for the medium to transfer heat from one place to another, you may as well store the heat in water.

Storing hot water will not get you through the winter, if you live in a cool climate.

It is my understanding that to get sand beyond 212°F (100°C), you’ll need to use electric heating elements. They would be placed at the bottom of the sand battery. Another way to get heat into a sand battery would be to heat up oil like they do on parabolic solar farms.

To get heat out of the sand battery, you would put the pipes at the top of the sand battery (since heat rises). Those pipes would need to be able to survive in heat that exceeds 300°C, maybe as much as 600°C.

You could also blow air over the hot sand, but you may end up with mold issues and silica dust in the ductwork. Silica dust is microscopic glass shards that end up in your lungs — you can imagine why I’m not a fan of that plan.

I’m looking into creating a sand battery by building a rigid foam insulation box under my driveway. I THINK this will maintain it’s structural integrity because the sand is dense enough to keep the dirt from crushing it. (Yes, I am planning to compact the sand in 1-foot lifts.). An alternative is to buy a prefabricated concrete septic tank (or something similar) but they only come in certain sizes and it would still need to be insulated.
Heat doesn’t rise…
 
Heat doesn’t rise…
D’oh! You’re right SuperVStech! Hot air rises, and I hope to have almost none in my sand battery. This heat will migrate through conduction, not convection. So I should try to put my electric heating elements throughout the sand, not at the bottom. Hmm, I could put them at the top for easier accessibility and maintenance.

Thank you CuriousCarbon, if that is your real name.
 
The thought was that the heat will compound. 200f water going through sand would go higher than 200f, maybe. Maybe it just makes the area thats 200f just larger. Not sure.


The area of 200° sand will get larger. Essentially, sand is a solid. The migration of heat will happen through conduction, not convection (or radiation). So you cannot get hotter than the heat source. No compounding).
 
there is actually a company in Finland building heated sand / dirt as community scale energy storage:

They are talking about months to years of stroage.
there is actually a company in Finland building heated sand / dirt as community scale energy storage:

They are talking about months to years of stroage.


there is actually a company in Finland building heated sand / dirt as community scale energy storage:

They are talking about months to years of stroage.

I’ve created a playlist for alternative forms of energy storage.
 
Just in case you are thinking of burying your containers under a couple feet of sand or dirt, be aware that they are not designed to support those kinds of loads, and would need to be heavily reinforced for that to be safe.
Shipping containers CANNOT be buried. I saw a YouTube video on this recently. They are of a post & beam type of construction. Yes, they are stacked 10-high on ships, but all the weight goes into the (vertical) posts at the 4 corners. The corrugated steel on the sides, top and bottom support no weight.

PLUS a shipping container will have a much shorter lifespan in the ground. Rust will form and progress faster.

Then there’s the lateral hydraulic pressure. When the ground gets wet, it slumps, and will exert a lateral force on the sides of the container. I said above, the sides are not structural.
 
I think that could be solved by using an exchange medium that has a higher boiling point than water. Some type of oil, maybe. A slowly moving oil/sand mixture could potentially hold a LOT of heat.
^^^That^^^

Sand has a low surface area in contact with the heat exchanger. Just a small amount of oil to fill in the gaps would make a huge difference.

Some mineral oil would probably be ideal.

I picture a well insulated tub, full of sand and / or oil, heated with a solar heat exchanger (or excess PV power). Water would flow through a separate loop heat exchanger in the tub and collect the residual heat.
 
This weather is fucking crazy. There, I said it

And it’s only going to get worse! 50 years ago, two oil embargoes were a wake-up call. The USA and most of the world hit the snooze button… repeatedly!

Now, when MOST Americans talk about climate change, they discuss adding air conditioning and making their homes more hurricane or tornado resistant.

Hey idiots! Wake up! Why don’t we attack the cause instead of building stronger castles?! Oh right. They’re idiots who don’t want to make simple changes in their lives.

There I said it.
 
No, we prefer to make changes in their lives.
 
The entire point of a sand battery is to store more heat than liquid water can in a smaller amount of space. If you want to use water (or water/glycol) for the medium to transfer heat from one place to another, you may as well store the heat in water. Storing hot water will not get you through the winter, if you live in a cool climate.

It is my understanding that to get sand beyond 212°F (100°C), you’ll need to use electric heating elements. Another way to get heat into a sand battery would be to heat up oil like they do with parabolic solar troughs.
.
View attachment 110654

Although hot air and hot water rise,
I hope to have almost none of either in my sand battery. This heat will migrate through the sand via conduction, not convection. So I should try to put my electric heating elements throughout the sand, not at the bottom. Hmm, I could put them at the top for easier accessibility and maintenance.

To get heat out of the sand battery, you would need to be able to survive in heat that exceeds 300°C, maybe as much as 600°C. Sand will not melt until 1700°C. Dammit! We’re back to oil as a medium in the pipes. Water will flash to steam at 100°C, and steam takes up 1000x the space as liquid water. Kaboom!

You could also blow air over the hot sand, but you may end up with mold issues and silica dust in the ductwork. Silica dust is microscopic glass shards that end up in your lungs — you can imagine why I’m not a fan of that plan.

I’m looking into creating a sand battery by building an insulated box under my driveway. If I can get it hotter than 100°C, the sides of the box will be made of 3 layers of Corrugated steel (Melting point 1200°C), with peaks and valleys offset to make a honeycomb structure; mineral wool (melting point over 1100°C) between the layers of corrugated steel that are screwed together.

If I cannot go higher than 100°C, I will use 2” thick Owens-Corning FOAMULAR rigid insulation panels (softens at 104°C and decomposes at 316°C).

I THINK either will maintain its structural integrity because the sand is dense enough to keep the surrounding dirt from crushing or displacing it. (Yes, I am planning to compact the sand in 1-foot lifts.). An alternative is to buy a prefabricated concrete septic tank (or something similar) but they only come in certain sizes and it would still need to be insulated.
Sam - Sand batteries are Awesome - but the Thermal Conductivity co-efficient of Sand is exceedingly low - so you wont get any conduction - you will need to insert Thick metal rods or plates to get the heat out. That is the real advantage of sand. It will stay hot (100s of Degrees) and wontly loose any appreciable heat for weeks (depending on thickness of the walls of the sand). Water will get cold very fast because it will loose it to the sides and to the air. You probably should also store the metal rods/plates INSIDE the battery until needed.
 
Sam - Sand batteries are Awesome - but the Thermal Conductivity co-efficient of Sand is exceedingly low - so you wont get any conduction - you will need to insert Thick metal rods or plates to get the heat out. That is the real advantage of sand. It will stay hot (100s of Degrees) and wontly loose any appreciable heat for weeks (depending on thickness of the walls of the sand). Water will get cold very fast because it will loose it to the sides and to the air. You probably should also store the metal rods/plates INSIDE the battery until needed.
Oh, and you should probably use resistive heating run by solar electricity - again you wont get any conduction via thermal solar
 
Weeks of storage - less conductivity is OK.
Any water intrusion would carry heat away.
If a (mostly) sealed box, could move air through the sand. e.g. run water or oil through a radiator and push a bit of air through it, into the sand. Low flow to minimize back pressure. Flow will fan out like spreading resistance, so geometry needs to be somewhat balanced, e.g. air in at one corner of box, out diagonally opposite corner.
Volume would breathe with temperature changes. Don't want to suck in outside moisture (has caused me a problem with gasoline tanks in some environments.) A bladder (bag) could allow expansion, and desiccant so dry and not growing mold.
 
Weeks of storage - less conductivity is OK.
Any water intrusion would carry heat away.
If a (mostly) sealed box, could move air through the sand. e.g. run water or oil through a radiator and push a bit of air through it, into the sand. Low flow to minimize back pressure. Flow will fan out like spreading resistance, so geometry needs to be somewhat balanced, e.g. air in at one corner of box, out diagonally opposite corner.
Volume would breathe with temperature changes. Don't want to suck in outside moisture (has caused me a problem with gasoline tanks in some environments.) A bladder (bag) could allow expansion, and desiccant so dry and not growing mold.
Yeah sorry - I was pointing out that low thermal conductivity is actually what you want (it is very good to have it). But it will mean that you do need a heat exchanger INSIDE the battery to get the heat out coz it wont just leak out passively
 
Sand has a low surface area in contact with the heat exchanger. Just a small amount of oil to fill in the gaps would make a huge difference.

Some mineral oil would probably be ideal.
filling the whole sand pit with oil? Hehe :) sounds like good plan. What could go wrong.

There are two primary ways of transferring heat:
Conductivity
Radiation

low thermal conductivity
the question is - is this an issue? If you got low conductivity you increase surface - people figured out how to cool a space station in vacuum, which is close to zero conductivity, still works.

How? Radiation - when you get your heat exchange hot enough it radiates heat and transfers it that way. Same the other way around - just heat the sand up to multiple hundred degrees and it will radiate into the pipe - no conductivity needed.
 
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