Use for excess energy without sending to grid?

[mountkay]

~300,000 thousand BTUs

This must be a typo. Pretty sure you ment to say 300 thousand or 300,000. Not 300,000 thousand. That would be 300 million. The equivalent of burning ~15 cords of wood in a day.

So assuming you ment 300k btu/day. Raising 1000cuft of sand 100F equaling 1.8M BTU would give you 6 days of heat.

Lets say you can reasonably do 25' x 25' x 6' sand. Thats 3750sqft. Ill round down to make it 3000sqft. So thats 18 days of heat if you raise the temp 100F. Lets say you raise it 200F, then you have 36 days of heat. A months worth.

It's safe to say that being able to store and then re-use 25% of what you tried to put into storage would be a high assumption

Getting bogged down in the finer points how much R-value isn't going to change it

I think youre selling R-value short.
R-value is usually assuming that at some point you are hitting the atmosphere, where your heat will very quickly dissipate. When you are buried in the ground, you will have the R-value for whatever foam you use for its thickness, but then on the other side of that foam (for 5 sides of chamber) you will have a massive amount of soil and the the r-value it provides.

 

[justinm001]

I think youre selling R-value short.
R-value is usually assuming that at some point you are hitting the atmosphere, where your heat will very quickly dissipate. When you are buried in the ground, you will have the R-value for whatever foam you use for its thickness, but then on the other side of that foam (for 5 sides of chamber) you will have a massive amount of soil and the the r-value it provides.

This is the part that isn't making sense. It sounds like you're saying that if you bury hot sand in the ground the heat won't quickly dissipate.

Dirt is very porous in which rain water pours drains through it. Even basements with thick concrete walls, insulation and drywall can't heat the ground around it.

My home has thick 4-6" foam insulation on the outside of the concrete then thick insulation on the inside and even has radiant concrete floors and yet it still needs the furnace to keep it warm.

Either you'll need enough sand to use as insulation to keep the cold dirt from cooling it or you somehow plan on keeping the dirt warm.

 

[mountkay]

It sounds like you're saying that if you bury hot sand in the ground the heat won't quickly dissipate.

I’m just saying it will dissipate slower than if it was above ground surrounded by air.

I don’t even know how you would do a calculation for R-value of soil in the earth because R-value is usually based on a thickness (per inch), so when you have a theoretical mile of dirt below your chamber, how would that be calculated?

Either you'll need enough sand to use as insulation to keep the cold dirt from cooling it or you somehow plan on keeping the dirt warm.

Im pretty sure the dirt is actually a better insulator than sand, so proper sizing would be important as at some point it would be beneficial to have the dirt insulating rather than sand.



It’s been a while since I watched any videos on this technology so I should probably go back and watch them before saying much more.

I do remember that this tech is better the bigger you make it, probably due to the fact that as you increase the surface area you are insulating, you get exponentially more volume of sand.

 

[justinm001]

I’m just saying it will dissipate slower than if it was above ground surrounded by air.

I don’t even know how you would do a calculation for R-value of soil in the earth because R-value is usually based on a thickness (per inch), so when you have a theoretical mile of dirt below your chamber, how would that be calculated?



Im pretty sure the dirt is actually a better insulator than sand, so proper sizing would be important as at some point it would be beneficial to have the dirt insulating rather than sand.



It’s been a while since I watched any videos on this technology so I should probably go back and watch them before saying much more.

I do remember that this tech is better the bigger you make it, probably due to the fact that as you increase the surface area you are insulating, you get exponentially more volume of sand.

The problem is once the heat hits the dirt it's going to dissipate. The dirt isn't an insulator as it's not controlled. Water will flow through it and cool along with dirt all around it cooling.

 

[mountkay]

Right off the bat, one of these companies is talking about heating to 300-500C. That’s 500-900F. So sounds like you can pump a lot of heat into a small space.

Here is their website.

Technology — Polar Night Energy

Technology

polarnightenergy.fi

At the moment we can offer a heat storage system with 2 MW heating power with a capacity of 300 MWh or 10 MW heating power with a capacity of 1000 MWh. Our heat storage system is scalable for many different purposes and we will expand the product range in the future

Sand Battery’s Efficiency Explained – Polar Night Energy’s ‘Sand Battery’ Has Efficiency Up To 95 Per Cent — Polar Night Energy

On what basis can we make the claim 'Efficiency up to 95%'? Here’s our Lead Scientist’s take on the efficiency of our energy storage system. Resistive heating of sand is essentially 100% efficient, but the efficiency is inevitably lowered by heat loss through the boundaries of the system. However,

polarnightenergy.fi

Resistive heating of sand is essentially 100% efficient, but the efficiency is inevitably lowered by heat loss through the boundaries of the system. However, there are several ways our solution tackles this problem.

1. Since sand is solid material, the heat is transferred inside the storage only by conduction. As the heat conductivity of the sand is rather low, the outer parts of the storage act effectively as insulators for the core and thus there always is considerably steep radial temperature profile inside the storage.

Simply put, unlike for water-based storages that have constant temperature everywhere, the outer layers of a sand-based heat storage have temperatures much below the average temperature of the system and the heat does not flow effectively from core to the outer layers and finally to the ambient space.

2. Obviously, even if the sand has the self-insulating property described below, we use good amount of conventional insulation at the boundaries of the system.

3. The heat transfer pipe system inside the sand allows us to prioritise the boundaries when discharging the storage and prioritise the core when charging the storage.

This means that even if some of the heat is about to be conducted to the outer layers, we can make use a good proportion of it instead of it getting lost. For the heat charged to the core of the system it takes very long time to reach the boundaries.

4. The scale of the storage affects a lot to the efficiency. This is so, because a smaller storage has more surface area compared to its volume than a bigger one, and the heat loss is essentially proportional to the surface area.

Simply put, the core of the storage can hold the heat for very long time without it getting lost, and the core is bigger for bigger storages.

5. The usage of the heat storage obviously affects on its efficiency. The shorter the storage period, the less heat is lost between charging and discharging. The desired storage period completely depends on the application and the needs of the customer, and it can vary from one day to several months.

 

[mountkay]

The world's first commercial sand-based energy storage system, or "sand battery," has officially been inaugurated in Vatajankoski, Kankaanpää on January 20th, 2023. Developed by Polar Night Energy, the sand-battery's test phase began in May 2022 and it was put into actual use about a month later, in June-July.

"The sand battery has been in operation for over half a year and has performed even better than we expected. It's the perfect time to officially inaugurate the battery as the heating season is at its busiest," said Markku Ylönen, Technical Director of Polar Night Energy.

Vatajankoski ’Sand Battery’ Inaugurated — Polar Night Energy

The ’sand battery’ developed by Polar Night Energy was officially inaugurated on January 20th, 2023. Finnish Minister of Economic Affairs Mika Lintilä was in attendance at the ceremony.

polarnightenergy.fi

 

[Hedges]

I did a quick and dirty pass/fail analysis that demonstrated "fail". Getting bogged down in the finer points how much R-value isn't going to change it.

So did I, thought it demonstrated "pass"

OK, if I fill my swimming pool (20 x 50 x 5' average) with sand and heat it +100C, I get a month of winter storage.
Heat it +500C and I'm all set for the winter.

Next concern would be insulation which can take the heat (and pressure). Deep end would hold 8' of sand.

 

[justinm001]

Vatajankoski ’Sand Battery’ Inaugurated — Polar Night Energy

The ’sand battery’ developed by Polar Night Energy was officially inaugurated on January 20th, 2023. Finnish Minister of Economic Affairs Mika Lintilä was in attendance at the ceremony.

polarnightenergy.fi

Notice how they don't state any details. What I gathered is they have a massive sand storage and it's so large the heat isn't reaching the outsides. This would work fine but requires a LOT of sand

 

[justinm001]

So did I, thought it demonstrated "pass"



Next concern would be insulation which can take the heat (and pressure). Deep end would hold 8' of sand.

Insulation is the only issue. Their solution is to have such a massive sand pit that the heat won't reach the outer layers

 

[hwy17]

My house sits on an expansive sand deposit... I suspect that them keeping their sand dry though is key to performance.

 

[OzSolar]

Next concern would be insulation which can take the heat (and pressure). Deep end would hold 8' of sand.

Temp is a big concern but pressure is not so much.

The typical XPS Owens Corning foam starts breaking down above 170F (ask me how I know, lol) but it is used underneath concrete slabs without issue. My own basement is a 8" concrete slab with 2 stories of house on top of that. 20 years and no cracks.

Not sure what insulation to use that won't get water logged and lose it's R-value.

My biggest concern is how to get the heat in and out. Nothing off the shelf is designed to deal with temps over ~200f. When I start thinking about how one might build it I go right back to "fail". That's just me though. I'm talking about real world today, others may be talking about theoretical using yet to be invented gear.

Recalling my radiant in floor design and install days: When the storage vessel gets below ~180F you are going to struggle to be able usable heat for air out. If you're doing hydronics you can get usable heat out of 100f or less water. That locks you into a really small delta T.

 

[Hedges]

Electric oven elements would put heat in. Run at reduced voltage such that they don't overheat.
Different resistance material would have positive TCR and could self-regulate. These elements, you might want a sensor and electrical feedback.

Metal tube with air blown through would extract heat.

If you engineered the thermal gradient through insulation, you could have foam outside, higher temperature layers inside. Get it wrong and the foam melts. Surplus space shuttle tiles?

Want gaps or porous layer outside foam to let moisture drain to a sump.

 

[OzSolar]

This must be a typo. Pretty sure you ment to say 300 thousand or 300,000. Not 300,000 thousand. That would be 300 million. The equivalent of burning ~15 cords of wood in a day.

So assuming you ment 300k btu/day. Raising 1000cuft of sand 100F equaling 1.8M BTU would give you 6 days of heat.

Yep, typo. That's the same math I was coming up with. Since nothing is 100% efficient that's an awful lot of work to get far less than 6 days of heat out of. There's no way a home gamer is going to build something capable of a delta t of 200f.

 

[justinm001]

Copper can handle about 400F and standard steel 800F with some well above that. Auto exhaust can get to 1600F iirc. I would run it as a closed loop full of some high temp oil that isn't pressurized. Heating with whatever heating element and then running hot lines through air ducts. This way you can control the flow based on temps so during the day it'll pump full speed but stop at night. Keeping that 95% efficiency.

 

[mountkay]

From the interview with this company:

Bigger is definitely better. They are designing systems for tens of thousands of people, although it was mentioned that a smaller system is possible, with an above ground cylinder.

They said insulation around the outside of the chamber is 0.5 - 1 meter thick.

They dont use heat pumps because its too hot! haha. Maybe with a small home system a heat pump would work.

I only got about halfway thru the video, ill watch the rest later on

 

[SolarRich]

The 12" insulated concrete slab in our house is used as a thermal battery. There are air ducts running thru the concrete that are part of the passive solar heating system of the house. This system is a blower to circulate the air thru the ducts/house with a resistive heater and 2 stage conventional AC unit.
I've been thinking about dumping excess PV power as heat or AC into the slab. When there is excess power going back to the grid then turn up the temp on the thermostat (if winter) or turn the thermostat down (for summer). The house thermostat is an arduino with an ethernet port and can be controlled via a program on the computer.
I have all the data from PV generation and power to/from the grid available on the computer. A simple program is what's needed to connect the 2.

Recently I got an openevse EV car charger. A program on the computer sends grid in/out wattage to the charger every 10 seconds. The charger will 0 out the power going to the grid if the car is plugged in and needs a charge.

Where I am in NJ the net metering is 1 to 1. So the grid is a big no cost battery for me. But I am wondering if some day they will make it not so attractive to use grid tie as I've seen in other parts of the US.

 

[sunsurfer]

Is there something I can use at 800-1kw that could make me money?

I cant believe no one has mentioned it yet. It's so simple, make candles bro. Melt some wax, take it to farmers on sat and $ell em. Retire early. Your welcome.

 

[spazatak]

Polar Night Energy might be able to store heat all winter with large super insulated systems, but residential, no way. Especially without insulation.

They claim it can store power "for months", but then it's said the sand is heated every day by solar and wind generators. On the polar night energy video, they state the volume of sand for a project for 35,000 people fit into a space 25 meters tall by 40 meters diameter. I did the math and it ends up less than one cubic meter per person?

Don't mean to hijack this thread because what I'm writing doesn't solve the storage issue, but why not a standalone system?. Wouldn't this system work great in cold parts of the country, or would it depend if you were offered net metering or not?

In this video here, someone in the comments wrote this..

House in Fargo ND. They used electricity to heat the house. footings have to be deep and most people have basements. In this case they lined the concrete with insulation and filled it with sand. They ran heating tape through the sand. The local power company had a special off-peak rate. The house was well-insulated and could go for several days in the middle of winter without power. I don't remember how they controlled the sand temperature but it wasn't that hot since the house was always 75 degrees F and there was no control between the sand and the concrete floor.

The above system could easily be powered with PV, no batteries or controller.

Or start out heating a insulated 2 cubic meter sand vessel and experiment with different heat exchangers/depths in it. I would try a 6” steel pipe for forced air close to the hottest section, and a small 1” copper for hydronics close to the top.

Expecting a sand battery to heat your house longer than overnight or maybe five days of cloudy weather without reheating it is expecting too much.. But that just on its own is an accomplishment.