How a Sand Battery Could Revolutionize Home Energy Storage

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My main concern would be giant sandworms, we have seen what they have done to Arrakis.

My grandfather had a sand radiator in his logging cabin for over 110 years ago. It was a metal box filled with sand that the smoke pipe of the stove zigzagged through. It kept the cabin warm 24 hours even in -40 Celsius.
Blessings and prayers from arctic part of Sweden 🇸🇪

I've told this story before. A friend of mine kind of built one of these himself. He built a south-facing solarium on the back of his house, but underneath the concrete pad he installed a three foot deep pit and filled it with pea gravel. He used simple PVC pipe and some small fans to blow air from the warm solarium into the gravel pit during the day. The cool air coming back would help regulate the temps in the summer. In the winter he could divert the warm air into his house to help lighten the load on his furnace. Colder return air would go back into the pit to be warmed up before going to the furnace. He could let it charge all day, even in the winter, and use the extra warm air at night when the heating demand was higher.
While these TES systems are certainly very nice, if you have the money, don't be afraid to see what you can DIY for a LOT less. All my friend had to buy for his was the gravel, some cement, some foamboard insulation, pipe and a couple of blower fans. For his skill level, it was easy work. It certainly wasn't as efficient as a custom built system, but it didn't need to be for the cost of entry and daily operation. How much power can a blower and a few relays use? If you are the handy kind of person who could us swimming pool hoses, wood and glass to make a solar thermal collector, well, here's some place to put all that energy.

We had TES in my home lounge when I was a kid in the 1960s in England. It was called a 'night storage heater', was about 1.8m x 1m x 1m and inside was a massive concrete block (or stacked smaller blocks). It was heated by off-peak (cheaper) electricity at night and emitted that heat energy during the day when electricity was more expensive. It had resistance wire to heat it at night and louvres, a fan and air channels that could be opened and turned on during the day to release the heat.

This is the storage option that interests me the most, largely because of its simplicity and resource demand to build. Very glad to hear there are smaller units being developed. It seems to me to be something that a community to could install. For me, living in a cold country, I can see how I can limit electricity demand but I struggle to limit heating demand.

Living in Maine I have a bias toward using wood for heating as it is cheap,and renewable here. I built a wood fired, sand battery to heat a friend’s home. It was simple to build and very efficient. We built it from plans he had acquired from the University of Maine back in the seventies. Some of the materials used should probably be updated to newer, better materials but I will describe it as we built it. It started with a concrete slab about 10x10x6” thick. We built a concrete block building 8x8x8 with a wood stove running down the middle of it. The stove was about 7’ long and 24”high and wide. The building was insulated on the inside of the brick with 4” of styrofoam and 6” of vermiculite under the wood stove to protect the concrete. We then filled the building with sand to a point about a foot over the firebox. We then put in what seemed to be miles of 1/2” pvc pipe arranged in manifolds feeding cold water in the bottom and hot water out of the top. Each run of pipe had a blow over valve in case it got too hot. We insulated the top with a foot of styrofoam and plywood screwed down on top. Around all of this we built a wood shed with a six cord capacity and room in front of the firebox to tend the fire. We used antifreeze in the water to insure that it wouldn’t freeze if it was left un attended in the winter. All of this was about 20’ behind his house. We dug a trench and insulated the pipes heavily about 4’ underground These pipes were brought into the basement and attached directly to an existing water boiler which could be valved off so you could use either heat source but with the same circulation equipment. My friend lights a small fire once or twice a day and provides all the heat he needs for his home. If I was to build it today I would use pex pipe and the styrofoam concrete forms rather than blocks.

Single family homes often include a garage. where I live, homes have basements and footings are dug at least 4 feet deep. After pouring foundation walls, garage areas are typically back-filled to create a solid base for parking cars. This would be an opportunity to burs a thermal sand reservoir without additional cost of digging.

My TES is an insulated 275 gallon IBC that cost me $50. My electricity all comes from solar panels and a grid-tied inverter. My hot water is from a Black & Decker flash water heater that cost me less than $200 new. Incoming cold water passes through a copper heat exchanger in the IBC, and that feeds the flash heater. These heaters have a temperature setting, so if your incoming water is warmer, they use less electricity. This is a way to use even VERY low-quality heat from solar thermal panels to lower your electricity use. For example, if my ground water pipes supply 64 F water, the flash heater has to warm it up 40 degrees to reach the 104 F setting. If the IBC warms it to 84 F, that cuts my water heating electricity use in half.

There was an episode of "This Old House" where they spoke with someone with a not so old house who built everything himself and he works in commercial HVAC. He used two cisterns and used a heat pump to transfer heat from one cistern to the other. This resulted in a cistern so cold that it was frozen and another with very hot water. He could run the heat pump whenever it made sense to run it based on energy cost, or energy availability (solar or wind). Then, whenever heating or cooling of any kind is needed, it could tap into the appropriate cistern for that capability. It think that is really awesome because whenever we're running a heat pump, it would be good to capture both extremes... it is basically doubling the efficiency. I'd like to capture the heat from my refrigerator to pre-warm the water into my water heater (though that probably would have a negligible impact since it wouldn't run long enough).

The main problem I see is the competition from hear pumps. Why store electricity as heat at 95% when I can store the electricity in a battery at 80% efficiency but then use a heat pump with a COP of 3.5 - 4 to provide home heating and hot water. Plus electric batteries can be used for AC in summer or during blackouts.

Love how you show stock footage of a cat in it's litter box and then jump to a food sponsor. Really gets the appetite goin

In Organic Gardening magazine in the 1970s they advertised plans for a Hunsa house. Block constructed with passages that guided hot air from a small fire in the center, and vented it through 20 tons of sand. A small fire burning for two hours a day could heart a house in Scandinavia all night in the winter .

Here in rural France we are used to having giant holes dug in our gardens as there is no mains drainage on these 200 year old stone houses. A BatSand battery would take up about the same space as a 3,000 litre 'fosse septique'. All our neighbours have huge gardens, ours is a hectare..so space isn't a problem. What is a problem is putting solar panels on the roof as there are no loft voids to keep inverters cool. We have our solar panels on a barn roof about 40 metres from the house. If you didn't or couldn't use solar a home sand battery could be used for time shifting the energy, France has a lot of nuclear power with nowhere to go during the night. Keeping the sand hot with cheap overnight power and distributing it to the property during the day would help balance the grid.

Yeah it's like a storage heater. We had them here in the UK in the 80's, 90's and 2000's but the heat was stored in bricks in the heater itself and insulated until the heat is released. They are designed to heat up when the energy use is low and so cheaper and release the energy in the evening in Winter time. The heat released from the isn't very hot, just warm.

Farmers use these methods for years in their glass houses. When the glass house is too hot at noon, the air is blown through a thick layer of gravel in the bottom of the house for cooling it down. At colder moments the heat is recuperated from the gravel to heat up the glass house.

07:10 clearly states in dutch 'daily loss of 30% - painpoint on top*' - ' Dagelijkse verlies van 30%- pijnpunt *on top''

Your house is also a thermal energy storage device. In the summer, cool it down during the day (with solar) more than you normally would and you can enjoy a good amount of cooling at night. Similar with heating in winter

You want high specific heat, not low, for storage (eg: more watt-hours to heat up a Kg of water or sand or ceramic - and of course get it back when needed).
There are heat storage devices such as ceramic based base board heaters. Thus, during the night when the utility rate is low, you heat up the ceramic in the baseboard heater - it traps that heat. Then, in the daytime when the thermostat demands it, louvers open to allow air to flow through and release the heat.
This has been sold for several decades in Canada.
The real issue is "heat quality" where the best way to store heat is as at hot a temperature as possible (needs really good insulation - because of the heat loss equation where heat is lost as 4th power of the temperature).

Phase change materials (PCMs) are substances that absorb and release heat when they change state. They can be used to store thermal energy for a variety of applications.
There are several materials that are considered as PCMs, their characteristics being increasingly investigated in order to incorporate them into thermal energy storage applications. Some of them include:
Inorganic systems (salt, salt hydrates and metal alloys)
Organic compounds (paraffins, fatty acids)
Polymeric materials (polyethylene glycol)
These present different temperature storage ranges and enthalpy energy storage characteristics. For instance, paraffins and salt hydrates are typically enough to guarantee thermal energy storage as incorporated in building materials; on the other hand, salts are used for storage at higher temperatures, such as the one needed in power plants.

For 60 years storage heaters using heavy blocks were quite common in areas without a gas supply in the UK. This was due to a lower tariff at night brought in with the introduction of nuclear power which can’t easily reduce it’s power output. It used to be less than 50% of the day rate, although now a bit more. The Nationalised electricity supplier would fit a special meter which changed over the readings, and a lot of installations had the switching for the heaters built in. Their use has decreased over the years as old heaters have reached the end of their life.

I think that thermal energy capture and storage generally deserves more thought and investment than it currently receives, and the relative ease and efficiency of storage is one of the main benefits.
A few years ago I designed and installed a system for capturing the waste heat from multiple small refrigeration sets in a medium sized cheese factory. Water cooled condensers were added to the refrigeration sets, and water was circulated through these via accurate flow control valves. Temperature probes on the refrigeration pipes leaving the condensers fed data to a PLC, which controlled the water flow through the valves. This was so accurate that the refrigeration outlet temperature was stable to within half a degree, and we could capture effectively 100% of the available thermal energy.
The warmed water was stored in an insulated stainless steel silo, then fed into the main boiler instead of cold water. The temperature of the water in the tank continued to rise overnight, so in the morning the main boiler got up to temperature much quicker and the factory was operational sooner. The output temperature of the boiler was also more stable, making it easier to keep processes in the factory stable.
There was a 25% reduction in gas usage in the main boiler, 10% reduction in electricity use in the refrigeration sets and a considerable increase in reliability in the refrigeration sets, with reduced failure rate and maintenance. and over-pressure cutouts on extremely hot days were no longer an issue.
Based on measurable parameters (reduction in electricity and gas bills) the payback was 14 months, with many significant "other" benefits.
I simply cannot understand why this type of system is not built into all factories and commercial premises which have refrigeration and a need for hot water or space heating.
I am definitely keen to see thermal energy storage brought into the domestic scene as well.

I have a few thermal batteries in my house. My water heater is an electric one that I heat with my woodstove in the winter and the I heat it with my excess solar power in the summer. We have lots of hot water year round here in Canada. Also my insulated cement floor is a thermal mass that heats up from my passive solar, southern windows in the summer but not in the winter (because of how I sized my roof overhang) and also in the winter the glycol that heated my water then goes into my infloor heating pipes and also warms the floor. It works very well and was inexpensive to install and maintain.
In the cellar I did not insulate under the floor so that it can stay naturally cool all summer and winter. My house is built into a south facing hillside and is 8 feet deep at the back but above ground at the front

Back in 1980 my neighbor put electric heat elements in a sand bed under a slab on grade home . It was heated during/ on off peak rates. Now with solar pv panels are so cheep it could be powered. In my build at the time I put 320 soft of hot water collectors into a 800 gallon ss tank I welded up in my basement that supplies radiant slabs & backed up with a wood fired boiler in the garage.

This was very enlightening Matt. Thank you for this very informative video.

In the late 1970s - early 80s, our local electric co-op in northern Minnesota promoted off-peak water heaters and home heating to try and smooth out power demand. We had a forced air, oil furnace. With the rise of OPEC, oil had become very expensive, so my dad converted. The hot water heater was like a typical electric heater, but 2x larger, made of plastic and super-insulated. The furnace was essentially a large box filled with bricks and a blower unit (took up a little less space in the basement space as had the oil tank, oil furnace and chimney stack). Both were charged up with heat during off-peak electrical usage hours. That was overnight generally, but during exceptional cold the power company would provide a bump in the afternoon. That didn’t happen very frequently. We paid a much lower rate for the off-peak power. To make it work required upsizing our transformer and line drop wire gauge, and installing a second, dedicated, off-peak meter, power feed, and electrical panel. Winters are cold in northern Minnesota, but it always kept us warm. The hot water heater worked ok for a family of four, but you couldn’t take long showers. Both the water heater and the furnace are still working fine almost 50 years later, with one replacement of the heating elements in the furnace. The only problem is the furnace was from Europe, and the manufacturer no longer exists, so replacement parts and service are hard to get/non-existent. With how well that old system has worked in a very cold environment, I’d have no qualms adopting one of these new versions of stored heat home heating.

In AZ, my whole backyard is sand. Literally, in the summer, I turn the hot water heater OFF because the sun does a good job keeping the water hot in the summer. I actually use my hot water heater in the summer as my cold water. Plus, it helps keep my electrical costs down by not heating the water in the summer.

I've been heating my greenhouses using sand batteries for about 20 years, and they work great.

Owned a home in the UK for a few years in the 1970s that used sandstone as a heat sink in a forced air system-very rare at the time. Electricity heated the system at night on the “white meter” when rates were low. Occasionally, we’d run out of heat during the day, but never before the pubs reopened. 😮 Electric blankets helped too. Brits recommended hot water bottles or foot warmers. Didn’t have a fire for the latter. Great times!

Been using sand batteries to heat my greenhouses for nearly 20 years, works a treat

I live in a very sunny area, and we got a solar water heater installed in our roof. It set me back like $500 but I spent $50 on gas last year, for the entire year

I’m so glad I saw this video, definitely taking us under consideration for new home construction

You do a great job of taking around topics👍

And... it gets everywhere.

Thank you, Matt. Your presentations are always inspiring and informative.

Thank u for always sharing your amazing knowledge to the world, I love your videos ❤ the alternative heating is really cool idea!

never heard about it, thanks for spreading the good word!

I'm in Michigan, and the proud owner of a pcm heat battery. I'm the first to install a Sunamp thermino i300.
Did a full replacement of my hot water tank and 1960s boiler with a thermino and condensing modulating combi boiler. So far I'm seeing massive savings in natural gas usage.
Loving it!

I don't like sand. It's coarse and rough and irritating and it gets everywhere. - Anakin

at 3:25 I love that you put Anakin there. A character known for his hate for his home planet being full of sand :D

@UndecideMF , Great report Matt , this is a great application to radiant heating floors distribution, for housing or even heated garage, parking lots (cut down on deicing/snow management).

I bought a 180 year old house and rehabbed it. I installed in-floor radiant heat. I used sand as the thermal mass. It was lighter and slower to release energy as concrete. In addition I didn't have to worry about floor deflection too much, though I beefed up the floor support a lot. While it takes a long time to heat up the sand at the beginning of winter its ability to hold and slowly release the heat means even in worst case where we loose power our house only drops about 5-8 degrees F in a 24 hour period, even taking into account we usually only loose power during winter storms.
So we don't modulate the heat up or down during winter and can keep the sand warm through a slow "trickle charge". Because I treat my sand like a "battery" I can use a small tankless hot water heater to keep it warm instead of a boiler.

We have a large brick chimney inside our home that is heated with wood ( from our property ) . Even after the fire goes out, it seems the large mass of warm brick keeps at least the living room warm for at least a day. ( but takes a lot to heat it up when we first light the fire ) Somewhat the same as what you are talking about here Matt.

This idea reminds me of an old idea for storing heat from solar collectors some time ago. The basic idea was to move heat from the collector to a rock storage bin, generally placed under the floor of the structure. These TES's strike me as an update to that same idea with a more mature, well thought out compartmentalization between the thermal storage media and the heat source/sink.

Very educational. Thank you for sharing 🙂

Batsand uses kW/h instead of kWh in most of their marketing, really makes me doubt how credible their claims are.

This makes way more sense if paired with geothermal where heat acquired = heat stored instead of solar or wind where electricity to heat to electricity.
Wing Chun works because you use the momentum of energy and redirect it, constantly trying to change an energy's form is the brute force method and results in avoidable loss and wear.

First US-households have other energy saving measures to tackle.
Most houses in the US have very bad thermal insulation !
One glass- panel windows are still Standard while in the EU 3-panel glass with infrared-reflecting coating are de-facto Standard!
Isolation of your home can save you lots of money and energy. With windows and wall isolation about *50%* of heating/cooling cost!

Great to see everyone's stories of low tech TES solutions over the years. I'm an engineer and I worked in solar thermal and thermal storage for a while. It's great to see it come back to life. I agree with some of your last thought about electric resistance heating coming back to life. If we have enough solar and renewable energy it makes sense again. I don't see solar thermal hot water coming back for residential because of all the moving parts required. PV is more versatile although less efficient.

The potential of thermal energy storage in transforming residential energy use is immense. It's exciting to see how TES can integrate with renewable sources to enhance home efficiency

Great review of very relevant technologies. Many thx to for showing NEStore and pointing its benefits.

I once saw a experimental house that collected sunlight through giant windows and just inside of those windows were a few tall pillars made out of many 150L oil steel barrels welded together, painted black and filled with sand.
The black steel would absorb the heat of the sun and heat up the sand within it, which then would slowly released the heat when the sun was down. It was not used as a primary heat source but as a big complementary one. The ones living there said it worked as intended and they were very saticfied with it.
Another house did similar through a green house part of the house that heated up a cob/brick wall and floor. The excess heat generated was then pumped into the house (or ventilated out depended on the temperatur). When the night came the floor tiles ans the backwall of cob/brick the slowly released the heat stored during the day.
None of these used water as a way to carry the heat, only air.

Great stuff! Thank you for sharing!

Just a minor point. Southern Alberta, Drake’s Landing is not “dark” in Winter or Summer. Cold, yes, but the region gets more sunlight per year then southern Italy.

You forgot to mention that these systems dont lose efficiency unlike current battery technology systems. So in theory those sand batteries can last a lifetime.

This is real freedom tech. Thanks for sharing this one Matt.
DIYable energy storage is where its at!

I personally have an off grid property that I live in year round, winter has been cozy as i have made a system with a 55 gallon water barrel, 2 small radiators (for heating the space), some pex and a 1.6liters/minute water pump. I am heating the water when i use other heating (electrical or propane) and using the heat stored in the water over night to keep the space warm as well as keep my lithium batteries from getting too low a temp. Total about $120. Never has my space temperature dropped below 50f(set temp when i am away/at work etc). If i ever get done wiring the new panels to the water heater i have installed in the barrel i will not have to use propane unless it's an emergency or multiple days of freezing and overcast/snow unless i add another barrel or IBC

Matt, at 6:18, please make sure you write units correctly. The kilowatt-hour is written as kWh not kW/h. You can also write it as kW•h or kW h. The units are of energy so kW --> power multiply by hour --> unit of time = a unit of energy.
The way to remember that is: if you have power per unit of time what does it mean? It means energy per time^2. So it's like an accelerating energy rate. But that's not the correct units because we're discussing energy storage which should be in similar units to joules (J). 1kWh is 3.6MJ
Fun fact: Power per unit time is useful as it measures the rate of change of power also called "ramp rate". It's useful for measuring how quickly a power plant is spinning up or spinning down to generate electricity for example.

If you build a new house you can make the TES part of the foundation of the house. Fill your empty foundation parts full of sand and make it into a TES, with solar panels on the roof to heat it.

thank you very much, sir. I enjoy your content, especially about renewable energy, and specifically the sand battery. I am from the Kingdom of Saudi Arabia, and I am interested in energy storage, not primarily for heating purposes. As you know, our weather is hot, but we focus on desalination of seawater and electricity generation. In any case, I am very grateful for your efforts in this field. Best regards! 😊

I plan to research this further and install if possible.

21st century version of bringing rocks into the cave that were heated by the sun all day to keep you warm while you sleep

I've been considering something like this when we build a home with underground water storage. Not a compact system, but 5-10k gallons underground in heated or cooled water with a high efficiency heat exchange system.
The critical failing between this and almost all the systems that are out there is that they will not work for people with low to moderate incomes. It's only going to be people with nice homes and a bit of land. What's going to work for everybody is going to be fissiom-based nuclear power for the next 30 to 40 years while we transition to fusion.

This is very informative channel. I would love to see this used in future.

I have always wanted a residential CHP fuel cell for my home. Being able to overflow from one of those into a heat battery could really go a long way towards boosting efficiency. The fantasy has always been to run it off a methane waste digestor, but that is really a fantasy.

This + a Rocket Stove = Rocket Mass Heater 🙌

keep producing great content 👍

My son bought a new home in South Phoenix in 2022. They have a tankless water heater so energy is only used when there's demand for the hot water. It gets to the shower or sink just as quick as having a tank.

During the previous winter, we frequently experienced power outages due to issues with our neighbors. Our home uses an electric water heating system and a fireplace that heats water. This heated water then passes through a heat exchanger to warm the house. We also have a 5kw solar station.
Our hot water needs are catered to by a 250-liter water boiler, which can utilize up to three heat sources. These include electricity, heat from the fireplace, and a gas heater. However, we never installed a gas heater, so one of the heater's in/out was unused.
I decided to connect this unused in/out to our heating system. Through home automation, I set it up so that during a power outage, the hot water from the boiler would serve as a heat source to maintain a comfortable temperature in the house. The system was configured to stop the heat exchange when the boiler's water temperature dropped to 32 degrees. Thus, I was able to use the heat range from 70 to 32 degrees.
This heat energy was sufficient to maintain the home's temperature during power outages, eliminating the need to start the fireplace. The boiler model we use is the Drazice OKC 250 NTRR/BP.
Essentially, this solution mirrors what was demonstrated in the video, but at a significantly lower cost :)

so glad to see the focus expanding to thermal storage. its extremely under appreciated. i been using the poured concrete foundation in my house for thermal storage for years and the reduction in energy use has been quite big

I love your videos!!! Continue with the awesome content!!!

My regional power company has an electric thermal storage system as an option for those that want to sign up for a “time-of-day rate” power plan (lower cost per kWh during off-peak period). The ETS apparently uses ceramic bricks, and has three installation options: room unit systems, central heating, and in-floor radiant.
It’s just that if the peak period wasn’t so wide (7am-11pm) and its cost/kWh so expensive, an ETS would be practical for more people. (Peak cost in winter is ~105% more than the cost of off-peak; in summer the peak cost is ~60% more than off-peak.)

This reminds me of the very simple water-jacket in the fireplace / woodstove coupled to an inground water tank. It's inexpensive , especially if not retrofitting. If you love your fireplace, this is certainly something to keep in mind. I do not know the exact efficiency rating, but if you live in forested country, it can really shine.

Emphasizing sustainability, another benefit of TES especially these solutions that the materials to make them are both environmentally inert and more ethically sourced than those of Lithium ion batteries. If these fail or need to be decommissioned, materials like sand and water pose very little risk to a local ecosystem.

This video made me wonder if a water heater blanket made with sand would be beneficial? Trapping the heat in sand might extend the time the water heater holds the thermal energy.

We've been looking for efficient energy storage for ages for our offgrid place.

I have decided that Matt's channel is the one to watch! No sandbagging here! 😂

6:06 :) "sand is dirt cheap" Frunkin' hilarious,

This is what we need more of
This is how we make self sustaining homes

We compound this, we store solar in water here, comes off the roof via wires, goes to the heat pump hot water service, then we use it when the sun don't shine. Once the water is heated (or realistically at the same time) we top up batteries for everything else.

It is actually the insulation that holds the heat in as anyone that lives in the desert can attest to, sand heats quickly and realeases the heat just as quickly. You can experience thermal swings from 100+ ferinheight to ~60 f when it transistions from day to night and the transistion only takes an hour to 3 hours.

😮 Building it into a foundation of a house might be a good idea, in my opinion. You already have to dig a pit to put in foundations anyway. It could solve the size issue if it's under the house itself. 🤷‍♂️ Just a thought anyway.

I could see this being useful in agriculture. Our barns aren't conditioned which is mostly a problem in winter with water lines freezing. But i wouldnt use solar panels to heat the sand. I'd go with those black pipe solar collector boxes and maybe a solar panel to run the pumps since the idea is to have passive heating. Or forego the solar panel and have a Seebeck generator buried in the wall of the sand tank.

Here in Norway, geothermal heat pumps have become more and more popular, as the price for installation have become cheaper.
Not the same thing as TES but, as you said, most of our energy consumption is for heating, so the principal is still the same. Use energy stored in the earth to heat exchange with some thing stored inside the house, usually water.

Think you hit the nail on the head - right device for the right use, given more thermal stuff things can probably get improved. Like mixing Wind with Solar and a battery to cover a wider amount of the year.

The next level up from this: designing houses so well insulated that they don't need thermal energy to heat or cool them!

Here's a novel concept why not build the interior walls from high density clay blocks or bricks as these will store alot of heat and make the exterior walls from low density highly insulative materials giving a building effectively a spine that acts as a thermal store. You could even run heating elements through the wall or add IR wallpaper to it and it's insulated from the exterior by your home.

Water is the best thermal battery. I have a hydronic buffer tank for my heating system that stops my boiler short cycling and stores about 1 day of heating and hot water making in the 50 gallons of water stored in a well insulated tank. I have massive thermal mass on my main floor, a 5.5" concrete slab with radiant tubes burried half way in it. That slab sits in a tub of closed-cell insulation. In essence it is a giant thermal battery. I used 5/8" sheetrock and neatly added scraps of sheetrock into my stud cavities, increasing mass further. These ideas can be designed into our buildings. If my system shuts down I have about 1 week of toasty heat stored. And during winter, once the system has brought that slab up to temperature, the operating energy is very low. Opening doors or windows, turning on ventilation has little impact on temperature as that mass makes temperature swings very slowly; like turning a massive ship. I installed 1 massive window facing south. In the winter the sun shines directly through that window and warms the floor, adding passive heating to the system. The summer sun is shaded. The summer benefits are the same, as that slab absorbs the cool air conditioning. This strategy works best with a very air-tight and well insulated home.

Back in the 1970s, we used to have "storage heaters" in many UK homes (they predated central heating). Basically, a feck off big lump of concrete, in a metal box, with a heater wire inside it. It "charged up" on cheap overnight electricity (who remembers Economy 7?), then let its heat out slowly over the course of the day. Rinse & repeat. Their problem was controllability: Once it was hot, it was going to give up that heat, whether you needed it or not... Sticking the whole shebang underground & in some insanely good insulation, then tapping the heat via another medium, sounds like an excellent idea. I also wonder, given how simple the system is, whether it's got DIY potential...

It's so expensive, it would require financing for most people.
Luckily, there are plenty of sandbanks.
I'll see myself out.

You can place the battery under the garage as long as its well insulated, it can also take the space of an outside wall surely

Interesting solution - that could be useful for apartment building or other large estate developments.

Humans are specifically designed to thrive on meat. There's a very good reason the vast majority of people who go vegan end up returning to a naturally omnivorous state.

I thank Biden for the inflation reduction act

Had one back in the sixties was great

Just one note, Southern Alberta is actually extremely sunny, not dark (except in the winter with reduced daylight of course).

Anybody remember "Copper Crickets"? Cooling the back of solar panels, then feeding that through concentrating collectors in-route to storage (perhaps a heat pump water heater) will reduce the cost of heating water and increase the output of the photovoltaic units by several percentage points on warm days. Also, there are thermal recovery units for air conditioners / heat pumps that would reduce water heating costs. Also, all of this will help make your basement look like "Das Boot", giving you more ways to impress friends with a tour of such a complex system.

Going big and going HOMES seems like a good idea. I live in a set of attached townhouses, buying a large sandheater and having it power 20 small homes seems like the sweetspot

Sand only has an advantage when high temperatures are acceptable. Sand has low specific heat (start from 3:10 minuts). You bring it as an advantage, but it is a real disadvantage as you need more of it, or higher temperature to store the same amount of heat energy. Sand has about 800 J/kg/K, water has 4000 J/kg/K. Volume based, sand has 1400 kJ/m3/K, water has 4000 kJ/m3/K.
Last winter I used 110 m3 of natural gas for heating and hot water (3.6 GJ). I already use some passive heating. This year maybe less as I added more insulation to the house. So I need about 20 m3 of water to store my heat energy for the winter. Assumed that losses are not that big compared to the stored heat energy. Losses will be a problem. Loss goes with surface, and storage goes will volume. So large heat storage installations can have less relative heat loss. At some time in the season It may be better to store directly via solar thermal panels instead of PV panels.

This tech can more easily be introduced in new construction. You could make it part of the basement design.
The draw back of this design is in off grid installations. Places like Maine can have long periods of heavy cloud cover and solar production can be very low. So you’d still need larger solar energy storage (batteries) and well as higher collection potential (more solar panels).
Modern designs are generally expected to be grid connected to keep cost down. But in rural locations we have to design for the worst case without the grid being an option.
For me, it always needs to be 2 independent systems.
- geo thermal + wood stove
- geothermal + rocket stove
- mini split + wood stove
- mini split + rocket stove
- sand heat + wood stove
- sand heat + rocket stove
It’s important to design homes for efficiency as well. Our current home designs are based on brute force a/c and heat.
I don’t think you mentioned it…How much electricity is needed to heat up the sand? How long does one heating cycle (input) last for (output) ? How much electricity is needed to reheat the sand?