How a Sand Battery Could Revolutionize Home Energy Storage

Sand. It’s coarse, it's rough, and it can make for  a great battery. And as weird as that might sound,  

it’s just one example of the many earthy  materials currently used for thermal energy  

storage (or TES). A while back, we covered the  debut of the world’s commercial sand battery,  

which is big enough to supply  power for about 10,000 people. Now,  

sand-based energy storage has reached a  new frontier: individual homes. Companies  

like Batsand are currently offering heat  batteries that bring hot and fresh sand  

directly to your door. Seems you can get  just about anything delivered these days.

But what’s stopped us from experimenting  with residential TES before? How will heat  

storage impact our lives in our homes? And where  exactly are homeowners supposed to put this stuff?

I’m Matt Ferrell … welcome to Undecided. 

This video is brought to you by Factor and all  of my patrons on Patreon, but more on that later.

Your utility bill probably already tells  you the story that we spend a lot of money  

heating and cooling our homes. In fact,  according to the University of Michigan,  

over 30% of total US residential  energy use is dedicated to heating.  

Water heating comes in at about 13%,  which is really just another kind of  

temperature control. According to the U.S.  Lawrence Berkeley National Laboratory,  

one-fifth of all energy produced in the United  States goes towards a building’s thermal load.

Residential battery systems like  the Tesla Powerwall are a great  

way to get around what some consider  the fatal flaw of renewable energy:  

intermittency. But the dominance of lithium-ion  batteries comes with a host of its own downsides, 

like some of those ecological  impact and potential safety issues.

Thermal batteries or thermal energy storage  (TES) devices are one alternative that’s  

worth watching. We’ve examined them  before, but here’s a quick refresher.

When it comes to TES, the acronym  is pretty straightforward: they’re  

batteries that store energy as heat.  You charge them by passing electricity  

through a heating element embedded in your  thermal medium. This medium can be water,  

sand or whatever, so long as it can hold  onto a lot of heat for a long time. We  

can then discharge and release the heat at a  later date through a basic cooling process.

When used in combination with  heat pumps and solar panels,  

TESs can do some amazing things. As far back  as 2012, Drake Landing Solar Community got  

a record-breaking 96% of their yearly  heating from solar energy. In 2015-16,  

that number jumped 100%. That was in  cold, dark Alberta, Canada, of all places!

TESs tend to have very good round-trip  efficiency rates (RTE), which is the  

percentage of electricity put into storage that’s  later retrieved. It’s very important for any kind  

of energy storage device. A 100% RTE would mean  that every drop of energy stored can be withdrawn  

and used later. It’s also thermodynamically  impossible. For context, lead-acid batteries  

have an RTE of about 70%. Lithium-Ion batteries  for large energy storage, like those in many  

industrial-scale energy storage facilities and  maybe even your home, have an RTE of around 90%.  

But commercial and industrial thermal batteries  are reportedly hitting RTE’s of 90% or more.

This got a lot of innovators thinking… if v TESs are working so well for big applications,  

why not bring them home? But can TESs  work on a small scale? And if they can,  

why haven’t we tried this sooner?

But first…why sand? I don’t like sand. If you’ve  ever visited the beach and made the mistake of  

ditching your flip flops a little too soon, you’re  all too aware that sand holds heat remarkably  

well. That’s because sand has low specific  heat, meaning it doesn’t need a lot of energy  

to heat up fast. And sand’s high density allows  it to store large amounts of thermal energy. No  

chemical reactions means sand batteries are  low maintenance and have long life spans.

We can also heat it to well above the boiling  point of water, and hold onto that heat with  

an RTE well above 90%. For these reasons we’ve  seen companies like Polar Night achieve viral  

buzz around their commercial sand batteries.  We just heat the sand with renewable energy,  

then we use air to move the heat from  the sand to your house. Seems easy,  

so why haven’t we been doing it all along?

We’ll dig a little deeper on this question later,  but there’s something else we need to dig into  

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why haven’t we been doing home TES all along?

The main reason is size. Mass matters,  

especially for storing heat! I don’t  know what your living situation is like,  

but I don’t really have room in my garage  for a 23-foot (7ish meter) tall silo of sand.

That’s where companies like Latvian-based  Batsand come in. It’s difficult to reduce  

these devices down to a residential size, so  Batsand cleverly plans to hide the sand tank  

underground … not unlike a septic tank. This  is a necessity, as even the smallest Batsand  

tank is going to measure 40 cubic meters. Though  it’s not all about space consideration — having a  

tank underground helps to keep everything well  insulated, kinda like a DIY geothermal system.

Better yet, sand is dirt cheap, non-toxic, and (if  it has been properly selected and cleaned of other  

organic materials) non-flammable. Numbers-wise,  the device is intended for 300-400 square-meter  

buildings and can store 10,680 kW/h. That’s  impressive, assuming you’ve got the recommended  

30-plus kW of solar panels on your property.  What’s the catch? We just touched on it … it's  

that massive sand tank. Just like a geothermal  system, digging your yard up isn’t cheap, I can  

talk about that first hand. Something to keep in  mind for later when we talk about price points.

Netherlands-based Newton Energy Solutions (NES)  have a very different kind of TES device to offer,  

though. They’re keeping it simple with a no-frills  design that falls somewhere between a TES,  

a water heater, and a buffer tank. Fun side-note:  a water heater is already a thermal battery,  

technically speaking. It’s just one that  can’t turn the heat back into electricity.  

But seeing as you’re already spending most of  your electricity on heat, that’s not much of  

an issue. No surprise then that the NEStore looks  and functions a lot like a water heater. In fact,  

if you don’t have enough space for both, the  NEStore can flat out replace your water heater.

The NEStore combines special vacuum insulation  with thinner-than-average tank walls. Together,  

these two small advantages allow the  NEStore to hold more water and much  

more heat than other devices in its weight  class. The system is available in two sizes:  

The smaller one has water volumes  of 214 liters and 20 kWh capacity.  

The larger one is 320 liters and a  29 kWh capacity. According to NES,  

even the smaller size can heat 600 liters of tap  water to 40 C (104 F). That’s a lot of showers!

As a nice sustainability cherry on  top, NES says their device is made  

from fully recyclable materials. Their  “plug-n-play” tech is meant to replace  

existing water heaters and work with  your PV systems. The company claims  

it can install a NEStore in your house in  under two hours. Of course, we’ll have to  

see what third-parties say once the NEStore  is on the market. This goes for Batsand too.

So if TESs are so great, and  can work on a residential scale,  

why have we overlooked them until  now? There’s a lot of little reasons,  

but the most prominent one is size.  Now this is oversimplifying it a lot,  

but as I mentioned earlier, bigger things  cool off slower, so if you want to optimize  

your thermal energy storage device, it  pays to be big. That’s thermodynamics 101.

But it’s hard to both go big and go home. It  puts these devices at odds with miniaturization  

and home deployment, and of course, really  drives up the price. These factors have  

traditionally made TESs a hard sell, especially  when standard, fossil-fuel-burning methods of  

heating are comparatively cheap and small. This  goes for the other use cases too. Why attach your  

solar farm or home solar panels to a less mature  technology when more mature storage technologies,  

like lithium-ion batteries, are available? And, whether you’re a homeowner or a utility  

company, it’s hard to take a risk on a  device that may never pay itself back.

The numbers also don’t look as good if you  try to convert heat back into electricity,  

because a small but significant amount of  power is “lost in translation.” Though,  

statistically speaking, you’re already spending  most of your power on heating your home,  

so saving and later using that energy as  heat really isn’t a problem. This means  

that TES devices work well in tandem with other  energy storage ones, like the Tesla Powerwall.  

Letting the TES handle the lion’s share of the  work in heating allows the chemical battery to  

handle other electrical applications. It’s  using the right tool for the right job.

However, every time energy is converted from  one form to another, there are energy losses.  

TESs have remarkable efficiency when their  stored power is used for heating. But their  

efficiency drops to a much less exciting 50–70%  when they’ve got to convert that heat back into  

electricity. Compare this to 90% for lithium-ion  batteries or even 70–85% for pumped hydro,  

and you can see why adoption has been slow.  That makes them less versatile than something  

like a residential chemical battery system, and  if you’re only able to afford one energy storage  

device, you’re probably going for the more  versatile and available piece of technology.

Speaking of affordability, that’s also a major  factor. The relatively small and cheap NEStore  

has a €5,000 to €6000 price tag, which is about  $5300 to $6400, depending on size. Those figures  

do include installation, though I worry those  numbers will go up once it leaves the preorder  

stage. Batsand’s smaller 14kW system will  run you a very reasonable €7,200 or about  

$7,700. But with installation it balloons to  a hefty €17,000 or $19,000 on the low end.

That kind of price point means these devices  aren’t going to fit into a lot of budgets.  

However, these high prices do buy you some  impressive RTEs. When I asked NEStore about  

theirs over email, a business development  representative said it had an RTE of 95%.  

Similarly, Andre Raimundo, the head of operations  at Batsand, told me over email that generally they  

store energy at a 92% efficiency, and use that  stored energy at a 94% efficiency rate. Granted,  

these are likely “best-case scenario” figures, but  they’re still very exciting. Even with this kind  

of performance, it’s challenging to get homeowners  to spend luxury prices on these kinds of things  

unless they’re really into energy independence  or greentech…like someone you might know.

For these reasons, thermal batteries have  been a niche technology for much of their  

200-year existence. Demand really only  started to blossom alongside renewables,  

partly because TES devices are only as green as  the energy we put into them. Take water heaters,  

for example. As recently as 2010, a typical  resistance electric water heater produced  

four times more emissions than gas water  heaters. How? Well, it takes a lot of  

energy to heat that kind of thing, and that  energy was mostly coming from fossil fuels.

But now, with green energy being more  abundant, and the problem shifting from  

generation to storage, electric resistance water  heaters (and by extension thermal batteries) are  

looking better and better. According to Sydney's  University of Technology, by 2030 resistance  

electric heaters will be radically more energy  and emissions efficient than gas heaters. Heat  

pump water heaters already are, and I’ve got  a video that goes into my experience with one.

And speaking of heat pumps, it’s looking likely  that TES devices could follow a similar path. I  

hope they do, considering how they could work with  the rest of your home energy system. Think about  

it: Your solar panels gather energy for your  house, including your heat pump and TES. Those  

devices will keep your home at a cozy temperature  all day. With the massive burden of heating taken  

off on your battery system’s plate, it has more  juice to spend on all your other electrical needs.  

The synergies at play here are just so cool.  What’s not love? Well, the cost of purchasing  

and installing solar panels, a heat pump, battery  system, and a TES. But we’re working on that.

Here in the US, TESs are more affordable  than ever thanks to the Inflation Reduction  

Act (IRA). That’s because many of the IRA  battery storage provisions also apply to  

TES units. That means you can get a whopping  30% tax credit on your TES device. This jumps  

to a 40% tax credit for projects made with  domestic materials. That should go a long  

way toward making them more affordable for  the average household. With incentives like  

this on the table, I think we’ll see an  expansion in domestic TES innovation and  

manufacture — and competition should help make  thermal batteries more affordable over time.

So where does this leave us? I really  do think we’re at the dawn of a new age  

here. Thermal energy batteries are just  starting to break into the residential  

market. When we circle back to  this topic in a couple of years,  

I won’t be surprised at all if there’s  a lot more companies on the scene.

But what do you think? Do you want  thermal energy storage for your  

home? Jump into the comments and let  me know. I’ll see you in the next one.