Building ultra cheap energy storage for solar PV
austinvernon.substack.com
austinvernon.substack.com
I think this niche of 'very long duration, very constant slow rate of discharge' is clever, and it would suit industrial heat consumers but could also suit district heating for buildings in a climate that's predictably in need of heating all winter long (Canada for example).
They seem to have a decent grasp of the fundamentals, both of the technology and how to commercially carve a niche. I wish them well, and thank you for the post.
1. In places with underground water reservoirs, these can be used for heat storage very similar to this. It's location dependant but I think there's European district heating networks doing this already.
2. Heat pumps for process steam are gaining ground. The temperature at which heat pumps lose competitivness is slowly rising over time. They mention storage at 600C. Heat pumps win under 80C and are up to 160C and aiming for 200C though at those temps cheap gas will probably win for now. Heat pumps can also recycle process heat and cool and heat at the same time.
3. Wind doesn't get mentioned. Wind doesn't pair as neatly with batteries as solar does but in places with seasonal storage issues the batteries can be used for solar and wind during summer and wind plus whatever (biogas/nuclear/hydro) in winter. They need to worry about both centralised big batteries and customer sited ones.
In general I'm supportive of the idea, but similar to the Nordic sand battery, when they start talking about generating electricity from the stored heat I take that as a signal that they've realised the alternatives above combine to really squeeze the market they have left and undermines my faith in the rest of the product.
Batteries will still be too expensive to arbitrage these seasonal differences effectively. Thermal electricity storage is orders of magnitude cheaper for storage, but worse at daily cycling
They've always had $20/KWh as a notional price but there's already talk of Sodium batteries in China getting near that price point, while having nearly double the round trip efficiency.
I have about 40kwh of storage. The batteries are in steel boxes and there are some basic precautions to take with them but lifepo3 has a very manageable risk profile quite different from lipo. Batteries and solar equipment continue to get cheaper, the same system I have is now 50% cheaper today then when I bought it, including tariffs.
The link really discusses more of a single neighborhood or medium industrial site possible type of technology. Really just a huge very hot pile of sand and steam turbine or propane cell generation. On a kwh basis it is probably not competitive with solar+battery unless your use case involved a lot of direct use of hot water or heating something.
> I have about 40kwh of storage
You're pretty close to the ideal location for solar + batteries. For much of Europe or the Eastern US, this amount of storage would be nowhere close to enough, by orders of magnitude - they need to make it through the winter, and generate heat from it, after all.
For each location, there's an ideal amount of storage and an ideal amount of overbuilt capacity, both depending on hardware costs (and contributions of wind to the energy mix).
In your case, both numbers are relatively small. With lower incident sun, persistent cloud cover, and the possibility of becalmed wind turbines, storage requirements can start to make thermal batteries or hydrogen storage economical.
A USB extension cable died, and it took an hour for the manufacturer to diagnose it over the phone, for me to find the right tamper bit to access it, then remove the cable.
Another time, PG&E was feeding the wrong voltage and frequency into our house. The power stayed on (our transfer switch knife cut off PG&E) but the solar array shut down because this is a weird fault. Again, it took about an hour to diagnose over the phone and fix (in this case, I temporarily turned off the PG&E service breaker. It ran diagnostics for about 30 minutes and turned the array back on).
Installation (included in purchase) was probably about 100 man hours though.
LiFePO4: safe, unless you crack them and ignite the liquid with a blowtorch, or something.
A trend in home batteries, that we see now (because of killer competition on the Chinese Market / export), is LiFePO4 batteries that have a included fire extinguisher module.
This adds another layer of security beyond:
* LiFePO4 (not oxygen producing)
* Most batteries are encased in a iron protective layer, this reduces the risk of punctures. And also act as a fire suppressor as any fire has a hard time escaping / limited amount of oxygen access.
* Depending on the batteries, they can be installed in a enclosed rack.
* The now often fire extinguisher module in a lot of pre-made batteries.
The chance of a fire from a LiFePO4 install is so small, that your more likely to get a fire from any other part of your house (probably your laptop or smartphone lol ).
Conversation instead of anonymous bashing would be appreciated.
Unless you have no good arguments, so I dare you, random aggressive strangers, I triple dare you!
So I really hope these guys will succeed where I can't even get it to work on paper, sometimes scale really is a requirement to make something work and this could very well be one of those.
Then your storage model becomes "a cloudy week" rather than "a whole season", and the storage scale changes significantly.
The difference between net zero across the year and 95% unlikely to need the grid on solar and batteries is a staggering difference, about 10x the panels and battery storage. But the equation changes drastically depending on local weather patterns and the solar irradiance difference from summer to winter.
BTW keeping your house connected to the mains costs $10-20 / mo, even if you consume nothing. Connection cost is one-time, but likely several thousand.
Or an EV. I only need enough instant battery capacity to last a couple hours. That would handle the vast majority of outages I ever experience, all by itself. If it looks like it is going to be longer, I grab the cable from the transfer switch and plug it into my Lightning. That would get me through a hypothetical week long outage.
I think the current consensus is that transmission to solve for regional solar differences is not cost effective. At least in the US, most places have plentiful land available nearby and it costs way less to overbuild the solar for winter than it does to try and bring it from some place with more plentiful sunlight.
Optimize the angle for the Winter. The Summer will do well enough anyways.
However the mounting systems, solar charger controllers, and inverters are mostly not.
The bulk of the cost of panels now isn't the panels themselves, but all the supporting infrastructure.
The seasonal variation can be as high as seven to one, so the total install has to be very very cheap to support a 700-1000% over build.
Though if you are on a grid that allows it, you might want to send summer power back into the grid for credits
Micro inverters or mppt with inverters.
With micro inverters you cannot over provision the panels in a useful way, each panel or pair of panels has a micro inverter.
The mppt plus inverter system you absolutely can do that... but it scales poorly. Shading of a single panel effects the entire string, so the more panels you add to over provision the worse that effect gets.
So yes but actually no.
Edit: turns out there are products for mptt strings called power optimizers that seem to help with this very thing I hypothesized.. at least one company offering them is SolarEdge
There's no free lunch here.
Honestly I'm pretty skeptical of residential rooftop solar - it's not even close to the solution, it's just a cost optimization we shouldn't actually need.
Storing a half-day's worth of electricity, and powering stuff from a solar panel at daytime, would likely let my apartment stop consuming external electric power in the summer.
Assuming my apartment consumes no more than 15 kWh during the hottest days (according to the meter), a moderate 8 kWh battery, and $1000 worth of solar panels, would suffice, given the room and a permission to mount the solar panels somewhere.
Maybe I'm failing to follow the intended argument here, but I do not see what is expensive about this. Houses are hollow; they do not weigh all that much. Dirt is cheap, especially when sourced locally.
> A typical site is a factory, power plant, or town with a large earthen mound at the edge. The mound might be the size of a house for a smaller factory, and up to many football fields for a large power plant. Surrounding the earthen mound will be high-density, low-profile solar arrays.
I agree that trying to give every suburban house its own rock pile would not be very practical.
I know. See my original comment at the top.
I’m also off grid, also suffer in the winter (although a spot of hydro power is going to alleviate that somewhat), and have also thought about thermal storage - I actually calculated that a 20ft container filled with sand could give us thousands of kWh, as long as the sand could get up to ~600C.
At that temperature you of course have to think about making really damned sure no water gets in there, but it makes the volume of material more manageable. Would still work with resistive heating, energy out would be trickier but not impossible to engineer something that wouldn’t explode.
As an investor - what RoIC do you want to see when doing initial analysis
(for example, $10M capex per system, with 10,000 systems TAM )
Now, do the economics shake out for storing heat to deliver in winter? No idea, but the idea is not far fetched. Outside of bitcoin mining, there are few uses which can soak up the increasing glut of midday PV generation. Anything that can seasonally store that (even at terrible efficiencies) is valuable. What is going to be the most economic option? No idea. My personal bet is iron-air batteries, but there are a lot of contenders in the space that are competing for widespread adoption.
You don’t get much long-term storage with your black paint as it’s just going to heat the surface. The point here is to heat up a big enough pile of dirt that you can draw out power months later.
Above that temperature, you need molten salts or liquid metals that are extremely corrosive. Your other option is to use gaseous media instead.
They've made no progress on getting the energy out of their heated dirt. They want to make a hot dirt powered boiler - run pipes through the dirt, put in water, and get steam. Not hot water, superheated steam. That's the hard part, and it will have to be custom.
Small steam turbines are available. Siemens has a whole range.[1] They start around 750KW, at the high end of automotive scale. Siemens can sell you a matching generator. When these guys can power one of those, it's real.
Right now, it's three guys. They need VC funding and a really good boiler engineer. The goal should be a working prototype at about 500KW scale. That would be a big enough prototype to get some meaningful efficiency measurements.
(Maintenance will be tough. You can't turn the heat source off.)
[1] file:///home/john/Downloads/SE-Brochure-Dresser-Rand-Steam-Turbines-2021-pdf_Original_20file.pdf
[1] https://www.siemens-energy.com/global/en/home/products-servi...
High-grade heat can be easily turned into electricity with a turbine, or reused in an industrial process (the entire point of a nuclear reactor is to create heat in this temperature range!) Medium-grade heat can still be used for some processes or used to generate electricity, but the electricity generation will be less efficient. Low-grade heat is under 100C and is a lot harder to use. You cannot economically generate electricity from it, or use it for most industrial processes, so use cases often focus on district heating.
The problem with these low-grade-heat district heating schemes, or more broadly any use of low-grade heat, is the economics. Let's take your idea. The efficiency from sunlight to heat is indeed high (much higher than PV panel -> resistive element) but the heat generated is all low-grade heat.
So what's the root cause here, why is low grade heat usually not economic to use? It comes back to two main causes: 1) efficiency, and 2) storage. Most power is generated from turbines that use heat - a type of heat engine. Carnot efficiency is the maximum theoretical efficiency of a heat engine. Carnot efficiency is η = 1 – Tcold/Thot where temperatures are absolute temperatures (Kelvin/Rankine.) In other words, 7.7% for 50C->25C (298K->323K), 37% for 200C->25C, and 61% for 500C->25C. Note that this is _theoretical_ maximum efficiency; real world efficiency varies quite a bit - from ~1/2 to ~1/10th of Carnot efficiency at peak depending on your heat engine. The second, storage costs, are even more important. You need to insulate your warm object to keep it warm, and if your heat is low-grade, then it is spread out across a huge volume.
Back to your idea, your "paint the dirt black" idea will generate far more heat, but very low-grade and entirely non-economic to use. You will have a somewhat warm pile of dirt, but nobody really wants a somewhat warm pile of dirt. This is the same reason why you see people, logically, tearing down their high-efficiency solar water heaters to install low-efficiency solar panels.
"Use solar panels to resistively heat the dirt", on the other hand, is less efficient and generates far less heat - but it generates high-grade heat. This startup proposes to eventually sell that heat to power plants, to generate electricity directly; and if you're doing that, the temperature of the heat is critical. As you can see from the Carnot efficiency, a power plant couldn't economically do anything with a warm pile of dirt, a solar water heater, or other similar technologies. But they _can_ do something with a source of high-grade heat - namely, they can run the turbines that currently run on fossil fuels. In other words, you can solve the seasonal solar curve problem and have constant electricity production year-round, even in northerly climes.
[0] Above - very roughly - 500C, it is harder to use the waste heat efficiently, because the engineering gets a lot harder, but the theoretical maximum efficiency is higher. That's one reason why there are a lot of efforts to try to build nuclear reactors working at these higher temperatures (see: molten salt reactors.)
For example, Nuc typically don't cross 400C, when Gas/Coal could work on 450C or even more.
Plus, non-Nuc could use some more exotic technologies, like MHD (magnetohydrodynamic) generator, to provide much more efficiency of power generation, or CO2 turbine to make installation much smaller. (Theoretically, somebody could build Nuclear MHD device, but it will not pass safety restrictions).
If you want to do practical district heating, you should look to the Soviets. Unfortunately, most of this information is available in Russian, on physical paper.
[0] http://waterworkshistory.us/DH/1967USSRreport.pdf page 18, figure 2
The steel-man case for Denmark is that trees usually do grow back, and indeed, global _tree_ cover is substantially higher than it was 35 years ago. But global _forest_ cover is still shrinking, and much of the wood entering Denmark comes from forests. Forest cover is more important than tree cover - for the aforementioned reason of albedo changes, but also biodiversity.
Where things really get absurd is when you begin to calculate the area of land you have to turn into a tree farm to keep your homes warm. Or when you calculate the market effects of buying a huge amount of trees - even if all _your_ trees were good ethical trees from a farm, you have just consumed a large amount of the supply and thus financially incentivized cutting down old-growth forests elsewhere - for example look at the history of Ikea’s wood use. If there were more Denmarks, and it was not just a small country with the population of the Chicago area, there would be massive worldwide devastation.
Don’t get me wrong, I am not an absolute opponent of biomass. It is true that burning things is a great source of high-grade heat. It can play a small role in a sustainable energy mix. But it is not the free lunch Danes think it is, and certainly not at the scale they consume it.
Solid state solar panels should be more reliable than any hydronic system.
Though I suppose their heat recovery system is probably hydronic.
Cutting out the conversion steps should be more efficient.
Also, they could use the waste cold air to cool the solar panels, which increases their efficiency.
The sand scheme involves putting hot sand into the top of the silo, and draining out sand into a heat exchanger at the bottom. So you can have more storage than you have heat exchanger capacity. The "ultra cheap" approach in the article requires resistance heaters and plumbing all through the cheap dirt.
Molten salt has also been used for this, successfully.
[1] https://www.solarpaces.org/nrel-results-support-cheap-long-d...
[2] https://www.wenatcheeworld.com/news/northwest/trump-congress...
LNG is standardized, it's readily available, and existing infrastructure already exists.
how is this new system better?
They compare to natural gas. Not the cheapest alternative.
>Pipes run through the pile, and fluid flowing through them removes heat to supply the customer
Just basic district level geothermal heat pumps do the same. You don't need to heat the soil. Just drill down and install pipes. Earth generates heat. What is the cost difference now?
This doesn't with everywhere though? Because of geology?
Why didn’t this submission redirect to mine?
(Unfortunately I didn't see the email until many months later, IIRC...)
I wonder if they have had issues trying to solve a problem so many people insist doesn't exist.
Solar PV is very reliable year long. It is the day-night cycle that requires batteries, for seasonal offset they do not work and probably never will.
In the off-season they still work just fine, they just make much less power. Which you can offset to some degree by a good balance between wind and solar at the grid scale (not at the private dwelling scale, unless you live rurally).
I'm on PV during the day time all year round in a densely built up region in Western Europe. In the summer we overproduce a ridiculous amount that we can't consume ourselves (though I'm getting better at finding good uses for it), in the winter it is touch-and-go during the day. Netmetering is enough to give me a negative electricity bill which goes towards paying whatever NG we still buy (which isn't a lot, we spent a good bit of money on insulating this house as much as we could without rebuilding it).
> I wonder if they have had issues trying to solve a problem so many people insist doesn't exist.
Nobody who knows anything about PV is going to insist the problem does not exist.
You acknowledged that you're wrong in the very same paragraph.
I suspect you're misunderstanding what the word reliable means in this context.
PVs are very reliable at converting photons to electrons. However if they don't get enough photons, like during night or winter up north, they're not a viable energy source for many uses.