7 ms·

Building ultra cheap energy storage for solar PV

99 points by theptip 1y ago

gaoryrt 1y ago
Why go throught the extra solar -> electricity -> resistive heating -> soil instead of directly doing solar -> heating a metal rod -> soil? Cutting out the conversion steps should be more efficient.
- 3eb7988a1663 1y ago
  If the electricity is free, efficiency does not matter that much. The capex of the storage system might matter a lot more. In which case, heating up a big mass might be more economically feasible than battery installations.
nabla9 1y ago
> The purpose of Standard Thermal is to make energy from solar PV available 24/7/365 at a price that is competitive with US natural gas. 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?
- hvb2 1y ago
  > Just basic district level geothermal heat pumps do the same. This doesn't with everywhere though? Because of geology?
ZeroGravitas 1y ago
They skipped a few real competitors that'll shrink their market: 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.
- conradev 1y ago
  Yeah, Form Energy exists to basically disprove this: 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 Form, like the authors, agrees that Lithium-ion is great for intra-day cycling and not suitable for is seasonal storage. Unlike the authors, Form believes it can engineer chemical storage with the requisite properties. Form’s batteries have something like 10 days of capacity relative to the size of their inverters.
  - ZeroGravitas 1y ago
    Form's basic idea is that low round trip efficiency can work as long as it's cheaper enough. 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.
scblock 1y ago
Energy storage yes, electricity storage no. Very limited utility and questionable use of solar PV, which has about a 20% conversion efficiency of solar energy to electricity. Seems like a lot of extra steps to make heat.
- 3eb7988a1663 1y ago
  One of the biggest uses of residential energy is heating/cooling. Especially in winter months where PV generation is significantly lower (I have seen numbers of 2-5x summer generation), having "free" heat could be quite valuable. 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.
iamthemonster 1y ago
Absolutely superb. The 'hot bricks in a box' concept of very high temperature thermal energy storage has been really coming into its own with the fall of solar PV costs, and it's quite suitable for industrial consumers of medium temperature heat. There's also a heated granite storage silo in Scandinavia that's recently gone into operation. The rate of heat transfer in the heat storage material is a classic constraint. 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.
throwaway81523 1y ago
This is confusing, why PV to heat the dirt? Black paint will do it from sunlight directly. Or circulating hot liquid. Way cheaper and more efficient than PV at collecting heat from the sun.
- buckle8017 1y ago
  There's very few materials cheaper than dirt. Solid state solar panels should be more reliable than any hydronic system. Though I suppose their heat recovery system is probably hydronic.
- hackernudes 1y ago
  My understanding is this is for excess PV capacity. But I think they should address this! Their plan is to heat deep inside a big pile of dirt using resistive heating elements and then pump the heat out in pipes. Maybe it's hard or expensive to add solar heating into the system? But why couldn't they pump it in? Maybe they don't have extra space because the dirt mound is covered in PV panels.
- theptip 1y ago
  Water will be limited to 100C, and tanks are going to be way more expensive to maintain. 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.
  - fabbbbb 1y ago
    Liquid doesn’t need to mean water? Traditional solar thermal systems use special liquids that can get way more hot than 100C.
    - cyberax 1y ago
      You can get to around 200C with oil-based media. But oil goes bad pretty quickly, and it leaches tons of crap out of everything. Above that temperature, you need molten salts or liquid metals that are extremely corrosive. Your other option is to use gaseous media instead.
metalman 1y ago
late to the game, there are villiage/town scale thermal batteries operating in northern scandinavia useing sand inside a conventinal style insulated silos, everything is off the shelf civil engineering equipment. any company offering similar tech will need a sharp pencil. I live off grid and am considering adding thermal storage as part of my system to allow for unatended background heating while on the road in the winter, where 2500 liters of water will provide pre heat for domestic hot water, and as a semi passive thermal siphon for area heating
- jeffbee 1y ago
  The University of California (Berkeley) is also building thermal storage. Currently they are excavating a 20-million-liter tank under one of the athletic fields.
jacquesm 1y ago
I've done a lot of spreadsheets on this kind of solution, but on a slightly smaller scale: a single family home. While it will work for a while it is not enough to meaningfully offset the seasonal cycle which is the thing that needs solving. Storing energy for a few days up to two weeks is (relatively) easy, storing it cheaply for up to 6 months is very hard unless you are willing to invest massively offsetting much of your savings. The pile of rock required to heat an average home for a couple of weeks handily outweighs the house itself. And that's without a double conversion, it is used and stays as heat, the idea was to moderate the leakage upwards as a source of heat by blowing air in a controlled manner rather than to convert it again. 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.
- myself248 1y ago
  Isn't it cheaper to just buy more panels, enough to meet your winter needs? Then who cares if they sit mostly idle for most of summer; energy not used is harmless. Then your storage model becomes "a cloudy week" rather than "a whole season", and the storage scale changes significantly.
  - hvb2 1y ago
    In almost all cases you lack the area for doing that. And that's not even considering exposure, as in winter most north facing panels on a roof won't get any direct sun because it's lower on the horizon
  - buckle8017 1y ago
    The panels themselves are cheap and getting cheaper. 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.
    - 1y ago
bilsbie 1y ago
Mods, I submitted this exact url four days ago: https://news.ycombinator.com/item?id=44963261 https://news.ycombinator.com/item?id=44963261 Why didn’t this submission redirect to mine?
- epistasis 1y ago
  HN doesn't work that way. Resubmissions are allowed, especially high quality ones that don't get traction. But links to prior submissions are always added, and usually only if there's good conversation about the prior link.
  - bilsbie 1y ago
    So because it didn’t have traction they created a new discussion?
    - epistasis 1y ago
      Once the mods invited me to resubmit one of my own links by email a few days after I had posted, because they thought it was a good link but it didn't get traction the first time. (Unfortunately I didn't see the email until many months later, IIRC...)
zackify 1y ago
Batteries are getting crazy inexpensive. You can get 16kwh for $1850 now https://www.youtube.com/watch?v=7bShGUPU3TQ https://www.youtube.com/watch?v=7bShGUPU3TQ
- deleted 1y ago
  [deleted]
- roarcher 1y ago
  ...if you want to take your chances with cheap junk in a safety-critical application. I watched about 3 minutes of that video and the number of issues that guy ran into was disturbing. You'd have to be nuts to put that thing in your house.
  - 3eb7988a1663 1y ago
    I am in no position to install a battery system, but if I were, I would definitely build a little cinder-block shed to hold the array. Offset that a good distance from standing structures and instant piece of mind.
- jacquesm 1y ago
  Please do not give that guy more exposure than he already has, his advice is going to get someone killed one of these days. He knows just enough to be dangerous.
  - Squeeeez 1y ago
    As my grandma used to say, regarding speaking a foreign language: "enough to get you beat up, not enough to get them to stop"
    - Squeeeez 1y ago
      Why the downvotes? 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!
buckle8017 1y ago
I've found that lots of people get viscerally mad when it's pointed out that solar pv is not reliable year long and that the batteries to make it seasonally reliable are wildly expensive. I wonder if they have had issues trying to solve a problem so many people insist doesn't exist.
- jacquesm 1y ago
  > I've found that lots of people get viscerally mad when it's pointed out that solar pv is not reliable year long 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.
  - buckle8017 1y ago
    > 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. You acknowledged that you're wrong in the very same paragraph. I suspect you're misunderstanding what the word reliable means in this context.
    - magicalhippo 1y ago
      The word you're looking for is viable. 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.
mastax 1y ago
Im shocked, and a little incredulous, thats its feasible to heat soil to 600C.
duffpkg 1y ago
I have a home in the southwest that is off grid and runs on solar plus lifepo3 batteries. It has been 5+ years now. My cost per kwh is below $0.008 as of today including all capital and maintenance. These numbers get a bit complicated, for example I run the AC much colder than I would if I was paying more for it. I have extra fridges and freezers I probably wouldn't if I had to pay higher per kwh. I "throw away" a lot of power too that I am not counting when the batteries fill up. 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.
- aaron695 1y ago
  [dead]
- simianparrot 1y ago
  How many hours of maintenance do spend on it on average per week? Or perhaps more appropriate if it’s rarely, per year?
  - hedora 1y ago
    Not the person you are asking, but our system is 5 years old and has required two hours of intervention work (zero scheduled maintenance). 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.
ziofill 1y ago
missed opportunity to call it “dirt cheap”
- SlowTao 1y ago
  See if they are looking for marketing people. If so, you're hired!
Animats 1y ago
The US National Renewable Energy Laboratory was working on energy storage involving a silo of hot sand.[1] But that was probably cut by the Trump Administration.[2] 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-duration-energy-storage-in-hot-sand/ https://www.solarpaces.org/nrel-results-support-cheap-long-d... [2] https://www.wenatcheeworld.com/news/northwest/trump-congressional-republicans-propose-big-cuts-for-western-renewable-energy-labs/article_9fe5ce72-377d-4029-b9b4-2ca5d71108e8.html https://www.wenatcheeworld.com/news/northwest/trump-congress...
hedora 1y ago
I wonder if any heat pumps can emit the 600C they target for the storage mounds. If the COP of such a device was over 1, they could store more heat energy than the PV’s emit in wattage. Also, they could use the waste cold air to cool the solar panels, which increases their efficiency.
alhirzel 1y ago
Snow load is not mentioned when using horizontal panels. In higher latitudes, solar is relatively uncommon because of the sunlight deficit in winter. Panels that are deployed are usually placed at an incline equal to the latitude (or even vertically) to capitalize on free snow shedding and to regularize/maximize year-round minimum output (i.e. bring up winter by bringing down summer). Mounting solar panels flat is sensible from the standpoint of this technology (no solar output needed in the winter, that's what the storage is for!) but may be breaking a lot of ground (and panels) with horizontal panels in snow country.
thelastgallon 1y ago
Between this and CATLs $10/KWh Sodium battery, its game over for fossil fuel based economies.
theLegionWithin 1y ago
ok but what's the upfront and maintenance costs for the buried bricks & pipes system? LNG is standardized, it's readily available, and existing infrastructure already exists. how is this new system better?

99 points by theptip 1y ago

Why go throught the extra solar -> electricity -> resistive heating -> soil instead of directly doing solar -> heating a metal rod -> soil? Cutting out the conversion steps should be more efficient.

3eb7988a1663 1y ago
If the electricity is free, efficiency does not matter that much. The capex of the storage system might matter a lot more. In which case, heating up a big mass might be more economically feasible than battery installations.

nabla9 1y ago

> The purpose of Standard Thermal is to make energy from solar PV available 24/7/365 at a price that is competitive with US natural gas. 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?

hvb2 1y ago
> Just basic district level geothermal heat pumps do the same. This doesn't with everywhere though? Because of geology?

ZeroGravitas 1y ago

They skipped a few real competitors that'll shrink their market: 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.

conradev 1y ago
Yeah, Form Energy exists to basically disprove this: 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 Form, like the authors, agrees that Lithium-ion is great for intra-day cycling and not suitable for is seasonal storage. Unlike the authors, Form believes it can engineer chemical storage with the requisite properties. Form’s batteries have something like 10 days of capacity relative to the size of their inverters.
- ZeroGravitas 1y ago
  Form's basic idea is that low round trip efficiency can work as long as it's cheaper enough. 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.

scblock 1y ago

Energy storage yes, electricity storage no. Very limited utility and questionable use of solar PV, which has about a 20% conversion efficiency of solar energy to electricity. Seems like a lot of extra steps to make heat.

3eb7988a1663 1y ago
One of the biggest uses of residential energy is heating/cooling. Especially in winter months where PV generation is significantly lower (I have seen numbers of 2-5x summer generation), having "free" heat could be quite valuable. 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.

iamthemonster 1y ago

Absolutely superb. The 'hot bricks in a box' concept of very high temperature thermal energy storage has been really coming into its own with the fall of solar PV costs, and it's quite suitable for industrial consumers of medium temperature heat. There's also a heated granite storage silo in Scandinavia that's recently gone into operation. The rate of heat transfer in the heat storage material is a classic constraint. 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.

throwaway81523 1y ago

This is confusing, why PV to heat the dirt? Black paint will do it from sunlight directly. Or circulating hot liquid. Way cheaper and more efficient than PV at collecting heat from the sun.

buckle8017 1y ago
There's very few materials cheaper than dirt. Solid state solar panels should be more reliable than any hydronic system. Though I suppose their heat recovery system is probably hydronic.
hackernudes 1y ago
My understanding is this is for excess PV capacity. But I think they should address this! Their plan is to heat deep inside a big pile of dirt using resistive heating elements and then pump the heat out in pipes. Maybe it's hard or expensive to add solar heating into the system? But why couldn't they pump it in? Maybe they don't have extra space because the dirt mound is covered in PV panels.
theptip 1y ago
Water will be limited to 100C, and tanks are going to be way more expensive to maintain. 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.
- fabbbbb 1y ago
  Liquid doesn’t need to mean water? Traditional solar thermal systems use special liquids that can get way more hot than 100C.
  - cyberax 1y ago
    You can get to around 200C with oil-based media. But oil goes bad pretty quickly, and it leaches tons of crap out of everything. Above that temperature, you need molten salts or liquid metals that are extremely corrosive. Your other option is to use gaseous media instead.

metalman 1y ago

late to the game, there are villiage/town scale thermal batteries operating in northern scandinavia useing sand inside a conventinal style insulated silos, everything is off the shelf civil engineering equipment. any company offering similar tech will need a sharp pencil. I live off grid and am considering adding thermal storage as part of my system to allow for unatended background heating while on the road in the winter, where 2500 liters of water will provide pre heat for domestic hot water, and as a semi passive thermal siphon for area heating

jeffbee 1y ago
The University of California (Berkeley) is also building thermal storage. Currently they are excavating a 20-million-liter tank under one of the athletic fields.

jacquesm 1y ago

I've done a lot of spreadsheets on this kind of solution, but on a slightly smaller scale: a single family home. While it will work for a while it is not enough to meaningfully offset the seasonal cycle which is the thing that needs solving. Storing energy for a few days up to two weeks is (relatively) easy, storing it cheaply for up to 6 months is very hard unless you are willing to invest massively offsetting much of your savings. The pile of rock required to heat an average home for a couple of weeks handily outweighs the house itself. And that's without a double conversion, it is used and stays as heat, the idea was to moderate the leakage upwards as a source of heat by blowing air in a controlled manner rather than to convert it again. 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.

myself248 1y ago
Isn't it cheaper to just buy more panels, enough to meet your winter needs? Then who cares if they sit mostly idle for most of summer; energy not used is harmless. Then your storage model becomes "a cloudy week" rather than "a whole season", and the storage scale changes significantly.
- hvb2 1y ago
  In almost all cases you lack the area for doing that. And that's not even considering exposure, as in winter most north facing panels on a roof won't get any direct sun because it's lower on the horizon
- buckle8017 1y ago
  The panels themselves are cheap and getting cheaper. 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.
  - 1y ago

bilsbie 1y ago

Mods, I submitted this exact url four days ago: https://news.ycombinator.com/item?id=44963261 https://news.ycombinator.com/item?id=44963261 Why didn’t this submission redirect to mine?

epistasis 1y ago
HN doesn't work that way. Resubmissions are allowed, especially high quality ones that don't get traction. But links to prior submissions are always added, and usually only if there's good conversation about the prior link.
- bilsbie 1y ago
  So because it didn’t have traction they created a new discussion?
  - epistasis 1y ago
    Once the mods invited me to resubmit one of my own links by email a few days after I had posted, because they thought it was a good link but it didn't get traction the first time. (Unfortunately I didn't see the email until many months later, IIRC...)

zackify 1y ago

Batteries are getting crazy inexpensive. You can get 16kwh for $1850 now https://www.youtube.com/watch?v=7bShGUPU3TQ https://www.youtube.com/watch?v=7bShGUPU3TQ

deleted 1y ago
[deleted]
roarcher 1y ago
...if you want to take your chances with cheap junk in a safety-critical application. I watched about 3 minutes of that video and the number of issues that guy ran into was disturbing. You'd have to be nuts to put that thing in your house.
- 3eb7988a1663 1y ago
  I am in no position to install a battery system, but if I were, I would definitely build a little cinder-block shed to hold the array. Offset that a good distance from standing structures and instant piece of mind.
jacquesm 1y ago
Please do not give that guy more exposure than he already has, his advice is going to get someone killed one of these days. He knows just enough to be dangerous.
- Squeeeez 1y ago
  As my grandma used to say, regarding speaking a foreign language: "enough to get you beat up, not enough to get them to stop"
  - Squeeeez 1y ago
    Why the downvotes? 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!

buckle8017 1y ago

I've found that lots of people get viscerally mad when it's pointed out that solar pv is not reliable year long and that the batteries to make it seasonally reliable are wildly expensive. I wonder if they have had issues trying to solve a problem so many people insist doesn't exist.

jacquesm 1y ago
> I've found that lots of people get viscerally mad when it's pointed out that solar pv is not reliable year long 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.
- buckle8017 1y ago
  > 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. You acknowledged that you're wrong in the very same paragraph. I suspect you're misunderstanding what the word reliable means in this context.
  - magicalhippo 1y ago
    The word you're looking for is viable. 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.

mastax 1y ago

Im shocked, and a little incredulous, thats its feasible to heat soil to 600C.

duffpkg 1y ago

I have a home in the southwest that is off grid and runs on solar plus lifepo3 batteries. It has been 5+ years now. My cost per kwh is below $0.008 as of today including all capital and maintenance. These numbers get a bit complicated, for example I run the AC much colder than I would if I was paying more for it. I have extra fridges and freezers I probably wouldn't if I had to pay higher per kwh. I "throw away" a lot of power too that I am not counting when the batteries fill up. 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.

aaron695 1y ago
[dead]
simianparrot 1y ago
How many hours of maintenance do spend on it on average per week? Or perhaps more appropriate if it’s rarely, per year?
- hedora 1y ago
  Not the person you are asking, but our system is 5 years old and has required two hours of intervention work (zero scheduled maintenance). 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.

ziofill 1y ago

missed opportunity to call it “dirt cheap”

SlowTao 1y ago
See if they are looking for marketing people. If so, you're hired!

Animats 1y ago

The US National Renewable Energy Laboratory was working on energy storage involving a silo of hot sand.[1] But that was probably cut by the Trump Administration.[2] 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-duration-energy-storage-in-hot-sand/ https://www.solarpaces.org/nrel-results-support-cheap-long-d... [2] https://www.wenatcheeworld.com/news/northwest/trump-congressional-republicans-propose-big-cuts-for-western-renewable-energy-labs/article_9fe5ce72-377d-4029-b9b4-2ca5d71108e8.html https://www.wenatcheeworld.com/news/northwest/trump-congress...

hedora 1y ago

I wonder if any heat pumps can emit the 600C they target for the storage mounds. If the COP of such a device was over 1, they could store more heat energy than the PV’s emit in wattage. Also, they could use the waste cold air to cool the solar panels, which increases their efficiency.

alhirzel 1y ago

Snow load is not mentioned when using horizontal panels. In higher latitudes, solar is relatively uncommon because of the sunlight deficit in winter. Panels that are deployed are usually placed at an incline equal to the latitude (or even vertically) to capitalize on free snow shedding and to regularize/maximize year-round minimum output (i.e. bring up winter by bringing down summer). Mounting solar panels flat is sensible from the standpoint of this technology (no solar output needed in the winter, that's what the storage is for!) but may be breaking a lot of ground (and panels) with horizontal panels in snow country.

thelastgallon 1y ago

Between this and CATLs $10/KWh Sodium battery, its game over for fossil fuel based economies.

theLegionWithin 1y ago

ok but what's the upfront and maintenance costs for the buried bricks & pipes system? LNG is standardized, it's readily available, and existing infrastructure already exists. how is this new system better?