5 ms·

This seems like it would be complicated by the many different chemistries and form factors available, and the wide variability between packs depending on how ol

by elihu 6y ago

This seems like it would be complicated by the many different chemistries and form factors available, and the wide variability between packs depending on how old or well-taken-care-of they are. If one were to set out to create a single large battery out of massive array of extremely heterogenous individual battery packs, what would that look like? I guess you could pair each battery pack with its own individual charger and inverter so they can all feed into some common bus at a given voltage and frequency -- sort of like the "microinverter" setup for solar panels. You could cut down on heterogeneity by only using one type of battery in one installation, and trade batteries between installations or even with external companies so everyone can get matching sets. Sort of like the card game Pit. You could also bin the batteries by quality, like how manufacturers of vacuum tubes have a hard time replicated electrical characteristics exactly from one tube to the next, so they sort them into bins after manufacture and ship them out as matched sets that came from the same bin.

Syonyk 6y ago
Any plan that involves taking packs apart and testing the pieces, then reassembling them, is useless for grid storage. You see it in the "DIY Powerwall" communities, when a decent number of the cells coming in are quite literally junk (fully discharged, shorted, etc), but anything like that particular group does, at scale, is a battery warehouse fire waiting for a time to happen. There's actually not as much variability as you might be inclined to think - in terms of pack voltages. China is their own set of problems I'm not familiar with, but in the rest of the world, most modern EVs are using a 3.7V nominal chemistry (2.5V/cell fully discharged, 4.2V/cell fully charged), and almost always in a 96S pack of some capacity or another (so about 400V fully charged, again, give or take a bit). If you're dealing with 3.7V cells in 96S packs, the rest of the pack details simply don't matter beyond individual pack management and balancing. The voltages of the storage rail are compatible across all of them. Some may be 50Ah packs off a PHEV, some may be 250Ah packs off a long range BEV, but they all operate at the same general range of voltages, and so can be put on the same voltage rail once they match. You'd want per pack fusing (probably a contactor assembly that can report current, and disconnect a misbehaving pack if the current goes too high), but at that point, if you can talk to the BMS on each of the packs, they'll just work. The only real gotcha with this is getting the pack voltages lined up with the main voltage rail in the first place. If the rail is sitting up at 390V (almost fully charged) and you put a 250V pack (fully discharged and then some) on it, the internal resistance isn't enough to prevent you from pushing an awful lot of amps into the pack and likely damaging something. So you'd have to have a separate set of chargers to get the packs close to the main rail voltage, but once it's within 5-10V, hook it up and it will equalize out safely. If the facility is somewhat climate controlled, you likely don't need to hook up the cooling loops for the packs (if they have them) - but you might want to, because the difference between a failed cell and a runaway pack is typically going to be the cooling loop. If a cell fails and runs away, a pack with good coolant flow probably won't propagate. You might not want to be near it, but... it probably won't burn the facility down. Without cooling flow, welp. Whole pack will just run away, one cell at a time, and that's the sort of thing you want to watch from a very safe distance. The practical limit on pack life is going to be how evenly matched the cell groups are. If the pack is worn evenly, all the cell groups will generaly decrease in voltage equally. But as the pack wears out, if one cell group loses capacity more than others (it may be a hot spot in the pack), you start having to cut off the discharge as that group hits the low voltage cutoff (while the bulk pack voltage is still acceptable). If this starts tripping the pack off too early, it's not going to be useful on the rail, and it's probably time to recycle it. Really, though, it comes back to how much risk you're willing to tolerate. An individual car battery pack is likely to be perfectly fine. A warehouse of 5000 of them, out of used/wrecked/who-knows-what cars... that's a little bit scary. If one of them runs away and isn't contained, you have a warehouse full of packs running away, venting violently toxic chemicals where there's no good option. If the vent plumes are not on fire, you stand a good chance of wonderful things like HF (there are less friendly things to humans, but not many). If the vent plumes are on fire, the resulting gasses may be mildly less toxic, but now you have what amounts to a giant hazmat warehouse fire. I'm really not sure what the right balance is, but with the challenges and risks of second life EV batteries, I honestly don't expect them to be particularly popular with any of the big energy companies.
- elihu 6y ago
  I was kind of imagining the battery packs being used more-or-less as-is, maybe broken down into individual modules, but not down to the individual cell and reassembled. That just seems like a lot of work, and you'd probably get bad results if you mixed cells with incompatible charge/discharge curves or whatever. I could imagine a facility where each pack is separate by a non-flammable barrier (concrete, firebrick, or whatever works in this case) to stop one out-of-control pack from igniting its neighbors. And then larger groups of packs being segregated from each other with thicker fire barriers, and so on. And coolant constantly pumped through the facility: the batteries, and maybe even the fireproof barriers between packs. The whole facility can be located away from cities or towns, so fires don't cause (as much) of a health hazard. Maybe a ventilation and filtration system that can capture the smoke and filter the worst pollutants in the event of a fire. This whole thing sound kind of messy to build, but then again it's just a centralized version of the related idea of using people's cars connected to smart bi-directional chargers as a backup power source for the grid. If it can (theoretically) be done with a bunch of geographically distributed individual cars, then it ought to be possible to do something similar in a centralized way with whatever safety precautions are needed.
- leoedin 6y ago
  Currently grid scale battery storage is often deployed in shipping containers, which has the advantage of providing some level of isolation between packs, and also means they can be spaced out over a bigger area.
  - Syonyk 6y ago
    That makes a lot of sense. If you put a few dozen packs in a TEU, you can disconnect that module and fog it with water if stuff goes wrong. A deluge on a pack running away will usually pull enough heat out to keep it from propagating. Now, you've ruined a container of packs, most likely (though auto packs are going to be decently waterproof), but you've prevented burning down a warehouse of packs.
sokoloff 6y ago
Some modern LEDs are also binned parts, as are CPUs.
rektide 6y ago
Making heterogenous individual packs sounds like an absolute disaster. That's why this is various car companies teaming up with specific folk: because they'll have big quantities of cells from each individual vehicle they get, and there will only be so many different types of cell. There will be big supplies of a couple different cells, ready to go in to applications of all different sorts. As it so happens, there's already a lot of agreement. Many many cells are either 18 mm, 21mm or 28 mm diameter cylinders & 650-700 mm long. "18650" cell is very common. 28650 used to be a "big" cell but it's not around as much I feel like. "2170" is a "21700" that is increasingly popular. Most of these cells have similar charge behavior, of applying a fixed amps up to a point, perhaps with temperature sensors to detect problems/slow down, and then a slower finishing charge, that ends around 4.2V per cell. Using solar grid-tie micro-inverters would probably work fine to join together a bunch of different packs.
- Reason077 6y ago
  And now, Tesla are developing an even bigger "4680" cell: https://evannex.com/blogs/news/tesla-s-4680-cell-is-a-stroke-of-genius-sandy-munro https://evannex.com/blogs/news/tesla-s-4680-cell-is-a-stroke...
  - CyanLite4 6y ago
    A little too much fanboyism with that link.
- barney54 6y ago
  Only Tesla uses cylindrical cells such as 18650s or 2170s. The other EV makers use prismatic cells or pouch cells.
  - rektide 6y ago
    I'd meant to mention pouch/prismatic cells, thanks. I had been under the impression that some of the big manufacturers had started using cylindrical cells, but I can't seem to find any evidence. Oops!
  - 6y ago
0_____0 6y ago
I've been looking for something like this for a while and haven't found one or had the time to develop it myself. Engineers out there take note. The business case for such a device is contingent on people actually utilizing these retired EV packs though, which may become harder to source as the manufacturers get better about reacquiring them for recycling.
djrogers 6y ago
Nahh, forget trying to bin cells and build new packs - just use them as is. Sell a PowerWall type thing made with a single 60/70/85KwH pack pulled from a vehicle after its downgraded to ~70% capacity. design your vehicle packs from day one for a second life as stationary energy storage, where size and weight don’t matter.
- yowlingcat 6y ago
  I think this kind of circular EV economy is the real big money logistics idea. There is, as you've astutely pointed out, no reason why this protocol shouldn't exist industry-wide. But, how do you solve the materials problem that closes the loop: somehow recycling old EV raw materials into new EV materials? AFAIK there still aren't great SOTA solutions to this. At some point, it's hard to have a nice closed cycle of production and waste-recyling for ecological and cost optimization purposes.
  - adrianN 6y ago
    Right now the market for recycling EV batteries is still pretty small because there just aren't that many old EVs around. I bet recycling will increase in a couple years.

by elihu 6y ago

Syonyk 6y ago

Any plan that involves taking packs apart and testing the pieces, then reassembling them, is useless for grid storage. You see it in the "DIY Powerwall" communities, when a decent number of the cells coming in are quite literally junk (fully discharged, shorted, etc), but anything like that particular group does, at scale, is a battery warehouse fire waiting for a time to happen. There's actually not as much variability as you might be inclined to think - in terms of pack voltages. China is their own set of problems I'm not familiar with, but in the rest of the world, most modern EVs are using a 3.7V nominal chemistry (2.5V/cell fully discharged, 4.2V/cell fully charged), and almost always in a 96S pack of some capacity or another (so about 400V fully charged, again, give or take a bit). If you're dealing with 3.7V cells in 96S packs, the rest of the pack details simply don't matter beyond individual pack management and balancing. The voltages of the storage rail are compatible across all of them. Some may be 50Ah packs off a PHEV, some may be 250Ah packs off a long range BEV, but they all operate at the same general range of voltages, and so can be put on the same voltage rail once they match. You'd want per pack fusing (probably a contactor assembly that can report current, and disconnect a misbehaving pack if the current goes too high), but at that point, if you can talk to the BMS on each of the packs, they'll just work. The only real gotcha with this is getting the pack voltages lined up with the main voltage rail in the first place. If the rail is sitting up at 390V (almost fully charged) and you put a 250V pack (fully discharged and then some) on it, the internal resistance isn't enough to prevent you from pushing an awful lot of amps into the pack and likely damaging something. So you'd have to have a separate set of chargers to get the packs close to the main rail voltage, but once it's within 5-10V, hook it up and it will equalize out safely. If the facility is somewhat climate controlled, you likely don't need to hook up the cooling loops for the packs (if they have them) - but you might want to, because the difference between a failed cell and a runaway pack is typically going to be the cooling loop. If a cell fails and runs away, a pack with good coolant flow probably won't propagate. You might not want to be near it, but... it probably won't burn the facility down. Without cooling flow, welp. Whole pack will just run away, one cell at a time, and that's the sort of thing you want to watch from a very safe distance. The practical limit on pack life is going to be how evenly matched the cell groups are. If the pack is worn evenly, all the cell groups will generaly decrease in voltage equally. But as the pack wears out, if one cell group loses capacity more than others (it may be a hot spot in the pack), you start having to cut off the discharge as that group hits the low voltage cutoff (while the bulk pack voltage is still acceptable). If this starts tripping the pack off too early, it's not going to be useful on the rail, and it's probably time to recycle it. Really, though, it comes back to how much risk you're willing to tolerate. An individual car battery pack is likely to be perfectly fine. A warehouse of 5000 of them, out of used/wrecked/who-knows-what cars... that's a little bit scary. If one of them runs away and isn't contained, you have a warehouse full of packs running away, venting violently toxic chemicals where there's no good option. If the vent plumes are not on fire, you stand a good chance of wonderful things like HF (there are less friendly things to humans, but not many). If the vent plumes are on fire, the resulting gasses may be mildly less toxic, but now you have what amounts to a giant hazmat warehouse fire. I'm really not sure what the right balance is, but with the challenges and risks of second life EV batteries, I honestly don't expect them to be particularly popular with any of the big energy companies.

elihu 6y ago
I was kind of imagining the battery packs being used more-or-less as-is, maybe broken down into individual modules, but not down to the individual cell and reassembled. That just seems like a lot of work, and you'd probably get bad results if you mixed cells with incompatible charge/discharge curves or whatever. I could imagine a facility where each pack is separate by a non-flammable barrier (concrete, firebrick, or whatever works in this case) to stop one out-of-control pack from igniting its neighbors. And then larger groups of packs being segregated from each other with thicker fire barriers, and so on. And coolant constantly pumped through the facility: the batteries, and maybe even the fireproof barriers between packs. The whole facility can be located away from cities or towns, so fires don't cause (as much) of a health hazard. Maybe a ventilation and filtration system that can capture the smoke and filter the worst pollutants in the event of a fire. This whole thing sound kind of messy to build, but then again it's just a centralized version of the related idea of using people's cars connected to smart bi-directional chargers as a backup power source for the grid. If it can (theoretically) be done with a bunch of geographically distributed individual cars, then it ought to be possible to do something similar in a centralized way with whatever safety precautions are needed.
leoedin 6y ago
Currently grid scale battery storage is often deployed in shipping containers, which has the advantage of providing some level of isolation between packs, and also means they can be spaced out over a bigger area.
- Syonyk 6y ago
  That makes a lot of sense. If you put a few dozen packs in a TEU, you can disconnect that module and fog it with water if stuff goes wrong. A deluge on a pack running away will usually pull enough heat out to keep it from propagating. Now, you've ruined a container of packs, most likely (though auto packs are going to be decently waterproof), but you've prevented burning down a warehouse of packs.

sokoloff 6y ago

Some modern LEDs are also binned parts, as are CPUs.

rektide 6y ago

Making heterogenous individual packs sounds like an absolute disaster. That's why this is various car companies teaming up with specific folk: because they'll have big quantities of cells from each individual vehicle they get, and there will only be so many different types of cell. There will be big supplies of a couple different cells, ready to go in to applications of all different sorts. As it so happens, there's already a lot of agreement. Many many cells are either 18 mm, 21mm or 28 mm diameter cylinders & 650-700 mm long. "18650" cell is very common. 28650 used to be a "big" cell but it's not around as much I feel like. "2170" is a "21700" that is increasingly popular. Most of these cells have similar charge behavior, of applying a fixed amps up to a point, perhaps with temperature sensors to detect problems/slow down, and then a slower finishing charge, that ends around 4.2V per cell. Using solar grid-tie micro-inverters would probably work fine to join together a bunch of different packs.

Reason077 6y ago
And now, Tesla are developing an even bigger "4680" cell: https://evannex.com/blogs/news/tesla-s-4680-cell-is-a-stroke-of-genius-sandy-munro https://evannex.com/blogs/news/tesla-s-4680-cell-is-a-stroke...
- CyanLite4 6y ago
  A little too much fanboyism with that link.
barney54 6y ago
Only Tesla uses cylindrical cells such as 18650s or 2170s. The other EV makers use prismatic cells or pouch cells.
- rektide 6y ago
  I'd meant to mention pouch/prismatic cells, thanks. I had been under the impression that some of the big manufacturers had started using cylindrical cells, but I can't seem to find any evidence. Oops!
- 6y ago

0_____0 6y ago

I've been looking for something like this for a while and haven't found one or had the time to develop it myself. Engineers out there take note. The business case for such a device is contingent on people actually utilizing these retired EV packs though, which may become harder to source as the manufacturers get better about reacquiring them for recycling.

djrogers 6y ago

Nahh, forget trying to bin cells and build new packs - just use them as is. Sell a PowerWall type thing made with a single 60/70/85KwH pack pulled from a vehicle after its downgraded to ~70% capacity. design your vehicle packs from day one for a second life as stationary energy storage, where size and weight don’t matter.

yowlingcat 6y ago
I think this kind of circular EV economy is the real big money logistics idea. There is, as you've astutely pointed out, no reason why this protocol shouldn't exist industry-wide. But, how do you solve the materials problem that closes the loop: somehow recycling old EV raw materials into new EV materials? AFAIK there still aren't great SOTA solutions to this. At some point, it's hard to have a nice closed cycle of production and waste-recyling for ecological and cost optimization purposes.
- adrianN 6y ago
  Right now the market for recycling EV batteries is still pretty small because there just aren't that many old EVs around. I bet recycling will increase in a couple years.