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I have been in a few "DIY Powerwall" groups which usually source the cells from old laptop batteries and this community is very aware of the fire danger so they

I have been in a few "DIY Powerwall" groups which usually source the cells from old laptop batteries and this community is very aware of the fire danger so they come up with hilarous solutions for their home racks like having plastic bags full of sand above the batteries so when they catch fire the plastic melts and the Lithium cells get covered in sand. Most people do try to have the cells on the side of - or inside outdoor metal sheds to minimize the fire damage

bob1029 3y ago
I think the entire premise is cursed. That is to say, if you are finding yourself with a need to store more than maybe one KWh of energy in a residential setting, you might need to reevaluate your overall architecture. A generator, while not ideal ecologically, is a perfect abstraction in engineering terms. Especially generators connected to pipelines. Those are the real win in safety - the energy is only received on site the exact moment it is required. Some trade offs with resilience but you don't have to go that far. On site diesel and LPG have proven safe and reliable as well. For me the batteries are just about transferring the load. If you need run time, you should find yourself a generator. For non emergency, non-UPS scenarios, sure you could maybe plan an off grid setup. But I think we'd be mixing use cases a little bit with this angle. Beyond a certain point, I don't think there exists a safe way to store certain embodiments of energy on site. Sandbags or no.
- jacquesm 3y ago
  I can see the other side of it too: some people would like to be carbon neutral one way or another, and with net metering laws under attack everywhere (because the government would like to tack on tax on your own generated power) DIY powerwalls are an efficient alternative if you don't look at the risks involved. Once you add risk into the equation it gets a lot more complex in a hurry. But that's the main driver behind all of these 18650 recycling projects. I built a fairly large pack for an e-bike (170 cells), the batteries cost some money but the peace of mind that gave was well worth it to me. But I actually can afford it. If you can't it isn't long before you realize that electronics are cheap but cells are expensive so if you can get a cheap source for cells suddenly you can build that powerwall. But to do so safely will more than offset the money saved on refurbished cells. And the workmanship requirements are also not exactly easy to come by and all it takes is a little mistake to have a fairly spectacular result.
  - geek_at 3y ago
    Very true and let's not forget the DIY Powerwall people are the real recyclers of old batteries. They are also the ones who ae in front of all auction houses that sell batteries of totaled EVs and give them a second life.
- csours 3y ago
  I think neighborhood batteries make a lot more sense - spread out the cost, if every neighborhood had a reasonable sized battery installation, the grid would be FAR more stable.
  - bluGill 3y ago
    Utility scale batteries Someplace outside the city. It doesn't really gain much to put them in a neighborhood and costs a lot more. When you are running on battery you need oversized inverters as you need to cover the worst case of the whole neighborhood. The more area your battery covers the less overbuilding you need because the closer you are to average. House scale battery works better (but has obvious safety issues) because if there is a power outage most people can shed a lot of load without discomfort and thus get by with must smaller batteries.
- bluGill 3y ago
  My home lpg tank (800 gallons) is far enough from my house that even if the worst case where the whole tanks opens up and starts on fire (I don't see how this is possible, but that is the only way I can think of to get enough O2 in the tank for a fire), my house is still safe. A home powerwall that was similarly far form other buildings should be safe enough. Look at utility scale battery installations and it is clear they have a lot of separate units, so fire in one won't spread to the next (or at least the fire department will be able to put it out before it spreads to more than a couple). However most people don't have that much space in their yard.

bob1029 3y ago

I think the entire premise is cursed. That is to say, if you are finding yourself with a need to store more than maybe one KWh of energy in a residential setting, you might need to reevaluate your overall architecture. A generator, while not ideal ecologically, is a perfect abstraction in engineering terms. Especially generators connected to pipelines. Those are the real win in safety - the energy is only received on site the exact moment it is required. Some trade offs with resilience but you don't have to go that far. On site diesel and LPG have proven safe and reliable as well. For me the batteries are just about transferring the load. If you need run time, you should find yourself a generator. For non emergency, non-UPS scenarios, sure you could maybe plan an off grid setup. But I think we'd be mixing use cases a little bit with this angle. Beyond a certain point, I don't think there exists a safe way to store certain embodiments of energy on site. Sandbags or no.

jacquesm 3y ago
I can see the other side of it too: some people would like to be carbon neutral one way or another, and with net metering laws under attack everywhere (because the government would like to tack on tax on your own generated power) DIY powerwalls are an efficient alternative if you don't look at the risks involved. Once you add risk into the equation it gets a lot more complex in a hurry. But that's the main driver behind all of these 18650 recycling projects. I built a fairly large pack for an e-bike (170 cells), the batteries cost some money but the peace of mind that gave was well worth it to me. But I actually can afford it. If you can't it isn't long before you realize that electronics are cheap but cells are expensive so if you can get a cheap source for cells suddenly you can build that powerwall. But to do so safely will more than offset the money saved on refurbished cells. And the workmanship requirements are also not exactly easy to come by and all it takes is a little mistake to have a fairly spectacular result.
- geek_at 3y ago
  Very true and let's not forget the DIY Powerwall people are the real recyclers of old batteries. They are also the ones who ae in front of all auction houses that sell batteries of totaled EVs and give them a second life.
csours 3y ago
I think neighborhood batteries make a lot more sense - spread out the cost, if every neighborhood had a reasonable sized battery installation, the grid would be FAR more stable.
- bluGill 3y ago
  Utility scale batteries Someplace outside the city. It doesn't really gain much to put them in a neighborhood and costs a lot more. When you are running on battery you need oversized inverters as you need to cover the worst case of the whole neighborhood. The more area your battery covers the less overbuilding you need because the closer you are to average. House scale battery works better (but has obvious safety issues) because if there is a power outage most people can shed a lot of load without discomfort and thus get by with must smaller batteries.
bluGill 3y ago
My home lpg tank (800 gallons) is far enough from my house that even if the worst case where the whole tanks opens up and starts on fire (I don't see how this is possible, but that is the only way I can think of to get enough O2 in the tank for a fire), my house is still safe. A home powerwall that was similarly far form other buildings should be safe enough. Look at utility scale battery installations and it is clear they have a lot of separate units, so fire in one won't spread to the next (or at least the fire department will be able to put it out before it spreads to more than a couple). However most people don't have that much space in their yard.