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Hey. You said you do off grid. I have a question. I own a 5 kW on grid setup for net metering. Works fine but now I want to use backups. I have two options, eit

Hey. You said you do off grid. I have a question. I own a 5 kW on grid setup for net metering. Works fine but now I want to use backups. I have two options, either lithium 100ah 48v which is expensive or 12v 200ah x 4 to make 48v. Cheaper but limited life because the home load would be on it entirely. I dont know. The calculation of kWh checks out to be 100ah x 48v = 4800wh. And for lead acid 200ah x 12v x 2= 4800wh. What do you suggest or is there something I am thinking incorrectly... space is not an issue BTW.

walrus01 6y ago
google "DIY powerwall" if you're up for a bit of a technical challenge. 4 x 12V 200Ah isn't big enough for most houses, unless it's like a cabin in the woods somewhere. and you're right that the cycle life of those and cost is high. but commercial li-ion based solutions are also expensive. However, if you can keep them at 80-85% state of charge, and rarely if ever discharge them below 30%, they should have lifespans 5-6x longer than the lead acid solution. in either solution you can't really consider the full volts * Ah capacity of the battery to be usable. If you were to ever use all of the watt-hours in a 12V 200Ah battery you'd kill it, you never want to go below 20% state of charge... so to be conservative the actual capacity of a single battery is something like: 12 * 200 = 2400 Wh, then (2400 * 0.70) = 1680Wh.
guerby 6y ago
Current LFP battery prices are around $120 per kWh delivered: I just ordered 14 kWh (48V 16S) for 1700 USD delivered. This is cheaper than an Apple laptop. A quarter of the price paid is shipping since it comes directly from China so source price is already under $100/kWh. A recent test by Will Prowse: https://www.youtube.com/watch?v=3U4ZfQ_IToI https://www.youtube.com/watch?v=3U4ZfQ_IToI $433 280Ah LiFePO4 Cells Tested: Cheaper than lead acid! Many people have the same good experience with these kind of cells: https://diysolarforum.com/ https://diysolarforum.com/ Added: 14 kWh will run a 20 Watt laptop for a month.
- driverdan 6y ago
  Where are you getting new LFP batteries for that price?
  - Peretus 6y ago
    There is a fellow down in Port St. Lucie Florida that has launched a 100ah LiFePO4 with a 10-year warranty for ~ $550usd each. I saw his shop in person when I purchased some solar from him and was quite impressed with the work they've done and the research and testing that has gone into their products. I had already purchased my batteries by the time I discovered his product or I would have purchased from him: https://outlandsolar.com/ https://outlandsolar.com/ My partner and I live aboard a 41ft sailboat and both work remotely as programmers. I installed 1920w of solar on the boat and get approximately 3.5-4.5kwh per day in output, depending on which way we are oriented while at anchor. I installed 600ah of LiFePO4 batteries @ 12v and when combined with that amount of solar, we have pretty much all the power we need. We frequently cook with an air fryer and have a dishwasher on the boat that we run daily-- all off solar.
    - driverdan 6y ago
      That price is really good. I'm curious what cells they used.
      - Peretus 6y ago
        I'm pretty sure they're Sinopoly cells, but I'm no expert. The BMS they use is quite impressive too, from what I could tell. While I was there in the shop they had a battery cut open and I was able to see inside.
    - cmason 6y ago
      Where/how do you fit ~2000W of solar on your boat? That’s impressive.
      - Peretus 6y ago

walrus01 6y ago

google "DIY powerwall" if you're up for a bit of a technical challenge. 4 x 12V 200Ah isn't big enough for most houses, unless it's like a cabin in the woods somewhere. and you're right that the cycle life of those and cost is high. but commercial li-ion based solutions are also expensive. However, if you can keep them at 80-85% state of charge, and rarely if ever discharge them below 30%, they should have lifespans 5-6x longer than the lead acid solution. in either solution you can't really consider the full volts * Ah capacity of the battery to be usable. If you were to ever use all of the watt-hours in a 12V 200Ah battery you'd kill it, you never want to go below 20% state of charge... so to be conservative the actual capacity of a single battery is something like: 12 * 200 = 2400 Wh, then (2400 * 0.70) = 1680Wh.

guerby 6y ago

Current LFP battery prices are around $120 per kWh delivered: I just ordered 14 kWh (48V 16S) for 1700 USD delivered. This is cheaper than an Apple laptop. A quarter of the price paid is shipping since it comes directly from China so source price is already under $100/kWh. A recent test by Will Prowse: https://www.youtube.com/watch?v=3U4ZfQ_IToI https://www.youtube.com/watch?v=3U4ZfQ_IToI $433 280Ah LiFePO4 Cells Tested: Cheaper than lead acid! Many people have the same good experience with these kind of cells: https://diysolarforum.com/ https://diysolarforum.com/ Added: 14 kWh will run a 20 Watt laptop for a month.

driverdan 6y ago
Where are you getting new LFP batteries for that price?
- Peretus 6y ago
  There is a fellow down in Port St. Lucie Florida that has launched a 100ah LiFePO4 with a 10-year warranty for ~ $550usd each. I saw his shop in person when I purchased some solar from him and was quite impressed with the work they've done and the research and testing that has gone into their products. I had already purchased my batteries by the time I discovered his product or I would have purchased from him: https://outlandsolar.com/ https://outlandsolar.com/ My partner and I live aboard a 41ft sailboat and both work remotely as programmers. I installed 1920w of solar on the boat and get approximately 3.5-4.5kwh per day in output, depending on which way we are oriented while at anchor. I installed 600ah of LiFePO4 batteries @ 12v and when combined with that amount of solar, we have pretty much all the power we need. We frequently cook with an air fryer and have a dishwasher on the boat that we run daily-- all off solar.
  - driverdan 6y ago
    That price is really good. I'm curious what cells they used.
    - Peretus 6y ago
      I'm pretty sure they're Sinopoly cells, but I'm no expert. The BMS they use is quite impressive too, from what I could tell. While I was there in the shop they had a battery cut open and I was able to see inside.
  - cmason 6y ago
    Where/how do you fit ~2000W of solar on your boat? That’s impressive.
    - Peretus 6y ago