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Comment by dieselgate

21 hours ago

Aren’t lead acid batteries great for this purpose? They have advantage over lithium in stationary setups because weight is not an issue and they can be “daisy chained” many many times. I’m unaware of more cutting edge alternatives and the way the electrical companies handle solar is confusing IME

11 comments

dieselgate

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rcxdude  21 hours ago

Lead acid batteries don't much like being cycled heavily. Even the ones explicitly designed for it (the average car battery is not) have about a tenth of the lifespan of lithium ion.

LiFePO4 is probably the chemistry best suited to it ATM. Lasts a long time, more stable, pretty cheap, and just a bit less energy density than other lithium ion options. Sodium-ion is looking promising but only just entering the market AFAIK.

  • mnw21cam  2 hours ago

    A tenth is perhaps an exaggeration. It depends on how you count your lifespan.

    A lead-acid battery mainly ages by cycle count. If you keep a decent quality battery charged up, and don't regularly discharge it too much, then there are claims they will last ten years. If you discharge them excessively each day, then you'll kill them really quickly.

    A LiFePO4 battery has a quoted cycle count. But really what matters is simply elapsed time - the battery will last about ten years if it isn't abused, and you'll be hard-pressed to actually do that many cycles in that ten years. It ages mainly by elapsed time, not cycle count.

    I used to argue that for an off-grid solar solution, you should get lead-acid batteries with capacity so that you are normally never discharging below 70%, and that this was still cheaper than getting LiFePO4 batteries with smaller capacity that you would discharge down to 20% each night. The lead-acid would then give you a larger reserve capacity for those instances where the weather is foul for a bit longer than normal and you don't get meaningful charging.

    However, since then LiFePO4 batteries have continued to decrease in price, there are new Sodium batteries available now, and I haven't done the calculations again - the best option may have switched over, or it may be so close that it doesn't really matter which one you choose.

  • ElevenLathe  19 hours ago

    Does this mean LA would be a feasible option for longer-cycle storage, IOW keeping a reserve topped up most of the year for those duldrums weeks with little solar or wind?

    • adgjlsfhk1  9 hours ago

      For long term storage, the right batteries don't exist yet (commercially). The good options are going to be one of sodium ion, flow batteries, or thermal batteries.

    • rcxdude  19 hours ago

      I think it still loses out to lithium-ion on cost/kWh, and batteries in general are still a bit expensive for storage on the timescale of months.

    • Schiendelman  10 hours ago

      In addition to the fact that it doesn't really work better for that either, it's just not as safe as lithium iron phosphate.

sieve  20 hours ago

I dumped my 24V dual LA battery setup for a single 24V LFP battery for my inverter/UPS backup. LFP supposedly has a 10-15y life based on the 4-5000 charge cycles most cells claim. Sodium ion is on the way as well. My setup gives me about 10-12h of backup for critical loads (my PC, lights, fans).

I have a 5 kWp solar plant that produces ~25kWh per day, but it is grid-tied. I considered a hybrid setup with LFP battery back up, but decided to separate the two systems to avoid a single point of failure.