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Saturday, April 30, 2016

Battery decisions

I just pulled the dead 12 volt deep discharge battery from my sailboat. It got me thinking. Well, the first thing I thought was: darn, those things are heavy. The second thing that came to mind was the fact that my household battery bank is getting on in years.

My household solar electric system is of moderate size. Storage consists of 12 golf cart sized batteries. Currently I'm using good quality Interstate brand. Trojans are good too, but since Interstate has local dealers that's what I went with. The big advantage of dealing locally is that I don't have to pay for shipping. Since shipping is based on weight and batteries are mostly lead, it would get pricey quickly.

Lead acid batteries are really old technology. They haven't advanced all that much in the last 100 years or so. Battery storage has always been the Achilles heel of alternative energy. While lead acid battery storage is adequate for off-grid homes, it doesn't scale well to power grid size. There are some massive battery bank systems out there for things like phone and Internet systems, but there are none large enough to power a big city.

At least, not until fairly recently. Battery technology is making some huge leaps. There's always been interesting things invented in laboratories, but those technologies never made it out of the lab. Now there are huge factories turning out high capacity batteries for everything form cell phones to electric cars. There's real economic incentives for cheap battery storage. Those clever ideas from the labs are starting to show up in factories.

It's almost at the point where it would make sense to replace my 19th century electrical storage system with something from the 21st century. Almost.

The house system should be able to last for another year or two. By then it might make economic sense to try something new. Of course, there's also the possibility that as new battery technology takes hold, lead acid will be deeply discounted. That would be fine too, as leas acid has proven to be good enough for my needs.



  1. SB,

    If you don't mind sharing, I'd be interested in some numbers related to your current solar system. Batteries, PV panels, capacity, average monthly usage, etc. and whether you're truly off-grid or hybrid. Just trying to get one more idea of the size of a working system.


    1. Started about 23 years ago with 8 -48 watt panels. Added another 200 watts years later.

      12 golf cart batteries wired to 24 volts. Still using the original 2500 watt Trace inverter. It can surge for 7500 watts for things like starting electric motors.

      Have an outback charge controller. Originally the panel array was wired to 24 volts, but when the new panel was added that was rewired to 48. The Outback controller can reduce the charge to 24 volts for the batteries.

      Grid power is available but it's used mostly like a back up generator would be used. There's no way to backfeed into the grid. When I first installed my system that wasn't a good option.

      Hope that thumbnail sketch helps.

    2. Yeah, that sheds some light. A few questions:

      1. Rough house square footage that system supports?

      2. In terms of capacity, do you find you always have plenty, just enough, or often struggle to scrimp to avoid running out, etc?

      3. How often and how many batteries have you had to replace (roughly)?

      4. What was the reason (and pros/cons) of rewiring the panels such that they didn't match the battery voltage anymore?

      5. If you did upgrade your battery bank, post-lottery winnings, what would you switch to?

    3. 1. 1500 sq ft?
      2. Runs about 80% of my needs. We get some long dark times.
      3. All batteries are replaced at the same time. They last about 10 years, which isn't too bad for golf cart types.
      4. Two big advantages for going to 48 volts. The 24 volt panel I added later wasn't a perfect voltage match so didn't work all that well. In series I got full advantage of the panel. The second advantage is less power loss from the panel array to the battery bank.

      5. Haven't really done all the research, but am interested in the Battery Wall.

    4. Assume you're talking about Tesla's Powerwall. Either way, a couple of interesting links:

      Elon Musk introducing the product:

      News on manufacturing and delivery:

  2. look into the Optima battery.Have one in my truck thats lasted 12 yrs.A bit pricey,but you never have any maintainence

  3. One of the main reasons I scrapped my off grid power system which was built in 1999 was the inadequacy of the purpose built deep cycle batteries I bought. They required a lot of maintenance, and at the very best only lasted three years. They were heavy, difficult to dispose of, and didn't really hold enough of a charge to justify the expenses of the system. I wound up just using the generator and letting the inverter and solar cells just sit there.

    1. Do you think the reason for the lack of usefulness was 1) the state of technology at the time, 2) poor solar system design, or 3) ?

    2. I'm glad I did all my own research and my own work. It was a PITA but worth it in the long run.

      Glad I stuck with off the shelf golf cart batteries. They are about as heavy as I care to move on my own.

  4. Another set of lead batteries might outlast you, so if they're cheap enough, they'd be worthwhile. Obamacare may kill us all off before long anyway! lol

  5. Start keeping an eye on this new development, Zinc-Manganese batteries.