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Monday, December 12, 2016

Good old lead acid batteries


There are two common types of home solar electric systems. There's totally grid connected. They are pretty straight forward. Solar panels are directly connected to grid. The energy generated is credited towards your monthly bill. Once it's installed the homeowner doesn't have to think about it. It just works.

The other common type is for off-grid systems. The solar panels feed your own battery bank. You are responsible for managing your power use and storage. It's more hands on, but you are independent from the grid and never get a utility bill.

There are some hybrids of the two major systems. Some grid-tied systems have small battery banks for emergency use during blackouts. Otherwise, even though their panels were generating power, they could not use it.

I've got a simple system that's set up to be mostly off-grid. The solar panels cannot back feed into the grid. However, I can change the battery bank from the grid. My configuration normally uses the grid like a backup generator.

Lately I've been using the grid a bit more than I'd like. My house battery bank is on its last legs. It's been in service for almost 11 years, a long time for golf cart batteries. Now a smart person would have put a little bit of money aside over the last 11 years for when the replacement comes due. Yep, that's what a smart person would do. I wasn't that smart.

By spring I should have the funds to replace the battery bank. I'm using 12, 6 volt golf cart batteries. They are wired up to provide 24 volts which supplies an inverter that makes normal house AC. The advantage of golf cart batteries is that they are common and can be carried by one person -a strong person, but not a freakishly strong person. They can be swapped out in a day.

There have been some advances in battery technology. Batteries have always been one of the big limiting factors of alternative energy. When I first put in solar electric I'd hoped batteries would have improved by now. They have, but not at a price point that makes sense to me. Maybe Tesla's gigafactory will eventually bring the prices down low enough for me to consider them in the future.

For now I'll be going back to good old fashioned flooded lead acid batteries. They lack the energy density of the new batteries, but it doesn't really matter. It's not like in an electric car that has to haul the weight of the batteries. My battery bank sits quietly in a box in the basement. Every few months I pop the cover and check the water level in the batteries and top them off if necessary.

Even though I've had to use the grid a bit more, my bills are still very low. Since my house was designed for off-grid power it uses energy efficiently. That being said, it will be nice to have a full power battery system once more.

-Sixbears

14 comments:

  1. Around here T-105,s are 113$ so 12 will be a chunk.

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    1. That's about right. Not too bad if you average it out over 11 years.

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  2. midnite visit to your local golf vendor?

    Wildflower

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    1. Let's see, the average golf cart has 6 batteries, so two golf carts. Should be able to just drive them away. :)

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  3. every so often fork lifts and golf carts by law have to change still perfectly good batteries for new ones

    will used work for you?

    Wildflower

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    1. They usually aren't worth it for bigger battery banks. I'd look them over for a shed or a small cabin.

      A battery bank is only as good as its weakest cell. Getting all batteries from the same batch, all new, saves grief in the long run.

      Maybe I'm too lazy to play around lifting heavy batteries over and over again to sort out the weak from the strong ones.

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    2. Say Wildflower, do you have a source for that? I'm trying to think of something other than medical equipment that the gov would mandate fresh batteries for. (maybe a California or Massachusetts thing?) I did a Google search, nothing comes up on first page.

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    3. It's less lazy than common sense to get the batteries right the first time around. I've also experienced the random reliability of second hand cells and done my back swapping dud ones out. You can get lucky ... or not!

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    4. My back doesn't want me to take the chance. :)

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  4. My son has solar panels and batteries that can be used for emergencies or to save on the utility bill.

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  5. Hi Six,
    Because I do use some solar everyday I am always conscious about energy usage. My entire house lights with CFL's except for the (9) Outdoor Security Lights. They don't activate with CFL's, I'm guessing the watt draw is to low for them to activate and turn on?
    Your thoughts!

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    Replies
    1. Might depend on your inverter. Some have a sleep mode that drops to low energy usage. They usually have a setting that can adjusted to the wattage needed to fully power it up. Yours might be set too high to trigger activation.

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