Adding more batteries to an existing off-grid system?

**organic farmer** · 08-16-2016, 08:32 AM

There is a thought that you current old batteries will cause the new batteries to age prematurely.

**solarix** · 08-16-2016, 09:36 AM

The charging characteristics of the new batteries will be different than the old ones (even if the same make and model) leading to non-optimum charging. The old ones will be overcharging while the new ones will be undercharged. You won't get a full charge capacity out of either one and their lifetime will be reduced. Its the perennial battery problem and what else you gonna do?

**SunEagle** · 08-16-2016, 09:37 AM

While most used FLA type batteries will shorten the life of new FLA batteries (due to build up resistances) those SPzS seem to be built a little different and may not have the same affect on new ones when you add them to old ones if they have not been discharged very deeply.

They are very impressive but I would imagine also very expensive compared to something like the Trojan 2V 720Ah battery.

But then again I am not a battery expert by any means.

**JohnnyR** · 08-25-2016, 02:22 AM

Thanks for responses, but how much shorter will it make the new batteries lives?

**Sunking** · 08-25-2016, 11:14 AM

Originally posted by JohnnyR

Can someone explain why it is not recommended to add more batteries to an existing off grid system? I have 24 Werbat 8 SPzS 720 batteries which on a sunny day are fully charged by mid afternoon so a lot of solar production is going to waste. Why can i not just increase the battery bank to give me a greater reserve for the evenings?

Adding batteries does NOT eliminate waste silly, it compounds the issue and makes it worse.

All Off grid systems have to be over sized with a lot of waste especially during the longer days of summer. It is one of the reasons you should never go off grid. Doing so makes you a heavy polluter, waste resources your kids cannot use, and cost you a fortune. That is what you chose to do, waste energy, waste resources and throw money away. when you went off-grid.

The solution is getting rid of some of your panels, or use more electricity. Adding batteries does nothing. You could double the capacity of the batteries, and by noon they too will be recharged. Your panels only replace what you use each day.

If you use say 2 Kwh each day, but your panels can generate up to 4 Kwh each day. So if you have a 10 Kwh battery, use 2 Kwh takes you down to 8 Kwh, then the panels generate 2 Kwh to bring the battery back up to 10 Kwh.

So you get the bright idea to increase the size of your battery to 15 Kwh. So you use 2 Kwh which takes the batteries down to 13 Kwh, then the panels replace the 2 Kwh to bring it back up to 15 Kwh.

Nothing changed except you lost a lot of money buying batteries you have no use for. What will make you even happier is when you added the new batteries wil only last as long as th eold ones so you get to spend a lot of money replacing even more batteries. That will make you real happy loosingg g alot more money faster. It should make you happy because you went off-grid to waste money and resources.

**Sunking** · 08-25-2016, 11:33 AM

Don't let the door hit you in the butt on the way out. If you went elsewhere, you would not have got the correct answer in a short time. All other sites are ran by companies who will tell you what you want to hear, then sell the solution to you sucker. I just saved you a ton of cash. You should be saying Thank You not FU.

You have a Non Problem or Make Believe problem. All off grid systems have to be over sized by design. .

**J.P.M.** · 08-25-2016, 12:11 PM

Originally posted by JohnnyR

You've said me jack sh*t bud. Just been rude so I'm saying FU

Guess you can't please everyone.

Was it something SK wrote (that does happen once in a while), or did you miss your meds or Wheaties today ?

**organic farmer** · 08-25-2016, 08:20 PM

The ideal sweet spot for battery capacity is how many days you need to go on battery charge without recharging.

PoCo normally goes dark every year for four to five days in my town, once maybe twice a year. Since I have lived here, I have never experienced any PoCo outage to last 6 days here. There are always news reports of towns losing power for longer. But my town is not very remote, so we always get our grid back up in less than 6 days.

Therefore the ideal battery size in our town is determined by daily need X 5 days.

With such a battery capacity the usual monthly PoCo outages once or twice a month of 6 hours to 2 days duration are normal hiccups that do not become a crisis.

That is how you determine battery size.

An unusual power outage crisis is inherently difficult to plan for. By the nature of being unusual events. you can not easily predict how long the PoCo will take to get their heads out of their arses. It is easiest to look at normal Poco outages, what normally happens every month 6 hour to 2 days outages, and what normally happens every year in this case 4 to 5 day outages, and you plan from there.

**Mike90250** · 08-26-2016, 02:45 AM

At some point, instead of buying more and more batteries, getting a generator & charger to keep a smaller bank, becomes more efficient, As outages get longer, and fuel costs go up, solar becomes a better way to recharge

**organic farmer** · 08-26-2016, 08:29 AM

During our first 8 years living here. We did not have a generator. Most homes here do. But we just tried to live on grid with the outages. We were tempted a few times to get a generator, but talking to neighbors, the amount of fuel generators consume is a lot. You may commonly go through $1000 / year [of more] in fuel for the darn thing.

That was what eventually convinced us to go with solar.

**ddrbnn** · 10-26-2021, 04:39 PM

Originally posted by Sunking

Adding batteries does NOT eliminate waste silly, it compounds the issue and makes it worse.

All Off grid systems have to be over sized with a lot of waste especially during the longer days of summer. It is one of the reasons you should never go off grid. Doing so makes you a heavy polluter, waste resources your kids cannot use, and cost you a fortune. That is what you chose to do, waste energy, waste resources and throw money away. when you went off-grid.

The solution is getting rid of some of your panels, or use more electricity. Adding batteries does nothing. You could double the capacity of the batteries, and by noon they too will be recharged. Your panels only replace what you use each day.

If you use say 2 Kwh each day, but your panels can generate up to 4 Kwh each day. So if you have a 10 Kwh battery, use 2 Kwh takes you down to 8 Kwh, then the panels generate 2 Kwh to bring the battery back up to 10 Kwh.

So you get the bright idea to increase the size of your battery to 15 Kwh. So you use 2 Kwh which takes the batteries down to 13 Kwh, then the panels replace the 2 Kwh to bring it back up to 15 Kwh.

Nothing changed except you lost a lot of money buying batteries you have no use for. What will make you even happier is when you added the new batteries wil only last as long as th eold ones so you get to spend a lot of money replacing even more batteries. That will make you real happy loosingg g alot more money faster. It should make you happy because you went off-grid to waste money and resources.

Sunking I share a very similar question as the OP's, but i'm pretty sure i have a good reason for wanting another battery. I'm living in a van with a few solar panels up top. My problem is that my batteries are filled up to 100% during the day and I'm running out of juice in the night, so in my case I think it makes sense to add another battery. I have a friend that has the same batt's as me and just dumped them for some newer ones -- would I be able to add one of my friend's used batteries to my existing system and have that benefit me? Is there something I don't know about how that will degrade my other batteries even more?

**SunEagle** · 10-26-2021, 05:03 PM

Originally posted by ddrbnn

Sunking I share a very similar question as the OP's, but i'm pretty sure i have a good reason for wanting another battery. I'm living in a van with a few solar panels up top. My problem is that my batteries are filled up to 100% during the day and I'm running out of juice in the night, so in my case I think it makes sense to add another battery. I have a friend that has the same batt's as me and just dumped them for some newer ones -- would I be able to add one of my friend's used batteries to my existing system and have that benefit me? Is there something I don't know about how that will degrade my other batteries even more?

Anytime you add an old battery to a new system the entire system drops down the the health of the oldest battery. Then you end up with an early death.

On top of adding a battery you also have to make sure you have enough charging amps from your existing solar panels. If not then you need to add additional panel wattage to increase your charging amps going into the battery system.

But another solution is to find a way to reduce your nightly load and not kill off your batteries.

**ddrbnn** · 10-26-2021, 05:12 PM

So the reason my batteries are getting too drained at night is because they’re also getting old. The question i’ve been having a hard time finding the answer to is: Does it make sense for me to add an old battery to an existing battery bank (that is already composed of old batteries)?

**Mike90250** · 10-26-2021, 06:43 PM

how many batteries in your existing battery bank ?

Adding more batteries to an existing off-grid system?

Adding more batteries to an existing off-grid system?

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