Best way to grow (or replace) this battery bank?

Chris Miller

We're currently running only 1000 watts of panel and 8 Trojan T-105-RE's in series to create a 48 v system. This is for our off-grid homestead in SW Texas.

We decided to bite the bullet and upgrade everything. We're going with 15 250 watt Canadian Solar panels and we're looking to add batteries to match the solar.

I thought about 2 more strings of T-105-RE's but then i'm dealing with 24 batteries, 3 strings, etc. Just doesn't seem ideal to me.

So what I was wondering is... is there a battery out there that is similar in price to 16 of the T-105's but that would allow me to run one string? I'm not afraid to go with a bigger battery - i just want something quality that will last. I really know nothing about battery technology but for me, staying on top watering the batteries isn't ideal either. Is there a better option?

Thoughts?

Thanks!

Photowhit

Re: Best way to grow (or replace) this battery bank?

I think you could respond to some of the questions on your prior thread here:

Age and use of your batteries would be an unknown we would want information about, you don't typically add new batteries to old.

So if your planning on replacing the batteries, as stated in the previous thread, you could look at forklift batteries, or L16s. You could find a forklift battery in the size your looking for NAWS doesn't list any 48 volt versions, but I'm sure they would order them for you. Here is where I ordered mine, Please note the different amp hour ratings dependent of discharge rate. For solar and batteries like the T105 a 20 hour rate is used.

Chris Miller

Re: Best way to grow (or replace) this battery bank?

Photowhit wrote: »

I think you could respond to some of the questions on your prior thread here:

Age and use of your batteries would be an unknown we would want information about, you don't typically add new batteries to old.

So if your planning on replacing the batteries, as stated in the previous thread, you could look at forklift batteries, or L16s. You could find a forklift battery in the size your looking for NAWS doesn't list any 48 volt versions, but I'm sure they would order them for you. Here is where I ordered mine, Please note the different amp hour ratings dependent of discharge rate. For solar and batteries like the T105 a 20 hour rate is used.

Thanks for the reply. I did answer that question, here:

http://forum.solar-electric.com/showthread.php?19537-Help-me-expand-this-system&p=153429#post153429

This is where I get lost though. L16's vs forklift vs rolls surrette, etc. What's the best way to go?

vtmaps

Re: Best way to grow (or replace) this battery bank?

Chris Miller wrote: »

I really know nothing about battery technology but for me, staying on top watering the batteries isn't ideal either. Is there a better option?

Unfortunately you are the power company and the customer. If the power company doesn't stay on top of things the customer will be unhappy and also get a major increase in their power bill.

There are automatic watering systems. There are automatic generator starters that can keep a battery bank from getting too discharged. The more you rely on automatic things, the more complex your system is. The more complex your system is, the more ways things can go wrong, and the greater your disappointment when they do go wrong. Complex systems often fail dramatically. For example: your watering system fails to work and the over/under watered batteries are not holding a charge very well. The generator runs more and more to make up for the battery's weakness. Finally the generator fails and the lights go out. Then you notice.

Bottom line: you must be eternally vigilant no matter how simple or complex your system is.

--vtMaps

Photowhit

Re: Best way to grow (or replace) this battery bank?

Chris Miller wrote: »

Thanks for the reply. I did answer that question, here:

Yes, but there are other questions there about your system. If you've read through the FAQ's on Batteries most of the general information would be there. If you want info that is more helpful to your system, your use, solar isolation, ability to load shift, max use time of year, and other info would be of value.

Chris Miller wrote: »

This is where I get lost though. L16's vs forklift vs rolls surrette, etc. What's the best way to go?

IMO, mass produced batteries will be the cheapest per amp hour used. The Trojans, a premium golf cart battery I would expect 5 years minimum and often 7 or 8 years of use. Rolls L16 size 6 volts I would expect minimum of 7 years and likely 10-12 (have heard of 15) Rolls 2 volt L16 size cells I would expect 10 years and likely 15. NAWS says their Crown Forklift batteries "...In a typical solar electric system they will normally last for about 20 years or more. We have been selling these for over 25 years and have the utmost confidence in their reliability." I expect 15 years out of my GB lift/traction battery. My battery lives outside so a bit harsh during the summer, though I hope to build a berm shelter for it.

northerner

Re: Best way to grow (or replace) this battery bank?

Chris Miller wrote: »

So what I was wondering is... is there a battery out there that is similar in price to 16 of the T-105's but that would allow me to run one string? I'm not afraid to go with a bigger battery - i just want something quality that will last. I really know nothing about battery technology but for me, staying on top watering the batteries isn't ideal either. Is there a better option?

Thoughts?

Thanks!

It's best to size the battery (and bank) to your system, such that you have not more than 8 to 12 individual batteries. The exception to that is if you plan to go with 2 volt cells, where you would need 24 for a 48 volt system. I would also look to see what is available locally at a reasonable cost, as shipping can be expensive for batteries (hazardous goods). In my case, I went with Trojan L16's, even though they were a bit more expensive. The dealer I bought from dropped them off at my place for no extra charge, as it was along their delivery route, (about 5 hours out of Edmonton). That more than made up the extra cost in shipping.

Chris Miller

Re: Best way to grow (or replace) this battery bank?

northerner wrote: »

It's best to size the battery (and bank) to your system, such that you have not more than 8 to 12 individual batteries. The exception to that is if you plan to go with 2 volt cells, where you would need 24 for a 48 volt system.

I guess this is where I am confused. I see no way of doing that with any of the batteries i've looked at with my 48v system. I would need 24 of the 2 volts, or 16 of the 6 volt L16 style to get up close to the 700+ Ah I need to match the 3750 watts of solar i'm putting in.

Someone should write a book on this stuff. The information online seems a bit contradictory across the various forums, solar equipment sites, etc.

vtmaps

Re: Best way to grow (or replace) this battery bank?

Chris Miller wrote: »

I guess this is where I am confused. I see no way of doing that with any of the batteries i've looked at with my 48v system.

Keep looking. you have many choices. Have you looked through the NAWS site? You can buy 6 volt batteries in a variety of ah ratings, and there are also 4 volt batteries that may work for you. --vtMaps

edit: http://www.solar-electric.com/6cs-25ps.html

Chris Miller

Re: Best way to grow (or replace) this battery bank?

vtmaps wrote: »

Keep looking. you have many choices. Have you looked through the NAWS site? You can buy 6 volt batteries in a variety of ah ratings, and there are also 4 volt batteries that may work for you. --vtMaps

edit: http://www.solar-electric.com/6cs-25ps.html

I have looked thru all of the batteries but perhaps I am just not quite ready to wrap my head around owning $10,000 in batteries. Looks like we'll go ahead with the 16 additional T-105-RE's and hope for the best. At around $100 each locally it just makes the best sense for us. There are many people out here living completely off grid who have run multiple strings of T-105's for 6-8 years without an issue. Hopefully we'll be as lucky.

The other option is to just change the system to 12 or 24 volt. I honestly don't know the benefits of going with one voltage over another I just know that when I was reading over the manual for the outback FM-80 it seemed like I was more limited with 12 and 24 volt... and that I could have more panel on the system if I went with 48 volt? That's the way I remember it anyway.

Off to find the complete idiots guide.... i'm obviously not as familiar with all of this as I thought. lol

Cariboocoot

Re: Best way to grow (or replace) this battery bank?

Math check:
3750 Watts (not KWH) @ 77% efficiency / 48 Volts = 60 Amps. Battery bank size: 600 Amp hours @ 48 Volts.

System sizing check:
Pick battery bank first, based on expected Watt hour consumption. Round up to nearest available battery size.
Match solar array and charge controller to that battery bank size. Trying to do it from the array to the battery to the loads is a headache, as you have seen.

As far as which batteries to get ...
Check local prices. Whichever type you can get the equivalent V @ Amp hours in for the best money is the one to go for.

You will not see a lot of performance difference between brands, but you will see some price difference.

Some examples (all Crown):
GC2 220 Amp hour @ 6 Volt $120 http://www.solar-electric.com/cr225am6vode.html eight in series * three parallel = 660 Amp hours @ 48 Volts, 24 batteries $2,880
L16 330 Amp hour @ 6 Volt $234 http://www.solar-electric.com/cr330am6vode.html eight in series * two parallel = 660 Amp hours @ 48 Volts, 16 batteries $3,744
2VC 625 Amp hour @ 2 Volt $652 http://www.solar-electric.com/repoba2vo625.html 24 in series = 625 Amp hours @ 48 Volts, 24 batteries $15,648
F24 635 Amp hour @ 24 Volt $3,072 http://www.solar-electric.com/crinba24vo63.html two in series = 635 Amp hours @ 48 Volts, 2 batteries $6,144

As always, the GC2/T105 size comes out cheapest for the power. Why consider the others? Fewer cells to check, fewer connections to make and keep up. With the forklift batteries you could rely on the deeper DOD capability and "downsize" for the Watt hours: http://www.solar-electric.com/crinba24vo53.html 530 Amp hours @ 24 Volts, two batteries $5,700 (about the same power as 848 Amp hours of 'standard' deep cycles).
But this is still nearly twice the GC2's cost.

Not telling you what to buy, just showing you how to analyze the choices. Part of that analysis, however, is judging for yourself if the extra money is a good trade-off for having fewer cells and connections to look after. (Also note that multiple battery strings should have a fuse each, so that's a tad more cost too.)

Cariboocoot

Re: Best way to grow (or replace) this battery bank?

Chris Miller wrote: »

The other option is to just change the system to 12 or 24 volt. I honestly don't know the benefits of going with one voltage over another I just know that when I was reading over the manual for the outback FM-80 it seemed like I was more limited with 12 and 24 volt... and that I could have more panel on the system if I went with 48 volt? That's the way I remember it anyway.

Because a charge controller can output its maximum current (80 Amps in this case) at any Voltage. So roughly you get:
12V * 80A = 960 Watts
24V * 80A = 1920 Watts
48V * 80A = 3840 Watts

The advantage of higher Voltage system is that the same Watts are delivered with less current, meaning less power loss to heating so they run slightly more efficiently. This can allow some down-sizing of wiring, so you save a bit of money there as well.

If you really need to store a lot of Watt hours, higher Voltage is the way to go (as opposed to more Amp hours). This should be explained in that sticky about battery Voltage and equivalent power. If it's not clear I'll have another go at it.

Photowhit

Re: Best way to grow (or replace) this battery bank?

Chris Miller wrote: »

...but perhaps I am just not quite ready to wrap my head around owning $10,000 in batteries. Looks like we'll go ahead with the 16 additional T-105-RE's and hope for the best. At around $100 each locally it just makes the best sense for us. There are many people out here living completely off grid who have run multiple strings of T-105's for 6-8 years without an issue...

This is not a bad choice, since you already have an investment in your current 8 batteries, $100 is a great price for Trojans($150 + core here), I wouldn't mix Trojans with different brands as they have different maintenance requirements!!!

For the record I did give you a link for a 800 Amp Hour 48V battery that can be had for under $5000 delivered(No core charge), did you not find that?

All batteries are built of cells for lead acid 2 volt cells, so if you look at it as a battery bank, a single string 48 volt bank will have 24 cells to water regardless of having individually cased cells or a single battery.

Other than 'Coots advantages, larger cells tend to last longer, check battery FAQ's, Also a forklift/Traction type battery will have interconnected cells, so less to setup and less connections to check (I haven't heard of the 'bonded' connections failing, but I guess they could)

Cariboocoot

Re: Best way to grow (or replace) this battery bank?

Photowhit wrote: »

All batteries are built of cells for lead acid 2 volt cells, so if you look at it as a battery bank, a single string 48 volt bank will have 24 cells to water regardless of having individually cased cells or a single battery.

The exception to this is Trojan's 2 Volt cells which are the 6 Volt batteries reconfigured so that the three individual cells in the unit are connected in parallel to increase Amp hours and reduce Voltage (6 Volt @ 320 Amp hours becomes 2 Volts @ 960 Amp hours). They're something to avoid in my opinion.