Battery bank options

[SportBiker]

I have a few ~250w 36v (10s) battery packs.

I want to make a house bank battery for my mobile office / camping van.

I also have a panel I am planing on mounting to the roof of the van. Stats below.

The main requirement is to run an inverter.

Running things at 36v seems like it will be tricky because a buck / boost mppt charge controller would be needed, and few inverters will work from ~36v.

I am leaning to reconfiguring the batteries to ~24v but not sure if I should go with 7s or if 8s may be better. Then I could use a common buck mppt controller and there are a lot of 24v inverters.

Would 8s be gentler on the cells for a ~24v operating range? Full utilisation of cell capacity isn't necessary, I'd rather have a pack that will last longer.

Thanks for any ideas.

Panel stats:
SW-02-5004US 07-2012
SW 235 mono / Version 2.0
PERFORMANCE UNDER STANDARD TEST CONDITIONS (STC)* SW 235
PERFORMANCE AT 800 W/m2, NOCT, AM 1.5
Maximum power
Pmax
235 Wp
Maximum power
Pmax
170.9 Wp
Open circuit voltage Voc
Short circuit current Isc
*STC: 1000W/m2, 25°C, AM 1.5
THERMAL CHARACTERISTICS TC Isc
37.5 V 8.19 A
0.004 %/K -0.45 %/K
Open circuit voltage
Short circuit current
SW 235
Voc 34.0 V Isc 6.60 A
Maximum power point voltage
Vmpp
30.3 V
Maximum power point voltage
Vmpp
27.5 V
Maximum power point current
Impp
7.77A
Maximum power point current
Impp
6.22 A

 

[flippy]

8s should work fine. for a 24v MPPT controller.

you can get a lot of inverters with the mpt built in....

 

[john61ct]

What is the capacity in Ah @24V nominal?

By 250W did you mean Wh (watt hours)?

 

[SportBiker]

Yes, they are 250 watt hour packs.

 

[john61ct]

So around 10Ah at 24V.

Not good for much beyond recharging a phone and a couple LEDs.

I consider 200+Ah to be a small House bank for off-grid use.

Couple Deka lead GCs from Sam's Club would last 4-5 years or more of daily deep cycling if well cared for, maybe $190.

 

[SportBiker]

I have five of them and they where almost free.

I figure I could easily get 1kwh of capacity. I don't think I can get enough solar on the roof to charge much more than that each day.

 

[john61ct]

1kWh is 83Ah at 12V, 41 at 24V.

Figure 2-300W panels in summer or if tilting.

Basic guideline is fill the roof fit as many watts as possible.

You'll end up getting a bigger bank anyway, pretty sure.