Panel Mixing, please comment on my proposal.

machineman

I need to add more capacity to my off grid system. (24V, 440ah batterys, CC XW60-150 mppt)

Existing 4 panels in series total: Vmp 72.8v, Imp 11.27 (total 820w)
Proposed 2nd string of 4 panels in series total: Vmp 70.16, Imp 11.53 (total 809w)

So with adding the 2nd proposed string in parrallel with the existing string:

Total combined current will be 22.8amp travelling from my roof 90ft to CC on 8ga. I calculate the Voltage drop <5%. - GOOD
Also I calculate I will boost my chargeing capability from 6% to 13% of the battery capacity (using 28.8v in the calc) - GOOD
My XW CC can handle 60amp and up to 150V. I calculate 56.6amps max (without factoring efficiency loss) - GOOD

So I will have a 2.64Vmp difference between the parrallel strings which will be combined on the roof. Is this OK? - ??

Thanks.

BB.

Re: Panel Mixing, please comment on my proposal.

From what I can see--Should work fine... The ~2.64 volts out of ~70 volts is not going to be a problem.

-Bill

Cariboocoot

Re: Panel Mixing, please comment on my proposal.

A Vmp difference of 2.64 on ~70 Volt strings is very small: roughly 3%. It won't be noticed.

If the 5% V-drop is acceptable to you, okay.

Your array total will be 1629 Watts, and probably produce a maximum current of 52 Amps to the batteries. That's just under 12% for the 440 Amp hours.

Looks workable to me.

machineman

Re: Panel Mixing, please comment on my proposal.

Ok thanks. This is good news, its been tough to find panels close to my odd ball Evergreen ES-A string Vmp. So I don't need any diodes or anything between the strings?

Cariboocoot

Re: Panel Mixing, please comment on my proposal.

machineman wrote: »

Ok thanks. This is good news, its been tough to find panels close to my odd ball Evergreen ES-A string Vmp. So I don't need any diodes or anything between the strings?

Nope. With only two strings you don't even need fuses on them.