What to do?

Re: What to do?

The Watts are the same no matter how the array is configured.
The question is: what are the actual specifications of these "24 Volt" panels? For them to work all in parallel on a 24 Volt system they need a Vmp around 35.
The good part is that with the Outback FM80 MPPT controller you can configure them as two is series and probably be assured of having enough Voltage to fully charge the battery bank.

Basics of array configuration: http://forum.solar-electric.com/showthread.php?16241-Different-Panel-Configurations-on-an-MPPT-Controller

Re: What to do?

Billy wrote: »

they are Renesola 156 series panels at 250watt each.
The vmpp=36.6 and the voc = 41.9 or 44.8 ?

The Vmp is the Voltage that matters for charging. In this case 36.6 is sufficient for a 24 Volt system.

However you could also configure them as strings of two in series; the higher Voltage would reduce Voltage drop in wiring if that is a concern. The Voc (44.8 most likely; two in series 89.6) would still not exceed the controller's 150 max even on the coldest day.

Another reason I mention this is that a 1000 Watt array would be four of these panels, and if you put them all in parallel you should use a combiner box with fuses or breakers for each panel. Configured as two parallel strings of two in series the over-current protection is not needed.

(Note: some so-called "24 Volt" panels have a Vmp of 30 or even 26 and are not suitable for 24 Volt systems in singles. These panels are actually designed for GT systems where array Vmp is very high achieved by putting several in series.)

Re: What to do?

For some reason your attachment isn't there.
So let's try mine: four PV's wired as two parallel strings of two in series.