NEWBIE on Best hookup - series or parallel?

System

Hi All-
This is probably newbie question and searched forum but could not find guidance so here goes. Parts for system include 15ea 60w panels w Voc=95, Isc=1.2, Vmp=60, Imp=1 with a 48 V 300Ah battery bank and 3 1500w double conversion pure sine wave inverters (that's why 48v). Looks like barely meet min charge current so 240/48v switcher is used for bulk charging off main. Switcher wants ~200 ~300vdc so could run 15 panels parallel to charge controller (not on hand) or 3 sets of 5 series panels into switcher (when off mains). Am not wedded to a particular array voltage, just 46-52vdc for inverters. Which would be the most efficient panel arrangement with MPPT (also not on hand yet). Thanks very much for upfront help.

Dick

System2

Re: NEWBIE on Best hookup - series or parallel?

Higher voltage.

There is a reason the Electrical Grid is operated at thousands, some sections even millions of volts.

Higher voltage = fewer losses.

Of course there other issues otherwise our household voltage would be 120KV instead of 120v but generally higher voltage, within spec, is better.

So set the system up so every thing is operating at the highest reasonable voltage.

For panels that means series connection until the max voltage of panels is met (likely many hundreds of volts) or the max voltage of MPPT controller is met. That is likely going to be not the max operating voltage but the max Open Circuit voltage it can handle from the panel.

Do not over voltage equipment!

High is good, too high just gets really expensive and all bets are off when equipment fails due to high voltage or current, even fires could be possible, though a good design will prevent that, best to not go there.

System2

Re: NEWBIE on Best hookup - series or parallel?

Thanks, that's what I suspected. Will aim for dc input used by switcher ( ~275v) and parallel the strings for amps. Only 900w but will get me started. Later.
Dick

niel

Re: NEWBIE on Best hookup - series or parallel?

now i am not too sure of your controller, but they usually have voltage limits that they can operate at and if it is an mppt style controller then they tend to operate less efficient when the input/output voltages are far apart and pwm controllers are even worse when there's large voltage differences. i tend to lien to parallel the pvs as losses by the regulation circuits are greater than the gains by smaller voltage drop percentages.

stephendv

Re: NEWBIE on Best hookup - series or parallel?

Correct me if I'm wrong, but a 60Vmp panel won't charge a 48V battery. And putting 2 strings in parrallel brings the Voc to 180V, much higher than any current MPPT controller can handle.
Are those the Kaneka panels by any chance?
See Crewzers post here: http://www.outbackpower.com/forum/viewtopic.php?f=9&t=3353&p=20200&hilit=kaneka#p20242

niel

Re: NEWBIE on Best hookup - series or parallel?

stephendv,
you are right as it would be necessary to have 2 in series of that particular pv if at a 60v vmp, but the kaneka is a 67v vmp pv and is enough to charge the 48vdc battery bank, there may be temperature issues with the pvs at some times during high ambient temps i agree. if it is indeed the kaneka we are talking about, there may have been some confusion by the op as it is a 60w pv and not a 60v pv. the open circuit voltage on the kaneka with 2 in series would exceed the max on currently available charge controllers. this pv was not really designed for charge controllers, but rather to feed gt inverters i would think.
gsa-60 specs:
watts-60w
vmp-67.0v
voc-91.80v
imp-.90a
isc-1.19a