adding on or new controller needed?

[Ralph Day]

Hi all
I'm thinking about adding some more pv, pointing west to give some more power in the late afternoon/evening for heat pump operation. My MX60 has 2.1kw presently with the max ever seen of 2300 watts (cold and edge of cloud happening). So I still have about 20 amps of capacity left on the MX60. Battery voltage 48vdc nominal.

Present panels are Sharp 72 cell 180 (2 panels) and 175 watt (10 panels).

NT 180 U1
180 watt
44.v open circ voltage (voc)
5.6amp short circuit current (Isc)

NT-R5E1U
175 watt
44.4v Voc
5.5amp Isc

I have access to some Sharp 200 watt panels (60 cells), but wonder about their compatibility if I try to add them to my MX60 controller.

ND 200U1F
36v Voc
28.42 Vpm (Max power voltage)
7.9 Isc

The 12 present panels are in 2x series parallel. Can I add a combiner/breaker/cabling to add the output of the 200 watt panels, or should I just plan on a separate charge controller for any I purchase and install?

Thanks

Ralph

[Rob Beckers]

Ralph, so your current setup has two panels in series, and then 6 of those series strings in parallel? So that's 144 cells as far as Voltage into the MX60 is concerned. Unfortunately you can't do 3 panels in series, because the MX60 has a limit of 135V DC on the input (on the coldest day, and each 72-cell panel can generate 54 Volt at those times).

Adding 60 cell panels in series won't match those 144 cell strings very well; three panels is way too much, two makes 120 cells, meaning your existing panels will only produce roughly 85% of what they normally would.

You could make strings of one 72 cell panel plus a 60 cell panel, and parallel a bunch of those (the Voltage would be high enough to charge a 48V bank, but just barely). That would work, but is a heck of a job in rewiring the existing array...

-RoB-

Edit: Wiring panels in series like this still has a cost in performance - Today's 60-cell panels run at much higher currents than yesterday's 72-cell panels, so that's not a good match. Bad idea! Sorry!

[Ralph Day]

Too true Rob. I think the way to go would be: a)3 or 6 x 200 watt panels with a dedicated controller for them

b) find 4 more 180 watt 72 cell panels and wire them into the MX60. Are they still available? Everything seems to be 200 watts and over now.

Ralph

[Rob Beckers]

Actually, the 72-cell panels are all in the 300 Watt region now. The 60-cell panels are around 240 - 280 Watt. The 60-cell panels in particular dropped in price: We're peddling 250 Watt 60-cell panels for 79 ct/W ($197.50 for the panel). Good (tier-1 brand) panels too, Canadian Solar.

Cheers,

-RoB-