I have been using a STXR2500UPG for several years; the complete system will be five years old in a few months. Because my inverter failed twice, my warrantee will expire soon, and the UPG seems to have a minor problem, I considering upgrading to a GT 2.5 or 3.0. It all seemed so easy until investigating the details.

My module array consists of 24 Siemens SR100's. Using the Xantrex Sizing Calculator, the PV max voc will be 575.28 V for one string. The system is located in southern California, several miles from the coast. That max voc number is for a lowest ambient temp of 23 F, which is very realistic for this area.

The 575 volt number is within the Zantrex spec, just bearly. Even the wire, #6 awg THHH/THWN is only rated to 600 volts.

Two strings of 12 modules would be below the Sizing Calculator minimum of 14/15.

All this makes me a little uncomfortable because of the small margins. So, I'm just looking for other ideas or reassurance that this would be a reliable configuration. Any ideas?

Get a GT2.5/3.0 and just take the strings that terminate at the ST's combinor and put them all in series. No new wiring is needed, just make you 6 parallel strings into one series string. Its only a few wire nuts and your good to go!

Thanks for your reply. Maybe you can give me a suggestion about the mechanical interface. My current system had six groups of four modules. The wire pairs, all 6 awg, plus a ground required a 2 inch conduit. The bottom of the wiring box on the GT series does not have a punch-out for conduit that big. Can I just make the hole bigger since wiring box would never go back to the factory if the inverter required repair?

Here how I do it,

Mark the #6 wires going to the Suntie combinor so you know which is the +/- and know which wires are pairs, Disconnect all the wires (AC and DC) Remove the Suntie.

Install the GT's backer plate so the GT and Sunties Tops would align, the GT is shorter and should allow space on the bottom for a new JBOX (PVC)

I would get one of the grey PVC electrical boxes from home depot for about 15 bucks. make a 2" hole in the PVC box and mount to the conduit

Inside the PVC box series connect the 6 strings (Blue wire nuts works fine) and the only pair exiting should be a single #10 AWG pair for the input to the GT.

FYI, when I say series connect, you take the negative of one string and connect to the positive of the next. When your done, you have a single +/- that is all 24 panels in series)

Exit the PVC box using 3/4 flex conduit to the GT's input box/disconnect.

Mount the GT on the Backer plate

Reuse the AC that went to the Suntie for the GT and reconnect.

I've done this a few times and works well. At most, its only 1-2 hours to do this AND mount the GT and have it up and running

I called Xantrex today to discuss the upgrade to the GT under what I think they call the Loyal Customer program. Now they tell me that the 2500UPG is still considered “repairableâ€￾ and not covered by the program. I had been lead to believe the program covered any 2500 that was still under warranty.

So, now I'm not sure what to do.

How come you didn't make the decision back in Feb?

6 months is a life time from the companys prospective and I'm sure Xantrex is forever updating and tweaking the warranty options.

Also, in the not to distant future ALL sunties will be out of warranty ... so what ever you decide, I wouldn't keep putting it off

Just to confirm that Xantrex still has this "Loyal customer" program in place. If you have original ST2500 and request repair for it on their online support form you will be offered a new GT3.0 with $999 + shipping... I just got mine this week...

I assume this does not work with the UPGD or STXR, unless they are out of warranty period?

I guess it will depend on how the GT tunes it's harvesting voltage. I have a GT 3.8, and am just north of you in Los Angeles. We've had a pretty cold week here, but between the sun being low on the horizon (bad angle) and no real production till after things heat up a bit, I see nowhere near the HV that the sizer says I will get.

GT3.8 sharp 208Wx 11 in a string 32F 11 Modules= 430.1V

I've never seen over 350V, and this has been a really cold week. I think the factors on their sizer are unrealistic, as what's the likelyhood it will be cold with full sun on the panels. I know the brightness affects the amps more than it affects voltage, but I just don't see the high voltages the sizer says I should see. Maybe the SW guru here can explain how it happens that way.
http://www.naturalstudies.org/~solar/Mi ... stall.html
check it out about 7am when it's light enough to start up.

I think that they are talking about open circuit peak voltage (for example, if the inverter goes into "islanding mode" and shuts down for 5 minutes). Vmaxpower is always going to be quite a bit less.

-Bill