Question about Xantrex GT inverters and string size

markf57

Newbie Alert!

I tried searching, but I couldn't find the answer.

I have a question about the Xantrex GT line. I've been playing around with the GT Series String Sizing Tool found here http://www.xantrex.com/support/gtsizing/index.asp?lang=eng. It's been quite helpful. It normally returns configurations for 1, 2, 3, and sometimes 4 strings. Even for the 3.X models. However, when I view the owners manual here http://www.xantrex.com/web/id/1890/docserve.aspx, it shows that only the GT 5.0 can have 3 strings (page 3-3) and no options for 4 strings.

What is this newbie missing? Can I have 3 strings on a 3.3 or 3.8? And if not, why does it show that option in the sizing tool and how the heck do you get 4 strings?

Thanks,

Mark

BB.

Re: Question about Xantrex GT inverters and string size

I believe the issue is that the (at least Xantrex GT) inverters do not have terminal strips for more than two (or three in the larger inverters) paralleled strings of solar panels.

However, if you have three or more strings in parallel, you need to add a series protection fuse or breaker for each string... So, typically this is done on an external combiner box somewhere between the array and the GT inverter.

As long as the voltage and current remains within the requirements of the inverter--any mixture of series/parallel arrays should be fine.

One thing to consider, now that panels are over 200 Watts each, it is possible to string together large arrays that are even just one series string for the larger inverters.

Typically, the larger panels are sometime cheaper per watt than smaller panels, plus there is less wiring/fuses/mounting required for the larger panels (fewer/no parallel connections with no fuse/breaker requirements, less connections)--so they can be cheaper to install (the large panels may require two people for handling, the sub 200 watt panels can be moved around by one person).

-Bill

Solar Guppy

Re: Question about Xantrex GT inverters and string size

BB right on, there should be no reason to use anything more than at most two strings.

With the Evergreens being the lowest cost per watt and come in 170 - 210 watt sizes, one can actually do a single string with all the Xantrex GT models ( 2.5/3.8/5.0 ) with a single string

markf57

Re: Question about Xantrex GT inverters and string size

Thank you both!

Thanks,

Mark

markf57

Re: Question about Xantrex GT inverters and string size

I wanted to follw-up with a few more questions about the inverter and combiner box.

1 - So if I run 3 strings to a combiner and the connect it to the inverter, does the inverter only "see" one string? So the MPPT of the inverter is treating it as one string? Wouldn't this hurt if one section was getting shade? Conversely, it you have 2 strings directly connected to an inverter, does the inverter apply MPPT per string?

2 - It appears that you would want to add the combiner box as close to the strings as possible so that you only have to run 1 wire a longer idstance. Is that correct? I guess it depends on local codes.

Solar Guppy

Re: Question about Xantrex GT inverters and string size

1) Yes, partial shading and parallel strings are bad ... with today's panels there is no reason to do this with a Xantrex GT. It would help if you explain why you were considering this?

2) Wire is wire. 3 separate combined at the inverter or combined on the roof and then to the inverter is all dependent on the gauge of the wire. Once combined you would use a physically larger wire and hence why the combiners are for the Xantrex GT part of the inverter in the BOS box

markf57

Re: Question about Xantrex GT inverters and string size

Solar Guppy wrote: »

It would help if you explain why you were considering this?

My goal is to be an more educated consumer.

I plan on have a PV system installed next year. As a requirement of the Colorado state rebates, the system needs to be installed by a pro, no DIY. I want to talk as intelligently as possible to my installing company.

The provider that is most likely to get the job has proposed a 3.15kw system. I'm wanting him to update the proposal to a 4.2kw system, but I'm trying to learn what that would mean in terms of more equipment. I'm trying to get the most effective system possible at the best possible price. So, I'm trying to learn about inverters and panels to see where the cutoff points might be. For example, the 4.2 would be 24 panels. Maybe that causes a lot more work and equipment and maybe 21 panels would be better.

I know you like Evergreen panels. I haven't found one installer that said they used them in my area.

Solar Guppy

Re: Question about Xantrex GT inverters and string size

markf57 wrote: »

I know you like Evergreen panels. I haven't found one installer that said they used them in my area.

Don't ask, Tell the installers what you want. Evergreen is near if not the largest manufacture now of PV panels

its 21 of the 200 watt panels in a single string with a GT4.0 ... can't be it for features, performance or cost

Installers have other motives, like who give the biggest deal of the installer. As an example, I know one in Florida that would use the beacon M5 just for the kick back he was getting from the manufacture.