5 kW grid-tie...Do I need a combiner box?

System · April 2008

I'm installing a 5 kW system on my house. I have 5 strings of 5 Sanyo HIP200BA3 modules and 2 SMA 3000US 3250 Watt inverters in Western Colorado. My wire run from array to inverters is 50' max. I plan to put 2 strings in one inverter and 3 in the other.
My question is this: If I combine strings at the array and bring them down to the inverters, they will over power the inverters. Is there a way to disseminate into 5 strings again before going into the inverters or should I just bring down 5 sets of wires?

All help is greatly appreciated

Solar Guppy · April 2008

Re: 5 kW grid-tie...Do I need a combiner box?

You will probably have to fuse each of the array that are grouped as a parrallel x 3, the isc would exceed the manufactures short circuit rating

mike95490 · April 2008

Re: 5 kW grid-tie...Do I need a combiner box?

Have you already bought these ?

A single Xantrex GT-5 would work, and I think you can combine in the terminals of the inverter (manual says 3 strings, but it looks like it will take 6 for GT5 - any owners have any say on it ?)

Local code may have other ideas about combiner boxes, DC fuses, wire runs etc...

Sizing Tool:
http://www.xantrex.com/support/gtsizing/disclaimer.asp?lang=eng

System2 · April 2008

Re: 5 kW grid-tie...Do I need a combiner box?

Yes, I already have the components. Just curious about running 5 sets of wires down to the inverters...is that the best way to get the maximum wattage from the array?

mike95490 · April 2008

Re: 5 kW grid-tie...Do I need a combiner box?

Ecoguy wrote: »

Yes, I already have the components. Just curious about running 5 sets of wires down to the inverters...is that the best way to get the maximum wattage from the array?

Well, if you are feeding 2 inverters, you only need 2 sets of wires. But they have to be larger. You may find better prices for 5 sets of wire @ 12ga, then 2 sets @ 8ga

And then combine next to the inverters, where it's easier to work (or replace a fuse) You may want to look at the 3/2 split in a year, maybe find which string has lower current (or shade) and use that one for the 3rd string on a inverter. Why pack 3 high performing strings on 1 inverter, it will get even hotter.

newenergy · April 2008

Re: 5 kW grid-tie...Do I need a combiner box?

You can't do this in 4 strings? Already bought the panels and they don't divide by 2? Voltage limitation?

Overpower the inverters?

The SMA 3000 takes two strings, so if you have 3 you're gonna have to combine.

Could you post more details, including what you've already bought and what you're flexible about?

Solar Guppy · April 2008

Re: 5 kW grid-tie...Do I need a combiner box?

Another reason NOT to use sanyo HIT's they are typically 50-60V panels and require more strings than regular Si panels on any decent sized array

For example, my 5kW array has 2 strings of 15 Evergreens in series for 5100 watts. Sanyo needs 5 strings for the same power

System2 · April 2008

Re: 5 kW grid-tie...Do I need a combiner box?

I have the SMA DC disconnect with each inverter which is supposed to accept up to 4 strings and then combine to 2 going into the inverter. According to SMA's sizing program for my location, 3 strings of 5 modules will not overpower...so, 3 strings in one inverter and 2 in the other, right?
When I originally configured this system, I went by the sizing program, the module info, and selected inverters. I didn't give much consideration to the connection of module strings with MC connectors to less expensive wiring for the 50' run. So I am now confronted with figuring this out.
Here's what I'm thinking now...
Using 2 junction boxes under the arrays (one for 3 strings, one for 2), I will connect the MC cables to #10 wire and run through metal conduit in the attic and down the outside wall to the disconnects. One conduit will carry 3 strings and one will have 2. This wire size should more than accomodate temp derating for a hot attic, conductors per raceway, etc.
Then connect at the inverters and everything is great, right?
I thought my biggest problem was figuring out how to bring the array wiring down to the inverters, but the more I look into it, the more confused I get.
Is this the best way to do this with the equipment I already have?

Solar Guppy · April 2008

Re: 5 kW grid-tie...Do I need a combiner box?

You can't just wire three arrays in parrallel without fuses. Your solar panels have a maximum current and putting them in parrallel with one string faulted exceeds that current ( two strings will be sending current into the third )

The inverter may have connections for 4 strings, that doesn't mean anything as you have to meet the PANELS UL listed ratings.

System2 · April 2008

Re: 5 kW grid-tie...Do I need a combiner box?

Each string will have a 6 Amp fuse in the DC disconnect (3.83 module Isc X 1.56). The max input Isc for the inverter is 24 Amp.

5 kW grid-tie...Do I need a combiner box?

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