combiner box confusion

[Smilin' Jack]

I am trying to align what I think I know about combiner boxes with reality. it looks like a combiner box is essentially an AC breaker panel, backwards.

I can't find any examples of how to configure a combiner box for a 6 KW 48 volt off grid system. it appears that what I want is:

strings of 4: 12 volt 270 watt panels in series, for 48 volts at 23 amps =1100 watts per string.
6 strings in parallel
6: 25 amp circuit breakers
a 150 amp breaker as a disconnect for the combined output
in a ten sting combiner box

or, I completely miss the point.

does anyone have a link to a setup for an off grid combiner box?

 

[MichaelK]

First thing that must be VERY clear. NEVER use any kind of AC rated breaker for a DC application. That is physically dangerous and a fire could result. So, use DC rated components only.

Your numbers do not appear to add up. As far as I know, there are no 12V panels producing 270W. All the 270W panels I've ever seen are either 30 or 37V panels. What does the sticker on the back of the panel say? You should see values for Vmp, Voc, Isc, Imp. What are the values for each of them?

Assuming they are standard 270W grid-tie panels, what you are likely to see is 8.7A at 31V. Four of those in series would be 8.7A at 124V. With six parallel strings of four panels, that would equal 8.7A X 6 strings =52.2A at 124V.

Here is a diagram of the 6 breaker combiner I use, from midnightsolar.com. You can get downloadable PDFs for everything at midnightsolar.com.

There is no spot inside the combiner for the output breaker. That is instead located in a midnight DC breaker box, designated as breaker #16 in the pic below.