Balanced strings in parallel

[Maff]

I am designing a 2.3kw on roof pv sytem at the moment but am having trouble sizing an inverter, for 15 modules in 3 parallel strings, so the easy option is to go for 14 mods in 2 strings. The question is could the strings be imbalanced? ie 1 string of 8 and 1 string of 7 in parallel, thus utilizing all of the roof space?

 

[MikeXl426]

The strings must be balanced. Either put different combination/sizes of panels in, or remove the 15th panel.

 

[Worcester]

What size system are you buiding?
15 panels at less than 160W / panel?
I would have thought you'd be better off using a larger output panel unless there is something very odd with the roof.

What panels are you proposing to use?

 

[Maff]

we are going to use BP solar185 panels, as it is our first install and is going to be our MCS accreditation we just wanted it to be nice and square etc, and the customer will ask why it couldnt be symetrical etc, but the small gain in yeild against the extra cost of a multi power point tracker inverter prob isnt worth the hassle.

 

[Worcester]

@Maff

Just ran it through PVSol for you, try a Power-One Inverter two MPP trackers, one configured with 2 strings of 4 panels and one with one string of 7 panels

Works for a 45 Degree East Facing roof and a 30 degree South Facing Roof.

There's a few people around selling them including one of the forum sponsors pvsolaruk

Here's a few links:
http://www.electriciansforums.net/p...rgy-forum/35037-small-dual-mppt-inverter.html
http://www.electriciansforums.net/p...inverter-giving-e013-wrong-input-setting.html

 

[Maff]

just a follow up I see you use PVSol we are considering purchasing it ourselves, is it a usefull tool, as there are quite a few programs on the market and you cant quite evaluate them fully by the free trials.

 

[Worcester]

That was the first pass, running it through in detail the Power-One Aurora PVI-3.0-OUTD will let you do a string of 8 and a string of 7 attached to seperate trackers.

Give Ken Hobbs at CCL Components a call Power Inverters | Solar Inverters | G83 Inverters and tell him I sent you.