Strange fault on DC string ?

MrTrance · Sep 19, 2013

Working in Wales yesterday, 9 255w panels and 1 SMA 2000HF Inverter.

So we have 1 string of 9 panels in series.

The roof was like this with each letter corresponding to a panel.

[A]--[C]
[DORMA WINDOW]
[D]-[E]-[F]-[G]-[H]-

ABC panels in landscape, the rest portrait.

All panels at same degree, maybe some shading on the D-I panels due to trees, maybe this is why I got this problem.

Right so my inverter was in the loft, I took one cable to panel C, the other leg to panel I, and then a man made link from D-A... back in the loft I had my meter on my legs testing for voltage and I only seen 105V DC max. Could not work it out at all, done over 100 solar installs and never seen this.

To get round this after a few hours of frustration, I made ABC into a circuit and D-I in a circuit and then made that into a series circuit in the loft (connecting + from top with - from bottom), thus giving me 300V roughly, what I was looking for in the first place!

I need an answer to this, has anyone had anything similar.

Solarworld 255w Poly panels.

Many thanks.

Gavin A · Sep 19, 2013

sounds like you reversed the polarity between the bottom and top row, with the 3 panels on the top row cancelling out 3 of the bottom row, leaving you effectively with just 3 panels. Something like that anyway.

SolarCity · Sep 19, 2013

Yeah, I agree with Gavin. If that isn't the issue you're having, I'll eat my arm.

Worcester · Sep 20, 2013

I reckon GavinA's got the right answer, certainly that would be my first check.

It's easy to do; we had a similar problem with one string on a 50kW project, string of 22 panels, and the last one (on a different row) had been connected in reverse polarity, had us looking for about an hour to figure it out though, what confused us further was that the next string was supposed to have 20 panels on it, so it really had us scratching our heads as to whether it was a faulty panel or simply miss-wired.

MrTrance · Sep 23, 2013

Could somebody explain how this fault is caused? Is the polarity is wrong way wrong usually my multimeter just comes up with a -300v or 300v? Confusedddddddd

Earthstore · Sep 23, 2013

If the panels D-I gave you 200V and panels A-C gave you 100V if wired in correctly that would give you 300V, however if panels A-C were connected to panels D-I but with reverse polarity (IE - and + the wrong way around) then it would cancel out 100V of panels D-I 200V therefore giving you just the total of 100V.

Does that make sense?

SolarCity · Sep 23, 2013

The link you took from D - A is affecting your polarity I would guess. I would guess that you have it made up as + > + rather than + > -

Gavin A · Sep 23, 2013

SolarCity said:
The link you took from D - A is affecting your polarity I would guess. I would guess that you have it made up as + > + rather than + > -

this.

Another way of describing it would be to say that you'd run the 2 strings in parallel rather than in series, so the string is operating at something like the voltage of the lowest voltage string.