Mixing Panels

[Bobina]

I have 40 BP 150w panels on (2) 3000w inverters (20 panels on each inverter).
Recently some of the panels went bad and BP replaced them with 175w panels (they no longer produced the 150w). I replaced panels on both strings and now there is quite a bit of difference in the output from each. One of the inverters shows 2450w output and the other shows 1100w output. Before the panels went bad each string was producing about 2400w at mid day. Is there a way to test the output of each panel and is it ok to wire the 150w and 175w panels in series together?

[Sunking]

Compare the specs of the two panels and post results.

What we are looking for is the Vmp and Imp of the new panels are at least equal too or greater than than the panels they replaced.

[Bobina]

The Vmp for the 150w panels is 34.5 and for the 175w is 36.1 and the Imp for the 150w is 4.35 and for the 175 is 4.9. I have 2 strings one with 18 150w and 2 175w panels and the other string has 14 150w and 6 175w panels. The inverter with the 6 175w panels on it shows 2450w and the one with the 2 175w panels on it shows 1100w.

[Sunking]

OK the panels should work just fine. But something is wrong with your number of panels in each string, and the voltage you are running.

20 panels x 34 Vmp = 680 volts. You are way over the limit. Is this system in the USA

[Bobina]

It is my understanding that the Vmp will drop to the lowest in the string. Am I correct? This system is in San Diego. What do you mean I am way over the limit?

[Sunking]

It is my understanding that the Vmp will drop to the lowest in the string. Am I correct?

Yes and no. Yes if it is wired in parallel, No if wired in series. In parallel current adds, in series voltage adds.

This system is in San Diego. What do you mean I am way over the limit?

Electrical code requirements require the highest system voltage in residential application is 600 volts maximum. Grid tied system operate between 200 up to 450 volts. If you your panels are wired in series with 20 cells of 34 volts each = 34 volts x 20 cells = 680 volts.

I do not know how your panels are wired. IF this was professionally installed, the contractors know the rules. I hope what you have is 10 panels wired in series, in parallel with another 10 panels wired in series.

[Mike90250]

There may possibly be some more bad panels, Another company had this sort of toruble several years ago, and first, they swapped bad panels, but after a year of call backs, they just exchanged the whole array. You pay the labor.

[Bobina]

I do not know how your panels are wired. IF this was professionally installed, the contractors know the rules. I hope what you have is 10 panels wired in series, in parallel with another 10 panels wired in series.

They were professionally installed and I checked them, they are wired 10 in series, in parallel with another 10. When I put a meter on the strings I get 300Vdc. But at the inverter it is only converting that to 1100w on one string of 20 panels. The 300Vdc from the other string (20 panels) shows 2450w at the inverter.

As Mike90250 stated I may have bad panels. Is there a way to find out which panels are working and which aren't? The voltage output leads me to think that the panels are all producing. I appreciate all your help.

[Sunking]

When I put a meter on the strings I get 300Vdc. But at the inverter it is only converting that to 1100w on one string of 20 panels.

You have 1 string of the two in parallel not on line. Either a wiring or panel problem.

[Sunking]

As Mike90250 stated I may have bad panels. Is there a way to find out which panels are working and which aren't? The voltage output leads me to think that the panels are all producing. I appreciate all your help.

Yes, but you have to get on the roof to find them. First isolate which string of the two is down, then isolate the panel(s). This is not something you should do as it can be very dangerous working with high voltages. One mistake and you will be electrocuted. 300 volts is enough to kill with 4 amps available. I advise calling your contractor or professional to look at the problem.

Sorry but I will not help you anymore with this. Just too dangerous for unqualified personnel without direct supervision.

[Bobina]

I'll do that, Thanks for all your help.