Over-paneled strings per mppt

[pollenface]

I recently had a 5kw grid tied system installed with 6.6kw of panels.

Due to roof space available on either side of the house (east & west), the installers put 2.6kw/360v on the East string and 3.9kw/540v on the West. This piques my curiosity because the inverter specifications recommend 3.3kw per string.

I have read a few bits and pieces about the occasional over-paneled string/inverter, but nothing well documented.

What's the consensus on this forum?

 

[svetz]

Being over-paneled isn't bad per se, it depends on how far over you are. I tend to think that up to 15% is a pretty good economical choice.

3.9/3.3 is 18%, so I can see why you're wondering about it. So, here's the reason why it's probably fine. You'll only see Clipping when the panels get more that 3.3 kW of solar energy, the array can only pull in 3.9 kW at STC conditions which on south facing panels might occur for a couple of hours for a few weeks twice a year if all goes well. At all other times, you won't be seeing 3.9 kW of solar energy.

As the panels are on the west side, they're probably already at a sub-optimal tilt for the maximum possible solar energy.

I'm over-paneled, 340Watt panels, 295 watt microwatt inverters, just a touch over 15%. I also have sub-optimal tilt on the panels though, last year when I expected Clipping, I got rain... so lucky me? So I've never actually seen clipping in my first year of operation.

So, is it a problem? You can simulate what's going on in SAM and find out, or just watch your peak output to see if they match the graph in the wiki entry. Anyway, hope that helps and good luck!

 

[pollenface]

It's all starting to make sense for me now. Thank you!