String sizing question

caleb

I currently have 2 strings of 3 panels (265W each) and they go from the combiner box back to a Flexmax FM80.  For the first several hours of the day, my chimney casts a shadow on one of the panels.  My understanding (which very well may be wrong) is that one panel being shaded will make the entire string mostly worthless.  If that's true, would I be better off doing 3 strings of 2 panels so that I can get more power?  What other downsides would I run in to if I were to move to 3 strings of 2?  Or is this even possible? (my combiner box is a midnight solar mpv3 so I should have room for one more string)

Thanks

mcgivor

You don't mention battery voltage, 2 × 265W would not have sufficient voltage, ~60V for a 48V system, if lower say 24V, then the losses would be reduced slightly by strings of 2, by how much would depend on when the shadow occurs, if it is before the peak production period it may not be significant. 

caleb

Thanks. Battery bank is 24V. The shadowing occurs right up until about peak hours. So I’m missing the production from ~9-12 from one string (or half the panels). 

Also worth mentioning, I don’t have room on the roof to adjust the panels to get rid of the shadow and obviously the chimney is where it is. Just trying to judge if it’s worth/possible to explore maximizing the output I get. 

mcgivor

There would be benifit by dividing to 3 strings of 2, given the hours stated.

BB.

Any way to get rid of the shadow (moving array, trimming tree, moving roof stack, etc.)?

If the shade is a tree, then as they grow, the shading will get worse (and eventually either the tree or the array will have to "give").

Another option--Face the shaded array towards the west... Collect more afternoon sun (may need to add more tilt), and can be a good thing (more hours of sun, longer charging time--Lead Acid batteries "like" more hours on charge--Vs a large array, high current, for "short" period of time).

-Bill

caleb

Thanks for the comment @BB. I mentioned up above it's a chimney and I don't have the option of moving it, unfortunately.  I also don't have the option of adjusting the array to get out of the shadow (no room on the roof to do so).  The only option I could look at is moving to a ground mount but I really don't have anywhere I could put a ground mount and not be in the middle of trees (not just a few, a bunch of really big pines, so I'd have to clear a massive amount to not have the shadowing even worse).  I could move the ground mount further away in a meadow area but it would put me probably 500-600 feet away from the inverter and charge controller.  That would also mean I'd have to trench that and our ground is extremely rocky (big boulders ranging from a couple hundred pounds to thousands of pounds) so it would be a large project (which is actually why they ended up on the roof in the first place). 

They normally do fine where they are mount, they're on my cabin that's only used on the weekends.  So in the summer I haven't had any problems and in the winter, the snow coverage on them is a bigger problem than the shadowing.  I'm really just trying to maximize my panels and if buying an extra cable and breaking them in to 3 strings of 2 works, then that's a pretty cheap and easy thing to do.

mcgivor

@caleb Can you post a picture of the array ? 

caleb

I'm looking through my pictures but haven't yet found any showing how the panels are mounted or even that side of the roof.  I'll keep looking.