Using a prime number of panels

[ron_jeremy]

Somewhere on this forum I read to avoid using a prime number of panels but I've since been unable to find that post. Can someone explain this and also if it's across the board or only applies to specific scenarios?

[Mike90250]

Not so much a prime number issue, but a practical issue. 3 panels, 5 panels, 7 panels are too many to often put into series, and you waste a panel if you need to go parallel.
PV arrays need to be designed, to match the controller inputs, just simply grabbing stuff and thinking it will all work somehow, is going to disappoint quite often.

[SunEagle]

Basically if you have an odd number of panels you may have issues if you have to wire them in any type of series/parallel configuration. The odd panel will make one of the parallel strings yield more than the others which could create a wattage loss at best or hurt your CC at worse.

So depending on what type of off grid CC or on grid inverter you are thinking about using sometimes an odd number of panels can be an issue.

[peakbagger]

If you are using microinverters it really does not make a difference. It gets trickier with string inverters but in some cases its an advantage if the math works out. Ideally strings are designed to operate at the high end of the voltage range as that cuts the amperage carried by the wires from the array to inverter. If an extra panel lets you bump the voltage range up then thats the way to go as long as you make sure you never exceed the maximum string voltage on cold sunny day with the snow on the ground.

[Sunking]

This mostly relates to off-grid battery systems. If you have a prime number like 3, 5, 7, 11... only gives you two possible panel configuration of all in parallel or all in series. With a grid tied system prime numbers are not an issue. If you have say 9 or 11 panels is no problem to wire in series om a grid tied. Now if you need two string, then it matters. What would you do with say 19 panels and cannot wire more than 10 in series. You loose a panel or gain a panel.

I am the one you heard it from. .

[nwdiver]

Somewhere on this forum I read to avoid using a prime number of panels but I've since been unable to find that post. Can someone explain this and also if it's across the board or only applies to specific scenarios?

Yeah... that sounds like advice from yester-year depending on the application. Most (all?) grid-tied inverters have multiple MPPT trackers now. For SMA depending on the panel you can have 7-14 panels on each tracker. So you can add up panels on each of the 3 trackers to make almost any number you want and it will work fine. Want 11 panels? One string of 11. Want 37 panels? 13 on Channel A and 12 a piece on channels B and C.

[sdold]

This is the off grid section, so it isn't about inverters, it's about charge controllers having one PV input.

[nwdiver]

This is the off grid section, so it isn't about inverters, it's about charge controllers having one PV input.

Ah... just read the OP and didn't recognize the section this post was in. Thank you for not responding like an A-hole