Two Questions for the seasoned pros of this great forum

[J.P.M.]

[QUOTE=solarix;n410602]1) I've never seen a problem due to expansion/contraction. Maybe in a commercial installation where the runs are much longer. There was a famous fire years ago on a big rooftop installation where they did not use expansion joints on the 100'+ runs of EMT conduit and and it pulled apart enough to cut into the wiring. Poof.
/QUOTE]

I haven't either - at least not on solar equipment.

In one sense, I think the whole question of small thermally induced dimensional differences in PV arrays is not the first thing that can cause a problem compared to all the other stuff that gets designed and checked when doing a good mechanical design on a PV system.

However, since Bruce asked the question, and since I believe I have some things to offer on the subject based on training and experience in the power/process industries that may be clarifying in nature, I mouthed off.

IMO only, your example is a good one of what happens when head's up engineering as well as common sense are not practiced, or at least an example of a little knowledge being a dangerous thing.

[scrambler]

1) I've never seen a problem due to expansion/contraction. Maybe in a commercial installation where the runs are much longer. There was a famous fire years ago on a big rooftop installation where they did not use expansion joints on the 100'+ runs of EMT conduit and and it pulled apart enough to cut into the wiring. Poof.

Thanks, so you would not be concerned if three rows of panels did not have any space between them?

2) Definitely use both MPPT inputs. With equal strings, the gain might be small, but why not make use of the possible optimization? Will be a bit more wire I suppose. Also, its always nice to be able to observe both strings separately on the inverter monitoring. We try to use equal strings whenever possible so years later, you can compare the two input voltages in case there is any question of failed panels.

Agreed, I was curious of how much of a difference it made.

Thanks