Is there an optimal way to lay out source circuit strings between solar modules in a PV array? Is it best to lay them out simply depending on what works best for the location of the combiner box or inverter?

Or is there a consideration for wire lenght such it would be better to snake back and forth through several panels in a section of an array rather than have one longe string with several panels in a row.

For instance if I have (2) rows of 12 panels for a total of 24 panels and I have 12 panels per string is it better to have the strings as 1 string having all 12 panels in a row or is it better to align the strings snaking through a 2x6 section of the array?

Thanks
 

Personally, I'd go with the method that used the least amount of wire.  Saves on the expense of the wire, but also minimizes voltage drop and I²R losses.

Optimize the configuration.

You'd normally want to hold wire losses to 5% or less.  Aside from that, it is good to go for the minimum power loss, not necessarily the shortest wire.  If you use a longer wire, make it heavier gage so that the power loss is at least equal to, or even less than the loss in the shorter wire.  Incremental power loss in resistance should be balanced against incremental cost of heavier gage wire.  Failing to reach that optimized solution may cost you too much money in resistance losses, or you might pay too much for the heavier wire.

We will design everything from now on using only S.I. units ... except for the pipe diameter.  Unk. British engineer

If this is a small, residential system with only 12 modules it does not make much difference from the perspective of wire cost and installation time.  For a larger system, it will be easier to wire if you simply go down the row and wire all 12 panels in series.  If you cross between rows, you will slow down the installation team and create opportunities for the installer to mess up.  You could end up with one 10 module circuit and one 14 module circuit rather than two 12 module circuits.  It sounds like a silly mistake, but it happens.  A lot of the time the physical layout is coordinated with the electrical layout.  If you want 12 modules in series, the rows are 12 modules wide.

The only exception I can think of is if there are particular shading issues.  You don't want modules than will be shaded in the morning wired in series with modules that will be shaded in the afternoon.  Put the modules shaded in the morning in one circuit and the modules which will be shaded in the afternoon in a separate circuit.

-JFPE
 

For a small system isn't it more important to not put the modules where they will shade at anytime.

We will design everything from now on using only S.I. units ... except for the pipe diameter.  Unk. British engineer

Thanks for the replies guys!

So in a large system optimizing the string conductor layout is much more important.  In a small system such as a small rooftop 18kw system optimizing of the 6 strings with 11 panels each is not soo much of a consideration or takes a back seat to other aspects such as installation ease and shading as mentioned above?