Prarctical impact of shading on solar panel output

[jac]

Like many boats - I have lines led aft across the cabin top.

The clear space to port not obstructed by lines will let me fit a 30w panel.

If I fit a larger panel of 50w some of it will be obstructed by multiple lines maybe only an inch above the surface of the panel and running the full length of the panel, therefore covering multiple cells.

question is - will the unobstructed 30w panel give me more useable charge than the larger obstructed one?

 

[JumbleDuck]

Like many boats - I have lines led aft across the cabin top.

The clear space to port not obstructed by lines will let me fit a 30w panel.

If I fit a larger panel of 50w some of it will be obstructed by multiple lines maybe only an inch above the surface of the panel and running the full length of the panel, therefore covering multiple cells.

question is - will the unobstructed 30w panel give me more useable charge than the larger obstructed one?

A solar panel is made up of individual cells wired in series to proved the volts. These cells are limited size, so the serial strings of them are connected in parallel to produce the amps. Generally speaking the strings are arranged along the long axis of a rectangular panel. The 50W panel on my coachroof, for example, has four rows of cells, wired as two long U's, if you see what I mean, which are then connected in parallel.

Roughly speaking the output of a cell is reduced by the shaded proportion, and since the current is the same through all cells it blocks the others likewise. Cover half of one cell in a string and you will reduce the current from that string by half. Cover half of another cell in the string and it won't make much difference.

So ... shadows which run along the strings don't necessarily have very much effect, particularly if they are narrow. Even a broad shadow, like a boom, is unlikely to knock out more than one string as long as it it runs along them. The killer is a wide shadow across the panel, which can easily knock out a whole cell in each string and thereby reduce output to zero.

Before fitting my panels I did a lot of experiments on a sunny day in the garden and came to the conclusion that as long as the strings went fore and after, shadows were nothing to worry about. In your case I would expect the 50W panel to do significantly better than the 30W, as long as the ropes are aligned with the strings of cells.

 

[jac]

Thanks Jumble duck - The panel would be oriented fore and aft, like the lines so that's reassuring to know.