You may find this a rerun.
The working voltage is pretty much dependant on the number of cells in series.
The standard is 36 cells at about 0.485V each.
A 40 cell PV adds 4 cells. 4 x 0.485 = 1.94V. That 1.94V is kind of "added" to the standard 36 cell panel.
The max power rating will kind of be skewed by the way they are rated, which works out to only 0.4325V/cell for 40, instead of 0.485V/cell for 36.
The max power rating is skewed because of the current being limited to the size of the cells.
The VW panel is a better example with 42 cells, rated 18.8V at 175ma at max power, 0.448V/cell. And mine put out over 220ma each into a 12V battery under less than ideal conditions.
Ebay, search 'VW solar'. 'Buy now', free priority shipping, 2 for $35. (Not me)
I just don't see how you will get anything better for your purpose for 5X the money of 2 of these VW panels.
The oposite example would be the so-called 'self-regulating' panels with 30 or 32 cells. No matter how much sun, the PV could not make enough voltage to overcharge a battery. The amps drop off a cliff at about full charge voltage, or if the sun is not about ideal.
How about 3, 4w or 5w PVs at 6V each in series?
That would put the V at max power about 25V,
and the amps over your target, and low light should be improved.
And there were some '18V' PVs being made for grid tie, but all I know of were expensive and 80W or more.
Or just throw a bigger PV at it, one that can maintain 0.450A at 17V.
G-
