Just the meter & panel connected. Meter dipped if I turned panel 90 degrees off center.
I suspected that. With nothing connected there would be no current flow, so the measurement must be voltage. The voltage with no load means very little.
Imagine you had a panel - any size - and it put out 18 volts (yeah, I know, we all bought the panels to charge "12V" batteries...). Then you put another identical panel beside it and connected the two in parallel (+ to + and - to -); you would get the same [b]voltage... but hey, there's twice as much panel!
Now do the same thing - try one panel then two - but this time have them hooked to a battery
that needs charging, and measure the [b]current (amps) which flows (with no controller). I bet adding the second panel gives a big increase because there is twice as much panel collecting light
, and thus twice as much power pushing into the battery. Warning if you try this: inexpensive multimeters routinely have low current capacity (mine is 10A), and large enough panels (like bigger than most of us are likely to ever have) could exceed that.
Another way to illustrate the same thing is to compare a small panel and large panel of the same design and construction
: they will likely produce the same voltage, but connect them to a load and of course the larger panel can deliver more... area matters, and open-circuit voltage doesn't say much.
Sorry, I can't give concrete numbers, because I haven't done this, because the panels are not cheap and thus I only have one.
Having the panels not perpendicular to the line to the sun is sort of like having less panel, because it catches less light
; it has less "effective area". Of course, not all the light
comes straight to the panel (they work surprisingly well in the shade, where all of the light is coming indirectly, from all directions), and that's why it would be interesting to know how much the output varies with aim, in full sun and in shady conditions.
I'm not questioning that the rock guard idea works - it sounds like a clever idea to me - I'm just trying to pin down how much can be gained by aiming better, and see what I might be missing in my understanding of the factors involved.