On
> Seems from my experiments that the volts do not go much lower when it is
> faced even 45 degrees away from
> direct sun.
> I am not sure if panels get the power from the sun increasing the amps,
> or just
> the volts, but if it is solely the volts, I was getting 20 when facing
> the sun,
> and still as high as 17 or 18 when it was no longer direct. And I was
> still
> getting well over 14 volts even with no sun, just light, medium bright
> day, but cloudy.
PV cells are current devices, not voltage devices. Reading just the
open circuit voltage will not tell you very much, most panels will
manage to produce near their rated voltage in quite poor light, but the
actual power produced would be low.
Stick a resistor (of a suitable rating, it will get very hot, very
fast) across the output and repeat your measurements. You should now see
significant differences in output as you move off being aimed at the sun.
The intelligent controllers in 'grid tie' inverters do something
called 'Maximum Power Point Tracking' where the controller tries find
the optimal current draw that obtains the maximum power for the
conditions and keeps that 'Maximum Power Point' as the conditions
change. (If you pull too much current, the voltage will sag and you
could end up worse off, the MPPT finds that 'sweet spot').
I think you can get MPPT equipped solar battery chargers. They will be
the more expensive sort :-). I think the simple solar charge controllers
are just a simple shunt voltage regulator to stop you from cooking the
battery in bright light. They make no effort to find the sweet operating
point of the attached panel for maximum efficiency.
So don't believe the results obtained from just sticking your volt
meter across the output terminals of a solar panel...
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