Agree, those panels are very optimistically rated. I have 10 of them wired
to a small grid-tie inverter, and while I don't know the efficiency of the
inverter, I would assume that "150 Watts" worth of panels should be
producing a bit more than 50-60 Watts in full sun...
On Tue, Jul 25, 2017 at 10:23 AM, Lee Hart via EV <email@example.com> wrote:
> From: paul dove via EV <firstname.lastname@example.org>
> >What is the wattage on that Lee. I calculate 3Watts. 0.25 X 12 V = 3 W
> >Harbor freight sells a 15 watt panel.
> >15 Watt Solar Panel
> I don't recall what wattage was claimed. But many of these panels will do
> things like advertise the short-circuit current, and open-circuit voltage,
> and multiply them together to get the claimed wattage.
> That's completely bogus. First, it assume perfect full sun, at the optimum
> angle, and a low ambient temperature. Second, you can't even get half the
> short-circuit current into a real load. Third, the voltage under load is
> substantially less than the no-load voltage.
> The more honest vendors will provide a voltage, current, and wattage under
> realistic conditions, driving an actual load.
> Even then, you have to consider how you will actually use the panel. In my
> case, the PV panel sits horizontally, on the shelf under my car's back
> window. Thus it is never at the optimum angle, the glass reduces the light
> intensity, and the temperature inside the car is always hotter than ambient.
> Excellence does not require perfection. -- Henry James
> Lee A. Hart http://www.sunrise-ev.com
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