Mark Zenier wrote:

Solar cells have a voltage vs. current curve that's roughly square.

|___ Open Circuit voltage
| ====____. maximum power point
V| \ \
| \ \ "Constant" Current
| \ \
| \ \
|---------------
I ^ available current depends on incident light

The no load voltage is determined by quantum physics and is roughly
constant. The current available is determined by the cell area and
the incident sunlight.

I laid out the panels on the lawn today. It was overcast and I had about
a forty five degree from the panel to the sun. I measured the short
circuit current at **1** amp. That's disgusting. The rated current in
specified light is roughly 4.5 amps per panel. I've paralleled them and
put the bypass diodes in. I also added a blocking diode in each one, as
I want to parallel a small toyish windmill laster on. Open circuit
voltage was a bit over 20 volts.

That 1 amp is troubling. I'll try again at noon tomorrow and pray it
improves.



In practical terms, if you don't put the cells in a situation where
they're outputting enough current to damage their internal wiring,
you can hook them up and they'll provide a roughly constant current for
charging a battery. You wouldn't want to use too high a voltage array,
as you could damage the battery. And if the sunlight goes away, as it
does every day, leakage back through the cell can discharge the battery.
So the simple "chargers" I've seen where switches to disconnect the
battery when its voltage got too high, or there wasn't enough sunlight.

Hopefully the blocking diode is of use.


If you want to be cost effective, you get a fancy charger that
transforms the load on the solar array to the maximum power point
to get the most bang for the buck.

I did a search for that when I saw your post. This one looks
straightforward. I'm wondering if the paralleled setup will work ok, or
if one of these is needed per panel..

http://www.solorb.com/elect/solarcirc/scc2/


This thing is getting interesting. I think I might have found a few 12
volt (six individual cells) fork lift batteries. If they're any good,
I'll be in photovoltaic paradise...



Mark Zenier Washington State resident


Thank you kindly



mike