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On Sat, 13 Jan 2007 08:38:40 -0800, ray lunder wrote:

On 12 Jan 2007 20:01:43 -0800, wrote:

I was curious if someone could explain why solar panels that charge a
12V system put out 19V? I used a multi-meter to check the voltage on my
panels and was at first alarmed that they output 19V but then upon
looking online I discovered that it's fairly common. Anyhow, was
wondering if someone would be game to explain why they make many solar
panels to output 19V (instead of a more common charging voltage such as
14.5V)?

Thanks,
Todd

That's "no load" voltage. It will change as the light goes down as
well. (you can still see 12v even if it's raining- you just don't have
much current generated with which to charge a battery). Also, don't
forget to subtract .7v for the blocking diode that's going to be in
series with your batteries.
19v seems to be a magic number for power generation at this level.
Alternators put out something like that too before it hits the
regulator pack. Also, this number will be high when a panel is brand
new and decrease a 1 - 11/2v as the panel breaks in. All perfectly
normal. It takes a higher voltage to charge a lower one and I suppose
a spread like that takes aging and panel shading into consideration as
well. Not sure if the internal resistance of a panel changes with
overhead vs angled sun position or not. The difference between the 19v
generated and the voltage state of your battery is thrown away in
heat, either in the battery or the panel so they can't make this
number too high.

This is incorrect as well. See my other post. All available current is
shunted by the diodes when open circuit, making heat. A lower battery
voltage reduces the wasted current but of course reduces the power
input to the battery and an excessive number of cells is money spent
for nothing.

The discouraging thing about solar panels becomes sickeningly obvious
when you hook up a multi meter and wave the shadow of your hat over
even just one of the cells. The amperage output drops by two thirds.
For a single 5A panel it makes your $400, plus the cost of mounting,
wiring and monitoring look rather foolishly spent.

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