Calculating Solar Panel Amperage

 
Hey guys. Long time no see. :)


I'm baffled by a seemingly ambiguous problem.

I know a 100w solar panel puts out ~20v no load. So that's 100w/20=5
amps theoretically in full sun.

Now,,, when the charge controller kicks the voltage down to ~14v, does
the battery then charge at 100w/14v=7.14 amps?

Or, do you go strictly by the panel output? It makes quite a
difference when you are calculating battery recovery time!

Many thanks,,,
 -

Bob

  Bob Adkins wrote:

To know for sure how much current you'll get at a given voltage (or vice
versa), you have to know the solar panel's I-V curve. A bit about the
I-V curve is explained here:

http://www.daviddarling.info/encyclopedia/I/AE_I-V_curve.html

The only way to know how much your panel will produce at 14V is to find
14V on the I-V curve for and read the associated current from the chart.
You can put a maximum power point tracker (MPPT) between the panel and
the charge controller to ensure the panel always operates at the maximum
power point, regardless of the charge controller's demands, but whether
that's economical depends on your situation.

 

Bob Adkins wrote:


No. 5 amps is a load, so the voltage will be lower than 20V at a 5 amp load.

Graham

 I put a double pole double throw switch on my dual 12" bassman cabinet
(this was back in hi school in the 60s) to make the cabinet series or
parallel... 4ohms or 16ohms... and when I plugged it into the 8ohm
amp, and flipped it back and forth, I thought 'Crap... no damn
difference... those guys were full of it with this impedance match
stuff'.  So to carry this silly analogy along, pretend the panel is
the amp and the charge controller is the load... sort of a variable
resistor in series with the battery (for discussion purposes) if the
load is real high ohms, you get 20V and not much current... if the
load is low ohms, you get as much current as the panels will put out,
but its loading down the voltage. There is a sweet spot where the
volts and current are Just Right (Like the Temperature of Goldilocks'
porridge). I really like Usenet.

 

I've heard of that. It's way closer than I need, because the weather
affects it a lot more than it would change on the curve.

I like Usenet too. Been around since '92, I think.

Thanks RH and BobG.
 -

Bob