# Solar panel power calculation - Page 2

Posted by Eeyore on October 20, 2008, 4:19 pm

Bruce Harvey wrote:

How exactly would a potentiometer help ?

Graham

Posted by daestrom on October 20, 2008, 11:16 pm

Bruce Harvey wrote:

In your example you show current at 1.0A at 6V and it rises to 1.7A at 10V.
What Bill is trying to tell you is that a solar panel won't have a rising
current like that.

The *maximum* current point is at 0V (Isc).  As resistance in the circuit is
increased, the voltage will rise, and the current stays constant for a
while.  In most silicon panels, the current is pretty constant from Isc up
to a point while voltage rises (as the external circuit's resistance is
increased from 0 ohms), then you reach the 'knee' of the V-I curve and a
further increase in voltage causes the current output to drop sharply toward
zero.  The maximum power is right at the bend of the 'knee'.

The only trick is, the 'knee' shifts with changes in panel temperature.

daestrom

Posted by Bruce Harvey on October 21, 2008, 4:51 am

The current does not stay constant for a while as you state but changes at a
lower but increasing rate. The 'knee' of the curve you describe is the
maximum power point as you stated and therefore the most efficient point to
produce power for that panel at that temperature with a given amount of
sunlight.

I did mention in my original reply that temperature and insolation are
factors to be taken into account but the OP may or may not need to know this
much detail.

OK point taken. This is an example I made up. It was a tool to describe what
kind of numbers the OP MIGHT get. Not an example of an actual panel test.

Bruce

Posted by Mike on October 23, 2008, 10:03 pm
On Mon, 20 Oct 2008 19:16:18 -0400, "daestrom"

A picture being worth a thousand words....

http://img171.imageshack.us/my.php?image=kyocerakd205gh2pengmarcqj7.jpg

--

Posted by Eeyore on October 20, 2008, 4:17 pm

JS wrote:

•
• Subject
• Author
• Date
 Re: Solar panel power calculation Martin Riddle 10-20-2008
 Re: Solar panel power calculation Bruce Harvey 10-20-2008
 Re: Solar panel power calculation Bill Kaszeta / ... 10-20-2008
 Re: Solar panel power calculation Bruce Harvey 10-21-2008