[RE-wrenches] PV voltage at Isc

[boB Gudgel]

On 2/5/2011 11:30 AM, Greg Egan wrote:
> Fellow Scientists,
>
> I got in a discussion with a wrench the other day.  He is under the 
> impression that when a PV module is at short circuit current there is 
> no voltage.  My understanding of electricity is that if there's no 
> voltage there's no current because current needs voltage in order to 
> flow.  I'm seeing it as a difference in potential, voltage that is.  
> If there's no difference in potential I don't understand why current 
> would flow.
>
> I googled it and the few links I checked out were on his side - zero 
> voltage at Isc.  All this is of course irrelevant to the business of 
> installing PV so if you don't care I don't blame you.
>
> So I still think that if you a precise enough meter that if you stuck 
> the test leads into the cables sticking out of the back of a shorted 
> PV module that you'd read some small voltage that was approaching 
> zero.  Any explanation of why I am right or wrong in plain English 
> (I'm not really a scientist) would be welcome.
>
> All the best,
>
> Greg Egan
> Remote Power Inc.
> Fairbanks, AK

Sorry for the extra response.....

Greg, in short, (pun intended),

A short circuit implies just that...  The leads from the PV array or 
module is shorted together.

In a perfect short, there is NO voltage across that short, but full 
current flowing through that short circuit connection.

In an open circuit, there is NO current through the circuit (it's open), 
and full voltage across those two wires.

In-between that short and open somewhere is the max power point 
delivered to the load (inverter, CC, battery, etc)

The load being a partial short.  (or is that a partial open ??)

boB

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