Internal Resistance of Solar cell

[noura17]

Hi,
I am trying to do coursework on measuring the internal resistance of a solar cell. The light intensity on the solar cell is not going to change so the only thing that can be changed is the resistance as a variable resistor is used.But I am not sure how to find the internal resistance when I don't know the current or voltage. Can anyone please help...

 

[berkeman]

Do you mean that you are trying to work out an overall model for a solar cell, and are trying to figure out how to model a resistance term?

A solar cell (a big photodiode) does have a bulk resistivity, in addition to outputting a photocurrent. It's mainly from just the resistance of the silicon itself, I believe.

I just bounced to wikipedia, and they have some good pages about solar cells. Here's the page with an equivalent circuit:

http://en.wikipedia.org/wiki/Solar_cell#Equivalent_circuit_of_a_solar_cell

Looks like there's an internal shunt resistance (probably for the internal leakage current) and an overall series resistance. Now, given that equivalent circuit, what ways can you think of to measure those two resistances?

 

[noura17]

I think i have to find:
Power = current * voltage.

theoretically if you make a graph voltage-current and you put all your resistor measuring points on it then you draw a line trough those point. that line will cross the voltage and current axis.
if you take tose two values then you have Rinternal= voltage/current
The voltage should be the voltage that you measure without resistor attached, the current should be the current when you short-circuit the the power-cell.
The Rload power is at his highest when Rload = Rinternal