Current at maximum power - PV cell

[Imperatore]

Hello there !

I got question regarding PV cell.
The current at maximum power I_m calculated from current-voltage characteristic doesn't equal to the one calculated from P(U_shunt, as you can see in the attached picture. http://prnt.sc/b864hx
Furthermore, the I_m from P(U) characteristic is about 2 times greater.
This is rather strange result for me. I am of the opinion, that these currents should be approximately equal. Maybe I am wrong and you will say it's nothing weird about these results.I hope so :)

 

[Simon Bridge]

To understand the result you need to know how the graph was arrived at.

 

[Imperatore]

It is my graph ;)

The current from P(U) is the current through the shut resistance, and I_m from current-voltage characteristic shows the current without shut resistance. It is that what you mean?
In here http://www.instsani.pl/images/PV8.ht4.jpg you can see, that these currents are equal.
Little confused now.

 

[Simon Bridge]

OK - compare the methodology: you should find you are measuring different things, or the same thing in different circumstances.

 

[Imperatore]

OK - compare the methodology: you should find you are measuring different things, or the same thing in different circumstances.

The current from P(U) is the current through the shut resistance, and I am from current-voltage characteristic shows the current without shut resistance. It is that what you mean?

Is it that difference?

 

[Simon Bridge]

Why not check and see if your results are consistent with standard models?

 

[Imperatore]

You mean that http://en.wikipedia.org/wiki/Theory_of_solar_cells#Equivalent_circuit_of_a_solar_cell ?

 

[Imperatore]

From that I get:
1) Characteristic U(I):
I_L=I_D+I_Sh and I_Sh= 0, so I_L=I_D=0,5
2) Characterisitic P(U):
0,5=I_L=I_D+1,17(it's measured I_Sh), so I_D=-0,67 mA

sth wrong

 

[Imperatore]

aby book explainig that pheno? It is written in every book I' ve examined that these two currents should be approx the same, what in my case obviously is not met.