This work deals with errors in determining the parasitic resistance of
photovoltaic cells. Serial and parallel resistances Rs and Rsh are determined
by the method of derivative for extreme conditions and method of IV curves
of the two different lights. The results of calculation are compared with
the resistances identified using a simplified model. Theoretical calculations
are verified on real terms, which were measured at the photovoltaic cells
SOLARTEC measurement system Pasan IId.