Several methods are currently available to determine the values of series and shunt resistance of a solar cell. A new method is presented here to numerically locate these values using the popular Newton–Raphson technique at maximum power point. Equations based on the Lambert W-function and their partial derivatives are provided so that all calculations may be performed in a Matlab or similar environment. The results of this new method are presented and compared with two published methods and the analytically obtained for a blue and grey type solar cell in earlier work (Charles et al., 1981). Additionally, three modules of various type (single, poly, and amorphous crystalline) were investigated. Values determined agreed with experimentally verified results and were obtained with quadratic convergence in all instances provided initial estimates of the roots were within vicinity of the actual roots.