A new method to evaluate the five illuminated solar cell parameters (series resistance Rs, the ideality factor n, the photocurrent Iph, the shunt conductance Gsh and the diode saturation current Is) is described. The method uses the measured current-voltage data and the resulting calculated conductance of the device. By using the conductance, the number of parameters which has to be calculated is reduced and then only four parameters have to be extracted. A nonlinear least squares optimization algorithm based on the Newton model is hence used to evaluate these parameters. To overcome the difficulty in initializing the cell parameters, the simple conductance technique is used. When incorporated into microcomputer-based data acquisition software, the program allows theoretical modeling of solar cells. Results obtained for a commercial solar cell and a module are given. Comparison with other commonly used methods is also discussed.