Maximum power point tracking (MPPT) is an important function in all photovoltaic (PV) power systems. The classical "hill climbing" and "incremental conductance" MPPT algorithms are widely applied in many papers and applications. Both algorithms perturb the operating conditions of the PV array and detect the changes in generated power. Since the detected change in generated power also could be a result of changes in irradiance, both algorithms are prone to failure in case of large changes in irradiance. This paper starts to discuss the size of the perturbation of the operating conditions for both algorithms, based on the single-diode model. The result is used to select the updating frequency for the two algorithms, in order not to run away under certain dynamic conditions. Both algorithms are implemented in an inverter and tested over 16 days of simultaneous operation. Basic statistical procedures, the paired t-test, have been applied to the data with the conclusion that the two algorithms perform equally good.