Because of its simplicity and ease of implementation, the perturb and observe (P&O) algorithm is the most commonly applied maximum power point tracking (MPPT) control scheme in photovoltaic (PV) applications. Two techniques are usually used for implementing the P&O algorithm: reference voltage perturbation where a reference value for the PV generator output voltage is used as the control parameter and direct duty ratio perturbation where the duty ratio of the MPPT converter is used directly as the control parameter. This paper presents an experimental comparison between these two techniques when used in a photovoltaic system feeding a resistive load. The influence of the step size and the speed at which the control parameter is perturbed is investigated. The various advantages and drawbacks of each technique are identified and energy utilization efficiency is calculated for different weather conditions. Practical results obtained using a 540Wp PV experimental setup show very good agreement with numerical simulations. (6 pages)