In this paper, an efficient testing system for measuring a PV module's I-V curve is proposed. The proposed system is based on a controlled DC-DC boost converter. The advantage of using a DC-DC converter is that this converter is typically used in PV systems to track the maximum power point and to control the charging of the battery. Consequently, this device is utilized for I-V curve extraction without the need for further external devices. The I-V curve is extracted by modifying the duty cycle of the triggering signal of the boost converter's switch. The proposed system has been tested experimentally using a 120 Wp PV module. The results show that the proposed system can successfully extract I-V curves of PV module. Notably, the performance of the tested module, as measured by this study's system as well as with a reference system, was found to be in the range of 61-67% of the performance given in the datasheet. Hence, this result highlights the importance of considering a measurement of the actual performance of PV modules when designing any PV system so as to avoid an undersized system. The proposed I-V testing system can be used as a simple tool to diagnose any shortages or low performance problems in PV system. © 2017 by the authors.