Abstract This study investigates the impact of the seasonal Harmattan aerosol loading on PV module efficiency at a station in Southwest Nigeria. To this end, a simple, open-source, cost effective electronic load I-V curve tracer was developed to compare the I-V characteristics of a pair of horizontally positioned 80 W monocrystalline modules for the duration of the Harmattan period. The control module was regularly cleaned manually and the other module left to accumulate the Harmattan dust deposits. In order to obtain the modules’ characteristic parameters, an Arduino-based pulse width modulation (pwm) duty cycle was implemented to vary simultaneously, the gate-source voltages, VGS, of two power metal-oxide semiconductor field-effect transistors (MOSFETs) acting as fast variable loads for the modules. Experimental results acquired from the prototype circuit demonstrate that this method provides a more accurate approach and faster response than the resistive load tracer method. The prototype instrument was able to measure and reproduce characteristic curves that are obtainable from the more expensive branded products. Resulting curves depict reduction in the short circuit current, ISC, the current at maximum power, IMP, the power output, PMP and the efficiency, η of the dusty module by more than 18% in comparison with the control module over the measurement period.