On-site characterization of PV modules using a portable, MOSFET-based capacitive load

As PV systems gain popularity, more installers are in need of better, lighter and lower-cost measurement equipment that can be used to detect problems with PV modules and arrays both before and after installation. This paper describes the design and implementation of a portable I-V curve tracer based on MOSFETs, with the capability of measuring open-circuit voltages (V_oc) up to 600 V, and short-circuit currents (I_sc) up to 30 A The modular design allows for changing the maximum measurable voltage and current, to allow for better resolution. The power circuit consists of 4 main components: a capacitor, two switches and discharge resistors. I-V measurements are taken by charging a load capacitor, which tracks the I-V characteristics of a PV module, and then discharging the capacitor once the measurement is complete. Using a capacitor over other types of loads makes the measurement faster, and keeps the energy consumed during measurement to a minimum, resulting in a simple thermal design. The resulting measurements are specific to the module temperature and incident light, and a conversion process to standard testing conditions (STC) is outlined for improved and standardized results.