Introduction
The performance parameters of photovoltaic (PV) modules are optimised at some reference condition, usually at Standard Test Conditions (STC: of irradiance, 25°C cell temperature and air mass 1.5 global spectrum). However, PV modules are deployed outdoors where operating conditions are far from the reference conditions. Different module technologies respond differently to changes in irradiance, temperature and air mass. In order to characterise the response of performance parameters to various conditions, a system capable of continuously monitoring the current-voltage (I-V) characteristics of seven modules, was designed. The low-cost data acquisition system was designed, built and installed at the University of Port Elizabeth, South Africa. Results obtained from monitoring I-V characteristics can be used to investigate and compare the actual power produced by modules under realistic operating conditions. The results may also be used for degradation and failure analysis. In this paper the design of the system used to sequentially measure I-V characteristics is presented together with some initial results. Results presented here show the effect of-irradiance and temperature on module performance parameters as well as a comparison between module energy production.