Two independent experiments are described that were performed on samples of EVA-laminated photovoltaic modules which form part of a grid-connected PV system in the Negev desert. Both types of experiment provide quantitative assessments of the rate at which module output power decreases when mirror-enhancement is employed under such conditions. One of the experiments, performed on 60 modules which have been exposed to mirror-enhanced solar radiation for the past 8.4 years, compared the measured I-V curve parameters of these modules with corresponding measurements that had been made 3.4 years earlier. The second experiment consisted of monthly I-V curve measurements, spread over the last 3.4 years, on three specific mirror-enhanced modules and on another three from which the mirrors had been removed. These experiments indicated that the mirror-enhanced modules are continuing to degrade at a comparable rate to an indirect estimate that had previously been made, i.e. approximately 1% per year. On the other hand, the modules from which mirrors were removed 3.4 years ago, although visually as ＇＇brown＇＇ as the others are degrading at an, as yet, unmeasurably small rate.