Electricity generated by photovoltaic (PV) systems can significantly offset the peak electricity demand. In this paper, we calculated the peak load that can be offset by 10 MWp distributed grid connected PV systems installed at Arizona State University (ASU) campus. We found that the peak electricity generated by the PV systems closely matched the peak demand curve and reduced the demand by approximately 20%. A massive, once in a thirty-year dust storm that hit Tempe on July 5th 2011 had a minimal effect on PV system's performance. From the availability of real time system performance and meteorological data, it was calculated that the performance of PV systems dropped by less than 5% due to accumulated dust and the performance was recovered by a precipitation of less than 0.2 inches five days later. We report the measured capacity factors of various PV systems to understand the effect of seasonal variations, module type and tracking system on system performance. We also compared the actual measured and simulated capacity factors for a PV system for different tilt and tracking cases.