Advanced analysis of PV system performance using normalised measurement data

The performance of grid connected systems is usually reported by AC energy (kWh/kWp) and performance ratio (PR) values (S. Ransome et al., 2003). If there are any outages or underperformance due to temporary faults or effects like shading these all need to be carefully corrected to give a true value for the performance otherwise these systems specific losses can dominate comparative kWh/kWp values. This paper proposes a way of calculating system performance using the final yield YF and the performance ratio versus plane of array irradiance G₁. When the system is performing well the data points are in a narrow range that can be curve fitted with empirical formulae. Underperforming points (which may depend on random events like outages) can be easily identified, as they are not lying on the narrow line. The expected yield in kWh/kWp can then be determined by folding in the curve fit to the good performance points by the expected irradiance and temperature data. These techniques are being used to test different module technologies and improvements such as anti reflection coated glass in Sydney, Australia and at ISET in Kassel, Germany.