Accurate measurements of solar irradiance for evaluation of photovoltaic power profiles

The measurement, as accurate as possible, of solar irradiance is the starting point for the evaluation of photovoltaic (PV) power profiles in an electricity market in which many gigawatts of PV power are connected to the national network. This paper discusses the setup of five meteorological stations in South of Italy and the yearly experimental results of short-term global irradiance on the horizontal plane and on the best tilted plane. The 'broken clouds' phenomenon causes noticeable peaks in the irradiance and thus in the PV power. Its knowledge and prediction can be very useful to the Transmission System Operator for the management of peak generation. The evolution of relative humidity can give important information if the direct measurement of irradiance is missing. Finally, simple models for the irradiance in clear/cloudy sky situations can be used as a first approximation tool to predict the PV power profiles for the electricity market.