An Improved Model for AC Power from Grid Connected Photovoltaic Systems and Comparison with Large-Scale Hourly Measured Data

The diffusion of renewable energy sources (RES) can lead to cost reductions for the ancillary services provided to the transmission system operator, in particular, when the RES production can be estimated with appropriate accuracy. This article presents significant improvements to photovoltaic (PV) power conversion models found in the literature for grid-connected PV systems. The refinement of the conversion model is based on public hourly data of irradiance and ambient temperature, referred to the sites of three groups of PV plants, to calculate the hourly average power injected into the grid. The values obtained are compared with the hourly average power measured by the distribution system operator meters on the PV systems. A double-step optimization procedure, based on seasonal analysis, sets up the various parameters in the PV conversion model. The key result is that the deviation between the simulated and measured annual energy is reduced to less than 2%. Moreover, with the proposed model the monthly energy deviations are limited to a few percentage points. This allows for significant improvements in the estimation of the production of grid-connected PV systems.