  The ability to accurately forecast power generation from renewable sources is
nowadays recognised as a fundamental skill to improve the operation of power
systems. Despite the general interest of the power community in this topic, it
is not always simple to compare different forecasting methodologies, and infer
the impact of single components in providing accurate predictions. In this
paper we extensively compare simple forecasting methodologies with more
sophisticated ones over 32 photovoltaic plants of different size and technology
over a whole year. Also, we try to evaluate the impact of weather conditions
and weather forecasts on the prediction of PV power generation.
