The document discusses the importance of monitoring photovoltaic (PV) systems to understand their performance. It provides examples of PV system performance data collected by the International Energy Agency PV Power Systems Programme Task 13 from Italy, various European countries, and the Netherlands. Analysis of this data shows varying performance by location and over time, demonstrating the need for ongoing monitoring to ensure optimal PV output. The task also works to improve PV monitoring practices and develop performance benchmarks based on collected data.