In this paper, a new approach to data acquired during monitoring of PV systems is proposed. It is based on modern informatics tools, like the commonly used XML or as well as new web services. The goal is to propose a universal data scheme (PVML) allowing analysis of the performance of a PV system of any type and size. Such an approach should be helpful in detection of faulty operation or even underperformance of the PV systems. The work has been carried out in the framework of the EC-funded Integrated Project PERFORMANCE.