The principle of energy production evaluation of PV systems is explained and parameter definitions are given at first. Then, a new method is proposed to verify detailed system parameters from ordinary, monitored data. Data acquisition system is used for the evaluation of long-term energy performance. Monitored data are normally utilized to calculate input radiant energy,output electrical energy, system yield (equivalent operated hours), system performance ratio and so on. The author has developed sophisticated verification procedures (SV method), where system performance ratio K, power conditioner efficiency K-C, temperature factor K-PT, shading factor K-HS, load matching factor K-PM and other array parameter K-PO can be identified from only 4 monitored points with other externally available information. Especially, time series data verification process can produce more realistic results of shading and mismatch losses respectively. As a realistic example, SV method is applied to data taken from 71 systems in the Japanese Field Test Project.