Large PV plants have different relevance of construction details. The aim of this thesis is to show the different impact of well-known influence factors especially in large PV parks with more than 10 MWp installed capacity. This thesis is based on the on PVSEC 2014 presented results of different relevance of influence factors on performance and will give full particulars on the effects of different strings cabling. To show this two large (>20 MWp) PV-plants located at peninsula Crimea could be used with nearly equivalent technical structure and less than 10 km distance between the locations. There it was possible to get access to monitoring values over more than 2 years. The main methodology is comparison of the parks and correction of the power production caused by local weather differences. Any additional differences and irregularities of other impact than caused by cabling are corrected and estimation of impact will be shown. Caused by the optimized park design it will be shown, that the design cabling in single row strings leads to 460 000 kWh less losses during one seasons in the 31.5 MWp park. In addition to the result for 1 year also a recommendation the best timeframe for setting up the changes will be given on additional investigations. The result can be used for optimizing the design of large PV plants and gives park designer also a feeling for the main influence factors.