Improving Performance Ratio Calculations through Optimizing Front POA Irradiance Sensor Positioning

Underperformance of PV plants against forecast can happen for many reasons. Here we investigate the placement locations of the irradiance sensors. With well-placed accurate irradiance sensors, the performance ratio can be more accurately determined. And this reduction in performance ratio variability, due to sensor locations, reduces the risks of the solar park investment. Kipp & Zonen produces pyranometers that accurately measure front and rear side plane of array (POA) irradiance as well as surface albedo. The primary site investigated is a bifacial, single-axis tracker system. For the front side, we evaluate the mounting position of the pyranometer within the plant and across the PV module. We have performed simulations using a ray-tracing toolkit, Bifacial Radiance, from NREL and in addition a 7 month validation in a utility scale PV plant with multiple pyranometers is underway. Within the plant both simulations as well as measurements show that edge mounted pyranometers measures about 2% more. Across the module for cumulative data, the variation in the simulation is larger than in the measurements. For the intra-day variation there is a good match between simulation and measurements. To help improve the performance ratio calculation a guidance for optimal placements of irradiance sensors is given.