Predicting the energy harvests of PV installations using rotating shadow band radiometer data

Actual solar radiation data are invaluable for determining the potential energy harvest and harvest uncertainties at proposed PV farm locations, and for benchmarking the daily performance of existing PV installations in the surrounding area. Benchmarking helps to determine if PV installations are producing the energy that they should, taking into consideration daily variations in solar radiation levels. This paper documents a procedure for using one-minute spaced rotating shadow band radiometer data to predict daily and hourly energy harvests (kWh per installed kW) and better understand their uncertainties. The data presented are for a desert site in West Texas. The panel orientations considered include 1. fixed mounts over a wide range of azimuth and tilt angles, 2. south-facing fixed-tilt single-axis trackers, and 3. dual-axis trackers. Results for one year are given, and the impact of sub-optimal fixed panel orientations and tracking methods are shown.