Energy Yield and Clipping Loss Corrections for Hourly Inputs in Climates with Solar Variability

High-frequency measurements of solar resource from the National Institute of Standards and Technology (NIST) PV test-bed in Gaithersburg, MD were down-sampled from 1-minute to 1-hour and used to predict energy yield and clipping losses. Three virtual systems based on the NIST ground array with increasing DC/AC ratio were compared. With hourly input, clipping losses were smaller and energy yield was larger than predictions with high-frequency input. Systems with higher DC/AC ratio were more sensitive to time-resolution. The average difference between hourly and 1-minute predicted energy yield was 2% during the month of July for a DC/AC ratio of 1.3. These results demonstrate the importance of high-frequency solar resource in climates with solar variability to avoid over-predictions of energy yield for inverter blocks with a DC/AC ratio greater than one. The results of this study were implemented to develop a sub-hourly clipping adjustment factor for a pre-construction project site codenamed, “Orion,” near Northbridge, Massachusetts.