A method for error compensation of modeled annual energy production estimates introduced by intra-hour irradiance variability at PV power plants with a high DC to AC ratio

Financial models of PV power plants that are created during the development phase of a project are typically based upon simulations performed at hourly timesteps. Historical irradiance data used in these simulations, such as a Typical Meteorological Year, are created from average irradiances over hour-long periods. We find that when actual weather conditions include significant intra-hour variability in irradiance, the annual energy production estimates based on modeling in hourly timesteps will not account for all inverter clipping which occurs during moments of high irradiance. This effect is particularly significant for systems with high a DC to AC nameplate ratio. At some PV plants already in operation, this phenomenon has been found to result in overestimated production estimates of nearly 5%. In this work, the average amount of this error is quantified for locations within the United States, and a methodology is proposed for compensating for it in post processing. This methodology applies a variable discount to each hour of the year for hourly energy output simulations based on irradiance. The discount function is intended to account for the difference in useful insolation as computed from hourly average irradiance data versus sub-hourly sampling rates.