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A Model Correcting the Effect of Sub-Hourly Irradiance Fluctuations on Overload Clipping Losses in Hourly Simulations
A. Villoz, B. Wittmer, A. Mermoud, M. Oliosi, A. Bridel-Bertomeu
Simulation, System Performance, Modeling, Clipping
PV Systems Engineering, Integrated/Applied PV
Subtopic: Engineering Design and Installation of PV Systems
Event: 8th World Conference on Photovoltaic Energy Conversion
Session: 4EO.2.2
1151 - 1156
ISBN: 3-936338-86-8
Paper DOI: 10.4229/WCPEC-82022-4EO.2.2
0,00 EUR
Document(s): paper, presentation


Simulations of PV systems that proceed in hourly steps can underestimate overload losses arising from sub-hourly irradiance fluctuations. The aim of this study is to estimate and address these additional overload clipping losses to improve the accuracy of the simulations in PVsyst. The current trend for designing PV systems is to increase the DC/AC ratio. This trend is mainly due to PV modules plummeting in price and PV plants being constrained by grid limitations. The increase in DC/AC ratio allows PV systems to maximize production for the same AC capacity, by having the inverters operating at full output power for more hours during the day. When the inverter is operating close to maximal power, it can happen that irradiance spikes drive it into clipping conditions. This behavior is not captured by a simulation that proceeds in hourly steps, which leads to a systematic underestimation of the clipping losses (1-5% or more over a year). The purpose of this study is to find a way to estimate from sub-hourly irradiance fluctuations a correction that can be applied in a general way to the clipping losses of an hourly simulation. In a first step, an analysis of hourly average irradiation data and sub-hourly data was done, to identify a way to calculate the behavior of overload clipping losses when applying a threshold. The analysis then went on using the same irradiation data for complete simulations in four climates and covering multiple cases of orientations of PV modules and DC/AC ratios. The goal of the study, to improve simulations in PVsyst that are done in hourly steps, was achieved by using coefficients extracted from the sub-hourly data, applied on a simple geometrical model. This model corrects the error on overload losses significantly and thereby reduces the average difference of minute- and hourly-based AC generation below 1% for each DC/AC ratio.