Abstract :
The irradiance fluctuations and the subsequent variability of the power output of a PV system are analysed with some mathematical
tools based on the wavelet transform. It can be shown that the irradiance and power time series are nonstationary process whose behaviour
resembles that of a long memory process. Besides, the long memory spectral exponent a is a useful indicator of the fluctuation level
of a irradiance time series. On the other side, a time series of global irradiance on the horizontal plane can be simulated by means of the
wavestrapping technique on the clearness index and the fluctuation behaviour of this simulated time series correctly resembles the original
series. Moreover, a time series of global irradiance on the inclined plane can be simulated with the wavestrapping procedure applied
over a signal previously detrended by a partial reconstruction with a wavelet multiresolution analysis, and, once again, the fluctuation
behaviour of this simulated time series is correct. This procedure is a suitable tool for the simulation of irradiance incident over a group
of distant PV plants. Finally, a wavelet variance analysis and the long memory spectral exponent show that a PV plant behaves as a lowpass
filter.
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