Cross-spectrum analysis applied to photovoltaic grids

A bivariate cross-spectrum (Fourier) analysis of incident irradiation R/sub g/ (independent series) and inverter power output - P/sub AC/ (dependent series), respectively module-working temperature - T/sub mod/ (independent) and P/sub AC/ is presented. Data were sampled between 24 and 31 August 2001 from a 10 kW/sub p/ grid-connected photovoltaic generator located at Valahia University of Targoviste, Romania. Continuous monitoring with a sampling rate of 10 minutes within this time interval allowed the construction of time series (N=1024). Several tests of crossed periodicity between selected series included squared coherency, gain, and phase shift. The most significant influence of R/sub g/ series values over P/sub AC/ series values was observed in the frequency interval 0.045-0.13. The P/sub Ac//T/sub mod/ bilateral periodicity is expected in 0.0049-0.0088 and 0.0117-0.0156 intervals. A significant influence of T/sub mod/ independent series over P/sub AC/ was assessed at frequencies of 0, 0.155, 0.288, 0.388, 0.413, 0.42, 0.452, 0.46, 0.468, 0.482, 0.49, and 0.5. For one week time series (24-31 August 2001), P/sub AC//R/sub g/ bilateral periodicity had a cycle of 1462.86 minutes /spl sim/ 24 hours. P/sub AC/T/sub mod/ bilateral periodicity showed 2 cycles (one cycle of 1462.86 minutes /spl sim/ 24 hours, respectively a second cycle of 731.43 minutes /spl sim/12 hours).