Geographic Smoothing of Solar PV: Results from Gujarat

We examine the potential for geographic smoothing of solar photovoltaic (PV) electricity generation using 13 months of observed power production from utility-scale plants in Gujarat, India. We use geographic correlation and Fourier transform estimates of the power spectral density (PSD) to characterize the observed variability of operating solar PV plants as a function of time scale. Most plants show a spectrum that is linear in the loglog domain at high frequencies f, ranging from f^-1.23 to f^-1.56 (slopes of -1.23 and -1.56), thus exhibiting more relative variability at high frequencies than exhibited by wind plants. PSDs for large PV plants have a steeper slope than those for small plants, hence more smoothing at short time scales. Interconnecting 20 Gujarat plants yields a f-1.66 spectrum, reducing fluctuations at frequencies corresponding to 6 hours and 1 hour by 23% and 45%, respectively. Half this smoothing can be obtained through connecting 4-5 plants; the diminishing returns of less than 1% occurs at 12-14 plants. The largest plant (322MW) showed an f^-1.76 spectrum. This suggests that in Gujarat, the potential for smoothing is limited to that obtained by one large plant. Preliminary results comparing generation data with 1-minute irradiance data suggest that the irradiance data may have different physical characteristics than the power plant data, suggesting work to estimate solar siting as a function of irradiance only may need review.