Power produced by utility-scale solar photovoltaic (PV) systems has fluctuations on both short and long time scales. Power spectral density (PSD) analysis provides information on the character of these power fluctuations. Examination of the correlation and step size of the power output between several PV sites within a multi-site system allows assessment of geographic diversification for addressing intermittency. Both techniques provide insight into the characteristics of firm power and/or demand response required to accommodate large-scale PV deployment. Copyright © 2007 John Wiley & Sons, Ltd.