Using High Resolution Solar Measurement in PV Variability Studies

Clouds, aerosols, water vapor and other atmospheric constituents influence solar energy reaching the earth’s surface. Each of these atmospheric constituents has it’s own inherent scale of temporal and spatial variability and they in turn influence the variability in the amount of solar radiation reaching the earth’s surface. This combined influence of the atmospheric constituents and their separate variability characteristics makes solar variability modeling a complicated task. Output from photovoltaic (PV) power plants is dependent on the amount of solar energy reaching the surface. Therefore variability in solar radiation results in variability in PV plant output. The issue of variability in PV plant output has become important in the last couple of years as utility scale PV plants go online and increase in size. Understanding variability in PV plant output requires an understanding of (a) the spatial and temporal variability of solar radiation; (b) the influence of this solar variability on PV plant output. The goal of this paper is to understand what temporal and spatial scales of variability in Global Horizontal Radiation (GHI) are important to a PV plants and what measurements are needed to be able to characterize them. As solar radiation measuring instruments are point receivers it is important to understand how those measurements translate to energy received over a larger spatial extent. Also of importance is the temporal nature of variability characterized not at a single point on the ground but over large spatial areas. In this research we use high temporal and spatial resolution measurements from multiple time synchronized solar radiation sensors to create solar radiation fields at various spatial and temporal scales using a wide range of interpolation techniques. These solar fields are then used to create plant power output for various size PV plants. As various interpolation schemes can produce different distributions we investigate the impact of interpolation schemes on GHI and power output distribution. While power output from PV plants is an important quantity the temporal variability of power is a matter of concern to utilities. In this paper we show how PV plant output varies across different time scales.