Areal Solar Irradiance Estimated by Sparsely Distributed Observations of Solar Radiation

Photovoltaic (PV) power generation is being decentralized and introduced on various scales in electric power systems that are expanding over wider areas. To understand the effect of PV power generation on these electric power systems (in areas ranging from power generation operation and control to voltage management of the distribution system), areal solar irradiance must be estimated for a target area, particularly, for the position and surface area that correspond to the PV power generation equipment location. By applying spatiotemporal kriging and covariance analysis to observed solar irradiance time series (obtained from sparsely distributed solar irradiance meters), we developed a technique that determines areal solar irradiance for an arbitrary location and surface area to estimate its surficial distribution. The weather conditions under which the spatiotemporal kriging technique can be applied were clarified using solar irradiance and meteorological observations during a one-year period at 25 observation points in the Kansai area.