Sparse solar irradiance observations from meters are used with spatiotemporal kriging and covariance analysis to estimate areal solar irradiance over arbitrary locations and surface areas. This technique was developed and tested using one year of solar irradiance and weather observations from 25 points in the Kansai area of Japan to understand the effects of decentralized photovoltaic power generation on electric power systems.

1. AREAL SOLAR IRRADIANCE ESTIMATED BY SPARSELY
DISTRIBUTED OBSERVATIONS OF SOLAR RADIATION
ABSTRACT
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.