As a solution for the global environmental issues and energy resource depletion issue, photovoltaic generation (PV) has been installed rapidly. However, PV generation output heavily depends on climatic conditions and it would give negative impacts on balancing between supply and demand in power systems. In order to secure the power quality, the unstable output from the natural energy resource driven generators should be considered directly in usual power system operations such as supply and demand balancing. The solar radiation forecast would take a key role in the future operation of power system; therefore, investigation of performance and its characteristics of the forecast accuracy is important. In this paper, standard deviation and time series characteristics of solar radiation forecast error are statistically estimated. This paper also develops a First-order Markov process model for solar radiation forecast error.