The paper considers the problems of optimization of wind and solar power plants (WPP and SPP) expansion and it operating modes in the prospective interstate power grid (ISPG) in Northeast Asia, taking into account the intermittence of their power output. A series of experiments with variations in the profiles of WPP and SPP in the model nodes were carried out. Also authors carried out some additional experiments with the increase in fuel costs for fossil fuel power plants due to environmental restrictions. As a result, an assessment of the character of the changes in the solution of the model for new installed capacities and their costs, depending on the variations for the profiles of the contributions generation of WPP and SPP to cover daily electrical load graphs, is obtained.