The hybrid pumped storage-wind-photovoltaic multi-energy complementary system has broad application prospects. However

its capacity design needs to characterize the complex relationship between the water volume and electric power

and its economic evaluation should consider the rules of electricity markets. This paper describes a new two-stage optimization framework for optimizing operation and capacity decision. First

a consistent assumption for the target gross output is presented; and a double-objective operation optimization model is developed. Then

a discrete decision space is obtained through optimization based on a large number of medium and long-term operation cases. Finally

the scheme with the maximized net present value (NPV) is selected. Application in a case study of the clean energy base in the upper Yellow River gives the conclusion as follows. New energy capacities corresponding to high

medium and low acceptance degrees of load loss risks are 3.2-3.9 times

2.4-3.0 times

and 1.6-2.1 times that of the mixed pumping and storage capacity

respectively. The peak to valley ratios of the system's monthly electricity delivery range from 1.36 to 1.45

indicating the power sources in the system are well complementary on the medium and long time scales.