Compared with traditional single storage technologies, a hybrid energy storage system (HESS) combines various storage methods, utilizing the advantages of multiple techniques and compensating for the shortcomings of a single storage technology. It is one of the effective ways to address the intermittency issues of renewable power output. Addressing issues of rapid fluctuation and randomness of renewable power, this paper proposes an optimization configuration method of a power-energy hybrid storage system (PEHSS) for renewable power plants (RPP). The proposed method decomposes and reconstructs the original output data of RPP, obtaining the high-frequency fluctuation information and low-frequency steady-state information. Subsequently, the high-power energy storage system (HPESS), such as flywheels and super capacitors (SC), can be configured with the high-frequency fluctuation information, which contributes to the suppression of power fluctuations for RPPs. Then the capacity of the energy storage system (ESS) can be calculated with the low-frequency steady-state information to achieve within-day peak shaving for RPPs. This research overcomes the shortcomings of traditional planning methods in multi-time scale configuration for HESS. The case studies verify the effectiveness of the proposed method.