Optimizing Hydro-Wind-Solar Systems for Synergy: A Multi-Objective Framework Balancing Ecology, Generation, and Water Supply

The signing of the Paris Agreement has significantly accelerated the growth of renewable energy sources such as wind and solar. However, these energy sources are inherently reliant on meteorological conditions, resulting in intermittency, volatility, and limited predictability, which present challenges for their integration into the power grid. Developing a hydro-wind-solar complementary system, leveraging the flexible regulation capabilities of hydropower, offers a promising solution to these types of challenges.

Determining the optimal capacity of a hydro-wind-solar complementary system is crucial for fully utilizing the regulation potential of hydropower and maximizing the complementarity of diverse natural resources. However, current capacity planning research focuses primarily on technical and economic metrics at the power generation level, often neglecting the comprehensive benefits related to reservoir ecology and water supply. Moreover, the current approach faces challenges in addressing complex multi-objective problems effectively.

To solve the above issues, this study proposes a novel framework based on the theory of synergetics to determine the optimal capacities for wind and solar power. Synergetics is an interdisciplinary approach that examines how individual components of a complex system interact and self-organize to achieve optimal performance and stability. When it comes to the proposed double-layer framework, an inner layer operation model aims at maximizing overall order degree is established to optimize the system's operational performance. Secondly, Kolmogorov entropy is introduced in the outer layer to characterize the synergy of different wind and solar capacity schemes, thereby selecting the one with the best synergistic effect. Additionally, techno-economic evaluation indicators are introduced to validate the framework's effectiveness. A case study of the clean energy system with cascaded reservoirs on the upper Yellow River was conducted, and the results indicate that:

(1) The proposed framework effectively meets the requirements of multiple complex objectives, and the optimal capacity scheme performs well in both economic and technical aspects.

(2) Compared to variations in wind and solar resources, inflow conditions and agricultural water demand have a greater impact on capacity planning and operational performance.

(3) The optimal capacity ratio of hydro to wind and solar in the upper Yellow River is around 1:0.59.

Considering the above, this study provides important theoretical support for expanding capacity planning methods in hybrid energy systems that rely on the dispatchable nature of hydropower.