Dual-module coupled rolling optimization for hydro-wind-PV-battery complementary system: Considering battery capacity degradation

Hydro-wind-PV-battery multi-energy system (HWPB-MES) is an effective technique route to enhance the utilization of large-scaled renewable energy sources. The integration of battery energy storage system (BESS) plays an essential role in reducing unfavorable operation of hydropower units and renewable energy curtailment. However, the impact of BESS capacity degradation on flexibility and operational risks of HWPB-MES remains an open challenge. Traditional planning methods tend to use replacement cost of battery from economic perspective, failing to adequately account for the interacting mechanism between battery capacity fading and hydro-BESS coordination pattern. To address the challenge, this study proposes a novel dual-module coupled rolling optimization methodology for HWPB-MES, which captures the mutual feedback mechanism between battery aging and multiple operational risks at both component & systematic levels. Meanwhile, based on the embedded hydro-BESS coordinating strategy, the correlation between frequencies of hydropower risky operation (start/stop and vibration zone crossing) and BESS remaining capacity is analyzed. Also, comparative case studies are carried out to validate the methodology based on region of Northwest China. Results show that the proposed strategy significantly reduces risky hydropower operation. However, with battery capacity fading to 80 % by fourth year, hydropower units are forced to experience a 7.7 % increase in start-stop cycles and a 6.9 % increase in vibration zone crossings. Shifting patterns of renewable curtailment and electricity shortages are witnessed with sharp rises of 14.5 % and 17 % due to BESS degradation, respectively. The proposed methodology clearly reveals the bidirectional interaction between reliabilities of battery storage and hydropower unit to regulate fluctuation of renewable energy, which provides a theoretical reference to enhancing the long-term stability and short-term flexibility of similar systems.