Bi-level optimization of integrated PV-storage and by-product hydrogen systems for sustainable chlor-alkali industry

The chlor-alkali industry, characterized by high energy consumption and high emissions, is facing an urgent need for a green transformation. To address this challenge, this study proposes an integrated energy system that combines PV generation, waste hydrogen utilization, and grid interaction with multiple energy storage technologies. A bi-level optimization framework, incorporating capacity planning at the upper level and operational regulation at the lower level, is developed to optimize system performance. To solve this framework, a non-dominated genetic algorithm is employed, enabling the simultaneous optimization of economic performance, energy efficiency, and CO2 emissions across four typical configurations. Among them, the hybrid scheme integrating fuel cell, hydrogen storage, and battery systems achieves the best overall performance, reducing annualized costs by approximately 14 %, CO2 emissions by around 62,800 tons, and hydrogen venting by about 28 % compared to the baseline. These improvements are enabled by efficient hydrogen-to-electricity conversion, dual-storage coordination, and dynamic electricity price arbitrage. Seasonal operation analysis reveals that hydrogen storage plays a critical role in ensuring winter reliability, while battery enhances summer economics by mitigating PV curtailment. Meanwhile, exergy analysis highlights that systems prioritizing direct hydrogen utilization and minimizing energy flow competition exhibit the lowest thermodynamic losses. Additionally, thermal regulation results suggest gas turbine-based systems are more suitable under the high heating/cooling demand due to high-grade waste heat recovery. This study shows the operational strategies of the system under different scenarios, offering a new possibility for pushing up the low-carbon, high-efficiency, and sustainable chlor-alkali energy system.