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• Retrofitting coal-fired power plants with renewables and hybrid energy storages. • Flexible green hydrogen production via electrolyzer to tackle energy curtailment. • Multi-regional and multi-temporal feasibility analysis of the carbon-free retrofit. • The carbon-free retrofit is techno-economically feasible in wind-rich regions. • The proposed retrofit in Jilin is more profitable than carbon capture and storage. In the context of global decarbonization, China announced to peak its CO 2 emission before 2030 and achieve carbon neutrality before 2060. The power sector dominates the total CO 2 emissions in China, where coal-fired power plants are both the largest source of power generation and CO 2 emissions, so exploring its decarbonized transition is essential to achieving the carbon neutrality commitment. To this end, this paper proposes a novel carbon-free retrofitting scheme for coal-fired power plants based on 100% renewable energy, hybrid energy storage system, and flexible green hydrogen production using energy curtailment, which can be techno-economically feasible for practical applications. Then, the multi-regional and multi-temporal profitability of this retrofitting scheme is comprehensively assessed to confirm the proposed hypothesis via a life cycle economic optimization model. Taking the province-level regions in China as case studies, the assessment results reveal that the proposed retrofitting scheme is technically feasible in all investigated regions, and economically profitable in Jilin, Shanghai, Liaoning, and Heilongjiang regions with rich wind resource. Particularly, the optimal net present value of the proposed scheme in Jilin is 24.04 billion CNY, higher than the figure for carbon capture and storage-based retrofit (5.79 billion CNY) and even the non-retrofitted plant (9.28 billion CNY), confirming its economic superiority in specific regions. The cost breakdown in Jilin indicates that the flexible green hydrogen production using energy curtailment can additionally provide 106.3 billion CNY hydrogen trading revenue to recover the overall retrofitting cost (104.7 billion CNY), while the retrofitting scheme without electrolyzer will suffer a 44.17 billion CNY deficit owing to the oversized configuration. Moreover, the long-term profitability analysis shows that the proposed retrofitting scheme in Jilin can always achieve the best profitability from 2022 to 2050 despite the decline of projected hydrogen price, with the net present value ranging from 24.04 billion CNY to 1.12 billion CNY. Overall, this paper provides a techno-economically feasible solution for the decarbonizing transition of coal-fired power plants, and the proposed retrofit can be piloted in regions with rich renewable energy resources and mature hydrogen trading market. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel optimization approach is developed for the Food-Energy-Water Nexus. • The energy and food industries exhibit synergy and competition for water use. • Synergy and competition scenarios quantify the state of industrial water use. • The inter-industry competitive and unsustainable water use are prominent. • Response paths are proposed based on administrative means and market allocation. Studies on the Food-Energy-Water Nexus can help researchers, policy makers, practitioners, and stakeholders identify opportunities to maintain the nexus' synergies and trade-offs. Water, the most sensitive element in the Food-Energy-Water Nexus, readily influences the stability, cooperativity, and safety of the nexus. The key initiative to ensure water security in the Food-Energy-Water Nexus is properly handling water for food and energy production, but the existed conceptual framework and evaluation system are incomplete. This paper uses the Driver-Pressure-State-Impact-Response model and the water footprint theory to construct an optimization approach to evaluate the synergy and competition for water between food and energy at five levels. This optimization approach was tested and implemented based on a case study of 31 provinces in the Chinese Mainland from 1997 to 2016. The results showed that the blue water footprint of 31 provinces was 263.48 Gm3 in 2016, and the gray water footprint was 1518.57 Gm3, which led to inter-industry competitive water use and water unsustainability. In 2016, the 31 provinces had developed into Industry Synergy Sustainability scenario (1 province), Industry Synergy Unsustainability scenario (9 provinces), Industry Competition Unsustainability scenario (16 provinces), and Industry Competition Sustainability scenario (5 provinces), presenting a spatially clustered distribution pattern. Except for Xinjiang and Jilin, the remaining 29 provinces gradually developed into sustainable or synergistic scenarios. The total production water footprint in the Industry Competition Unsustainability scenario reached 4.08 m3/kg in 2016, while the Industry Synergy Sustainability scenario was only 3.67 m3/kg. This paper proposes two response paths, based on market allocation and administrative means, to facilitate the gradual evolution of the Industry Competition Unsustainability scenario into the Industry Synergy Sustainability scenario. These paths contribute to the efficient and sustainable integrated management of food, energy, and water globally. [ABSTRACT FROM AUTHOR]