An MINLP-based decision-making tool to help microbreweries improve energy efficiency and reduce carbon footprint through retrofits

• Microbreweries have difficulty economically competing with larger breweries. • A mixed-integer nonlinear optimisation model is developed for microbrewery retrofits. • An optimal configuration can reduce operating costs by 62.9 % and emissions by 77.1 %. Microbreweries have greater production costs per litre of beer compared to large breweries, as well as higher carbon footprints. Due to the range of different retrofit technologies available and the different capacities and configurations of microbreweries, it is not always clear what retrofits will improve operations. Therefore, this work proposes a novel mixed-integer nonlinear programming decision-making tool to be used by any microbrewery, that determines the technoeconomic feasibility and sizing of energy efficiency-improving retrofits, including solar and wind power, battery storage, anaerobic digestion, boiler type selection, heat integration by heat storage, and carbon capture via dual-function materials. The model was demonstrated on a real UK microbrewery case study. The model gave an optimal configuration of a 10 m 3 anaerobic digester, 30 solar panels outputting 380 W each, an 800 W wind turbine and a 2.3 m 3 heat storage tank, reducing annual operating costs by 62.9 % and carbon dioxide emissions by 77.1 % with a payback period of 8 years. The tool is designed to be flexible for use by any microbrewery in any location with any brewing recipe and allow the owner(s) to develop more profitable and sustainable microbreweries. Tweetable abstract Microbreweries can implement mathematically optimised renewable energy, heat integration and anaerobic digestion to reduce operating costs by 62.9 % and carbon emissions by 77.1 %.