Cost and CO2 emissions co-optimisation of green hydrogen production in a grid-connected renewable energy system

Green hydrogen, a crucial component for producing renewable fuels, is particularly needed in sectors that are challenging to electrify directly. This research focuses on green hydrogen production in a grid-connected hybrid renewable energy plant, which requires strategic planning to meet long-term hydrogen purchase agreements while minimising costs and emissions. Unlike previous studies that relied on full foresight of renewable energy availability, electricity price, and CO 2 intensity in the electricity grid, this research introduces a novel long-term planner. This planner utilises historical data and short-term forecasts to plan daily hydrogen production, addressing the impracticality of the full foresight assumption which often leads to underestimations of both cost and CO 2 emissions. The long-term planner co-minimises cost and CO 2 emissions, determining the total hydrogen production for the upcoming day based on the remaining hydrogen production and the time remaining until the end of the delivery period, which can range from a week to a year. This approach provides operational flexibility, enabling reductions in cost and CO 2 emissions. The findings reveal that significant reductions in CO 2 emissions can be achieved with relatively small increases in the levelised cost. In daily operation, the levelised cost of hydrogen is marginally higher than that of the full foresight; the CO 2 emissions can be up to 60% higher. Despite a significant portion of the produced hydrogen not meeting the criteria for green hydrogen designation under current rules, CO 2 emissions are lower than those from existing alternative hydrogen production methods. These results underscore the importance of balancing cost considerations with environmental impacts in operational decision-making. The study suggests that improvements to current rules regarding the green labelling of hydrogen could involve implementing transparent accounting based on hourly CO 2 emissions and reducing the specific CO 2 emission threshold for green hydrogen production. This research contributes to the field by demonstrating a practical approach to hydrogen production planning and highlighting potential areas for policy improvement. • Historical and short-term forecast data are utilised to plan for long-term hydrogen targets. • Significant CO2 emission reductions can be achieved with a relatively small increase in cost. • Calculation of CO2 emissions based on full foresight can be significantly underestimated.