  Green hydrogen is essential for producing renewable fuels that are needed in
sectors that are hard to electrify directly. Hydrogen production in a
grid-connected hybrid renewable energy plant necessitates smart planning to
meet long-term hydrogen trading agreements while minimising costs and
emissions. Previous research analysed economic and environmental impact of
hydrogen production based on full foresight of renewable energy availabilty,
electricity price, and CO2 intensity in the electricity grid. However, the full
foresight assumption is impractical in day-to-day operation, often leading to
underestimations of both the cost and CO2 emissions associated with hydrogen
production. Therefore, this research introduces a novel long-term planner that
uses historical data and short-term forecasts to plan hydrogen production in
the day-to-day operation of a grid-connected hybrid renewable energy plant. The
long-term planner co-minimises cost and CO2 emissions to determine the hydrogen
production for the next day taking into account the remaining hydrogen
production and the time remaining until the end of the delivery period, which
can be a week, a month, or a year. Extended delivery periods provide operation
flexibility, enabling cost and CO2 emissions reductions. Significant reductions
in CO2 emissions can be achieved with relatively small increases in the
levelised cost. Under day-to-day operation, the levelised cost of hydrogen is
marginally higher than that of the full foresight; the CO2 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, CO2
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.
