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This study investigates the impact of including (or neglecting) the variable efficiency of hydrogen electrolyzers as a function of operating power in the modelling of green hydrogen produced from variable renewable energy sources. Results show that neglecting the variable electrolyzer efficiency, as is commonly done in studies of green hydrogen, leads to significant overestimation of hydrogen production in the range of 5–24%. The effects of the time resolution used in models are also investigated, as well as the impact of including the option for the electrolyzer to switch to stand-by mode instead of powering down and electrolyzer ramp rate constraints. Results indicate that these have a minor effect on overall hydrogen production, with the use of hour resolution data leading to overestimation in the range of 0.2–2%, relative to using 5-min data. This study used data from three solar farms and three wind in Australia, from which it is observed that wind farms produced 55% more hydrogen than the solar farms. The results in this study highlight the critical importance of including the variable efficiency of electrolyzers in the modelling of green hydrogen production. As this industry scales, continuing to neglect this effect would lead to the overestimation of hydrogen production by tens of megatonnes. • Variable efficiency electrolyzers are compared to fixed efficiency electrolyzers. • Fixed efficiency can lead to overestimation in hydrogen production by up to 24%. • Low fidelity time resolution has a modest impact on modelling hydrogen production. • Fixed efficiency electrolyzers underestimate the optimal size of hydrogen plant. • Results are validated using data from six renewable energy sites in Australia. [ABSTRACT FROM AUTHOR]

Renewable green fuels (RGF) such as hydrogen are the global energy future. Air pollution is compounded with climate change as the emissions driving both development problems come largely from the same source of fossil fuel burning. As an energy exporter, Australian energy export dominates the total energy production and the RGF has become central to the current proposal of Australian government to reach net zero emission. The hydrogen production from solar panels only on 3% of Australia's land area could compensate 10 times of Germany's non-electricity energy consumption. In the unique geographic position, Australia's RGF export attracts significant costs for long distance onboard storage and shipping. While the cost reduction of RGF production relies on technological advancement which needs a long time, the storage and shipping costs must be minimised for Australia to remain competitive in the global energy market. The present review concentrates on Australian export pathways of lifecycles of liquid renewable green fuels including renewable liquified hydrogen (LH 2), liquified methane (LCH 4), ammonia (NH 3) and methanol (CH 3 OH) as liquid RGF have the advantages of adopting the existing infrastructure. This review compares the advantages and disadvantages of discussed renewable energy carriers. It is found that the cost of LH 2 pathway can be acceptable for shipping distance of up to 7000 km (Asian countries such as Japan) but ammonia (NH 3) or methanol (CH 3 OH) pathways may be more cost effective for shipping distance above 7000 km for European counties such as Germany. These observations suggest the proper fuel forms to fulfill the requirements to different customers, and hence will highlight Australia's position as one of major exporters of renewable energy in the future. Detailed techno-economic analysis is worth to be done for supplying more quantitative results. A review for Australian renewable green fuel export pathways. [Display omitted] • Australian export pathways of liquid renewable green fuels were investigated. • Different fuel forms should be chosen for different customers. • Australia's position as a major exporter of renewable energy is highlighted. [ABSTRACT FROM AUTHOR]