The production of significant amounts of “zero-carbon” hydrogen via electrolysis is a key pathway for enabling large capacities of intermittent renewables to be integrated within power systems. However, electrolyser utilisation factors are low due to the low annual capacity factors of renewable power sources. To improve the utilisation factor (and so improve the hydrogen yield per MW of electrolyser stock) without compromising the carbon footprint of the hydrogen, requires large installed capacities of other zero-carbon power sources (e.g. nuclear and CO2-sequestered power plant) of higher capacity factor. The role of the electrolyser stock becomes one of managing these characteristically different power inputs to ensure the residual load placed on fossil-fuelled plant is as steady as possible.

An analysis is presented of an islanded power system containing large deployments of electrolysers, wind, dispatchable “zero-carbon” thermal (ZCPP) and conventional fossil-fuelled thermal power plant. By operating the electrolyser stock as a load management mechanism the transient load profile placed on fossil-fuelled thermal plant can be adjusted (to fill valleys and create plateaus). This approach is then applied to identify a preferred utilization strategy for the electrolyser stock. Three implementation cases for the electrolyser stock are studied for periods of distinct wind availability. The main objectives are to maximize (i) the hydrogen yield; (ii) the utilization factor of the electrolyser stock; and minimize (iii) the carbon intensity of electricity (CIe). The presented results are based on demand and upscaled wind generation data obtained from the Eastern Denmark power system.

It is found that for a wind penetration of 100% of system maximum demand, the effect of integrating an installed capacity of ZCPP totalling 35% of system maximum demand is to reduce the carbon intensity of electricity by more than half that of a power system where no electrolysers are implemented. This can be achieved while creating a virtually flat daily load profile on the conventional fossil-fuelled plant, which will yield additional carbon savings.

Maximum benefits are attained using ZCPP both for electricity generation and hydrogen production, operating them in such manner that the output directed to cover the consumer demand increases at peak times (thus decreasing the output directed to electrolysers).

A trade-off exists between the carbon intensity of electricity delivered to consumers, the rates of hydrogen produced and the utilization factor of the electrolyser stock. At 100% wind penetration 370 tones of H2 per day can be produced with a utilization factor of 26% for the electrolyser stock and CIe is then 0.41 kg CO2/kWhe when 50% of the aggregate ZCPP output is directed to the electrolyser stock. Yet the amount of zero-carbon hydrogen produced can be increased up to 471 tons of H2 per day and then the utilization factor increases up to 33%, but then CIe increases up to 0.48 kg CO2/kWhe. Depending on the energy system under consideration and on the hydrogen and electricity demands to be covered, optimum values for these three variables can be found to maximize the net carbon benefits derived from a large implementation of electrolysers.