Additionality is a key requirement for the renewables based electricity to be used by electrolysers to produce renewable hydrogen. Additionality could be defined as the requirement that renewables-based electricity used in electrolysers for the production of renewable hydrogen is additional to the renewables-based electricity which is used to meet the renewable penetration target with respect to final electricity consumption. Different approaches to additionality have been considered in the debate over the last year. All of them require some degree of temporal (and geographical) correlation between the consumption of electricity by the electrolysers and the generation of the additional renewables-based electricity. This Policy Brief questions whether a degree of temporal correlation is really necessary to ensure the additionality of the renewables-based electricity consumed by the electrolysers. The additionality of the renewables-based electricity consumed by the electrolysers could be ensured over a year-long period, in line with the way in which the general renewable energy penetration target is defined, by the implementation of a system based on guarantees of renewable origin. Such an approach would also facilitate the operation of electrolysers at their optimal utilisation rate.