This study investigates the implications of different standards for certifying renewable electricity used in electrolytic hydrogen production. It compares electricity procurement strategies for a constant hydrogen demand in selected European countries in 2025 and 2030. The study finds that local additionality is necessary to ensure low emissions. Annual and monthly matching cases show that baseload operation of electrolysis can lead to higher emissions due to reliance on fossil-fuelled generation. In contrast, hourly matching does not increase system-level emissions but can result in high costs for constant supply if only wind, solar, and short-term battery storage are available. Flexible operation or hydrogen storage reduces the cost penalty of hourly versus annual matching to 7%–8%. Hydrogen production with monthly matching can reduce system emissions if electrolysers operate flexibly or the renewable generation share is large. The largest emission reduction is achieved with hourly matching when surplus electricity generation can be sold to the grid. The study concludes that flexible operation of electrolysis should be supported to guarantee low emissions and low hydrogen production costs. The results show that hourly matching provides the lowest emissions and costs, but requires flexible demand or storage. The study also highlights the importance of a clean grid and the need for flexible operation to ensure low emissions and cost-effective hydrogen production. The findings suggest that strict regulations on temporal matching are necessary to ensure low emissions and that the order of implementation of monthly and hourly matching in the proposed legislation is inconsistent with the study's results. The study recommends a stricter regime in the short term that relaxes once system targets are met. The study also shows that hourly matching offers several benefits, including significantly lower attributional emissions and incentives for demand flexibility and storage. The study concludes that regulations with low emissions and a small cost premium are possible.This study investigates the implications of different standards for certifying renewable electricity used in electrolytic hydrogen production. It compares electricity procurement strategies for a constant hydrogen demand in selected European countries in 2025 and 2030. The study finds that local additionality is necessary to ensure low emissions. Annual and monthly matching cases show that baseload operation of electrolysis can lead to higher emissions due to reliance on fossil-fuelled generation. In contrast, hourly matching does not increase system-level emissions but can result in high costs for constant supply if only wind, solar, and short-term battery storage are available. Flexible operation or hydrogen storage reduces the cost penalty of hourly versus annual matching to 7%–8%. Hydrogen production with monthly matching can reduce system emissions if electrolysers operate flexibly or the renewable generation share is large. The largest emission reduction is achieved with hourly matching when surplus electricity generation can be sold to the grid. The study concludes that flexible operation of electrolysis should be supported to guarantee low emissions and low hydrogen production costs. The results show that hourly matching provides the lowest emissions and costs, but requires flexible demand or storage. The study also highlights the importance of a clean grid and the need for flexible operation to ensure low emissions and cost-effective hydrogen production. The findings suggest that strict regulations on temporal matching are necessary to ensure low emissions and that the order of implementation of monthly and hourly matching in the proposed legislation is inconsistent with the study's results. The study recommends a stricter regime in the short term that relaxes once system targets are met. The study also shows that hourly matching offers several benefits, including significantly lower attributional emissions and incentives for demand flexibility and storage. The study concludes that regulations with low emissions and a small cost premium are possible.