This study investigates the temporal regulation of renewable supply for electrolytic hydrogen production to reduce carbon dioxide emissions. The authors use an energy system model to compare different electricity procurement strategies for meeting a constant hydrogen demand in selected European countries in 2025 and 2030. The scenarios vary in how strictly they match the renewable generation to the electrolyser demand in time and space. The results show that local additionality is necessary to guarantee low emissions. Annual and monthly matching can reduce emissions if the electrolyzers operate flexibly or if the renewable generation share is large. Hourly matching, with the possibility of selling surplus generation to the grid, achieves the largest emission reduction and is the most cost-effective option, provided that flexible operation or buffering hydrogen with storage are used. The study concludes that flexible operation of the electrolysis should be supported to ensure low emissions and low hydrogen production costs.This study investigates the temporal regulation of renewable supply for electrolytic hydrogen production to reduce carbon dioxide emissions. The authors use an energy system model to compare different electricity procurement strategies for meeting a constant hydrogen demand in selected European countries in 2025 and 2030. The scenarios vary in how strictly they match the renewable generation to the electrolyser demand in time and space. The results show that local additionality is necessary to guarantee low emissions. Annual and monthly matching can reduce emissions if the electrolyzers operate flexibly or if the renewable generation share is large. Hourly matching, with the possibility of selling surplus generation to the grid, achieves the largest emission reduction and is the most cost-effective option, provided that flexible operation or buffering hydrogen with storage are used. The study concludes that flexible operation of the electrolysis should be supported to ensure low emissions and low hydrogen production costs.