REFHYNE II will install a 100MW PEM electrolyser at Rheinland refinery in Cologne, Germany, using renewable power to produce green hydrogen and oxygen, which will be fed-in to the existing refinery networks to decarbonise refinery operations. The electrolyser will be based on a state of the art 5MW PEM stack integrated into pre-engineered 20MW electrolyser trains, with factory assembled balance of plant to reduce the amount of bespoke work required to integrate electrolysers into new sites. The project will be delivered by the same team responsible for the REFHYNE project that has installed a 10MW PEM electrolyser at the same site, exploiting the experience of the consortium to deliver a timely and cost-effective project. REFHYNE II will achieve a viable business case for large-scale electrolysis at refineries by valorising the hydrogen and oxygen streams in the refinery and receiving RED credits for the hydrogen produced, while minimising the cost of hydrogen through improvements in efficiency and capital cost. A research task will explore the upgrading of waste heat to higher temperatures for use in the refinery, to further improve the business case. Power will be sourced through novel PPAs with named renewable plants. Emissions avoidance will be achieved by displacing the hydrogen currently produced on-site through SMR and adapting the refinery to allow the electrolyser to act as a flexible load and hence contract direct with renewable generators, to increase renewable penetration into the grid. Research work packages will support the deployment of 100MW+ scale electrolysers at refineries and industrial sites across Europe and enable GW-scale electrolysis systems to be implemented. Finally, a thorough dissemination work package will exploit the results of the project by delivering key messages to target audiences, and supporting three fast follower sites (of which at least two will be located in EU13 countries) to rapidly replicate the results of the project.