Quantifying the Additionality of Grid-Connected Hydrogen in a Decarbonising Energy System

This study quantifies the additionality of grid-connected hydrogen production, i.e., the additional CO2 emissions and system costs incurred when electrolysers divert variable renewable energy (VRE) from the grid. Using a power system model for the current and a future Great Britain (GB) power system with high VRE penetration, we define a fair cost and fair carbon intensity to analyse hydrogen with additionality produced via different electricity sourcing strategies: buying from the grid (on-grid), from VRE generators before the market (VRE-ahead), and using curtailment. It is found that the additional thermal generation led by grid-connected hydrogen production prevents hydrogen from being cost-efficient and clean. In the future GB power system with high VRE penetration, using curtailment is the most cost-effective option. Offsetting the additional emissions from hydrogen production requires substantially more VRE capacity in a future decarbonised system than in the current one, though the additional emissions are less in a decarbonised system. This risks increasing the cost of offsetting the additional emissions from hydrogen production in the future.