Hydrogen Co-Firing and the EPA’s Greenhouse Gas Limits for Power Plants

For the above reasons, EPA should specify that any hydrogen co-firing BSER is predicated on burning only low-GHG hydrogen.60 The absence of such a limitation may blunt the climate benefits of the Proposed Rule—or even have the perverse effect of causing a net increase in GHG emissions relative to the status quo.61 Beyond the threat of high-GHG hydrogen, co-firing with hydrogen associated with sign. [...] Severability of the Low-GHG Hydrogen Limitation In the Proposed Rule, EPA asks whether the final rule should state that the low-GHG hydrogen limitation is legally sev- erable from the other components of any hydrogen subcategory.68 In other words, should the hydrogen co-firing BSERs 59 DOE Technology Assessment, supra note 45, at 19–20. [...] Given the realities of grid operation, the most accurate way to measure emissions from grid-connected electrolyzers involves looking at the emissions intensity of the “marginal” generator serving the local grid at the moment of hydrogen production. [...] So, when the marginal emissions rates during electrolysis and incremental EAC accrual are the same, the emissions of the incremental EAC-accruing resource will accurately represent the emissions attributable to the hydrogen. [...] Because the marginal resource can change so quickly and so often within a single day (see Figure 2), the emissions of the EAC-accruing generator become a worse proxy for the emissions of the electrolyzer when there is a large time gap between the electricity consumption and the incremental EAC accrual.100 The marginal generator is less likely to change when little time has passed.