Modeling of emissions and financial impacts of additionality. Approaches to assess the cost and impact of consequent electrolytic H emissions2 production based on the two alternative definitions of additionality. a, The definition of “competition” (purple dotted box) reflects the approach of Ricks et al. and allows competition between investments in the resources contracted for H2 production and other investments in network resources. b, The definition of “non-competition” of additionality (yellow dotted box) follows the approach of Zeyen et al where contracted H2 resources are optimized after investments in non-H2 associated grid resources. Here contracted H2 resources refer to battery storage, wind power, solar generation, electrolyzers and H2 storage resources to meet H2 request and meet the specified time matching requirement. Note that the reference grid in both additionality frameworks is the same, while the grid optimized with H2 the resources are different (as indicated by the different colors of the circles). Credit: Giovanniello et al. (Natural energy2024).
Countries around the world have introduced new policies aimed at mitigating climate change and reducing carbon emissions. Many of these interventions focus on deploying more sustainable systems to deliver electricity at scale and introducing new technologies powered by electric energy, such as electric vehicles and electrolyzers (this is (i.e. electrical devices capable of splitting water into hydrogen and oxygen atoms).
The use of electrolyzers has recently received significant attention as a means of producing and storing hydrogen gas (H2), which is vitally important for a variety of applications, from synthesizing ammonia for fertilizers to making fuel cells to power large vehicles or trains.
Although electrolyzers can be powered using renewable energy sources, if powered by current electricity grids, these devices could potentially lead to even higher carbon emissions than conventional methods of producing electrolyzers. hydrogen.2.
Assessing the impact of grid-connected electrolyzers on decarbonization efforts is therefore of utmost importance, particularly in the United States where an emissions-indexed Production Tax Credit (PTC) for those who produce hydrogen.2 have been established. This financial incentive grants projects with low greenhouse gas emissions over their life cycle a tax credit of up to $3 per kilogram of hydrogen produced.
Researchers at the Massachusetts Institute of Technology (MIT) examined how different interpretations of contracted variable renewable energy (VRE) sources (i.e., energy sources that depend on changing weather conditions, such as energy solar and wind) and energy system policies can affect costs. and emissions linked to the electrolytic production of hydrogen.
Their article, published in Natural energyshows that different assumptions regarding VREs used to power grid-connected electrolyzers can significantly influence the resulting carbon emissions estimates.
“The literature provides conflicting guidance on the requirement for appropriate temporal matching between the electricity consumption of electrolyzers and the variable renewable energy (VRE) subscribed to qualify hydrogen (H).2) as “low carbon,” Michael A. Giovanniello, Anna N. Cybulsky and their colleagues wrote in their paper. “We show that these results are strongly influenced by different interpretations of additionality. »
Changes in power sector resources due to H2 production. Credit: Giovanniello et al. (Natural energy2024).
Giovanniello, Cybulsky and their colleagues conducted their analyzes using an energy systems model called DOLPHYN. This model allowed them to estimate the emissions and costs of grid-connected electrolyzers under different scenarios or hypothetical conditions.
The researchers specifically explored the differences between scenarios in which VRE resources helping to meet electricity demand beyond hydrogen production do or do not compete with contracted VREs for hydrogen.2 production. Additionally, they focused on distinct scenarios in which VRE requirements were hourly or annual.
The results of the team’s analyzes suggest that these different interpretations result in different estimates of carbon emissions. Therefore, approaches to defining timing requirements for determining PTC eligibility and assessing the actual impact of grid-connected electrolyzers on emissions should take these influencing factors into account.
“Significantly lower emissions are achievable under annual matching assuming that VREs for non-H products2 the demand for electricity does not compete with the ERV contracted for H2“, contrary to the hypothesis that all VRE resources are in direct competition,” the researchers explain in their article.
“Further analysis of four policies relevant to the energy system suggests that this latter interpretation of additionality is likely to overestimate the emissions impacts of annual adaptation and underestimate those of hourly adaptation.”
The results of the analyzes carried out by this team of researchers could potentially inform policy development, in particular the drafting of eligibility conditions for PTC tax credits. Furthermore, this study could pave the way for other work aimed at modeling the economic and environmental impact of H.2 production projects involving the deployment of electrolyzers.
“We recommend starting in the short term with the annual matching of hours for the allocation of the H2 Production tax credits in the United States, with terms similar to the “non-competition” framework, followed by a gradual introduction and then phasing out of time adequacy requirements as the network is profoundly decarbonized,” the researchers wrote.
More information:
Michael A. Giovanniello et al, The influence of additionality and time-matching requirements on emissions from grid-connected hydrogen production, Natural energy (2024). DOI: 10.1038/s41560-023-01435-0
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