Green Hydrogen Characterisation Initiatives: Definitions, Standards, Guarantees Of Origin, And Challenges

Hydrogen can be produced from many different renewable and non-renewable feedstocks and technological pathways, with widely varying greenhouse gas emissions. For hydrogen to have a role in future low-carbon energy systems, it is necessary to demonstrate that it has sufficiently low carbon emissions. This paper explores how green hydrogen has been defined, reviews nascent green hydrogen characterisation initiatives, and highlights the main challenges that standards and guarantee of origin schemes must overcome to develop a market for green hydrogen. Most existing green hydrogen initiatives are in Europe. In anticipation of a future market for green hydrogen, international standards are starting to be discussed by national and international standardisation organisations and policy makers. A range of approaches have been taken to defining green hydrogen and guarantees of origin. These vary on whether green hydrogen must be produced from renewable energy, on the boundaries of the carbon accounting system, the emission thresholds at which hydrogen is considered green, and on which feedstocks and production technologies are included in the scheme. Decisions on these factors are often influenced by other national and international standards, and the legal framework in which the green hydrogen supply chain operates

Principles of classical statistical mechanics: A perspective from the notion of complementarity

Quantum mechanics and classical statistical mechanics are two physical theories that share several analogies in their mathematical apparatus and physical foundations. In particular, classical statistical mechanics is hallmarked by the complementarity between two descriptions that are unified in thermodynamics: (i) the parametrization of the system macrostate in terms of mechanical macroscopic observables $I=\{I^{i}\}$; and (ii) the dynamical description that explains the evolution of a system towards the thermodynamic equilibrium. As expected, such a complementarity is related to the uncertainty relations of classical statistical mechanics $\Delta I^{i}\Delta \eta_{i}\geq k$. Here, $k$ is the Boltzmann's constant, $\eta_{i}=\partial \mathcal{S}(I|\theta)/\partial I^{i}$ are the restituting generalized forces derived from the entropy $\mathcal{S}(I|\theta)$ of a closed system, which is found in an equilibrium situation driven by certain control parameters $\theta=\{\theta^{\alpha}\}$. These arguments constitute the central ingredients of a reformulation of classical statistical mechanics from the notion of complementarity. In this new framework, Einstein postulate of classical fluctuation theory $dp(I|\theta)\sim\exp[\mathcal{S}(I|\theta)/k]dI$ appears as the correspondence principle between classical statistical mechanics and thermodynamics in the limit $k\rightarrow0$, while the existence of uncertainty relations can be associated with the non-commuting character of certain operators.Comment: 8 pages, no figure; elsart style. Version accepted in Annals of Physic