As of there is no universal accepted criteria for Green Hydrogen.
Blue, grey & green hydrogen were based on methodology of extraction.
Called Green hydrogen if renewable energy sources is used for electrolysis of water H2O.
But what about biogas if used for H2 production. Will it be called green hydrogen?
If we talk for pumped storage energy for green hydrogen production then first solar or wind energy used for pumps operation & then hydro power to produce green hydrogen. Costing to be evaluated for each method. So definition of green hydogen baais RE alon seems confusing & may delay targets. So universal definition is must. Japan came with a good definition. No doubt green hydrogen from only RE will promote green energy but we need to trade of between targets of green hydrogen & availability of required RE capacity. Water is another factor. Will discuss later.