“Additionality” means that the green hydrogen would have to produced from new renewables projects, so that they do not utilise existing clean electricity facilities that would otherwise help decarbonise the power grid.

Under the agreed EU Delegated Act, developers will have to install new renewable energy assets at most three years before the electrolyser starts producing hydrogen, although projects coming into operation before 1 January 2028 will be exempt from the rules for ten years.

“Time-matching", or "temporal correlation”, relates to how frequently producers would have to prove that their electrolysers have been powered by 100% renewable energy — usually hourly, weekly, monthly or annually — and therefore to what extent they can use grid electricity at times when the wind isn't blowing and the sun isn't shining, and then send the same anount of renewable energy back to the grid at a later date.

EU rules state that hydrogen production has to be matched to renewable electricity production on a monthly basis up until the start of 2030, when it will have to be matched within the same one-hour period

"Geographic correlation" refers to how close the hydrogen-producing electrolyser is to the source of renewable energy it uses. Distances can be set to ensure that an electrolyser in, say, Germany, is not powered by solar panels in Spain through renewable energy credits, which in practice could mean that green power is sent to a grid that doesn't need it, with the electricity actually used by the electrolyser coming from fossil-fuel power plants.

The EU rules say that a project's renewable energy assets have to be located in the same electricity bidding zone as the electrolyser.

All three rules would prevent fossil-powered grid electricity being used directly or indirectly to produce "green hydrogen".

Germany wants EU to postpone controversial additionality rules 'so green hydrogen can be produced more cheaply'