US regulators have tabled new emissions guidelines that will promote the co-firing of hydrogen in gas-fired power stations — but only if they use green H2 that meets strict well-to-gate emissions criteria, and potentially EU-style additionality rules.

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Under the new “technology-based” regulations proposed last Thursday by the Environmental Protection Agency (EPA), new and existing fossil gas-fired power stations would have to choose between two decarbonisation pathways: use carbon capture and storage (CCS) with a 90% capture rates by 2035, or opt for 30% co-firing of hydrogen by volume by 2032, ramping up to 96% by 2038.

Any hydrogen co-fired in these plants would have to meet strict emissions intensity criteria of 0.45kg CO2e/kg of H2 produced — the same threshold for the Inflation Reduction Act’s maximum $3/kg tax credit — meaning that green hydrogen made from renewable energy or pink hydrogen made from nuclear power would be the only H2 likely to qualify.

The EPA is also considering applying EU-style requirements for additionality, temporal correlation, and geographic correlation (see panel below).

Coal-fired power stations still operating in 2040 would have to use CCS with a 90% capture rate.

Only new fossil-fuel-fired peaking plants providing back-up power at times when the wind isn't blowing and the sun isn't shining — with a capacity factor of less than 20% (ie, operating at the equivalent of full capacity for a fifth of the year, on average) — would be allowed to emit at a rate of 160lb (72.5kg) of CO2-equivalent per MMBtu, by burning either fossil gas or distillates (1 MMBtu = 293kWh).

The raft of new standards is being proposed by the EPA under section 111 of the Clean Air Act (CAA), the legislation that was used by former US Presidents Obama and Trump to bypass Congress to bring about massive emissions savings from the US power station fleet, and, in the case of Trump, an uptick in fossil-fuel burn.

Now, after eight years of legislative wrangling over Obama and Trump’s respective interpretations of the CAA — both of which ended up in court — the Biden-era EPA wants to update the Act’s emissions guidelines for new and existing power stations for the first time since 2015.

New fossil fuel-powered generation capacity and that undergoing major modification would be subject to a the EPA’s new performance standards, while existing capacity would be subject to “EPA guidelines” under the Act.

The EPA said it expects the CCS pathway to generate better emissions savings than the co-firing of hydrogen.

“Depending upon the phase-in periods for both CCS and hydrogen, the CCS pathway could provide greater cumulative emission reductions than the low GHG hydrogen pathway,” the EPA said in its draft proposal.

But CCS has yet to be proven to operate commercially at a 90% capture rate. Shell’s Quest CCS project in Canada, one of the biggest in the world, was found last year to be achieving a capture rate of just 48%.

Nevertheless, the use of hydrogen in power stations has also been panned on account of its inefficiencies. With round-trip efficiency of less than 40%, every 10kWh of wind or solar energy sent to the electrolyser would yield less than 4kWh of electricity at the other end of the process, making the cost of electricity from the power station very expensive.

And critics argue that switching to hydrogen is just a ruse to keep existing fossil-fuel capacity on line, pumping out yet more carbon emissions — especially as Hydrogen Insight is not aware of any commercially available gas turbines that can burn more than 20% hydrogen in a natural-gas mix.

But proponents say that hydrogen can be used to decarbonise existing fossil-fuel assets while providing back up to variable renewable supply.

Additionality, temporal correlation and geographic correlation

“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;

“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.

"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, Texas, is not powered by solar panels in California 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.

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