A new study has laid bare the extra climate benefits of using renewable electricity directly where possible, compared to converting it to green hydrogen and using that instead to reduce greenhouse gas emissions.
German energy-transition think-tank Agora Energiewende has calculated how much carbon dioxide-equivalent (CO2e) would be saved when replacing fossil fuels using different zero-carbon options — in power production, heating, transport and industry — when starting with a megawatt hour (MWh) of renewable electricity.
So switching from a gas boiler to a heat pump would save 602kg of CO2e for every 1MWh of renewable energy, but converting that electricity to green hydrogen and burning the H2 in a boiler would only save 129kgCO2e — 4.66 times less, says the study, Breaking free from fossil gas: A new path to a climate-neutral Europe.
Replacing a diesel car with a battery electric vehicle would save 833kgCO2e per MWh, compared to 277kg with a green-hydrogen-powered fuel-cell car — almost exactly three times more.
Using e-fuel derived from green hydrogen in a diesel car would achieve even lower greenhouse gas savings per MWh — 116kgCO2e.
Replacing coal- and combined-cycle gas-fired power plants with 100% wind and solar, would result in GHG savings of 867kgCO2e and 340kgCO2e, respectively, per MWh of clean electricity. But replacing those plants with green hydrogen-fired combined-cycle facilities would achieve savings of 328kgCO2e and 140kgCO2e, respectively, per MWh of renewable electricity.
Of course, hydrogen-fired power plants would be able to supply clean electricity on demand, whereas the amount of wind and solar power available at any given time depends on the weather and the time of day. Agora did not provide figures for storing wind and solar using batteries or other non-hydrogen options.
In the steel sector, using green hydrogen instead of coking coal when extracting iron from ore, and then powering an electric-arc furnace with renewable electricity to turn iron into steel (rather than relying on a coal-fired blast furnace) would save 580kgCO2 per MWh of clean power, making it the most climate-friendly use of green H2 in the study.
But swapping natural gas for green hydrogen in an industrial boilers would be far less efficient than using industrial heat pumps directly, with emissions savings of 570kgCO2e for the latter — four times higher than the 146kgCO2e for the former.
Industrial heat pumps can only produce temperatures of up to 200°C, but higher temperatures of up to 500°C can be produced using electric boilers, which do require more electricity than heat pumps, but are still 60% more efficient than hydrogen-based systems, says the report.
Other commercially available electric heating options can produce temperatures of more than 1,000°C, such as infrared and microwave heaters, plasma technology, and induction, resistance and electric-arc furnaces.
But replacing existing manufacturing facilities with electric options would represent a high upfront capital cost that may be unappealing to companies, which might prefer to make the easier switch by converting their fossil-gas boilers to run on green hydrogen.
Agora says that due to the extra climate benefits of using renewable electricity directly, rather than indirectly as green hydrogen, policy makers should concentrate on using renewable H2 only in “no-regret” use cases.
“In the short to medium term, the use of limited renewables generation for indirect electrification stands in direct competition with its more efficient use for direct electrification, making it critical to prioritise indirect electrification only in “no-regret” and difficult-to-electrify applications, such as high-temperature processes and feedstock use in industry, especially where it can replace highly carbon-intensive existing fossil-based hydrogen,” the report states.