When it comes to decarbonizing our everyday lives, one prominent strategy is to “Electrify Everything” – that is, switch to electric versions of technologies such as cars, stoves, furnaces, and so on. An alternative is to use green hydrogen-based fuels. Their big advantage: they can often be swapped in for fossil fuels such as gasoline (in cars) or methane (in stoves) without any need for retrofit.
But hydrogen-based fuels have limits, a new paper suggests. “While (green) hydrogen [fuels are] indispensable for our net-zero energy transitions, we should not bet on them to broadly replace all that is oil or all that is natural gas today,” says study team member Falko Ueckerdt, head of the National Energy Transitions Team at the Potsdam Institute for Climate Impact Research in Germany.
Without careful thought about how hydrogen-based fuels are produced and where they are used, this strategy could even wind up increasing carbon emissions compared to fossil fuel technologies, Ueckerdt and his colleagues found.
Hydrogen-based fuels are produced by using electricity to split water into hydrogen and oxygen, then adding carbon from carbon dioxide to make hydrocarbon fuels. Essentially, they amount to an indirect form of electrification.
And that circuitous routing of energy poses a problem, the researchers found when they conducted a life cycle analysis of fossil fuels and their electric and hydrogen-based equivalents.
It takes a lot of electricity to split water molecules. As a result, using hydrogen-based fuels in a particular application requires 2-14 times as much electricity as direct electrification, the researchers report in Nature Climate Change.
The problem: a double whammy of inefficiency. Energy is lost converting electricity to hydrogen-based fuels, and combustion engines aren’t as energy efficient as electric ones.
This means that hydrogen-based fuels only yield a climate benefit when they’re produced with clean electricity, on the order of 90% renewable or better. With the current mix of electricity generation in Germany, using hydrogen fuels in cars, trucks, and planes would triple or even quadruple greenhouse gas emissions compared to standard fossil fuels.
Yet electric cars or trucks have emissions comparable to or lower than fossil fuel versions, even with the current energy mix in Germany and many other regions.
Hydrogen-based fuels are not only inefficient but expensive. Even with 100% renewable energy production, it would cost €800 to avoid one ton of carbon dioxide emissions with hydrogen-based gasoline and €1,200 for hydrogen-based methane gas. Meanwhile, the current price of carbon in Europe is just €50. The bottom line is that hydrogen-based fuels don’t currently make much economic sense, and that’s a major barrier to scaling up their production capacity.
With continued technological development and increasing carbon prices, hydrogen-based fuels could become a cost-competitive backup plan to replace remaining fossil fuels by 2040 or 2050, the researchers say. But we need to drastically reduce carbon emissions now. “For most sectors direct electrification is more competitive and more available,” Ueckerdt says.
This means that switching to electric for things like automobiles and home heating systems is a fast and reliable way to decarbonize. The alternative, keeping combustion technologies in place and relying on the future development of a hydrogen-based fuel system to decarbonize them could actually lock in fossil fuel dependency, the researchers argue.
Still, there are some applications that are very difficult or impossible to electrify. These include long-distance aviation, chemical production, steel production, and some other high-temperature industrial processes. Use of hydrogen-based fuels should be prioritized for these “no-regrets” sectors, they say.
Governments can help develop the potential of hydrogen-based fuels by creating schemes that create demand for the fuels (thus increasing production capacity and driving down the price), while taking care not to neglect direct electrification, Ueckerdt says.
Source: Ueckerdt F. et al. “Potential and risks of hydrogen-based e-fuels in climate change mitigation.” Nature Climate Change 2021.