Why synthetic fuel can’t challenge the efficiency of batteries—yet

Jason Fenske, the creator and host of the YouTube channel Engineering Explained, recently dove into the complicated subject of synthetic fuels and rolled out his trusty whiteboard to break it all down. If the concept of synthetic fuels is new to you, don’t be intimidated: A synthetic fuel is basically any fuel we’d burn in an engine that doesn’t come from crude oil. Synthetic fuels have been posited as one way to keep internal combustion viable in the coming decades; Porsche claims they could be used to shrink a combustion engine’s CO2 footprint to that of an electric car.

So how do you make fuel if you don’t pull it out of the ground and refine it? Do you just pull it out of thin air? That’s basically the gist of it, as Fenske explains. Hydrogen and CO2 from the air are combined to produce hydrocarbons suitable for internal combustion. This solves an energy storage conundrum that comes with current battery vehicles, but it also creates some problems.

Unfortunately, each time one kind of energy is converted into another, some energy is wasted, typically via heat. In the process of harvesting the electricity needed to create the hydrogen and then produce a synthetic fuel, plenty of manufacturing and distribution steps take their toll on the efficiency of the overall system. Fenske points out that, according to an SAE paper published last year, even the least efficient battery/motor setup is twice as efficient a power delivery system as an engine running the most advanced synthetic fuel.

Tom Perazzo Porsche 911
Brandan Gillogly

What this all means is that synthetic fuel is clearly not a viable replacement for fossil fuel—or battery power, for that matter. The manufacturing process is also very expensive, which should come as no surprise. Fossil fuels have been subsidized for decades and despite relatively inelastic demand, fuel prices have remained steady when adjusted for inflation. However, if those subsidies disappear, or if demand for fuel decreases as electric vehicles become more popular, fossil fuel prices may creep up and create even more interest in synthetic-fuel development.

The takeaway? The prospect of relying on synthetic fuel to drive our favorite classics is not something to lose any sleep over just yet. On the contrary, the fact that Porsche sees so much promise in this technology gives us all hope for affordable fuels that could keep our combustion-powered collections purring well into the future.

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