Your Weekend Car Might One Day Run On Synthetic Gasoline Made From Farm Waste, Water, And Sunlight

Recently, an Audi made a trip up the Furka Pass in Switzerland. Nothing hugely exceptional there, except for the fact that it ran on “Solar gasoline,” a phrase that reads like “gluten-free Wheaties” or “cruelty-free fur” in that it seems implausible at face value. You can’t simply pull gasoline out of the sun’s rays, but you can use sunlight to power the production process of synthetic gasoline. A company called Synhelion is already doing it, and here’s how it works.

First off, you need a feedstock of some sort. That’s crude oil in the case of traditional gasoline, but Swiss cleantech company Synhelion starts with biogenic waste, a fancy catch-all for food scraps, leaves, all the bits from farming you don’t want in your food, sawdust, and even, um, fecal matter. It’s organic waste, or stuff you’d find in a compost pile, and Synhelion sits on it until little microorganisms digest it, producing biogas that’s a mixture of methane and carbon dioxide. This biogas is then the feedstock for everything else in the process, and that’s where sunlight comes in.

To turn biogas into hydrogen and carbon monoxide, you’d need water and a ton of heat. Somewhere north of 2,012 degrees Fahrenheit, which is enough to melt aluminum, or facilitate cremation. That’s where heliostats come in, clever moving mirrors that track the sun and reflect its light toward a concentrated point. In this case, the concentrated point is a solar receiver, and excess heat energy is stored in thermal banks so Synhelion can keep making synthetic fuel long after the sun goes down. From there, a reactor uses that heat to turn the biogas and water into synthetic gas, which can then be further synthesized into drop-in gasoline, diesel, and AvGas.

It’s a hugely different process than Porsche’s carbon-capture synthetic fuel, but it yields similar results—ready-to-use gasoline that’s greener than bringing sequestered carbon up to the surface. It’s worth noting that Porsche’s process is greener as it uses carbon dioxide that’s already in the air meaning it’s truly net-neutral, but Synhelion’s process isn’t that far off. After all, anaerobic digestion of biogenic waste is something that normally happens as part of the compost process, so why not capture the byproducts and use them to make fuel to power the sort of old cars we drive on sunny weekends?

Cars like this 1985 Audi Sport Quattro, which just became the first car to run on this “solar gasoline.” As the fuel is a direct drop-in replacement fuel that looks and burns like normal gasoline without any of the weird side effects you’d get from, say, ethanol, this Group B homologation special required no modifications whatsoever. The resulting drive seems remarkably unremarkable, good news for the prospect of bunging some in the tank of your fun car and going for a rip.

It feels safe to bet that over the next century, the combustion engine as we know it won’t die, but the fuel for it might change in certain parts of the world. Sixty years ago, most new cars ran on gasoline containing tetraethyllead. Thirty years ago, it was likely that your gasoline contained methyl tert-butyl ether as its sole anti-knock additive rather than any ethanol. Today, fuel containing 15 percent ethanol by volume is growing more and more common in America. It’s possible that in 50 years, fuel will change even more, and it’s reassuring to see synthetic fuels gaining traction so we can keep occasionally driving the machines we love.

Top graphic image: Synhelion

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