What fuel made from the sun could do for the planet

This week, in a field outside Dusseldorf, Germany, five acres full of mirrors will begin concentrating sunlight on a 200-foot-tall tower. If all goes according to plan, the result will be the first major step toward harnessing the power of the sun to create sustainable, carbon-neutral fuel to power long-haul flights and even some industrial processes that presently require fossil fuels.

The DAWN Project has been developed by Swiss company Synhelion to begin industrial-scale production of so-called “solar fuels,” which the company argues have the potential to significantly reduce planet warming carbon emissions.

The process is different from the more familiar use of sunlight in green energy: photovoltaic cells that capture the sun’s rays and convert them directly to electricity. In contrast, the Synhelion approach is to harness the power of the sun to create liquid fuels that can “drop in” to existing technology and function just as existing fuels do, without the need for any retrofitting, adaptation, or infrastructure changes.

The facility sits just outside of Dusseldorf, Germany, and contains five acres full of mirrors that concentrate sunlight. This energy then generates steam, which powers the reactor where fuel is made.

Electrification is often touted as the principal green alternative to fossil fuels, but there are currently some areas— such as marine and aviation transportation— where that hasn’t been feasible, says Philipp Furler, Synhelion’s co-founder and CEO.

“Those sectors are difficult to decarbonize because they require very high energy density,” he explains. Energy density refers to the amount of energy that can be provided in a given volume.

An egg, for example, has a higher energy density than a piece of lettuce of the same size. Similarly, kerosene has an energy density as much as 50 times greater than the most advanced current lithium-ion technology – which is why, says Furler, “you’re not flying with a battery from Europe to the U.S.”

That is why, he says, there are  some areas where liquid fuels “are here to stay. And the mission is basically to replace fossil liquid fuels with sustainable liquid fuels.”

How is solar fuel made?  

When jet fuel is burned, it releases water and carbon dioxide—lots of it. Shipping and aviation account for an estimated eight percent of global greenhouse gas emissions. What Synhelion aims to do, says Furler, is to reverse the combustion process.

“We take water and carbon dioxide, and we revert it back with renewable energy into a synthetic fuel, thereby closing the carbon cycle,” he says.

If that sounds suspiciously like alchemy, it’s rooted in sound science.

Solar fuel could pack a lot of power into a little space, making it ideal for energy intensive transportation such as shipping or long haul flights.

Sustainable fuel stored in tanks like these has a number of benefits. It packs more power than a battery, and it can easily be stored and transported.

Solar energy helps power a reactor that turns water and carbon into liquid hydrocarbons.

The first step is acquiring a carbon source. One possibility is to remove carbon dioxide directly from the atmosphere, by passing air through systems that use either filters or chemicals to extract the CO2. That has the benefit of being truly carbon-neutral, in that no more carbon dioxide is released into the atmosphere than has already been removed from it. Unfortunately, because CO2 constitutes a mere 0.04 percent of all atmospheric gases, removing and concentrating it on an industrial scale is an immense challenge.

“The problem with pulling it out of air is, it’s hard to be efficient, because it’s very dilute,” says Matt Bauer, program manager for the Concentrating Solar-Thermal Power Program at the U.S Department of Energy. “If you have a more dense fuel source as an input, you can do this many times more efficiently.”

Furler agrees, and so— at least until direct air capture becomes more efficient and economically viable—Synhelion is focusing on using biomass, and specifically agricultural waste products.

Mirrors then focus sunlight on a “receiver” atop the tower, generating steam that combines with the biomass and water that are fed into a reactor in the tower. This drives a chemical reaction that creates a synthesized gas of carbon monoxide and hydrogen, which is then liquefied by a further series of chemical reactions nto liquid hydrocarbons.  

The process doesn’t completely eliminate emissions; some carbon will still be emitted that will not then be immediately recaptured. But compared to traditional jet fuel, says Furler, “it’s a significant reduction of 85 to 90 percent.”

While the new DAWN facility advances commercial solar fuel production, scientists say it will still take decades to efficiently manufacture enough solar fuel to replace fossil fuels like diesel and kerosene.

Is solar fuel the future?

In 2014, Furler and his fellow PhD students at ETH Zurich demonstrated the feasibility of the process on a very small scale: producing a test tube of jet fuel in the lab using sunlight, water, and CO2.

“A huge effort and probably the most expensive kerosene ever,” he jokes.

Five years later, they scaled up their operations, producing carbon-neutral fuels from a small-scale demonstration project in the center of Zurich. They wrote up the results of that demonstration in a paper for Nature; progressively larger proof-of-concepts followed. With DAWN, Synhelion anticipates being able to produce solar fuels on an industrial scale.

“We want to have around a 100,000 tonne capacity by 2030, and then roughly 1 million tonnes by 2033,” he says. That’s just a drop in the bucket compared to the approximately 350 million tonnes of jet fuel currently consumed annually, but Synhelion’s goal is to contribute approximately half of Europe’s synthetic aviation fuel demand by 2040 and to continue growing.

Ultimately, the goal is to produce fuels on a large enough scale that they can also power carbon-intensive industries such as cement manufacturing. Synhelion notes that its partners include Cemex, one of the largest building materials companies in the world, as well as aviation-specific companies such as the Lufthansa Group and Zurich Airport: an indication that solar fuels are becoming more viable.

In the meantime, DAWN’s progress will be watched closely by those pushing for a suite of approaches to more rapidly bring us to a carbon-neutral world.

“I think too often in the public’s mind, electrification is all we need to accomplish,” says Bauer. “And that in a lot of analysis is going to be really hard. So if we can create tools like this, that don’t put so much burden on both the technologies and the quantity of technologies for electrification, that’s going to more rapidly get us to where we want to be.”

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