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Carbon-Neutral Proposal for Global Aviation

Can solar power-generated fuel help mitigate global warming? A new technology promises to curb carbon dioxide emissions while also reducing global reliance on fossil fuels.

Emissions on the Increase
Currently, the aviation sector of the global economy accounts for 6% of the total anthropogenic carbon dioxide emissions.1 Post-pandemic growth in tourism and global trade is projected to further increase this contribution by 60–90% by 2040.2 In addition to carbon dioxide emissions, the aviation sector also accounts for substantial emissions of nitrogen oxides (NOx), sulphate aerosols, unburnt hydrocarbons, and black carbon particles (soot).3

Reducing greenhouse gas and black carbon particulate emissions from the aviation industry certainly would help mitigate global warming and restore climate stability. Completely eliminating aviation greenhouse gas and black carbon soot emission would be even better.

Until recently, the goal of eliminating aviation greenhouse gas and black carbon soot emission seemed impossible. Battery-powered electric cars—where the batteries are recharged by electricity from solar power generation—are already a demonstrable technology, but batteries sufficient to power commercial aircraft are much too heavy to yield anything other than a trivial payload.

Solar Aviation Fuel System
A team of nine Swiss and German engineers led by Remo Schäppi has proposed and demonstrated a new technology that could replace 100% of the fossil fuels used to power the global aviation industry with a fuel source that is carbon-neutral.4 Carbon-neutral means that aircraft would not add any carbon dioxide or methane to the atmosphere during their flights.

Schäppi’s team built a solar fuel production system on the rooftop of the Swiss Federal Institute of Technology’s Machine Laboratory Building in Zurich. This solar fuel production system uses concentrated solar energy to convert carbon dioxide and water vapor from the atmosphere into a mixture of molecular hydrogen (H2) and carbon monoxide (CO), otherwise known as syngas. It then uses a solar-powered gas-to-liquid unit that converts the syngas into liquid hydrocarbons or methanol, which can be substituted for the aviation kerosene that presently fuels all the commercial and military aircraft in the world.

The carbon-neutral aircraft fuel source developed by the engineers would return to the atmosphere no more carbon than what the solar fuel production system would remove. Also, it would release no sulfur aerosols, aromatic hydrocarbons, or soot into the atmosphere. This advantage over fossil fuel sources is significant because soot emissions are a major contributor to global warming, as I explain in my book Weathering Climate Change.5

Upscaling for Economic Fuel Production
Schäppi and his colleagues’ system proved the feasibility of producing pollution-free aircraft fuel from carbon dioxide and water drawn from the atmosphere through the exclusive use of solar power. They also demonstrated in the paper how their system could be scaled up to provide enough aircraft fuel for the entire aviation industry.

The engineering team proposed the construction of solar towers akin to the Ivanpah solar tower in California’s Mojave Desert (see figure). At the Ivanpah facility, solar panels on the ground surrounding the tower focus solar energy onto the top of the tower. The heat generated at the top of the tower is more than sufficient to produce syngas from carbon dioxide and water vapor drawn from the atmosphere.

Figure: Ivanpah Solar Tower in the Mojave Desert
Credit: Aionnides, Creative Commons Attribution

The team calculated how much desert land would need to be devoted to solar power generation to produce sufficient methanol to support the entire 2019 global aviation industry. The land area needed is 45,000 square kilometers (17,000 square miles) at 31° latitude. Less land would be needed for lower latitudes and more for higher latitudes. The engineers chose 31° latitude since that latitude matches the northernmost part of the Sahara Desert.

Even at a latitude of 31°, only 0.5% of the Sahara Desert would be needed to produce enough fuel for global aviation. Schäppi and his colleagues recommend choosing a part of the Sahara Desert where no humans live and where virtually no plants or animals survive. Such a choice would have no measurable economic impact or ecological degradation on the region.

Economic Viability
Although a simple scale-up like this proposal would not produce aviation fuel cheaper than the present price of aviation kerosene before taxes, it comes close and has the potential to become cheaper. Taking into account the cost of constructing, operating, and repairing the solar energy generating systems, the cost per liter of aircraft fuel would be $1.40. The present price of aviation kerosene before taxes and delivery is a little less than a dollar per liter. In the United States, commercial airlines pay $1.45/liter for the lowest grade of aviation fuel.

The engineers’ idea may be more economically viable than they think. If their proposal were to be scaled up even further to provide a substantial fraction of the fuel needs for marine shipping and automobiles and trucks, the price/liter of fuel would be driven down more. Also, much of the cost comes from the construction of the solar power-generating units. Once construction is completed, the price of generating the fuel would be substantially reduced.

If one compares the cost of processing fossil fuels now with the solar fuel system proposed by Schäppi’s group, the new technology becomes more than economically competitive. It becomes an economic no-brainer. What Schäppi’s team proposes gives us yet another example—in addition to the many I describe in Weathering Climate Change—of how we can mitigate global warming and stabilize Earth’s climate while we boost, rather than cripple, the world economy. It is another demonstration of the biblical principle that God has given us all the resources we need to manage Earth’s resources for our benefit and the benefit of all life.

Endnotes

  1. Volker Grewe et al., “Evaluating the Climate Impact of Aviation Emission Scenarios Towards the Paris Agreement Including Covid-19 Effects,” Nature Communications 12 (June 22, 2021): id. 3641, doi:10.1038/s41467-021-24091-y.
  2. Grewe et al., “Evaluating the Climate Impact of Aviation Emission.”
  3. Grewe et al., “Evaluating the Climate Impact of Aviation Emission.”
  4. Remo Schäppi et al., “Drop-In Fuels from Sunlight and Air,” Nature 601 (January 6, 2022): 63–68, doi:10.1038/s41586-021-04174-y.
  5. Hugh Ross, Weathering Climate Change (Covina, CA: RTB Press, 2020), 37, 190–191.

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