Anthony Patt, as a co-author on the study, you examined how solar fuels could enter the market and become competitive. What sorts of policies would it take to help make this possible?
Anthony Patt: Our analysis of policy instruments shows a need for technology support similar to what has existed for solar and wind energy. Both of these used to cost roughly ten times as much to build and operate as fossil generators, back when governments first started to support them. The current price ratio for solar kerosene compared to fossil is of the same order. A comparison with other renewable energy technologies shows that with a similar support mechanism, it ought to be possible to bring the cost of solar kerosene down to the current cost of fossil aviation fuel.
What are the most important barriers?
Anthony Patt: The hardest part is overcoming the high initial price barrier. Carbon taxes are not likely to be effective. If we were to tax fossil aviation fuel to the point where its cost to airlines was the same as solar fuels, which is what would be needed, it would mean making it ten times more expensive. Nobody would want to pay this additional cost for flying, and politicians would be unwilling to impose this burden on people. With solar and wind power, however, other policy instruments fit the context much better. They imposed a small additional cost on the total electricity consumed, and used this revenue to fund the cost that wind and solar added to the system. Similarly for fuels, we would need to impose only a small additional cost on flying, thanks to the current market dominance of fossil fuels, in order to finance investments in renewable fuel production. This would certainly help the solar reactor and solar fuels to take hold in the market.
In your opinion, what would be the ideal policy instrument to help solar fuels in the market?
Anthony Patt: The instrument most suited to the fuels market would be a quota system. This would function as follows: airlines and airports would be required to have a minimum share of renewable fuels in the total volume of fuel that they put in their aircraft. This would start out small, e.g. such as 1 or 2 percent. It would raise the total fuel costs, but only minimally; the initially small quota would add only a few Swiss francs to the cost of a typical European flight. The quota would rise each year, eventually towards 100 percent, meaning only solar fuels would be burned. The rising quota would lead to investment, and that in turn to falling costs, just as we observed with wind and solar. By the time solar fuels reach 10–15 percent of the fuel volume, we ought to see the costs for solar fuels nearing those of fossil kerosene. It is a strategy that is politically feasible and straightforward to implement.
What locations would be suitable for large production facilities?
Anthony Patt: A solar reactor needs direct sunlight, with no clouds in the way. It makes sense to build them in arid environments, such as those in South Spain and North Africa, the Arabian Peninsula, Australia, in the southwest of the United States, in the Gobi desert of China, or in the Atacama desert of Chile. The process chain does condense water from the air as one input, yet even desert air is moist enough to supply the needed quantities. Finally, desert land is relatively inexpensive, without competing uses. Solar fuels would be a global commodity similar to fossil fuels today, and indeed would rely on the same basic infrastructure for shipping and delivery.
Aldo Steinfeld: Suitable locations are regions for which the annual direct normal solar radiation is higher than 2000 kWh/m
2
per year. In contrast to biofuels, which are limited by resource provision, global jet fuel demand can be met by utilizing less than one percent of the worldwide arid land, which does not compete with food production. To put this in context, 2019 global aviation kerosene consumption was 414 billion liters; the total land footprint of all solar plants required to fully satisfy global demand would be about 45,000 km
2
, equivalent to 0.5 percent of the area of the Sahara Desert.
