An all-in-one solar-powered tower makes carbon-neutral jet fuel a reality
The aviation sector has always been overlooked for its role in climate change. It is responsible for about five percent of global anthropogenic emissions, with heavy reliance on kerosene, or jet fuel, a liquid hydrocarbon fuel derived from crude oil.
In fact, there is no clear alternative to power long-haul commercial flights on a global scale, until now.
Enter Aldo Steinfeld, a professor from ETH Zurich.
Steinfeld and his team have designed a fuel production system that employs water, carbon dioxide, and sunlight to produce aviation fuel. Their strategy, published Wednesday in the journal Joule, is hopeful of making the aviation industry carbon neutral.
"We are the first to demonstrate the entire thermochemical process chain from water and CO2 to kerosene in a fully-integrated solar tower system," Steinfeld, the corresponding author of the paper, said in a statement. Prior attempts to produce aviation fuels through the use of solar energy have mostly been restricted to the laboratory.
The system uses solar energy to produce synthetic alternatives
Steinfeld and his colleagues developed the system as a part of the European Union’s SUN-to-LIQUID project. The EU aims at a 75 percent share of renewables in the gross energy consumption - as part of its energy roadmap for 2050.
Achieving this target needs a large share of alternative transportation fuels that includes a 40 percent target share of low carbon fuels in aviation itself. The four-year solar fuels project, which was kicked off in January 2016, hopes to address this.
Steinfeld and his team developed a system that uses solar energy to produce drop-in fuels that are synthetic alternatives to fossil-derived fuels such as kerosene and diesel. According to Steinfeld, solar-made kerosene is compatible with the existing aviation infrastructure for fuel storage, distribution, and end use in jet engines. It can also be blended with fossil-derived kerosene, he said.
The solar fuel-production plant boasts of 169 sun-tracking reflective panels
A year after the project kickstarted, in 2017, the team began to scale up the design and build a solar fuel-production plant at IMDEA Energy Institute in Spain. The plant has 169 sun-tracking reflective panels that redirect and concentrate solar radiation into a solar reactor mounted on top of a tower.
Then, the concentrated solar energy drives oxidation-reduction (redox) reaction cycles in the solar reactor, which contains a porous structure made of ceria. The ceria — which is not consumed but can be used over and over — converts water and CO2 injected into the reactor into syngas, which is a tailored mixture of hydrogen and carbon monoxide.
Next, the syngas is sent into a gas-to-liquid converter, where it is eventually processed into liquid hydrocarbon fuels that include kerosene and diesel.
Improving the design to increase efficiency
"This solar tower fuel plant was operated with a setup relevant to industrial implementation, setting a technological milestone towards the production of sustainable aviation fuels," said Steinfeld.
The published paper reports a nine-day run of the plant during which the solar reactor’s energy efficiency — the portion of solar energy input that is converted into the energy content of the syngas produced — was around 4 percent.
Steinfeld said that his team is working intensively on improving the design to increase the efficiency to values over 15 percent. They are also exploring ways to optimize the ceria structure to absorb solar radiation and developing methods to recover the heat released during the redox cycles.
Abstract: Developing solar technologies for producing carbon-neutral aviation fuels has become a global energy challenge, but their readiness level has largely been limited to laboratory-scale studies. Here, we report on the experimental demonstration of a fully integrated thermochemical production chain from H2O and CO2 to kerosene using concentrated solar energy in a solar tower configuration. The cosplitting of H2O and CO2 was performed via a ceria-based thermochemical redox cycle to produce a tailored mixture of H2 and CO (syngas) with full selectivity, which was further processed to kerosene. The 50-kW solar reactor consisted of a cavity-receiver containing a reticulated porous structure directly exposed to a mean solar flux concentration of 2,500 suns. A solar-to-syngas energy conversion efficiency of 4.1% was achieved without applying heat recovery. This solar tower fuel plant was operated with a setup relevant to industrial implementation, setting a technological milestone toward the production of sustainable aviation fuels.