Aviation as the most crucial transportation means in the world widened its wings in a historically brisk phase by moving from the 100 million passengers mark in 1960 to 4.56 billion by 2019. With this huge uptick in demand, consumption of fossil fuels increased drastically as well, the 68 billion gallon usage in 2005 increased to 95 billion gallons in 2019. This accounts for the emission of 915 million tonnes of CO2 gas which equals a share of 2.5% of worldwide CO2 emissions.
Should there be any alternatives?
As IATA has predicted a jaw-dropping passenger demand of 8.2 billion by 2037, alternate fuel means should hit the industry to keep it afloat amidst the environmental concerns and fuel shortages.
For the time being, viable fuel alternatives for fossil fuels are being introduced and are currently being tested. Among them, solar fuel has entered the industry with interesting figures that hold promise.
The role of renewable energy
As the name suggests, energy generated from whatever source that does not deplete when used is a form of renewable energy. Sunlight, wind, ocean tides, and biomass tops the list of sources that can be used as renewable energies. Fuel that comes from renewable sources is called sustainable fuel and in the aviation context Sustainable Aviation Fuel (SAF).
What is solar aviation fuel?
Solar aviation fuel is a synthetic fuel. Synthetic fuels share the same qualities as jet fuel but the fuel production is done artificially. Like the one addressed in this article – producing synthetic fuel from sunlight and air – there are two other ways: producing synthetic fuel from biomass and electronic waste. Fuels produced from any of the above means look identical to usual jet fuel and can be used for almost any vehicle including airplanes.
Sunlight to fuel, yet another sugary saying?
Solar aviation fuel is often called sun-to-liquid fuel as the energy required for the thermochemical reaction is supplied by solar energy. As the name suggests, sunlight is not directly going to be converted into solar fuel, but sunlight is providing the required heat for reactions.
Production of solar aviation fuel in simple terms
The solar fuel production process is complex and requires certain technical know-how to fully understand. But here is a simplified explanation.
Atmospheric air is a conglomerate of many gases including carbon dioxide. During the process, carbon dioxide from air is extracted in the first place and subjected to a greater temperature along with the water. Then they dissociate into oxygen, hydrogen, and carbon monoxide. All of the oxygen content is taken out from the mixture to produce syngas: the mixture of hydrogen and carbon monoxide. Having the syngas produced completes the process by 50%.
Then via a process known as Fischer–Tropsch process, syngas is converted into kerosene or petrol, or any other liquid hydrocarbon fuel. Once produced, these carbon-neutral liquid fuels are termed solar fuels as the energy required for the dissociation process was taken from concentrated sunlight via solar concentrators.
Swiss airlines taking the lead
Switzerland is home to a world-leading solar fuel company – Synhelion. The company has already begun generating solar kerosene to be used within the transportation industry. Lufthansa Group and the flag carrier of Switzerland, Swiss Air joined hands with Synhelion toward the goal of zero-emission in the transportation industry by replacing jet fuels with solar kerosene. With that, Swiss Air will be the world’s first airline to use sun-to-liquid solar fuel in an aviation application.
Synhelion has confirmed, that the use of solar fuels is identical to jet fuel usage and compatible with any existing fuel infrastructure within the aviation industry, which is a huge plus point. Going beyond the aviation industry, Synhelion has set a mission to cater to the entire transportation industry to cut down 8 billion tonnes of CO2 emissions each year.
How long will it take to become commercially viable?
No matter how clean the production of any alternative fuel is, it has to be commercially viable. Moving with solar power is vital as it is the most available resource. But most airlines do not have the capability to spend an astronomical amount on establishing a solar refinery even if it is a one-time cost.
So far, the production of solar fuels has been too sluggish; it takes more time and effort to produce a few liters of solar kerosene. ETH Zurich, a research university in Switzerland has its own solar refinery mounted on the lab roof. As commented by professor Aldo Steinfeld of the university, technical feasibility is already proven for the production of kerosene from sunlight.
Deserted regions with high solar radiation are found to be more effective locations to set up solar refinery plants. The land cover due to the installation of solar concentrators is way less than 1% of the global avid lands and does not impose a threat to farming and agriculture. Hence, selecting land will not be the major hitch during the progress.
Expected production rate
Synhelion expects to produce jet fuel from the sun-to-liquid method from 2023 to the market. In 2025, the company aims for 500,000 liters for a year and then takes a long shot to produce 875 million liters per year. Even though, this figure is just a peanut when compared with the global jet fuel demand. Hence, dedicated political and industrial support is a must to take this to the next level in the coming years. The production rate of solar fuel should reach a level making them ubiquitous and competitive with pricing and then only customers will tend to move towards alternatives.
Burning solar kerosene
Here is a myth buster: even though solar kerosene is listed as a sustainable fuel, it emits green house gases (GHG). Solar fuels are also liquid hydrocarbons. But they only release what it took from the atmosphere when producing them. So it maintains the equilibrium and remains carbon-neutral at all times.
Pros and cons of solar aviation fuel
Minimizing carbon dioxide emissions. When fully implemented, zero emissions should take over the entire industry.
Some other sustainable aviation fuels such as Liquid Hydrogen (LH2) have a different volumetric density compared to the usual jet fuels. Hence, aircraft fuel tanks and other infrastructures should be upgraded to match the fuel type. But with solar kerosene, the use of the existing infrastructures is possible.
The solar heat generated by the concentrated sunlight is storable. Synhelion is working on a solid heat storage technology and they will be able to store solar heat at temperatures above 1,000°C in the near future. The stored energy can then be used to fuel production during the nighttime as well. Which is a huge plus point making the plant self-sustaining.
Higher initial investment cost.
A slow rate of production. Even an industry-scale plant is not capable of catering to the current demand.
The verdict on solar aviation fuel
All the fossil fuel-consuming industries including the aviation industry are now required to focus on environmental-friendly fuel alternatives. At the time of speaking, pivotal initiatives have been taken by experts to move with sustainable aviation fuels. Among them, producing fuel from solar energy entered the industry with crossed fingers and industry-scale production facilities are becoming a reality. Sooner, Swiss Air will be the first airline in the world to power an aircraft with solar kerosene and will be a positive impact encouraging operators to go green. As there ain’t no such thing as a free lunch, even solar kerosene has its own drawbacks that need more time and comprehension to tackle.
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Jet pilot @NASA
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