For several years now, biofuels have been used as a partial substitution in fuelling airplanes.

The first test flight for a commercial airline, a cooperation between Virgin Atlantic and Boeing, took off in 2008. The technology has improved over the last decade, and there are now five processes for making internationally approved Sustainable Aviation Fuel (SAF) using anything from biomass, algae, municipal solid waste to sugars, according to the Air Transport Action Group (ATAG). SAF can replace 10-50% of traditional jet fuel in airplanes according to ATAG.

According to the European Commission, approximately 3% of the European Union’s greenhouse gas emissions are from the aviation industry, and the sector contributes 2% of emissions globally. Because biofuel is compatible with current plane engines, no fleet changes are necessary, according to Grace Cheung, Head of Public Engagement & Sustainability, Corporate Affairs Department at Hong Kong-based Cathay Pacific, which uses biofuels. “Biofuels for aviation are produced to meet the same strict specifications as with conventional jet fuel, and as such, once blended, can be ‘dropped in’ to existing fuel infrastructure and handled in the same way. There is no need to alter engines or other components in aircraft, and there is no discernible difference in performance,” Cheung said.

The currently insufficient supply of biofuel for the world’s airlines and the relative newness of the fuel does make it more expensive. However, alternatives are continually in the works; “the aviation industry and our partner stakeholders also aim to create scalable supplies that are cost-competitive with traditional jet fuel,” according to Paul McElroy of Boeing Commercial Airplanes Strategy and Technology Communications.

Alaska Airlines a pioneer in blending bio- and aviation fuel for its aircraft said that sustainable fuels were approximately six times more expensive per gallon than kerosene in 2017. That gap has narrowed to between two and three times the cost of conventional fuel, according to GeekWire.

“There’s really just not a commercial supply of biofuel,” explains Carol Sim, Environmental Affairs Director at Alaska Airlines. “On the flights that we have done, it’s been batch-scale production—not commercial production—which drives higher costs. If you can produce fuel to scale, the economies are going to be much better.”

When the US Navy first partnered with the US Department of Energy and the US Department of Agriculture for the Great Green Fleet initiative – a program designed to use a biofuel blend to power ships and aircraft – the initial cost was US$26 per gallon for 900,000 gallons of 50/50 blend fuel, according to Atlantic Council. However, the US Navy eventually purchased more than 7.7 million gallons of unblended biofuel at the cost of US$2.05 per gallon, the Atlantic Council continued.

“As with many new technologies, costs are higher at present, but they are expected to become competitive in the longer term. The cost of biofuel also varies across regions, where, in some areas, there are incentive schemes that enable biofuel to be used at little to no additional cost when compared with jet fuel,” Cheung explained.

By 2025, only 2% of the world’s demand can be achieved with SAF, according to ATAG. In 2014, Cathay Pacific “invested in a US-based company, Fulcrum BioEnergy, which has technology that essentially can convert household waste into biofuels. Together with the investment, through an offtake agreement, we have secured a supply of 375 million gallons over ten years, which represents around 2% of our fuel consumption. We expect to start receiving the fuel from 2022,” Cheung explained.

Boeing currently provides its customers with the option of using biofuel in new airplanes on their journeys to the airlines’ home base, according to a Boeing news release. Alaska Airlines was the first to take them up on their offer upon delivery of three airplanes. Currently, Alaska Airlines uses SAF solely in passenger planes. Boeing is also working on researching, developing and commercialising new aviation biofuel points of supply with partners on six continents, according to information provided by McElroy.

According to McElroy, “Boeing and other manufacturers are developing electric and hybrid-electric airplanes that have potential for the air cargo industry. These aircraft will be relatively small until technological advances increase battery density and reduce weight.”

He added that smaller hybrid electric jets would be in production in the mid-2020s, while long range, large commercial aircraft are unlikely to use electric power in the foreseeable future.

The use of ‘green diesel’ or HEFA+, made from fats, oils and greases, would “make a price-competitive, sustainable supply available that could meet more than 1% of global aviation needs,” said McElroy.

Currently, Boeing and stakeholders are working with the Federal Aviation Administration to seek approval of ‘green diesel’ as an aviation fuel.