Used chip fat has been suggested as one answer to sustainable aviation fuel shortages. CHARLOTTE BAILEY explores the scalability of cooking oil and asks: just how many portions do we need to eat apiece to cross the Atlantic?
“If you make it, we’ll fly it” proudly proclaimed Shai Weiss, CEO of Virgin Atlantic, as the pioneering Flight100 – the first transatlantic airliner fuelled exclusively by Sustainable Aviation Fuel (SAF) – took off from London’s Heathrow airport in November 2023. However, despite SAF being universally acknowledged as a key tool in aviation’s short-term decarbonisation arsenal, it’s evident that this so-called ‘sustainable’ option may not be the scalable solution the industry requires to meet its 2050 net zero targets.
Approved production pathways
In November 2023, Virgin Atlantic's Flight100 became the first commercial airliner to cross the Atlantic using 100% SAF. (Virgin Atlantic)
Powering the Boeing 787 Dreamliner’s Rolls-Royce Trent 100 engines were 60 tonnes of SAF, provided by fuel supplier Air bp and Virent, produced using the hydroprocessed esters and fatty acids (HEFA) pathway (and subsequently blended with synthetic aromatic kerosene at a 88% to 12% ratio). There are currently 11 authorised manufacturing methods (evaluated and approved by as ASTM International) to produce ‘drop-in’ SAF, with another seven under evaluation. However, although the International Air Transport Association (IATA) noted that total SAF volumes created reached over 600m litres in 2023 (double the amount produced in 2022), it’s still just a fraction of a percent of overall volumes required.
The April 2023 Roadmap for the development of the UK SAF industry states that although the HEFA pathway dominates current production, the ‘waste oils and fats this approach requires are limited in their availability’. However, it remains a go-to pathway as it ‘offers comparatively low technical risk and capital costs,’ with existing fossil-based refineries able to be retrofitted for the process. HEFA is also the cheapest of all currently certified production methods. (The UK aims to have at least five commercial-scale SAF facilities under construction by 2025, with the Department for Transport (DfT)’s Advanced Fuels Fund allocating £53m of funding between nine sustainable initiatives.)
Scaling supply
In 2024, SAF production is likely to meet just 0.53% of the demand for aviation fuel. (Air bp)
Crucially, although global SAF production is expected to further triple to 1.85bn litres in 2024 (0.53% of aviation fuel’s estimated requirement), IATA adds that approximately 85% of SAF facilities coming online over the next five years will utilise HEFA technology: relying on already-limited supplies of animal fats, industrial grease and used cooking oil. Although funding to certify or scale SAF production using a myriad of other feedstocks – including agricultural residues, ethanol, municipal waste and even used tyres – is ongoing worldwide, the prevalent preference for HEFA does pose a question. With used cooking oil synonymous with fried food, just how many chips would we need to eat to feed our appetite for sustainable aviation fuel?
Turning chip oil into fuel is, after all, nothing new: in 2018, McDonalds alone estimated it collected approximately 618,000 litres of used oil from 165 London branches, which was converted into approximately 532,000 litres of biodiesel. The American fast food giant took things a step further in 2019, when five onsite restaurants at Dallas Fort Worth International Airport partnered with fuel supplier Neste to turn its oil into ‘low-emission renewable fuels such as SAF’. However, used cooking oil contributed to over 50% of the UK’s renewable road-based transport fuel in 2023, with the DfT noting: “In particular, we are conscious of the possibility that high levels of HEFA use in aviation could lead to diversion of feedstocks that could be used in a more efficient manner to produce biodiesel for difficult to decarbonise road transport modes”.
Hungry for answers
How many portions of chips do we need to eat in order to fuel the demand for SAF?
So theoretically, could putting your money where your mouth is – scaling used cooking oil supply through simply eating more chips – take off? Flight100 (a Boeing 787 Dreamliner) took a 3,543 mile journey from London Heathrow to JFK International Airport, with a total of 264 seats. Admittedly, although the technology-proving flight’s Permit to Fly precluded the commercial selling of tickets, ICAO’s carbon calculator estimates a fuel burn per economy passenger (presumably of a fully-loaded aircraft) to be 299.3kg per seat, rising to 598.5kg per premium passenger.
Although fuel manufacturers are understandably secretive about their own proprietary conversion technology, when France made biodiesel legal in 2022, secretary of the French Green Party MP Julien Bayou described a reprocessing rate of waste oil at up to 90% volume; citing “we don’t have oil in France, but we have oil from the fryers”. This would indicate the 88% HEFA content of Flight100’s 60 tonnes (75,000 litres) of SAF would, excluding catalysts and other agents, have required some 73,300 litres of chip oil.
Hungry to investigate, I approached some local chip shops, who explained that an average 15 litres of cooking oil (changed daily – although some outlets do not) produced an average of 350 medium-sized portions. That’s 0.23 litre of oil per portion, and employing the conversion of 0.8kg per litre, equates to 0.184kg of oil per meal. Using the estimated 90% volume conversion, one plate of chips therefore equates to 0.1646kg (0.21 litres) of potential SAF.
This therefore means that it would take 357,143 portions of chips to fuel a transatlantic Dreamliner with 60 tonnes of neat, unblended SAF. The 198 economy guests would need to eat around 1,818 plates of chips each to offset their 299.3kg fuel burn, with the premium guests each needing to scoff some 3,636 portions apiece.
Avoiding obvious additional issues of weight and balance encountered by such continued calorific excess, to put this into perspective: a UK Federation of Fish Friers 2019 survey estimated that British consumers eat approximately 382m meals from fish and chip shops every year. That’s only 69.9m kgs worth of oil, or 69,000 tonnes of SAF: enough for just 1,150 transatlantic flights. Meanwhile, a record 1.6m passengers travelled to and from North America from Heathrow in December 2023 alone: enough to fill 6,060 Dreamliners.
When the chips are down…
LanzaJet brought the world’s first ethanol-based SAF facility online in January 2024. (LanzaJet)
In conclusion, the ‘frequent frier’ concept is only arguably as ridiculous as the aviation industry’s insistence that HEFA-produced SAF holds the key to short-term decarbonisation, something many legislators, governments and innovators are now fully recognising. Invariably, used chip oil will remain a mere ‘drop in the ocean’ of the wider SAF scalability challenges prevailing within an industry that – as the UK’s sustainable aviation fuel consultation acknowledges– must embrace “newer technologies, which are currently more expensive but use a wider range of feedstocks”.
One promising pathway is power-to-liquid (PTL), pioneered by the likes of LanzaJet, which brought the world’s first ethanol-based SAF facility online in January 2024. With the UK also proposing an additional mandate to supply PTL fuels, expect vodka-to-SAF calculations in due course.
“It is the government’s policy that will make the difference,” concluded IATA Director General Willie Walsh, affirming that “governments must prioritize projects to incentive the scaling-up of SAF production and to diversify feedstocks with those available locally”. Thankfully, this does not include a focus on fast food outlets, as owing to the sheer volume of chips per person involved, the ‘frequent frier’ loyalty programme is unlikely to prove popular.