Cleantech’s emerging importance for aviation

On the 19th of November, 2009, gangly prototype solar powered plane Solar Impulse HB-SIA taxied down the Dübendorf airfield runway in Switzerland for the first time.

This inaugural day out on the runway allowed low-speed taxi testing, with the prototype going through a series of acceleration and braking manoeuvres. The next stage is to involve taking the prototype up to its 35 km/h take-off speed and having it do its first few “flea hops.” The two founders of the project—pilots Bertrand Piccard and André Borschberg—aim to take the plane on a round-the-world flight in 2012.

Unfortunately, the commercialisation of purely solar powered passenger planes is likely to remain a dream for the next few decades. What might pose more short term options for making aviation cleaner?

The international Air Transport Action Group (ATAG) has decreed that first generation biofuels such as those grown from sugarcane and corn don’t have the necessary performance and safety attributes for modern jet engine use. However, 2nd generation biofuels from feedstocks such as jatropha, camelina and algae are able to meet the high performance and safety specifications for jet fuel. The ATAG estimate that these biofuels can provide an 80 percent reduction in overall CO₂ lifecycle emissions compared to fossil fuels.

There are many companies, large and small, now targeting jet fuel applications of biofuels. See Bio jet fuel breakthrough?, Game-changing day for jet biofuels, and China National Petroleum, UOP team on biofuels project).

Dutch airline KLM is investing in developing the capacity for biofuels in airplanes. On the 23rd of November 2009, a KLM Boeing 747 with one of its four engines powered by a 50-50 blend of biofuel and conventional jet fuel successfully completed a one hour flight in the Netherlands with 40 passengers. This was the first ever commercial flight to use biofuels, even though airlines have been dabbling with and seeking publicity from biofuel trials for years (see Virgin takes off with commercial biofuel test flight).

Biofuel seems to be the quickest, cheapest and most sustainable way for the aviation industry to reduce emissions because:

• It can be grown in a large number of places in comparison to the limited number of locations where fossil fuels can be drilled
• 2nd generation biofuels can be grown on marginal land and poor quality soil
• There are only a relatively small number of airport fuel depots and aircraft. This makes the integration of biofuels into the aviation system a lot easier than in the more dispersed, less controlled automobile industry.
• ATAG forecasts that aviation biofuels will become cost-comparable with normal jet-fuel by 2020, but volatile oil prices make this difficult to predict

The industry is showing faith in biofuels. European aircraft-maker Airbus said it believes that alternative fuels could power 15 percent of global air traffic by 2020 and 30 percent by 2030.

What about fuel cells? In early 2008, the first manned fuel cell powered flight took place (see Boeing tests fuel cell-powered plane). A light two-seat Dimona motor-glider with a 16.3 meter (53.5 foot) wingspan was flown for over 20 miles powered only by a PEM fuel cell provided by a UK venture-backed company called Intelligent Energy.

This demonstration is now paving the way for the use of fuel cells in commercial planes to provide auxiliary power (i.e. power for purposes other than propulsion). In October, French airline Airbus signed a deal with Intelligent Energy as part of a research project to install hydrogen fuel cells on their planes for generating on-board power (see Airbus to take off with fuel cell auxiliary power).

There appear to be significant technical challenges in being able to design a powerful enough hydrogen-based fuel cell system to ever be sufficient for aircraft propulsion.

Improvements in aircraft aerodynamics, engine efficiency and air traffic systems have all combined to make passenger flight more than 70 percent more fuel-efficient than it was 40 years ago. Yet despite these improvements, CO₂ emissions from aviation have increased 25 percent over the last ten years alone, because more people are flying.

Which underscores that change is needed in commercial aviation, and quickly.

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