June 24, 2011

Is aviation sustainable?

Yes, it is.

Air transport is the most difficult area in which to eliminate fossil fuels, but on the other hand:

We're going to have fossil fuels for many decades, should we want them, albeit at lower levels than today - we have time to find the cheapest and most convenient way to replace aviation FF consumption.

In the long run, 3x greater efficiency is possible, and synthetic FF-free fuel is unlikely to be more than 3x as expensive per gallon.

First, while jet fuel is probably the hardest use for oil to replace, there are a number of ways to use it more efficiently. Short term changes include replacing or reducing use of older, much less efficient planes; filling planes more fully (increasing load factor); longer and more gradual descents, reducing powered flight time; reduced time in the air waiting to land; electric "tugs" on the ground); slightly slower flying speeds; and a long list of others - ( http://www.nytimes.com/2010/10/09/business/09air.html?_r=1&th&emc=th ). A lot of the changes are operational, so they're very fast. Others, like the Boeing Dreamliner, are being delivered now. This might be expected to reduce fuel costs by roughly 1/3.

2nd, fuel is only very roughly 40% of airline costs, and oil is only part of the cost of fuel (jet fuel is higher quality, and therefore more expensive). Combined with the efficiencies discussed above, this means that if oil prices were to rise by 100%, airline ticket prices would only go up by 25%. That's not going to stop people from flying.

3rd, it's very unlikely that oil prices will rise by 100% in a sustained fashion. First, oil prices above $150 would slow down economic growth. 2nd, all of the major uses for oil have substitutes that are cheaper when oil rises above roughly $80. If oil prices went to $150 and stayed there for any length of time, consumers would move to carpooling, mass transit, hybrids, EREVs, EVs, rail, heat pumps, etc, etc, very very quickly. Both of these effects would keep prices from rising further, and probably reduce them from that peak.

4th, in the long term, design changes can reduce fuel consumption by 70%:

"CAMBRIDGE, Mass. — In what could set the stage for a fundamental shift in commercial aviation, an MIT-led team has designed a green airplane that is estimated to use 70 percent less fuel than current planes while also reducing noise and emission of nitrogen oxides (NOx). http://web.mit.edu/press/2010/green-airplanes.html


"the team has found that the SUGAR Volt concept (which adds an electric battery gas turbine hybrid propulsion system) can reduce fuel burn by greater than 70 percent and total energy use by 55 percent when battery energy is included. Moreover, the fuel burn reduction and the ‘greening’ of the electrical power grid can produce large reductions in emissions of life cycle CO2 and nitrous oxide. Hybrid electric propulsion also has the potential to shorten takeoff distance and reduce noise. "


5th, fuel can be synthesized from electricity, seawater and atmospheric CO2 right now, but the costs are high - roughly $10/gallon. The Green Freedom project promises synthetic fuel for $4.50 per gallon, pretty close to where we are today, but if they never fulfill that promise we can still synthesize fuel, albeit at higher cost.

30 years is enough time for aviation to become more efficient - that will keep it going another 20-30 years. 50-60 years is enough to develop and streamline substitutes like biofuels, synthetics liquid fuels (from renewable electricity, hydrogen from seawater electrolysis and atmospheric carbon), or liquid hydrogen.

Green Fredom is probably a very, very long-term thing. Things like CTL, GTL and syncrude will continue for a very long time. It would require a very strong commitment to completely get rid of fossil fuels in the medium term.

The actual balance between efficiency improvements and reductions in synthetic fuel costs remain to be seen, but it's highly likely that we'll see synthetic fueled jets with operating costs equal to those of today's airlines.