Boeing's proposal to certify a Sustainable Aviation Fuel (SAF) engine by 2030 is by no means a stretch technology wise. It has less to do combustion of the fuel as an energy source as it does making design changes within the engine and fuel tanks to keep elastomeric materials malleable and functioning. There is no reason to delay any aircraft before this occurs.
As much as everyone likes to speculate on a hydrogen airplane, it is likely that costs associated with Synthetic Aviation Fuels, and in particular synthetic kerosene made from renewable energy, are going to decline due to scale and technological advances.
True, today the costs of eFuels are prohibitively high, which is why the EU is proposing a mandate of a blend initially.
"In a recent study commissioned by T&E, Ricardo Energy and Environment estimated a cost of 137 - 233 €/MWh (i.e. 1.3 - 2.2 €/litre) for e-kerosene in 2020 depending, that is almost 2 to 3 times the average price of fossil kerosene."
Projections which look at economies of scale and technology improvements show cost equivalency of synthetic kerosene (eFuels) to fossil fuels by 2050.
- eFuel Allianceinformation brochure This is what climate-neutral fuels will cost in the future
Once one considers the added effects of contrail formation, Sustainable Aviation Fuels (SAF) make even more sense.
"Synthetic e-kerosene is produced from synthetic crude in much the same way as e-diesel but is refined to be suitable as a jet fuel. The development of new aircraft based on novel fuels require significant research and development, investments, and accompanying regulation to ensure safe, economic aircraft. Commercialisation and certification of aircraft can take more than 10 years. Drop-in fuels like e-kerosene are the most immediate solution that would only require development of the supply infrastructure.
As with e-diesel, fuel impurities are removed, but the exhaust from e-kerosene combustion still contains CO2, CO, NOx and particulate matter. Emissions of the first three pollutants would be at a similar level to fossil-derived kerosene, but the concentration of particulate matter is likely to be lower.
Aviation has difficulty reducing these emissions due to technical solutions adding weight to the aircraft and requiring technical complexity that could have an impact on passenger safety. In addition, an issue unique to aviation is that the fine particulate matter results in contrails, creating cirrus clouds that contribute to short-term global warming. The effects of NOx emissions from aeroplanes are complex. On the one hand, they increase ozone formation, which has negative effects on respiratory health (at ground level) and is a greenhouse gas but NOx also shields the earth’s surface from harmful UV radiation at high altitudes. While on the other hand, NOx tends to reduce methane levels, which is itself a significant greenhouse gas."
Now as to the question of how much renewable energy is required. It is estimated for the EU that the entire transportation sector, including aviation, will use renewable energy equivalent to that in the electrical grid. Certainly a large amount, but not so large as to be entirely infeasible. One would presume that the same trends would apply to other localities.
"To achieve full decarbonisation of transport with T&E’s Base Case forecast, about 2,800 TWh/y will be required by 2050. This represents a significant scale-up between 2030 and 2050. For comparison, the predicted demand for renewables from the decarbonised electricity grid in 2050 is predicted to be about 3,350 TWh/y.
This study shows that the potential for additional renewable electricity in the EU28 countries comfortably exceeds the projected demand to decarbonise transport and the electricity grid by 2050. Studies show that the total exploitable potential for renewable electricity (solar PV, onshore wind, off shore wind & geothermal) in the EU28 countries is about 27,000 to 28,000 TWh/y. "