Electric aviation is advancing faster than many critics expected. Batteries will not remain confined to tiny experimental aircraft, and short regional routes are a credible early market. But electric aircraft will not replace every jet. Long-haul aviation requires enormous energy at very low weight. Even with better batteries and airframes, liquid fuels will retain a large role for decades. The question is therefore which sustainable aviation fuels can reach scale at a price airlines can eventually afford. Germany has now designed a €2-billion…