The world has started a massive energy revolution - replacing fossil fuels with renewable energy resources. For aircraft transport this means battery power now for smaller and shorter range aircraft, then hydrogen or hybrid power for medium size and range, and eventually renewable fuels for larger aircraft and longer range.
Over 400,000 fossil fuelled GA aircraft must be replaced or refitted to complete this revolution. But in addition, the lower operating costs and almost silent flight will expand existing markets and open up new ones. This revolution has already begun with the first battery-powered aircraft being used for pilot training.