If you want to go green, just keep your aircraft properly maintained, it will last forever! Barring a serious crash an airframe can outlive a person with proper maintenance. You will have to deal with avionics swap-outs, that technology has a short life-cycle. Also some items like wiring, fuel system components, and engines parts need replacing over time. That is where the focus for "green" solutions should center for small homebuilt type aircraft.

Joe