A bit of background: I have been enthralled with the idea of learning to fly an airplane for quite some time. My dream is not to fly a 747, but rather something much smaller, like a Cessna or Piper. Then, a few years back, with a little prodding from my wife, I wandered into the local airport to inquire about flying lessons. Well nothing has happened yet, but it did rekindle my interest. Along the way, I discovered the cottage industry of homebuilt (or kit-built) aircraft. At last I found a way to own my own aircraft without requiring me to win the lottery first! Or so I thought. This is still a very expensive proposition, learning to fly, owning an airplane, etc. I'm still trying to get used to the cost of home ownership, so this would be a very noticeable expense.
But I still think about it. A lot.
One of the things I notice about homebuilt aircraft is that they often ship kits without an engine. This is because the engine choices are varied. Some people choose certified aircraft engines, like stuff built from Lycoming. Others restore antique car engines, most notably the Corvair or Volkswagon beetle engines, in one form or another. There are also new engines being made by companies like Rotax and Jaiburu that fit certain niche markets as well. All of these engines are piston engines, burning gasoline.
A few other things I noted: Beginner pilots typically get what is called a VFR rating. That stands for Visual Flight Rules, and loosely means daytime flying, in clear skies. There are other restrictions too, but essentially, no night flying, and not without good visibility. Another pilot rating, VFR OTT stands for VFR Over The Top, which means you can fly over a bunch of clouds, provided you can find a clear patch to land in at your destination. So essentially, most piloting is done on a clear day, with lots of sunshine. (Keep in mind I'm not talking about commercial air traffic here.)
Also, airplanes tend to have a lot of surface area on the wings - usually about 100 square feet or more. That's a lot of room that could be used for solar panels. How far along is this technology now? Can it produce enough current to power an electric motor to consistently put out about 100 hp? (I know electric motors typically don't measure output in horsepower, but I'm unschooled in this, so bear with me.) My point is, a small plane has modest requirements on an engine. Sustained 100 hp on a sunny day would do just fine, in most cases. Bring along enough battery power to last 45 mins to an hour, and you have a good safety backup in case the weather turns bad.
For most recreational pilots who typically fly for the fun of it, such a plane would be a great thing. Motor gliders are pretty close to this idea too. Imagine being able to fly a complete trip without any fuel costs. Or environmental impact, which is my real goal with this.
If a viable electric motor was developed for aircraft like this, it could grow in popularity without the automobile industry paying much attention to it. In my opinion, that would probably be a good thing. I don't trust the car makers of today to offer me REAL environmental solutions. They are too entrenched into what they currently provide. Even a switch to hydrogen is so they can continue to operate under the same business model. A car that does not require fuel is not something they have chosen to pursue. I suppose they have their reasons. I have mine for wanting that very thing.