I invite people to look at gasoline to electric boat motor conversions.
I have. it's still horrendously expensive. Here at least.
For what I can get a small diesel engine for, I'll put up with the noise. What am I saying??, I love the noise! :0)
I am looking at doing a small River boat to use where I'll be going which has a river nearby and winding through the whole area. You are allowed up to a 5HP motor here without having to have a license or the boat registered. Just bought an 8Hp China diesel so I'll make up some stickers with a big 5 on them and that will put off any inspectors. Mate of mine has a 15 Hp Outboard with the 5Hp stickers on it and gets waterways inspectors stopping him every so often because the thing is traveling so fast. He says he has a big prop on it and pretended to labor the thing when he takes off and hasn't had an issue.
Electric is still expensive when one considers batteries, controllers and the motor. Solar panels would be OK for A day Cruiser that sits most of the time as it would always be ready to go when you came to use it providing that isn't every day. I suspect the range increase while motoring would be negligible because the panels are going to be at the wrong angle 99% of the time and it's not like there is going to be room to put 5Kw of panels up there to compensate.
Still a thing for people with more disposable $$ than me I think..... or just more into boats and electric power.