I'd have to cross my neighbours land unfotunately, so cost & permission wise it would be too much hassle
That does makes things more awkward. I think I'd be worried that the limitations a small solar set up would impose would become frustrating though. You may not be able to use the gym when you want to in the winter or on a cloudy morning or evening in the summer. As Spoon says, you may find yourself needing a heater in the depths of winter.