You can make flexible solar panels, and you can make them in non-rectangle shapes. They are, I believe, commercially available.
Most solar panels are rectangular because the surface they’re on is rectangular, and rectangles are easy to tessalate so you don’t need (too many) different sizes/shapes to cover a large area. Making them flexible means making them thinner and less durable – which isn’t worth the flexibility for a vast majority of applications – though in some niche cases, it sees use.
I’ll let someone else answer the first part, since I don’t know enough about it to ELU5
Latest Answers