You don’t have to put solar panels on the roof to go solar! I’ve used a sun-powered calculator for as long as I can remember. No batteries to change out, no charging cord to keep track of. You just put it on a sunny windowsill ever now and again and it’s all charged up. I can’t imagine why anybody would purchase any other kind of calculator, unless you live in a cave.
Solar calculators are inexpensive, and they’re available from a basic plus-and-minus machine with big keys (my favorite) to a full-function scientific or engineering calculator.