I was really impressed by a couple of german guys, who managed to fit a solar powered engine into a fidget spinner. The idea amused me so much, that i think, it is worth to be mentioned here. If you like, visit https://www.kickstarter.com/projects/*******/youla-the-brand-new-solar-powered-spinner?
For myself, it is totally worth it, to get a kickstarter account and order some for my family. Enjoy!