If it's gonna be for a school project, I think Solar Energy would be a good start for you. Solar panels are readily available in the market right now and there are a lot of projects that you can use as reference for this. However, you have to consider what type of device do you wish to power up with this energy source because the energy produced may not be enough for it's application. Wind Energy can also be a good option. Try to do some research on these and see if you think it'll work for you.
