0frollard 9 years ago ReplyUpvoteBuild a stationary bicycle that has an alternator in place of the 'resistance' on the flywheel. Hook the alternator up to a regulator circuit to make 12 volts. Get some solar panels and hook them to an appropriate sized fan. Pedal as hard as you can to generate power. This will undoubtedly make you sweat. Use the solar panel to help you in generating 12 volts by keeping you cool.