Use a battery
Use a generator
Use solar panels
Use wind turbines
Use hydroelectric turbines
Use fuel cells
Use thermoelectric generators
Use piezoelectric materials
Use hand-crank generators
Use dynamos
Use a steam turbine connected to an alternator
Use a magnet and coil to induce current
Connect a circuit to a power source
Convert mechanical energy into electrical energy
Convert light energy into electrical energy
Convert heat energy into electrical energy