You can have two 55 gallon plastic barrels for example one is full of water. Connect these two barrels together with a 6 inch pipe. In the pipe centered between the two barrels you have a small generator turbine. Lift up the barrel that is full of and it will flow through the pipe to the other barrel and produce an electrical current. If you add some buoyancy to the two barrels you can float it on the ocean for example.