Manchester, famous for bobbins in the cotton era, has now invented the "bobber" - an electricity generator which uses rising and falling floats to create power.
Tests at Manchester University suggest that the device could outperform windfarms by harnessing the motion of waves.
Peter Stansby, professor of hydrodynamics, said: "When you hear that a wind turbine produces two megawatts, that actually indicates the maximum output. The Manchester bobber's output of five megawatts is the mean power output, with the potential of much more."