Verdant’s Free Flow turbine, a three-bladed, downstream, ­horizontal-axis device that has evolved through four generations of design since 1989, has been battle-hardened in the currents of New York City’s East River as part of the Roosevelt ­Island Tidal ­Energy (Rite) project.

For the Cornwall Ontario ­River Energy (Core) scheme in the St Lawrence River, which forms part of the boundary between Canada and the US, the technology is being adapted to suit a continuous-flow setting, rather than tidal cycles.

“The