Wind turbines, check. Solar panels, sure. But “sea dragons”? That’s a whole new category of renewable energy. Developed by Swedish energy firm minestoab, the sleek winged machines appear to swim underwater—hence the name—converting kinetic energy from tidal streams and ocean current streams into power. Partnering with utility company skupina_sev.en, Minesto has been testing and iterating configurations of the machines in the North Atlantic Ocean, home to the 18 Danish islands known as the Faroes. No slouches when it comes to green energy, the community already captures half its energy from renewable sources. And now it will have sea dragons. The apparatuses operate similar to a kite flying in the wind—but in this case, there’s an underwater turbine tethered to the seabed or surface platform. As the machine’s kite wing rides the underwater current, that hydrodynamic lift force propels the turbine at a speed far greater than the water’s flow rate, dramatically boosting energy produ...