Electrons will soon be flowing from a prototype windmill off Maine’s coast in a first-on-the-continent event. The University of Maine’s Advanced Structures and Composites Center will connect the VolturnUS offshore wind turbine to the electrical grid on Thursday. VolturnUS is the first grid-connected offshore wind turbine in North America. The 65-foot-tall turbine, the first floating turbine of its kind in the world, is a prototype, one-eighth the scale of a 423-foot rotor diameter design. The unique floating hull design was made using advanced material systems. The turbine was towed down the Penobscot River from Brewer, where it was launched May 31, to ocean waters off Castine. It’s been hooked up to the grid and will be the first offshore windmill to generate electricity.