It is a decades-old dream: a single, vast North American electric grid, from the Atlantic to the Pacific, from Mexico to the Arctic Circle. Such a continent-wide supergrid would let officials transmit the tens of gigawatts of wind-generated power from the Great Plains to cities on both coasts. It would let Pacific Northwest hydropower flow to Chicago and let Texas wind power find its way to Massachusetts, Mississippi and Montana. The benefits, measured in financial and reliability terms, would be fantastic. And yet despite many studies and even several attempts to create such a grid, it has never been achieved. The technology and the political will have been lacking.

In 2016, though, engineers will make a major stride in the former. An ambitious project known as Tres Amigas, eight years in the making, is finally getting under way. Eventually it will link the three largest North American grids: the Eastern Interconnection, the Western Interconnection and the Texas Interconnect