The number of wind power installations connected to the electrical grid in the US has exploded in recent years, driven in part by government tax credits for renewables, but all of them have been confined to land so far. That changed today, when North America's first-ever offshore wind turbine, the VolturnUS (pronounced as one word, "vol-tern-us"), was installed on a floating platform off the shore of the Penobscot River in Brewer, Maine. In the coming days, the turbine is set to be towed across the river to a site further out into the waters of the Atlantic, where it will be plugged into the electrical grid through an undersea cable. By Tuesday, it will spin to life, becoming the first operational machine of its kind on the continent.

The project is a collaboration between the University of Maine and many other private and public organizations, and cost about $15 million, most of which was funded by a 2009 grant from the US Energy Department. The turbine itself will only generate a relatively measly 20 kilowatts of electricity, enough to power about four homes.

But the 65-foot-tall machine is just a prototype. It's meant to collect data over the course of 2013 for a pair of larger, $96 million, permanent offshore winds that backers aim to deploy off the coast of Maine in 2016. Those will be able to generate 6 megawatts, enough to power 6,000 homes. That entire project is vying for more federal money against other offshore proposals in Maine and across the country, as the Portland Press Herald reports. In the mean time, the smaller VolturnUS prototype will serve as America's first, and so far only, attempt to compete with other countries that have much more mature offshore wind industries.