Prior to the [Great] war, most electrical systems in Denmark were direct current (DC). During the war, the utility serving the area north of Copenhagen introduced alternating current (AC). In 1919 the utility installed a wind turbine at Buddinge and connected it to its lines—a first worldwide, a full two decades before the Smith-Putnam machine in Vermont was connected to the grid.
This is an edited extract from my forthcoming book, Wind Energy for the Rest of Us. (The book will be available in mid to late 2016.) I am posting this passage here because of a common misconception that the Smith-Putnam turbine was the first wind turbine connected to an electrical network. The question arose because an article for the November/December 2009 issue of IEEE Power & Energy Magazine. This is an important historical detail because it shows how advanced Danish work was with wind energy during the interwar years. For more on the Agricco turbine, see Wind Power for the World, and here.
The 40-kW Agricco was an odd mix of new and old, but surprisingly advanced for its day. The turbine used true airfoils in the blades for the first time, but it used five or six blades instead of the four blades recommend by [Poul] la Cour. The rotor used struts and stays to brace the blades, much like later Danish wind turbines. And the Agricco used fantails to orient the rotor into the wind. Nevertheless, tests in the early 1920s found that the Agricco wind turbine was twice as efficient as la Cour’s design.
To produce utility-compatible AC, the Agricco employed an asynchronous or induction generator for the first time. This choice proved significant and would later influence other wind turbine designers in Germany and France. If Agricco’s designers had chosen a synchronous generator, they would have had to design a complex, costly, and difficult to maintain pitch mechanism for regulating the speed of the rotor and hence the speed of the generator. Using an induction generator greatly simplified the design and its interconnection with the grid.
As with la Cour and later Danish experimenters, the wind turbine was envisioned as part of the electrical network, providing power to the grid for everyone to benefit. Unfortunately, there was little demand for wind as diesel fuel became more readily available at the end of the war and Agricco reached a dead end. Danish historians describe the Agricco as the right windmill—at the wrong time.