Poul la Cour was mostly known internationally for his revolutionary experiments with wind turbine models in small wind tunnels. His book, The Test Turbine, was based on these experiments, and for several years, it was an international primer on wind turbines.
In the book, la Cour demonstrates that wind roses were useless for electricity production. He argued the ideal turbine should have as few wings as possible, be a fast runner, and have wings with an aerodynamic profile. He also said the bevel of the wings should be surprisingly small, a last conclusion that still puzzles people today.. How can the wings rotate even though they are almost perpendicular to the wind? This was well documented by la Cour, however, and his ideal wind turbine very much resembles the modern designs, although new materials like glass fiber enable far more aerodynamic profiles than Poul la Cour dared hope for.
Compared to the farm wind turbines of his time, his ideal wind turbine could produce three times as much electricity with the same wing length.