Makers of giant wind turbines are hoping that artificial intelligence can bring back some of the industry's mojo. While developers have spent $1.1 trillion on new wind farms over the past dozen years--helping transform the global energy landscape with renewable power--more money is going into new solar systems these days. Also, governments are phasing out subsidies, including programs in the U.S. that have offered $22 billion in tax breaks to turbine projects in the past 15 years. To remain an attractive, lower-cost option for utilities, companies like Vestas Wind Systems A/S and Invenergy LLC are investing in technologies to squeeze more electricity from every propeller rotation. Modern turbines with blades that stretch 450 feet (137 meters) in the air already can twist and turn and spin faster or slower to adjust to ever-changing breezes.