Front Generator Wind Turbine

While commercial wind turbines have been trending toward larger sizes, from 300 kW capacity in 1990 to 7.5 MW in 2011, sometimes it is worth bucking the trend. Professor J.C. Chiao and his postdoc Dr. Smitha Rao of the University of Texas at Arlington have taken this contrarian philosophy to the extreme. They have developed a MEMS-based nickel alloy windmill so small that 10 could be mounted on a single grain of rice. Aimed at very-small-scale energy harvesting applications, these windmills could recharge batteries for smartphones, and directly power ultra-low-power electronic devices.

The micro-windmills (technically called horizontal axis wind turbines) have a three-bladed rotor 1.8 mm in diameter mounted on a tower about 2 mm tall. The mount is a friction hub, but this probably becomes an air bearing when the rotor is spinning. The thickness of the windmills is about 100 microns.

Despite their size, the micro-windmills can endure strong winds, owing to being constructed of a tough nickel alloy (rather than the silicon and silicon oxide layers typical of MEMS designs) and smart aerodynamic design. “The problem most MEMS designers have is that materials are too brittle,” Rao said. “With the nickel alloy, we don’t have that same issue. They’re very, very durable.” Several thousand such windmills could be made on a single 200-mm (8-inch) silicon wafer using Rao's clever design and primarily conventional MEMS fabrication processes, resulting in very low per unit prices.

Let's get to the meat. As amazing as these devices are, can they actually be of any use? Unfortunately, detailed design information on the micro-windmills does not seem to have been published as yet, and predicting the exact performance of a horizontal-axis wind turbine is still a bit of a magic art (in the absence of serious computer modeling.) However, I have put together some rough estimates to get a feel for the potential performance levels of such micro-windmills.