Technology Quarterly | Monitor

Japan's winds of change

Energy: Redesigned wind turbines can wring more power out of mountain winds, which are otherwise difficult to exploit

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ONE reason for Japan's reliance on nuclear power—with all its attendant difficulties of building reactors safely in an earthquake zone—is its lack of indigenous energy sources. Yet it does have one that seems under-exploited, namely the wind. According to a report published in 2009 by the Global Wind Energy Council, Japan, which generates 8.7% of the world's economic output, has just 1.3% of its windpower capacity. The world's third-largest economy is 13th in global windpower.

According to Chuichi Arakawa, a mechanical engineer at the University of Tokyo, that is because Japan has too much of the wrong sort of wind. The typhoons which regularly strike the place are simply too powerful. (In 2003, for example, such a storm crippled six turbines on Miyakojima, near Okinawa.) And the ordinary winds are less useful than they might be because Japan is so mountainous. For engineering reasons turbines must be mounted on vertical poles, regardless of the slope of the landscape. But on a hillside that means the wind (which tends to follow the ground when it is close to the surface) hits the blades of the turbines at an angle, instead of face on. That makes power generation less efficient.

Help, though, is on the way. Engineers at Fuji Heavy Industries (FHI), a large manufacturing company, have come up with a turbine that they think can withstand the sort of battering that brought down those on Miyakojima, and also turn the irregular mountain winds to advantage. The crucial differences between FHI's new turbine and a traditional one are in the location and setting of the blades. In a traditional turbine the blades are in front of both the pole and the nacelle (the structure that houses the generator). In addition, the plane of the blades is parallel to the pole. This is called an upwind design.

By contrast, FHI has opted for a downwind design, which puts the blades behind both nacelle and pole. This allows the rotor plane to be tilted so that it faces directly into winds blowing up the hill without snagging on the pole. According to Shigeo Yoshida, who is in charge of research for the project, that makes the arrangement 5-8% more efficient in such circumstances than an upwind turbine would be.

As a bonus, the downwind design is less temperamental in high winds. That is because the blades, being behind the pole and at an angle to it, can be given more freedom to yaw about than they would have in an upwind turbine. This puts less strain on them than if they were fixed. So far 25 downwind turbines have been constructed in Japan, and dozens more are in the pipeline. Windpower will remain an unpredictable power source, of course. But as Japan has recently been reminded, a bit more diversity of supply would not hurt.

This article appeared in the Technology Quarterly section of the print edition under the headline "Japan's winds of change"

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