Wind turbine on Awaji Island falls from base

A wind turbine on Awaji Island collapsed due to typhoon No. 20, a case that was widely covered in the mass media among instances of damage to renewable energy equipment this summer. The wind power generation equipment is in Hokudan Earthquake Memorial Park in Awaji City, Hyogo Prefecture, and features a rated output of 600kW (Fig. 19).

Fig. 19: The wind turbine in Awaji City destroyed by typhoon No. 20 (picture: Nikkei BP)

Typhoon No. 20 reached Tokushima Prefecture on the night of August 23, retaining its strength, and landed in the area near Himeji City of Hyogo Prefecture before midnight on August 24. The collapsed wind turbine in Awaji City was discovered by a resident of the nearby area, who passed by the turbine in the early morning of the 24th.

Hokudan Earthquake Memorial Park was constructed to convey the lessons learned from the Great Hanshin-Awaji Earthquake to future generations. The wind turbine stood in the parking facility across the road from a tour facility. The turbine was installed by "Hokudan," a third-sector corporation in Awaji City, in April 2002.

The collapsed wind turbine was manufactured by Mitsubishi Heavy Industries, Ltd. The tower had a height of 37m and the turning diameter of the blades was 45m. Many local governments constructed wind turbines in parks and other places as symbols of renewable energy promotion around 2000, and the turbine at Hokudan Earthquake Memorial Park was one such example (Fig. 20).

Fig. 20: The wind turbine before it collapsed (source: Homepage of Awaji City)

When we observed the site, the 37m tower was broken at the base and had fallen over, with the blades facing down and the nacelle facing up. Two of the three blades were bent up, but they remained connected to the nacelle, barely retaining their original form. However, one of the blades was displaced from the nacelle and the broken parts were scattered around the collapsed turbine (Fig. 21).

Fig. 21: The turbine collapsed, with the blades facing down (picture: Nikkei BP)

Fig. 22: One of the blades was broken and the parts were scattered (picture: Nikkei BP)

The sale of power generated by the wind turbine was discontinued in May of last year due to the failure of the grid connection system, according to Awaji City. But the turbine continued to receive power from the grid and the yaw control system for changing the blade direction by detecting the wind direction was functioning.

The cause is currently being investigated, considering the possibility that one of the blades was displaced by strong wind, causing the collapse of the tower due to a loss of balance, as well as the possibility that the tower collapsed first, causing the blade to separate from the nacelle.

According to the disclosed information, the wind turbine was designed based on the standard design wind speed of 34m/s set for the region and satisfied the safety criteria specified by the Building Standards Act. However, the picture of the broken portion taken immediately after the collapse shows that the anchor bolts fixing the tower to the foundation were broken. It is suspected that there was a defect in the design or the construction method of the foundation (Fig. 23)

Fig. 23: The foundation at the bottom of the tower was broken (source: METI)

The Ministry of Economy, Trade and Industry (METI) checked the site after the accident. On September 19, METI instructed operators of wind power generation facilities throughout Japan to submit reports on design types, etc, of foundations, commenting, "The cause of the accident is currently being examined, but it is possible that the accident was caused by the structure, etc, of the foundation, based on the results of the field survey."