Hitachi has developed a new offshore wind turbine designed to milk more power from light-wind locations. The 5 MW turbine features a rotor sweep diameter of 136 meters (446 ft), 15 percent greater than the previous model from the company, ideally suited for areas with average annual wind speeds under 7.5 m/sec (16.7 mph).
The turbine uses a downwind rotor configuration, meaning the wind passes the tower structure before hitting the blades. This configuration is designed to reduce wind loads and avoid crosswinds, even when generation is stopped due to high winds; an important feature for locations with frequent typhoons or hurricanes. A sensor can also be installed ahead of the rotor for disturbance-free data, allowing for greater yaw control (and thus energy output).
Hitachi will test run the system starting in October at the onshore Fukashiba Wind Power Station in the port of Kashima, with a tentative release date of early 2017. The company previously developed 2MW and 2.5MW wind turbines for light-wind regions.
Generally speaking, locating wind turbines offshore is more advantageous than projects on land despite higher installation costs, since winds are more reliable and consistent, blowing 40 percent more often than on land. There's also less of an aesthetic issue with offshore turbines, and for a country like Japan with lots of coastline but limited land, they are an important element of renewable energy plans.
That said, some offshore locations have winds that are lighter or more variable, such as off Japan's main island of Honshu. But most turbines typically require wind speeds of around 12 m/s (26 mph) or more to maximize their energy output. Turbines that can squeeze more power from light-wind locations open up more potential sites, and produce more energy during less windy periods.
The company is also developing a wind turbine to withstand the stronger winds found off Japan's southern island of Kyushu.