In order to increase the power output of the straight-bladed Darrieus wind turbine, our research group developed a variable-pitch with a four-bar linkage mechanism that consists of a main link, second link, blade link, and eccentric link. In this study, we investigated the effects of controlling the eccentric-link length through computational fluid dynamics (CFD) analysis. The CFD results showed that the variable-pitch condition with the variable eccentric-link length during wind turbine rotation had higher torque on both the upstream advancing side and the downstream retreating side of the rotor than did the variable-pitch condition with the constant eccentric-link length. As a result, the variable-pitch condition with the variable eccentric-link length during wind turbine rotation had a higher power coefficient than did the variable-pitch condition with the constant eccentric-link length.
To improve the forecast accuracy of the annual energy production from wind power, the characteristics of the atmospheric stability distribution are summarized using data from wind observation towers at ten sites in Japan. The bulk Richardson numbers indicate that stable conditions prevailed at seven out of ten locations. An analysis of each met mast indicated that the prevailing stability varied by season and differed not only according to the area but also according to the wind farm scale. These differences are thought to result from the distance to the sea and the wind shear. In addition, we compared the results according to the observational data and the bulk Richardson number calculated using the Weather Research and Forecasting model（WRF） during each season. The prevailing atmospheric stability at the observation points is affected by the atmospheric stability of the land and the surrounding ocean. The results of previous research and this study indicate that considering the atmospheric stability enables more correct estimations of the annual wind power energy production. If possible, seasonal and local differences in the atmospheric stability should be considered to better estimate the wind power generation.
Many of the offshore wind farm projects planned in Japan are in near-shore areas, and scanning LiDARs are increasingly being installed to observe wind condition. Before scanning LiDAR observations, a hard target calibration is conducted. In conventional hard target calibration, fixed structures around a scanning LiDAR are used as hard targets, but drones are expected to replace them because it is sometimes difficult to find suitable fixed structures for hard targets. We performed a hard target calibration using a drone and found that the results were very good and accurate enough to be used for elevation angle correction by sine curve fitting. In the future, the use of drones in hard-target calibration is expected to increase.