Lightning incidence on wind turbines in winter

In Japan, transmission lines or wind turbines in the coastal area of the Sea of Japan have suffered from higher frequencies of serious troubles due to lightning in winter than those in summer. Lightning which hits tall structures in winter in Japan has turned out to be mostly upward lightning, and the number of lightning hits to such structures is far more than that in summer although lightning flash density in winter is much lower. To evaluate lightning risk to tall structures in such an area, an experimental formula to estimate the frequency of lightning hits on wind turbines in winter in Japan is proposed. From 2008 to 2013, lightning hits to wind turbines were observed at 27 sites in Japan under a research project of NEDO (New Energy and Industrial Technology Development Organization). The aspects of attachment of upward lightning observed in this project are also reported on.