Measured gust events in the urban environment, a comparison with the IEC standard

The installation of small wind turbines and solar photovoltaic (PV) modules in the built environment requires a detailed understanding of wind resources to maximise turbine power output and minimise damage due to wind loading. While urban sites are known to be highly turbulent, less is known about the composition and frequency of gust events. To date a number of catastrophic wind turbine and solar PV structural failures have resulted from inadequate design for extreme gust events. In this study a 12 month wind resource measurement campaign was undertaken at an urban site. Gust events that satisfied the IEC 61400.2–2013 definition of an annual extreme operating gust were found to occur 100 times during the 12 months interval. These events had a 23% higher mean amplitude, and 21% shorter rise-and-fall time than that assumed by the standard. In addition, a site gust factor of 1.76 was determined, a value 26% higher than given in IEC 61400.2–2013. Consequently, IEC 61400.2–2013 appears not to predict the frequency and amplitude of extreme gust events at this given site suggesting there exists a risk that structural components may be under-designed for installation in urban sites.