RR1081 - Review of small wind turbine construction instructions and specifically for structural supports and foundations

This research investigated the possible role of weaknesses in small wind turbine construction instructions in the potential for structural collapse associated with the structural supports and foundations. Build instructions relating to nine turbines of differing scale and design were obtained with industry cooperation. Analysis showed that although the stipulations were generally clear, the overall design intent of the details and criticality of certain aspects were not conveyed. As ostensibly similar details can be made to function intentionally in radically different ways, it is concluded that deviations from the required procedure could be better guarded against if the design intent and criticality were made explicit in each case. This would particularly benefit installers working across a range of products from different manufacturers. Site practices could also be improved to achieve the required bolt tensions and structural grout integrity with greater surety.

Some good practices in assurance processes for the siting checks, engineering assessments and construction were seen including photographs and records of as-built details. Wider adoption should be encouraged to improve confidence in integrity.

Factors potentially contributing individually or in combination to failures were identified in a number of areas. Known concerns about the potential under-prediction of fatigue design loads using the simplified design method in the small wind turbine standard (IEC 61400-2) were underlined. Given the transition period to 2017/19 until more stringent controls apply to new and ongoing certifications, coupled with issues on the prior exclusion of the tower and foundation from the scope of certification in the UK, industry groups such as RenewableUK's Small and Medium Wind Strategy Group who made a positive contribution to this study, are called on to renew their efforts encouraging manufacturers to proactively review the adequacy of existing and future certified installations.

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Updated 2021-04-15