Turbine Testing: Setting Standards for Smaller Devices

As small and medium-sized wind turbines steadily become more popular worldwide, so does the need for confidence in their ability to perform as designed, both safely and reliably. This has resulted in a complex and challenging testing and certification regime. So what are these testing challenges and how can they be best tackled?

The testing criteria for small and medium-sized wind turbines are largely driven by international standards. For example, the UK's Microgeneration Certification Scheme (MCS) - which covers wind turbines with a rated power of less than 50 kW and a rotor swept area less than 200 m² - places heavy reliance on the British Wind Energy Association (BWEA) Small Wind Turbine Performance and Safety Standard, which in turn references a number of international standards in the IEC 61400 series.

Not-dissimilar criteria exist in the US and Canada, but rely on the AWEA 9.1 Standard instead. The Small Wind Certification Council (SWCC) is the body currently leading activity on this in North America.

Both the BWEA and AWEA standards are underpinned by and rely on IEC 61400-2: 2006, which provides the design criteria for small wind turbines. The 'dash 2' standard gives guidance on the design of a small wind turbine using either a simplified load approach or a more detailed and complex aero-elastic modelling approach, or a combination of the two.

The standard is applicable to the design of both horizontal axis wind turbines (HAWT) and vertical axis wind turbines (VAWT). In addition, there is a requirement to test the durability and safety and function of the turbine.

Standards to come

The next edition of the standard (Edition 3: 201x) is due to be published shortly. To deliver this next edition, an IEC maintenance team has been working very intensively for two years and has reviewed many of the criteria in the light of lessons learned and current best practice.

The resulting new version of the standard will give greater guidance, among other things, on the use of the simplified load approach and dealing with extreme wind conditions.

The performance of the turbine is assessed against the criteria in IEC 61400-12-1: 2006, the power performance standard, and IEC 61400-11: 2003, the acoustic performance standard. An evaluation of both of these aspects is crucial in determining a turbine's suitability for a particular wind regime, purpose and location.

Defining medium wind requirements

A UK Medium Wind Standard is currently at the draft stage and is scheduled to be published before the end of this year. Moving forward, it is hoped the international community will address the perceived issues with medium-sized turbines to make a UK standard unnecessary. While medium-sized turbines are unlikely to be the mainstay of wind farms of the future, they are likely to play a significant part in distributed and community wind projects, which means an appropriate standard supported by government incentives is likely to benefit all stakeholders in the longer term.

Alistair Mackinnon is operations manager wind energy at NEL, which is part of the TÜV SÜD Group.

Image: Small wind turbine via Shutterstock