Special site classification

Wind & Water Wind Farm Modeling
1

Dear all

I studied two site for wind assessment analysis. In both sites average speed is less than 7 m/s (6.8 and 6.95 m/s). One site have almost a steady seasonal wind profile but the other one has high seasonal variation. For instance average wind speed in July is 12.7 (m/s) and in January is 3.7 (m/s). According to IEC 61400 both site classified within class III and all of designing parameters will be the same(is it true?). So can we install the same turbine (class III) in both sites without any other consideration? Of course different capacity factor can be made, but is the “extreme conditions” will be different in two sites? I studied IEC standards carefully but I cant find any recommendations about it.

Best Regards,

Masoud Rezvanian
Sun-Air Research Institute, Ferdowsi University of Mashhad

2

Dear Masoud,

I’m assuming you are referring to the IEC 61400-1 design standard. The design conditions stated in that standard are used to design the turbine. However, any given site likely has different conditions than what the turbine was designed for. Thus, a separate analysis–called a site-suitability analysis–is performed using actual site conditions to ensure that a given design is appropriate for a given site.

Best regards,

3

Dear Jason

Thank you for your kind reply.

  1. The IEC 61400-1 standard does not mention the impact of seasonal changes in wind speed on turbine design. The concern of my colleagues and I is whether high winds in one season will have an impact on wind turbine class and extreme conditions (especially in the design phase)?
  2. Can you provide a reference for “site-suitability analysis”?

Best Regards,

Masoud Rezvanian
Sun-Air Research Institute, Ferdowsi University of Mashhad

4

Dear Masoud,

Here are my answers to your questions:

  1. The IEC design standards do not directly consider seasonable variability when defining the wind turbine class. Instead, the IEC standard relies, e.g., on the annual average wind speed (Vave) and the extreme wind speeds based on the 50 and 1 year recurrence periods at hub height (e.g., Vref = 50-year extreme 10-minute average wind speed at hub height).
  2. While I’m not specifically endorsing DNV GL (there or other certification bodies that perform similar services), there is a good high-level summary of site suitability analysis here: dnvgl.com/services/site-spe … bines-3952.

Best regards,