When Numbers Don't Tell the Whole Story

Wind farms are sometimes considered in places where one or more environmental factors are slightly outside the official limits recommended for safe turbine operation, while most other environmental factors might be well within acceptable ranges.

Bureau Veritas Renewable Technical Advisory (BV RTA) Center of Excellence introduced a simple method to evaluate if a site is suitable for wind turbines, even when one or two quantitative attributes appear problematic. The idea is to consider how these environmental factors work together and affect fundamental turbine suitability to provide a quick and reliable benchmark before more complex testing is done.

Why Is This Important?

The international wind turbine design standard, IEC 61400-1, sets safe limits and requirements based on certain environmental factors:
 

• Average wind speed

• Turbulence (how gusty the wind is)
• Air density (which affects how much force the air can apply on the turbine)

Depending on site specific meteorology, a given wind energy location might exceed one of these limits (e.g., wind speed is high), and be well within limits of others (e.g., turbulence is low, and air density is low). The BV RTA model helps developers and engineers combine all these factors to better understand if the site is still safe for long-term operations.

How the Method Works (In Simple Terms)

The basic idea is:

• Step 1: Compare the site’s average wind speed with the standard limit (IEC value).
• Step 2: Adjust this comparison by factoring in air density and turbulence.

Using this method, we can determine if the site is truly riskier for a given turbine model design, or if it only seems risky because one number does not tell the full story.

The math behind the method isn’t simple, but the result is:

If the adjusted wind speed is below the limit – the wind site is likely safe for the turbine under consideration.

If the adjusted wind speed is above the limit – more detailed review is needed.

What Data Was Used?

To validate the method’s accuracy, BV RTA used data from 77 wind projects:

• with 3835 turbines,
• across 59 countries, with greater than 50% of the cases in the United States.

Here’s what the IEC 61400-1 designated categories were, averaged for the 77 projects:

• Average wind speed: 8.28 m/s
• Turbulence: 10.07%
• Air density: 1.14 kg/m³

This data helps create a benchmark for future projects. When a new site is being evaluated, we can compare it to what has worked in the past and continuously improve the method.

Why These Adjustments Matter

Turbines aren’t affected by only how fast the wind blows, but also, in combination, how forcefully and how unpredictably the wind behaves.

• Air density and force: More dense air contains more air molecules per cubic meter and thus pushes harder on the turbine blades. So, a high wind speed in light (less dense) air is less intense than the same wind speed in heavy (denser) air.
• Turbulence and wind variation: Wind that changes speed rapidly (is more turbulent) causes more stress and therefore turbine wear as time passes.

By adjusting the raw wind speed numbers to reflect air density and turbulence, the BV RTA model gives a truer picture of the turbine-relevant environmental conditions at the site.

Key Findings

After adjusting for air density and turbulence, many sites that looked unsuitable at first fell within acceptable limits.

For Example: At a high elevation wind farm in New Mexico conditions seemed too windy at first (10 m/s vs 7.5 m/s allowed). But once adjusted for lower air density and turbulence, the gap reduced significantly—from 2.5 m/s to 1.61 m/s. That made it more acceptable from a turbine safety perspective, and with further analysis a suitable turbine was found.

Final Thoughts and Recommendations

This method is a great first step in evaluating wind farm sites because it:

• Helps identify potentially suitable sites earlier
• Offers a quick, independent check before doing more sophisticated simulations
• Provides context when comparing multiple sites.

However, this method

• is not a replacement for simulations done by turbine manufacturers,
• does not account for all risks, especially those tied to extreme weather events or long-term wear.

So, it’s best used as a benchmarking tool to guide decisions, not to finalize them.

In Summary

This BV RTA method gives wind project developers, and those considering wind project acquisitions, a clearer picture about whether a site may be prone to problems for a given turbine model, or if it needs more careful investigation.

Even if a site breaks one individual IEC 61400-1 criterium, it might still be a valuable and acceptable location for a wind farm once you look at the whole picture. 

For more information about this method, contact us at NAMPower@bureauveritas.com.