How to Get the Most Out of a Wind Energy Project

WWW.RENEWABLEENERGYWORLD.COM

The success of wind energy projects hinges on robust performance guarantees, effective contractual terms, and vigilant operational oversight. A wind turbine’s measured power curve from performance testing determines a wind turbine’s ability to deliver the promised energy output.

By combining technical advancements with thoughtful contractual arrangements, developers and operators can secure both short-term revenue and long-term project stability. This article explores key aspects of performance guarantees, testing methodologies, and actionable strategies to address challenges in ensuring wind turbine efficiency.

Performance guarantees: the foundation of accountability
Performance is primarily assessed using power curve indicators, which directly inform revenue generation and financial stability anticipations. Power curve tests, governed by the IEC 61400-12 standards, measure a turbine’s energy output across varying wind conditions. Independent test engineers like ArcVera typically conduct these tests, which form the backbone of performance warranties outlined in turbine sales contracts.

The performance guarantee – with warranty levels commonly set as 100% minus uncertainty – defines the pass/fail criteria. While the IEC standard sets a baseline for how the test is to be executed, additional negotiated terms set in turbine sales contracts shape the test requirements for how the turbine measurement is quantified.

Accountability through performance warranties
Performance warranties hold original equipment manufacturers (OEMs) accountable in two significant ways:

1. Project-Specific Accountability:

• Liquidated damages: OEMs are subject to financial penalties if a project fails its power performance test. 
• Proactive efforts: OEMs often go beyond contractual obligations to ensure a pass. 
• Issue remediation: Challenges identified during tests can be addressed by OEMs, even if outside contract terms.

2. Reputation-based accountability:

• Market perception: A history of test failures can erode trust and reduce market competitiveness. 
• Aggregate testing results: Consistently poor performance can lead to loss of reputation and business opportunities. 
• Collective effort: Issues substantiated by trustworthy tests. 

The testing paradox: high costs, persistent uncertainty
Executing performance tests can often be seen as prohibitively expensive due to equipment such as met masts, lidars, and advanced power measurement tools. Common requirements preferred by turbine manufacturers (such as avoiding speed-up effects on met masts or lidars by restricting their placement and limiting the valid wind direction sector) increase costs by discouraging the sharing of wind measurement equipment across multiple test turbines. Including multiple turbines in the test is typically required to protect for cases where a turbine with atypical performance is nominated. Additional requirements including filtering are used to ensure the test reflects the turbine’s design conditions, not site-specific conditions, but these requirements frequently prolong tests, further increasing costs.  

Yet, even with rigorous testing and heavy constraints on the measurement and the associated increased costs, high uncertainty levels applied to the performance guarantee remain, further diminishing the perceived merit of executing performance tests.

Optimizing testing and warranty frameworks
Right-sizing uncertainty in performance guarantees

Though it is a sensible requirement to test multiple units, it would be reasonable to expect uncertainty levels to decrease with increasing sample sizes. The IEC standard includes language on reduction of uncertainty for testing multiple units, but application has proven too unwieldy in practice.

A solution for some has been to apply “uncertainty caps” in a performance warranty to limit uncertainty . However, this arbitrary value is not based on the actual test data or method, and instead relies on a subjective historical accounting based on tests not entirely reflective of realities on the ground.

It can be gleaned from completed tests that instead of applying Standard Uncertainty (based on a 68.3% level of confidence), a 50% level of confidence (or 0.675?) can better align with historical test results while still honoring both the test data and methods, so long as multiple units are tested.

Streamlining testing methodologies

Other opportunities to apply proven methods and technologies for smarter testing includes:

• Reverse power curve analysis: Utilizing methods like IEC 61400-12-1 Annex C.8 to ensure consistency across all wind direction bins, reducing the impact of directional biases. This can replace any limiting of a valid wind direction sector frequently required by OEMs that go beyond the IEC Standard. 
• Numerical site calibration: Offers an efficient alternative to traditional calibration, especially for complex terrain. This technology is commonly used in commercial applications in wind energy and across many industries – it has been demonstrated to be useful and appropriate for performance testing.  
• Ground-based lidars:  Standards still require the use of “short” met mast to monitor drifting accuracy although that phenomenon is rarely observed and can be anyway dealt with post-calibration, a step that would be required in case of failure. Eliminating the mandatory requirement for short-met mast monitoring to rely purely on Lidars can reduce costs without compromising accuracy. 

Standards adoption advancements, or lack thereof?
Despite decades of progress, the industry has been slow to adopt updated standards, for example:

• IEC 61400-12-1 Edition 2 was released in 2017 and Edition 3 in 2022, but are(Edition 3, 2022) is underutilized, with many project stakeholders still using Edition 1, a 20-year-old standard version. 
• IEC 61400-12-2 (2013) for Nacelle Anemometry is not utilized often but has been proven to be  a valuable guideline 
• IEC 61400-12-4 (2020) for numerical site calibration is a technical report that represents a forward movement towards acceptance but with no near-term plan to become a standard.  
• IEC 61400-50-3 (2022): Use of Nacelle Mounted Lidars is a standard that is not commonly used or allowed, save for specific instances and with heavy additional constraints. 

Performance monitoring beyond initial testing
Numerous performance concerns can only be properly observed years into a project’s life cycle. With deficiencies in performance best addressed by the OEMs, who know their own design better than other stakeholders, effective performance management should extend beyond the initial test periods. Periodic testing and monitoring can include:

• Park-Wide Nacelle Anemometer Analyses: Helps identify operational inefficiencies and outlier turbines that were not part of the initial test. 
• Subsequent Testing Campaigns: Regularly testing select units ensures continued accountability and highlights any degradation over time. 

Addressing OEM-owner trust gaps
OEMs play a pivotal role in improving turbine performance. While they often provide updates and enhancements, developers and operators rely heavily on their commitment. This dependency can lead to trust gaps.

To bridge this, contractual mechanisms can incentivize OEMs to maintain performance standards, such as service contracts with embedded performance guarantees, and long-term performance bonuses tied to lifecycle monitoring results.

Business-as-usual, enhanced: practical recommendations
1. Control costs:

• Limit wind measurement constraints by employing reverse power curve techniques. 
  Replace traditional site calibration with numerical calibration where feasible. 
  Restrict testing campaigns to one year, progressively reducing OEM-imposed filters.Increase value:

2. Increase value:

• Apply reduced uncertainty levels (e.g., 50% confidence) for multi-unit tests. 
• Utilize park-wide nacelle anemometer tests to address outlier turbines and operational issues.

3. Monitor performance proactively:

• Conduct periodic site-wide analyses. 
• Retest nominated units from the original performance campaign. 

Ensuring wind turbine performance is a multifaceted challenge that requires a strategic balance of guarantees, testing rigor, and ongoing monitoring. By refining uncertainty methodologies, adopting advanced testing standards, and fostering collaborative relationships between developers, operators, and OEMs, the wind energy sector can mitigate risks, optimize costs, and enhance overall efficiency. These efforts not only strengthen the financial and operational stability of individual projects but also contribute to the long-term credibility and growth of the industry. By embracing innovation and continuous improvement, stakeholders can address persistent challenges and drive the wind energy sector toward a more sustainable and reliable future.