Comparison of pre-construction and operational energy yield assessments for wind farms across the US

Enertis Applus+ (“Enertis”) is a global consulting and engineering firm with extensive expertise in the renewable energy and energy storage industries. Enertis, in partnership with our sister company Barlovento Applus+ (“Barlovento”), currently offers world-class wind resource and energy yield assessment (“WR&EYA”) capabilities and technical knowledge. Barlovento has been providing WR&EYA services globally for over 20 years and is a member of the MEASNET laboratory network and accredited according to the IEC-17025 standard.  

In order to validate Enertis’ and Barlovento’s WR&EYA methodologies and results on US wind power projects specifically, Enertis has partnered with a leading US wind power project owner / operator (the “Partner”) in order to conduct pre-construction WR&EYA validation studies, as well as operational energy production estimate (“OEPE”) benchmarking and deviation analyses, on a selection of the Partner’s US operational wind projects.  

The methodology used by Barlovento for WR&EYA is based primarily on industry-known and widely accepted MEASNET and IEC standards. Additionally, Barlovento, as part of MEASNET and EWEA (WindEurope), works along with other members carrying out inter-comparisons between the methods and results of wind resource assessments, including CREYAP exercises, MEASNET proficiency tests, and IEC Certification Advisory Committee proficiency tests, among others.  

This report outlines Barlovento’s general methodologies used for pre-construction WR&EYA and OEPE, discusses the results of, and draws a comparison between the pre-construction WR&EYA and OEPE, compares the pre-construction WR&EYA P50 against the original pre-construction energy production estimate (by another consultant), and provides insight of the results, accordingly.    

This (first draft of the) report outlines the methodologies and results noted above, for one US wind farm. The wind farm is outlined in the table below.    

Wind Farm	Wind Farm 1	Wind Farm 2	Wind Farm 3
General Location	Southwestern US	TBD	TBD
Average hub height altitude  (m.a.s.l)	413	TBD	TBD
Total installed capacity (MW)	57.5	TBD	TBD
Number of WTGs	23	TBD	TBD
WTG rated power (MW)	2.5	TBD	TBD
Rotor diameter (m)	116	TBD	TBD
Hub height (m)	90	TBD	TBD
WTG IEC Class	S	TBD	TBD

Table 1. Wind Farm main characteristics 

For the operational energy production estimates, two scenarios were assessed. While scenario 1 is the methodology that we typically apply to an OEPE (using operational data to inform and quantify certain go-forward loss values), the purpose of scenario 2 is to facilitate a direct and unbiased comparison of the OEPE to the pre-construction WR&EYA (in terms of loss value estimation – using standard pre-construction loss assumptions for certain categories).  

For Wind Farm 1, a deviation of 5.2% has been estimated between the P50 (probability of exceedance) pre-construction WR&EYA and scenario 2 OEPE. For scenario 1 OEPE where certain operational loss values (such as actual plant, WTG and grid availabilities, grid and environmental curtailments, and certain other losses) were informed by and quantified using historical operational data; use of the operational data to inform the aforementioned losses, had a significant (greater than 10%) impact on the OEPE net production between scenarios 1 and 2.   

We acknowledge that the operational energy production estimate approach applied in scenario 1 is typical and reasonable for operational assessments and further highlights the not uncommon overestimation seen in pre-construction energy production estimates in the industry, that is often not uncovered until a project has been operational for some time. Based on our deviation analysis to assess the possible causes for the overestimation in the pre-construction WR&EPE, the main reason appears to be attributable to wind flow modeling and wake effects across a relatively complex site.

Our pre-construction WR&EYA is within 2.5% of the original pre-construction energy production estimate (produced by another reputable consultant), with the deviation attributable to the wind flow modeling software used. This pre-construction deviation aligns with wind industry standards for intercomparison, as it falls well within the deviation range highlighted by industry benchmarking studies (ref. 1).   

Validation studies for additional wind farms are underway for future iterations of this report, with a goal of providing more insight into anypossible estimation bias and deviations between pre-construction energy production estimates’ and operational energy production estimates’ results. As in any industry, it will be beneficial to reduce the deviations found between pre-construction WR&EYA compared to actual wind farm energy production.     

See more: Our New Validation Study on Wind Resource & Energy Yield Methodologies

For more information, reach out to our Wind Advisory Services Director: nicholas.capaldo@enertisapplus.com