Power Production Estimates

Hrafnkel has been providing independent yield assessments for wind turbines for over 20 years. In addition to first and second appraisals for financing, we also offer reviews of third-party yield reports.



Yield assessment of potential sites

Before a new project is developed, an initial assessment of the wind power potential at a potential site is often helpful. Based on available information in the immediate or wider area (wind measurements, wind farm yields, bioindicators, model data, re-analysis data, etc.), Hrafnkel can create an initial estimate of the wind potential to be expected at a site. The aim of this preliminary estimate is to recognise unsuitable sites at an early stage.

A more advanced variant of the preliminary estimate consists of using a LiDAR or SODAR to carry out a wind measurement over several weeks at the potential site. By means of a long-term correlation of this measurement data, a relatively reliable statement about the expected wind potential at a site can be made after just a few weeks. As Hrafnkel has its own LiDAR and SODAR and these instruments do not require any authorisation for installation, we can carry out this type of measurement campaign with a short lead time.



Power production estimate based on wind measurements

The "traditional" way of preparing a power production estimate is based on wind measurements at the planned site: In addition to the classic measurements with cup anemometers on measuring masts, measurements with LiDAR or SODAR are increasingly being used for yield assessments.

The available measurement data is checked, validated and, if necessary, completed and corrected in order to obtain a continuous time series with measured values in 10-minute increments. In order to minimise the influence of seasonality on the data series, the time series should ideally cover full years. The expected production of a wind turbine of the planned type at the measurement site is determined on the basis of the time series.

The measurement site and the planned wind farm as well as any existing/planned wind farms in the vicinity are represented in a digital terrain model. This terrain model is created with the WAsP software and contains a digital elevation model, the roughness of the terrain surface and any obstacles that could be relevant in the WAsP flow model. In the further process, the time series is corrected using a long-term correlation in order to then determine the expected average annual production over the lifetime of the planned wind farm by means of modelling in WAsP or WAsP-CFD.

Hrafnkel's yield assessments are based on the German Technical Guideline for Wind Turbines (Technischen Richtlinie für Windenergieanlagen), PART 6 (TR 6) Determination of Wind Potential and Energy Yields. Deviations and individual methods are possible depending on agreement and the characteristics of the measurement data and available information. Numerous yield assessments by Hrafnkel have been used as the basis for bank financing of wind power projects.



Power production estimate based on production data

Yield reports can also be prepared using production data from a nearby wind farm. For this purpose, the available SCADA data from the wind turbines is imported into our database with a resolution in 10-minute increments and prepared for further analysis. This includes adding any downtimes, checking the consistency of the data and compensating for downtimes and periods of curtailed production. The aim is to obtain a time series that is as consistent as possible with the ideal production without losses over at least one year and ideally over several years.

The reference wind farm and the planned wind farm as well as any existing/planned wind farms in the vicinity are represented in a digital terrain model. This terrain model is created with the WAsP software and contains a digital elevation model, the roughness of the terrain surface and any obstacles that could be relevant in the WAsP flow model. In the further process, the time series is corrected using a long-term correlation in order to then determine the expected average annual production over the lifetime of the planned wind farm by means of modelling in WAsP or WAsP-CFD.

Hrafnkel's yield assessments are based on the German Technical Guideline for Wind Turbines (Technischen Richtlinie für Windenergieanlagen), PART 6 (TR 6) Determination of Wind Potential and Energy Yields. Deviations and individual methods are possible depending on agreement and the characteristics of the measurement data and available information. Numerous yield assessments by Hrafnkel have been used as the basis for bank financing of wind power projects.



Scope of power production estimates

In addition to a detailed description of the planned site, the planned wind farm, the measurement campaign and its processing, its verification and presentation of the characteristics of the wind climate, a power production estimate from Hrafnkel includes the following points, among others:



Options for power production estimates

Hrafnkel's power production estimates can be prepared in German, English and French.
In addition to the usual scope of Hrafnkel's yield reports, the following options can be added on request (incomplete list of examples):