Wind resource assessment and energy yield forecast for wind farms according to FGW TR 6
Wind resource assessment and yield forecast according to FGW TR 6: site-specific wind analysis with reliable P75 and P90 values for your financing.
The economic success of a wind project depends on a precise analysis of the wind potential. We prepare site-specific wind resource assessments and energy yield forecasts using modern methods and many years of experience; they serve investors, developers and permitting authorities as a basis for decisions. A wind resource assessment, also called a wind potential analysis, determines the wind potential at a site and derives the expected energy yield from it, based on wind measurement with mast, LiDAR or SoDAR.
Wind potential describes the wind conditions at a given height above ground, such as mean wind speed, wind power density and frequency distribution. The energy yield follows from this for the hub height and power curve of the turbine. The measurement campaign should generally cover at least twelve consecutive months so that seasonal variations are captured. The measured data are related to the typical climate using long-term reference data; the measurement period and long-term correlation are to be determined according to the guideline applied and on the basis of the site, measurement quality and reference data. Added to this are a site visit, flow modelling, the wake losses of neighbouring turbines and further losses such as availability, electrical losses or curtailment. An assessment can only be verified once it refers to a single turbine or a park and is documented in a traceable way. The gross energy yield here means the mean annual yield over 8,760 hours before deduction of losses, at full availability; the net yield takes the assumed losses and availability into account. From the measured data, the wind distribution by sector, turbulence intensity, wind shear across the rotor area, air density and the 50-year extreme wind are derived. The measurement is transferable only to the extent that it represents the terrain: transferability has to be assessed on the basis of terrain, flow conditions and site representativeness, and is considerably more limited in complex terrain than in simple terrain. Remote sensing devices such as SODAR and LiDAR can complement masts. The required data availability depends on the guideline applied and the quality of the measurement campaign. The anemometers used must be calibrated; whether and when recalibration is needed depends on the guideline applied, the instrument and the requirements of the calibration laboratory. Data quality is assessed according to the procedure set out in the guideline applied, and deviations are included as additional uncertainty.
The assessments meet the applicable standards and guidelines, in particular FGW TR 6, as well as MEASNET; for wind measurement with remote sensing devices, IEC 61400-50-2 is relevant, while IEC 61400-12-1 concerns the power performance measurement of wind turbines. They are handled by our accredited testing body, the EWS Testing Center; accreditation confirms the competence of the testing body within its defined scope, while the achievable measurement uncertainty depends on method and data basis and determines the reliability of the P75 and P90 values. The guideline requires an uncertainty analysis for at least four areas: wind data basis, wind field modelling, wind farm wake effects and turbine data. The partial uncertainties are combined according to the rules of measurement uncertainty.
P90 is the yield that is reached or exceeded with a probability of 90 per cent; for P75 it is 75 per cent. Banks and investors use these values as a conservative planning basis for financing, investment decisions and the technical due diligence for wind farms. In Germany, site quality also determines the remuneration: the reference yield model relates the forecast yield to the yield at the reference site and derives from this a correction factor for the applicable value under § 36h EEG 2023. For the measured data, the RSD verification of LiDAR and SoDAR can play a role.
