Planning · Wind Resource · Measurement & Modelling

Wind Resource at the Turbine Site

Wind resource is the primary determinant of turbine yield. The energy in the wind increases with the cube of the speed — 10% more wind means approximately 33% more energy. Accurate determination of the wind resource at the site is therefore the most important planning step.

Data Sources — From Coarse to Precise

Source	Resolution	Use
DWD Federal Wind Atlas	1 km × 1 km	initial site indication, free of charge
MERRA-2 (NASA)	0.5° × 0.67°	long-term reference for correlation
ERA5 (Copernicus)	0.25° × 0.25°	standard for long-term reference data
Mesoscale model (WRF/WAsP)	50–250 m	site-specific detailed modelling
On-site measurement (mast/LIDAR)	point-specific	bankability, manufacturer guarantee

Height Extrapolation Using the Hellmann Power Law

When the measurement is taken at 100 m height but the hub height is 150 m, extrapolation is required:

v(h₂) = v(h₁) · (h₂ / h₁)^α

α (Hellmann exponent) depends on terrain roughness:

Water surface, smooth sea: α ≈ 0.10
Open flat terrain (stubble field, heath): α ≈ 0.16
Structured terrain (fields, hedgerows): α ≈ 0.20
Village edge, forest clearings: α ≈ 0.28
Closed forest, urban area: α ≈ 0.40

Example: 7.5 m/s at 100 m, Hellmann α = 0.2 → 7.5 × (150/100)^0.2 = 8.15 m/s at 150 m.

Weibull Distribution

The frequency distribution of wind speed at the site typically follows a Weibull distribution with two parameters: A (scale parameter, similar to the mean) and k (shape factor). k describes the variability:

k = 1.8 — variable wind (uplands, forest)
k = 2.0 — standard onshore
k = 2.2–2.5 — steady wind (coast, offshore)

On-Site Wind Measurement — Met Mast or LIDAR

	Met Mast (60–140 m)	Ground-Based LIDAR
Height range	up to mast tip	30–250+ m (simultaneously)
Accuracy	± 1%	± 2–3% (calibrated ± 1%)
Cost	80,000–200,000 EUR	120,000–250,000 EUR purchase, 30,000–80,000 EUR rental/year
Setup time	4–8 weeks	1 day
Permit	building authority for heights > 30 m	none
Bankability	MEASNET-certified OK	since 2020 certified per IEC 61400-12-1 Ed. 3

Long-Term Correction

A measurement period of 12 months is not sufficient for a 20-year yield forecast. The measurement data are correlated against MERRA-2 or ERA5 long-term data (40+ years):

Determine the correlation between on-site measurement data and the long-term series at the nearest grid point
With good correlation (r > 0.8): transfer the long-term mean to the site via regression
Derive P50, P75, P90 yield forecasts for bankability

Banking standard: Banks finance on the basis of the P90 forecast (90% probability of achievement). At good-quality sites, P90 is approximately 90–93% of the mean value; at upland sites 85–88%.

Wind resource measurement chain: 5 data sources from DWD Wind Atlas (1 km) through ERA5 and mesoscale model to LIDAR and met mast (point-specific). Hellmann height extrapolation v(h2) = v(h1) x (h2/h1)^alpha with alpha = 0.10–0.40 by terrain. Met mast (plus/minus 1%, 80–200k EUR) vs. LIDAR (plus/minus 2–3%, 30–80k EUR/year)

Wind resource — data sources, height extrapolation and measurement technology comparison

Wind assessment for your site?

We connect you with MEASNET-certified wind assessors — from the desktop study to a 12-month LIDAR campaign including long-term correlation.

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Frequently Asked Questions

Is the DWD Wind Atlas sufficient for the investment decision?

For the desktop pre-screening, yes. For the investment decision, NO — banks and investors require an on-site measurement or at least a certified desktop study with long-term correlation.

How long must the on-site measurement last?

At least 12 months (standard); at upland or complex terrain sites 24 months. Shorter measurement periods are possible but the uncertainty of the long-term correlation increases.

What does a certified wind study cost?

Desktop study without on-site measurement 8,000–20,000 EUR. With LIDAR measurement over 12 months 80,000–150,000 EUR. With met mast over 24 months 200,000–400,000 EUR.