Structural Stability Report for Wind Turbines

The structural stability report demonstrates through calculation that the turbine can withstand all load effects over its service life — from dead loads through wind and seismic loads to special loads such as icing or malfunction. It is a mandatory component of the BImSchG application and must be confirmed by an independent inspection engineer.

What is verified?

1. Load assumptions: Dead load, wind per DIN EN 1991-1-4 + site-specific wind zone, seismic per DIN EN 1998, ice load, snow, temperature
2. Turbine structures: Tower (steel, concrete, hybrid), rotor blades, nacelle, bearings, connections
3. Foundation: Shallow foundation, pile foundation, or hybrid — design against soil pressure, overturning, ground failure
4. Soil mechanics: Geotechnical survey, bearing capacity, settlement, groundwater
5. Service-life strength: Fatigue analysis for 20–25 years of operation
6. Special loads: Lightning strike, ice imbalance, emergency shutdown

Load effects on a wind turbine — all forces to be verified in the structural stability report

DIBt Guideline as the central basis

The "Guideline for Wind Turbines" issued by the German Institute for Construction Technology (DIBt) consolidates the structural requirements for onshore wind turbines. It references the DIN Eurocodes and adds turbine-specific requirements:

• Load combinations from wind + operation + special cases
• Site wind zones (1–4 per wind map, with topography correction)
• Requirements for the manufacturer's type certification ("type certificate")
• Specifications for anchorage and foundation

Type certificate as simplification

The manufacturer's type certificate covers the turbine structure — you "only" need to commission the foundation and site-specific report.

What does the report cost?

Indicative range: EUR 10,000 – 35,000 for the site-specific analysis per turbine (foundation + subsoil + site adaptation). Degressive pricing per turbine for wind farm commissions. Factors:

• Number of turbines + subsoil variation at the site
• Foundation type (shallow vs. piled)
• Subsoil complexity (karst, buoyancy, slope)
• Inspection engineer fee (additional, regulated by HOAI/HBVI)

Who prepares this?

Structural engineering firms with wind turbine experience — e.g. Nordex Engineering, Woelfel, Ingenieurbuero Burger, or the manufacturers' in-house structural departments. The inspection engineer is commissioned separately — they confirm the report and are approved by the building supervisory authority.

Frequently asked questions

Is the manufacturer's type certificate sufficient?

No — the type certificate covers only the turbine structure (tower, rotor, nacelle). The foundation + site-specific adaptation must be calculated on a site-specific basis, because every site has different subsoil conditions.

What does the building supervision cost?

In addition to the structural stability report, construction supervision inspection fees apply — typically 0.5–1.5% of the construction cost. For a 5 MW turbine with EUR 5 million investment, that means EUR 25,000–75,000 per turbine.

What about the old foundation during repowering?

For repowering, a new foundation is usually built, because the load assumptions for modern turbines far exceed those of the old turbines. Some manufacturers offer adapter foundations for existing turbines — rarely practical.

Who is liable in the event of turbine damage?

The operator (with their insurers). Correct structural analysis + inspection protects against insurance disputes. Archiving all inspection reports for the entire turbine service life is mandatory.