Windenergie 3 - Design Methodology

09 April 2026, Po Wen Cheng

What is Design?

• A plan or drawing produced to show the look and function or workings of a building, germent, or other object befor it is made.
• The art or action of conceiving of and producing a plan or drawing of something before it is made

New designs: bladeless wind turbines, diffuser augmented wind turbine, reciprocating airfoils,...

• There is not much wind to be harvested at the ground level
• There is no way to beat Betz law by using diffusor (the effective rotor area is the area of the diffusor)
• Vibration is the main source of fatigue for wind turbines (or any structure)

The Structured Design Process

1. Market research
   • Which is the market that we want to sell to? (geography, technical requirements, customer basis,...)
   • How big is the market?
   • Who are the most important players?
   • What are the underlying economics of the market?
   • What is the margin of profit of the customer?
2. Product requirements / specifications
   • External and operating conditions (IEC wind class, turbulence intensity, water depth, corrosion,...)
   • Main turbine parameters
3. Conceptual design
   • First estimate of the key dimensions of the wind turbine
   • Build up a wind turbine model for the dynamic simulation to determine the system loads
   • First aerodynamic design of rotor blade to determine the power curve
   • First drawing of the main components
   • Task: FMEA (Failure Mode and Effects Analysis)
4. Preliminary design
5. Detailed design
6. Product check and validation
   • Factory tests
   • Reliability tests
   • Vibration / climate chamber tests
   • Component fitting tests
   • ...

Design Criteria and Requirements

Noise

• Has mechanical and aerodynamic causes
• Relevant for onshore especially in connection with discomfort
• Underwater noise can affect marine mammals, especially during the installation phase
• A high tip speed ratio could be an option for offshore wind turbines, such as 2-blade rotors, if noise not relevant

Tip speed: $v = \omega \cdot R$

Noise is proportional to tip speed increase to the 5th power
Current tip speeds approx. 70-80 m/s, anything above that would induce compressible air flow

Because of this, larger turbines have slower angluar rotation (same tip speed), but more torque

Capacity Factor

Specific power: $P = \frac{\text{Rated Power}}{\text{Rotor Area}}$

High capacity factor - steadier power output to the grid and more efficient use of the electrical infrastructure

The cost optimum depends on the accuracy of the cost modeling. In this case, the const optimum is a function of the mean wind speed and the specific power

If you have many fish per square meter, you don't need a big net to meet demand
If you have less fish per square meter, you need a much bigger net (increase the rotor diameter) With increasing rotor diameters, the cost of operation etc. rises, so there is an optimum in between

For low wind speed sites, the cost optimum is at a lower specific power

For high wind speed sites, the optimum moves to higher specific power

External Conditions

• AEP-Target for a given regime (e.g. IEC Wind class, turbulence class, extreme wind speed)
• Grid requirements on power quality and faults response (higher harmonics, flicker, Fault-Ride-Trough etc...)
• Operating conditions
• Lighning, fire, birds protection

Operation Capabilities

Large fluctuations of the power output requires interventions from the grid opreator to balance the demand and supply

Cost

• Cost of energy: LCOE
• Cost shall consider the wind turbine cost: Balance of plant, installation, decommissioning
• Trade.off between the component cost and the total system cost
• LCOE of renewable energies is driven by the CapEx, while OpEx is significantly lower than fossil fuel power plants (because of the fuel costs)

Design Options

Vertical Axis vs Horizontal Axis

• Aerodynamics of HAWT are much simpler than of VAWT, easier to predict, less fluctuating loads
• Synergies: offshore and onshore wind turbines are basically the same, which makes a different design (VAWT) much more expensive to research, produce, ...

Two Blades vs Three Blades

• Two blades have higher tip speeds and thus louder noise - so only viable for offshore
• Good thing: Two blades can be installed both at the same time with the nacelle. Cheaper to build
• Again: Synergies: Different designs for offshore and onshore are more expensive, because everything has to be developed twice