Tall Concrete Wind Turbine Towers

Markus Wernli, PhD, PE

BergerABAM

Outline

1. Market Conditions for Tall Towers

2. Tall Tower Technologies

3. Design Considerations

4. Tower Construction Example

5. Conclusions

Established Wind Industry

• 75 GW Installed Capacity in the U.S

• 5% of Power in U.S. from Wind Energy

• Over 20% of Power in Kansas from Wind Energy

• $128 Billion Invested over Past Decade

Growth of Wind Industry

U.S. Wind Power Installations by State

AWEA Second Quarter 2016 Market Report

KS

Development Path of Wind Turbines

Source: NREL/CP-500-43374, Wind Energy Technology: Current Status and R&D Future, 2008

Where the Wind Blew in 2008

Annual Average Wind Speed at 50 m

KS

Where the Wind Blows Today

KS

Where the Wind Blows Tomorrow

KS

Average Turbine Size Installed during

period (only turbines larger than 100 kW)

DOE Wind Technologies Market Report 2014

Trend in Turbine Hub Height in US

DOE 2014 Wind Technologies Market Report

Reasons for Slow Growth of Hub

Height in U.S.

• Tubular steel towers become exponentially more

expensive for heights beyond 100 meters

• Plenty regions that can be developed with

conventional hub heights

• Risk avert industry

• Additional FAA permit requirements for structures

exceeding 500 feet

• Tall towers need to be installed with means of

specialized lifting equipment

• No established wind industry in prime target

markets for tall wind turbines

• Lack of long-term wind measurements at 140

meters

Tall Tower Technologies

Anatomy of a Turbine

• Rotor

• Nacelle

• Turbine

• Tower

• Foundation

By Photo: Molgreen, Animation:Amada44

Advantages of Concrete Towers

• Taller towers to higher, steadier winds

• On-site or off-site component fabrication

• Site assembly with fewer fatigue critical joints

• Enhanced dynamic performance

• Reduction of foundation volume

• Lower maintenance costs inherent with concrete

as the construction material

• Increased service life due to the high fatigue

resistance of prestressed concrete

Current Proprietary Tower Systems on the Market

Enercon

Advanced Tower

Systems

Inneo Torres

Tindall

Enercon

Source: Enercon

Postensa (Advanced Tower System)

Source: Advanced Tower Technology

Acciona

Source: Acciona Wind Power

Tindall

Source: Tindall Corporation

Wind Tower Technologies

Source: MidAmerican

Hexcrete Tower

Source: Iowa State University

Tower Section Connection

• Column Connection Only

• Grouted Keyway

• External PT bars

Source: Iowa State University

Fabrication in Precast Plant

Source: Iowa State University

Transport

Conventional Flat-Bed

Instead of…

Special Transporter

Source: Iowa State University

GE Space Frame Technology

Source: GE Renewable Energy

Keystone Tower Technology

Source: Keystone Tower Systems

Design Considerations

Design Codes and Guidelines

• International Electrotechnical Commission

IEC 61400-1 “Wind Turbines Part 1: Design

Requirements”

• ASCE/AWEA “Recommended Practice for

Compliance of Large Land-based Wind Turbine

Support Structures”

• ACI ITG-9R-16 “Report on Design of Concrete

Wind Turbine Towers”

• DNV-GL “Guideline for the Certification of Wind

Turbines”

• Local Design Codes

Simplified Load Distribution

Assumption

Mandatory Design Checks for Concrete Towers

Dynamic Characteristic of Tower

Relevant Frequencies:

1P = Rotor Evolution

3P = Blade Passing

Fatigue Check

Source: Tindall Corporation

Concrete Fatigue Strength Fatigue Spectrum

Woehler Curves for Concrete per CEB-FIB MC90

Design Check of Foundation

Overburden Soil

Foundation Lift-Off Soil Bearing Check

Soil Pressure

Soil Pressure

Tower Construction Sample

Assembly of Hexcrete Tower

Source: Iowa State University

Assembly of MidAmerican Tower

Source: MidAmerican Energy

Conclusions

Conclusions

Concrete towers are a cost effective solution

for tall wind turbines and will be built in the

U.S. as the wind industry develops in low wind

velocity and high wind shear markets