A trailblazing windmill

How Tvindkraft got its extraordinary blades and proved that they could work

 

The builders of Tvindkraft accomplished more than just constructing the world’s largest modern wind turbine. They also managed to solve some major challenges in modern wind turbine design.

In the mid-1970s, there were very few examples or references available to guide the construction of a wind turbine. The windmill team in Tvind were able to find workable technical solutions that paved the way for other windmill builders and with time the wind energy industry.

The windmill team also pioneered the design of pitchable, cantilevered, fibreglass blades, which is the standard in all modern wind turbines today.

 

Humility and cooperation

Cooperation was key to the success of the Tvindkraft project.

Volunteers understood that they were building on old windmill traditions and that they could utilise the experience of others. They regularly consulted people with engineering experts who could assist with calculations and theories. In return, the Tvindkraft team could share how they had solved various technical issues which they had gained through hands-on experience.

As the windmill builders were happy to adopt good ideas from others, they came across their most significant technical solution, when they cooperated with friendly experts who volunteered their services.

 

The Tvindkraft blades revolutionised modern wind energy

To construct the long cantilevered blades, the windmill team recognised the necessity for a robust attachment point at the root of the blade. One possible solution had been demonstrated by Ulrich Hütter, a professor at the German Space Travel Institute in Stuttgart, a few decades earlier. Hütter’s innovative approach involved running continuous fibreglass strands down the blade’s length and wrapping them around the bolt holes in the mounting flange, securely attaching the flange to the blade. This attachment method became known as “the Hütter flange”. Representatives of the windmill team went to Stuttgart to learn about this technology but didn’t find a solution for the shape of the blade.

Back in Denmark, Helge Petersen from Risoe, then Denmark’s Nuclear Test Station, also offered to help. His experience was with aerodynamics and agreed to design the blades for Tvindkraft in his spare time.

The last part to be resolved was how the blades should be fastened to the hub. A solution with fibreglass strands wound around the bolts was chosen, similar to Hütter’s solution but later included a double flange and double rows of bolts.

The adapted Hütter flange and Tvindkraft’s practical adoption proved the concept worked once the turbine became operational. It was a crucial technical contribution to the development of wind turbines as we know them today.

 

A smaller scale windmill to copy

The windmill team building Tvindkraft also built a much smaller turbine in parallel. It was constructed using the same blade mounting technology that had been perfected on the Tvindkraft blades.

This smaller windmill was called the PTG mill. The moulds of the 4.5 m long blades were made available for other windmill builders to borrow, so they could make their own blades.

The Tvindkraft and PTG mill blade design, alongside a willingness to share the technology, were key elements that revolutionised modern wind turbine technology.

 

The builders of Tvindkraft pioneered the design of pitchable, cantilevered fibreglass blades, which is the standard of all modern wind turbines today. ”Pitching” means that we change the angle of the blade to control rotor speed – while it’s running. “Cantilevered” means that the blade is attached in one end, without any supporting rods.
German Ulrich Hütter experimented with wind energy for decades. He developed a new technology using composite materials and found out how to fasten strands of fibreglass around the bolts in a wide flange.
Robust blades that could withstand the forces of nature were needed. Inspired by the Hütter flange, fibreglass strands were wound around the bolts of the blade. A solution with double flanges and double bolts was applied.
The 27 metres long, 5 tons heavy Tvindkraft blade with the down-scaled, open-source blade from the "PTG windmill" by its side. The mold from the latter could be borrowed at no cost. Soon, other wind power experimenters opened small factories where fiberglass blades were produced and sold to people who wanted to build household wind turbines.

"Tvindkraft: The giant that shook the world"

“Tvind’s blade design—primarily its use of the Hütter flange—and their willingness to share the technology they had developed with other experimenters was the key element that led to what would become today’s wind industry, say Danish wind historians.”

Read Gibe & Möllerström’s article from

“An overview of the history of wind turbine development”

The WInd Mill team pioneered modern wind turbine engineering.

The builders of Tvindkraft accomplished more than just constructing the world’s largest modern wind turbine. They also managed to solve some major challenges in modern wind turbine design.

In the mid-1970s, there were very few examples or references available to guide the construction of a wind turbine. The windmill team in Tvind were able to find workable technical solutions that paved the way for other windmill builders and with time the wind energy industry.

The windmill team also pioneered the design of pitchable, cantilevered, fibreglass blades, which is the standard in all modern wind turbines today.

 

The builders of Tvindkraft pioneered the design of modern wind turbine blades.

Humility and cooperation

Cooperation was key to the success of the Tvindkraft project. Volunteers understood that they were building on old windmill traditions and that they could utilise the experience of others. They regularly consulted people with engineering experts who could assist with calculations and theories. In return, the Tvindkraft team could share how they had solved various technical issues which they had gained through hands-on experience.

As the windmill builders were happy to adopt good ideas from others, they came across their most significant technical solution, when they cooperated with friendly experts who volunteered their services.

 

Robust wind turbine blades that could withstand the forces of nature.

The Tvindkraft blades revolutionised modern wind energy

To construct the long cantilevered blades, the windmill team recognised the necessity for a robust attachment point at the root of the blade. One possible solution had been demonstrated by Ulrich Hütter, a professor at the German Space Travel Institute in Stuttgart, a few decades earlier. Hütter’s innovative approach involved running continuous fibreglass strands down the blade’s length and wrapping them around the bolt holes in the mounting flange, securely attaching the flange to the blade. This attachment method became known as “the Hütter flange”. Representatives of the windmill team went to Stuttgart to learn about this technology but didn’t find a solution for the shape of the blade.

Back in Denmark, Helge Petersen from Risoe, then Denmark’s Nuclear Test Station, also offered to help. His experience was with aerodynamics and agreed to design the blades for Tvindkraft in his spare time.

The last part to be resolved was how the blades should be fastened to the hub. A solution with fibreglass strands wound around the bolts was chosen, similar to Hütter’s solution but later included a double flange and double rows of bolts.

The adapted Hütter flange and Tvindkraft’s practical adoption proved the concept worked once the turbine became operational. It was a crucial technical contribution to the development of wind turbines as we know them today.

 

 

A new technology using composite materials in wind turbine blades.

A smaller scale windmill to copy

The windmill team building Tvindkraft also built a much smaller turbine in parallel. It was constructed using the same blade mounting technology that had been perfected on the Tvindkraft blades.

This smaller windmill was called the PTG mill. The moulds of the 4.5 m long blades were made available for other windmill builders to borrow, so they could make their own blades.

The Tvindkraft and PTG mill blade design, alongside a willingness to share the technology, were key elements that revolutionised modern wind turbine technology.

 

The historic Tvindkraft  wind turbine blade alongside its downscaled version.