Confirmed: Tvindkraft Designed to be Slightly Larger than Smith-Putnam

By Paul Gipe

Erik Grove-Nielsen has confirmed that the Tvindkraft wind turbine was designed to be slightly larger than the Smith-Putnam wind turbine and become the world’s largest wind turbine in 1978.

The Danish wind turbine was designed to be 54 meters in diameter, just slightly larger than the 53.4 meter (175 feet) diameter Smith-Putnam wind turbine that operated briefly on Grandpa’s Knob near Rutland, Vermont in the mid 1940s.

Grove-Nielsen, a pioneering wind turbine blade designer, has chronicled the history of Danish wind energy on his web site Winds of Change. He tracked down the story of why Tvindkraft’s designers picked 54 meters for the rotor’s diameter.

The story began as a rumor in response to a series of articles on the generator rating of the famed Smith-Putnam wind turbine.

As I noted in Beating a Dead Horse–More on Smith-Putnam’s 1,000 kW Rating, Göran Ronsten had reported an interesting anecdote on Facebook. Ronsten says that in 2002 Per Lundsager told him that the Tvindkraft turbine at the Tvind school on the west coast of Denmark’s Jutland peninsula was designed to be just slightly larger than the Smith-Putnam turbine. Thus, Tvindkraft is 54 meters in diameter.

Grove-Nielsen fleshes the story out from a recently published book Amdi og Tvind by Peter Tygesen.[1] He helpfully translated the pertinent passages from Danish.

The story begins with Amdi Peterson of Vestjysk Energikontor at Tvind seeing a television report on a conceptual study by Frede Hvelplund and Hans Jørgen Lundgaard Laursen for a wind turbine to provide heat on the island of Tunø in 1975.

Amdi calls Hans Jørgen Lundgaard Laursen and urges him to visit Tvind. Amdi asks Laursen to design him a wind turbine for heating the Tvind school, and he lays out three requirements.

  • The blades must be made of fiberglass using Ulrich Hütter’s blade technology (and hence the Hütter flange used on Tvind).
  • No patents. In the tradition of the Danish Folkehøgskole movement, the technology will be available to everyone.
  • The wind turbine should be the biggest in the world.

Both Amdi and Laursen knew of the Smith-Putnam wind turbine of the 1940s and how it had thrown one of its stainless steel blades. They knew it was 175 feet in diameter. Tvindkraft–the name for Tvind’s wind turbine–was designed specifically to be larger to claim the title of world’s largest wind turbine.

Tvindkraft went into operation 25 March 1978 and is still in service today. It too eventually lost a blade, but a set of replacement blades were installed in 1993. (Grove-Nielsen provided testing and instrumentation of the replacement blades for Risø’s blade test station at Sparkær, Denmark.) Tvindkraft is the longest-running megawatt-scale wind turbine in the world, if not simply the longest-running wind turbine period. It has been operating 44 years as of this writing.

Originally it was designed to generate both electrical heating, as in Kvelplund and Laursen’s conceptual study, but also grid-compatible electricity. It still performs those functions today.

For students of wind energy, it’s significant that Amdi and Laursen specified the size of the wind turbine based on its rotor diameter–and not generator capacity. After all, it is the rotor diameter that determines how much energy the wind turbine will capture. Danes understood this even then.

The story of Tvindkraft remains fascinating for what it tells us can be accomplished by “people power.”

Tvindkraft: The Giant That Shook the World Turns 42

Tvindkraft: The story in text and pictures

Tvindkraft: Why the windmill was built

Tvindkraft: The wings are the core

Beating a Dead Horse–More on Smith-Putnam’s 1,000 kW Rating

When is a 1,250 kW Wind Turbine Only 1,000 kW? Setting the Smith-Putnam Record Straight

[1] Peter Tygesen. Amdi og Tvind. 1171 København K: Gads Forlag, 2022. og Tvind, pages 299 and 300.