History of Danish Wind Power - Wind Power for the World: The Rise of Modern Wind Energy - page 69

The Tvind turbine proved to have a long life. After more than
30 years it is still in operation in 2012 with all the original parts,
except for the blades and blade bearings, which had to be changed
in 1993-1994. Compared with the fate of international projects
for big wind turbines from this early period, supported with heavy
budgets from national research funding and big industries, it is a
remarkable achievement for which Tvind was awarded with the
European Solar Prize 2008.

3.13 Blades for a New Wind Turbine Generation

While NASA learned from Danish wartime and post-war experience
with wind power and the big Tvind turbine was growing, the
new Danish pioneers gradually developed the first home-built
wind turbines into a simple and efficient industrial product. The
first generation of commercial turbines followed Riisager's concept
using mechanical yawing and stayed blades with wooden main
beams.
An important inspiration for the next steps in the development
came from the Tvind project. One of the basic ideas of the Tvind
people was expressed in the slogan “Let 100 windmills bloom!”
(which in a short time showed to be an understatement). In
order to boost this development, all the technology and the
experience from the project was made available for everybody.
As a consequence, a team of students built a small wind turbine (PTG
turbine) at the same time as construction of the big wind turbine
took place. Its 4.5 m self-supporting fibreglass blades, downscaled
from the full size blades for the big turbine, became an important
help for the new Danish wind turbine industry [17].
The small blade mould was lent out to anyone who would like
to build their own wind turbine. A mould set, copying the PTG-
blades, was used by a group of wind power enthusiasts in southern
Jutland in 1977. As they gave up the project at an early stage, the
mould was bought by Erik Grove-Nielsen, who after some years of
study at the Technical University in Copenhagen and experience
with aerodynamics from work with model planes and sailplanes,
started producing blades in a remote farm in Økær, Middle-
Jutland.

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See chapter Økær Vind Energi—Standard Blades for the Early Wind Industry by

Erik Grove-Nielsen.