Networks of Wind Energy Enthusiasts and the Development of the “Danish Concept” - Wind Power for the World: The Rise of Modern Wind Energy - page 154

but this group hardly provided regulation to the industry.
However, after 1979, Denmark required certification of wind
turbines in order to have access to a subsidy that was essentially
an investment grant of 30%. The system was set up to additionally
encourage participation by making the certification process free
for Danish manufacturers and providing payment to the companies
for the time the turbine was at the test station. The test centre
for small windmills was established in 1978 and was given the
licensing task by the government in 1979. The first certified
turbines were the Gedser-type machines, or Riisager-inspired
designs, that produced 22 kW or 55 kW of power which were
considered to be “second-generation types”.
Most of these machines included the NIVE-inspired design
types using Økær blades with variations for the diferent
manufacturers. The test station noted that while “design principles
exist that ensure mechanical integrity and proper functioning on
at least a short-term basis”, longer-term performance was still
under question which limited the ability of the test station in terms
of establishing design requirements (Petersen, 1980; Pedersen
1984). Initially, requirements from the test station allowed for
both air-brakes as well as braking by yaw, rotating the
turbine out of the wind, but this was amended in subsequent
documentation which required a “fail-safe” braking system that
is disengaged when the system is active and is kept in series with
each element of critical safety importance for both the electronics
as well as vibrations. In addition, two independent braking systems
were required to ensure that over speeding, as experienced with the
early Herborg and other turbines, was not a problem. Other early
guidelines address manually operated breakers for grid
disconnection, relay systems for automatic grid disconnection, a
designated “operator”, as well as metering and payment rules for
electricity generated by small wind turbines owned independently
and connected to the grid. These fundamental requirements
regarding braking and grid interconnection were then extended
under the 1981 subsidy extension act to include a link from the
fundamental requirements to the operational status of stopped,
normal operation and emergency shutdown, as well as specific
requirements regarding system security, static tower and

foundation loads, and load tests as performed by the test centre.