According to Lennart Nilsson from the company, three Zephyrs sited on the Baltic coast at Falkenberg equalled the performance in October of two Vestas 225 kW machines nearby, even though winds at the site of the Danish machines were ten per cent stronger. The Zephyr has a two bladed rotor with passive pitch and a teetering hub. The two speed generator is rated at 250/75 kW and the rotor diameter has been increased from 26 to 28 metres.
Nutek, the Swedish National Board for Industrial and Technical Development, supported development of the Zephyr with SEK 4 million, far less than it has granted for other wind turbine development. Fortunately for Zephyr, though, the community of Falkenberg has strongly supported the local company by ordering and buying the three turbines installed near the village. Despite its original scepticism, Nutek is now encouraging Zephyr to develop a bigger version of the design, rated at 750 kW or more.
"That would certainly be an interesting challenge," says Nilsson. "And the model we have now can be further developed. We could start by by minimising weight, for example." He hopes to sell five to ten turbines during 1994, to local utilities in the county of Halland and elsewhere.
For the designer of Zephyr, Sven Svenning, already a legendary figure in Swedish wind power, the certification of Zephyr is a long awaited victory. He first dabbled in wind power as a teenager during World War Two by refurbishing a rusty old windmill in the courtyard of the family farm. Working as an engineer, first with a crane manufacturer and then at SAAB's aeroplane division, his skills as an inventor allowed him to retire from nine to five work and live off the royalties of his inventions.
Svenning then turned his attention to development of passive pitch rotor blades -- the outboard section of the blades pitching by the force of the wind when the rated wind speed is exceeded. The Zephyr also has some other innovative features. The main shaft is asymmetrically located, to compensate for the uneven loads caused by the rotational direction. When the rotor is at a standstill, the blades are directed towards the tower. When the rotor turns, the blades are straightened by the centrifugal force, a feature that diminishes the loads on the turbine.
After some 20 years developing this concept, Svenning is happy to see it launched on the commercial market. He is now concentrating on further development of Zephyr, but not by scaling it up into a giant turbine, but by scaling it down to a small 20 kW model. The interest among farmers for small wind turbines is growing rapidly in Sweden, although there are no subsidies available for machines less than 60 kW. But it could be that Svenning knows more about what is blowing in the wind than Nutek.