http://www.windpowermonthly.com/article/1391775/exclusive-vestas-tests-four-rotor-concept-turbineDENMARK: Future technologies will be given a jolt of fresh thinking as Vestas prepares for a year of testing and validating a 900kW multi-rotor concept turbine, which is being installed near Roskilde, Denmark, this week. Eize de Vries talked exclusively to Vestas engineers about the potential of the concept turbine.
It is set to become a blueprint for larger-scale future products for specific markets, and the company plans to test core scaling rules, risks and opportunities, and transport and installation challenges in new markets.
The concept turbine incorporates four refurbished pitch-controlled V29-225kW turbines with unchanged 29-metre rotor diameter, one of the thousands built from the first half of the 1990s.
The multi-rotor concept also features two vertical operational levels with a cylindrical tower element in between and 30.5-metre height interspacing between the levels. Two chassis units, each incorporating a yaw bearing, an active yaw system, and a left and right rotor arm assembly, are integrated within the tower structure.
The first twin-rotor unit is mounted atop two conical bottom sections at a height of 29 metres and the second at 59.5 metres, and the tip height thus adds up to 74 metres.
In the horizontal plane the nacelles are arranged in pairs on each level with close 1.5-metre tip clearance, and mounted separately on left and right side tubular-steel arms. These arms in turn are flexibly attached to a turnable central chassis.
One of the main aims is to find ways to circumvent the negative consequences linked to the infamous square-cube law.
This scaling law dictates that as installations grow bigger, power output scales with the rotor diameter squared (P ~ D2), but mass increases with the diameter cubed (m ~ D3). Turbines thus become heavier if size increases, and without counter measures to lessen these effects.