Alternative Power: Vertical Axis Wind Turbines

Heard of wind farms? Almost every one of us must have at least once seen the tall wind mills situated in wide open terrains or small hilltops in the suburbs. However, a more efficient and reliable way of producing electricity from such wind mills is to place them off-shore. These are often mounted offshore floating on water of great depths. The advantage in doing so is that the air flow there is more steady and strong due to absence of obstructions.

These turbines till date had their generator rotor shaft mounted horizontally (parallel to ground). But such structures need huge buoys needed to keep them floating thus making them expensive. However, Technip and Nenuphar, two French companies have come up with a major breakthrough in the design of such wind mills. These designs can produce much cost reduction in the initial capital cost and better provisions for installation.

In the new design, the main rotor shaft of the generator is placed vertically contrary to the usual horizontal position. This lowers down the center of gravity of the unit. So, even if the arrangement stands 100(m) tall, the concentrated weight of the generator is placed at a height of just 20(m) above the sea level. This would make the top portion lighter and a smaller floating system is needed at a less shallow level. A horizontal-axis turbine with same ratings and same height needs it’s heavy generator to be placed at least 60(m) above the sea level and hence the buoy runs up to 100(m) deep. Some experts say that the same design will not suit that well for on-shore turbines. That is so because the wind speed gradient with height is lesser on-shore than off-shore.


Nenuphar Wind Turbine

However some experts have contrary opinions regarding the blade shaped of the new design. All the previously made designs had curved blade so as to distribute the forces evenly on the blades. The new design has straight blades connected to shaft only 2 struts at the bottom. So the blades are prone to bending, say experts. One of such plants of capacity 2MW is scheduled to be installed in the Mediterranean Sea in late 2013.

The thing to be observed is that would the vertical blades and struts withstand the air force? And whether the new design provide enough cost cuttings to make it economically feasible or not?