Tuesday, 13 December 2011

A Tougher and lighter wind turbine blade design

11 Dec 2011

A researcher from Case Western Reserve University has designed a stronger and lighter wind turbine blade design. First, a little insight into the issue of blade strength: As superior as large wind turbines are where cost and performance are concerned, the weight of their blades can cause problems. It is difficult to make such long (more than 200-feet in diameter) blades strong enough to bear their own weight, and especially at high speeds.

There is a tendency of objects in general to resist a change of speed (velocity)-called inertia. It affects everything that moves. When the wind turns a wind turbine blade, the rest of the blades are forced to move with it since they share the same hub (the rotating part at the center of the turbine). However, the weight of the blades impedes that by holding them back.

It is almost as if there is a force pulling back on the blades, and this force actually bends the blade a little, but the problem with this is the blades are not really flexible--therefore, instead of bending, they break. This force (inertia) is the same one that you have to overcome when you first start running, and when you are trying to accelerate your vehicle. This is why vehicles burn additional fuel to accelerate. Weight adds to this inertia problem, which is why heavier objects (such as vehicles) are harder to stop and harder to get moving. Typical wind turbine blades are designed to withstand the stress that normal operation would cause, so they don't break often.

This is why the same problem of inertia can be improved by making wind turbine blades both lighter, to reduce inertia itself, and stronger, to better withstand the inertia they are subjected to,.. and of course at a reasonable cost. Lighter wind turbine blades are easier to turn, and hence more efficient. So this is also important to their performance. Back to the new blade design: The researcher from Case Western Reserve University designed the 29-inch blades for a 400-watt turbine using polyurethane (a polymer) and reinforced it with carbon nanotubes.

"The idea behind all this is the need to develop stronger and lighter materials which will enable manufacturing of blades for larger rotors", Loos said. "Results of mechanical testing for the carbon nanotube reinforced polyurethane show that this material outperforms the currently used resins for wind blades applications", said Ica Manas-Zloczower, professor of macromolecular science and engineering and associate dean in the Case School of Engineering. "They will be used to emphasize the significant potential of carbon nanotube reinforced polyurethane systems for use in the next generation of wind turbine blades". Carbon nanotubes are still very expensive, but can be extremely lightweight and very strong compared to all-metal and composite materials.