Blade failures:Analyzing the failures of earlier wind turbines it is easy to see the major source of problems. Manufactures of these systems designed their blades with a goal of reaping all available power from the wind, which required elaborate pitch control mechanisms. They were designed to run within a certain wind speed range and then shut down if that range was exceeded. Although they worked reasonably well, they were both expensive and prone to failure. Because of the difficulty and expense of making the repairs, failures like these often rendered the turbines useless.
A worthy blade must be able to start the rotor at minimal wind speeds. It also must loose efficiency at a speed that is at or near the maximum output of the generator. If it quits to early we don’t get the maximum out of the generator. If it hangs in to long our generator is driven at an overload and we may damage the windings in the motor. The number of blades, length, overall size, profile, and pitch all has a profound effect on the operating range of our generator.
Arriving at our final design required some research and a lot of trial and error. In the corner at the far end of the shop there are many sets of blades that at their moment were “the” blades, nine sets in all. Most of them performed exactly how they were supposed to. It just didn’t happen to be the performance we were looking for. In the end we have a blade, which is really two blades in one. The profile near the hub provides great power (lift) at lower wind speeds and produces drag at higher wind speeds. As we approach the mid-way point of the blade it changes into a higher speed low drag profile, which really balances out performance.
We believe that Breezy 5.5’s final rotor and blade design is the most dynamic we could hope for. A four blade upwind system, it reaches kick-in speed quickly. The output is very linear up to 23mph wind speed where it begins to top out at 5.5 kilowatt. The drag/lift properties of the rotor are at such proportion that wind speeds above 23 mph yield very little more output power alleviating the need for any pitch control at all. Sure, we have given up some output with such moderate approach, but we’ve got a reliable, long lasting rotor that has survived every straight-line wind gust that nature has thrown at it to date, some reaching nearly 70mph, and never missed a beat!!