Hardly a week goes by without at least one press release about a new and improved wind turbine design hitting my email inbox. These company press releases touting a breakthrough technology are picked up and propagated by media outlets, which unfortunately bestows credibility on the company. Even more unfortunately, well-intentioned people who want to generate some of their own electricity take the bait.
So, what’s wrong with all of this? And why does the small wind industry take umbrage with these seemingly new designs? Nearly all of the new “breakthrough” technologies share an amazing number of similarities.
Promise: An unusual design, other than the typical two- or three-bladed horizontal axis wind turbine (HAWT). Some are vertical axis or squirrel cages, shrouded or funnels, or some other unusual rotor configuration.
Reality: The designs are simply a regurgitation of something unusual-looking. Although they are eye-catching, they never worked, which is why the designs were abandoned decades ago.
Promise: Rooftop units with small rotors or ground-mounted, designed to generate (“spin”) at lower wind speeds to avoid the added expense of the tower.
Reality: As above, it’s all about collector size and where the fuel is. A whirligig with a small rotor will likely only ever generate enough electricity to overcome the resistance losses in the wire run. Also, note that spinning does not equate to generating electricity. For kicks, calculate the units that go into the power equation in a much-touted 2 mph startup wind speed. Then compare this number with the units in a 10 or 15 mph wind. Do this using P ~ V3.
Promise: The designer claims “thinking outside the box” with an innovative idea, bringing new insights to a stagnant technology.
Reality: Wouldn’t it be good if the innovator knew what’s actually inside the box before beginning to think outside of it? In other words, shouldn’t a designer understand why successful wind turbine designs—small ones, as well as the tens of thousands of utility- and larger-scale wind farm turbines—all look like they do? They should also understand why hundreds of unusual rotor designs were abandoned decades ago and are not being implemented by established manufacturers.
Promise: Conceptual designs claiming unprecedented efficiencies.
Reality: Show real performance data from multiple real-world installations. Wind tunnel or lab test results and website calculations are the equivalent of wild guesses as to what a generator will do in the real world. Short-term and controlled tests of a prototype from one installation at an ideal site don’t reflect real-world performance. For confidence, you need performance data from a production model (not a prototype) from an independent third-party or owner.
Promise: They solve non-existent problems. These range from being bird-friendly to vibration-free, and everything between.
Reality: Let’s take just one example: bird-friendly. The intimation is that two- and three-blade HAWTs kill birds. Unfortunately, large utility-scale wind turbines do kill some birds. Taken in perspective, however, bird mortality with the largest of turbines is far lower than the impact from conventional energy sources (none of which, it seems, are held to the same environmental standards that are imposed on renewables). The few surveys or studies on bird mortality done on small wind installations might suggest a possibility of a handful of bird deaths over the entire life of the installation at sensitive locations—far less than one summer’s bird mortality from many picture windows or domestic cats. Bird mortality is hardly the concern with small wind turbines that these claims make them out to be.
Promise: All-too-frequent headline: “Revolutionary new design…”
Reality: Product sophistication and fine-tuning come from evolution—building on prior art—not revolution. Small wind turbines have been around for nearly 85 years. We’ve had time to sort out what works and what doesn’t based on the science of physics and fluid dynamics, and with engineering and mathematics. Over the history of wind turbines, the designs that have proven themselves to work are two- or three-bladed HAWTs.