Future Energy Fellows post

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Human beings have always been obsessed with flight. The idea of gliding through the air has motivated many great minds through human history to create everything from poetry to complicated flying contraptions. For almost as long as we have wanted to fly, humans have also strived to capture the wind. One of the earliest wind turbines dates back to 200 B.C. in Persia, using sails to capture wind and grind up seeds. The desire to take what mother nature has provided and transform it into some we can use has continued on to this day. While the humble archaeological remains of the reed and wood windmill are a far cry from Gamesa’s 128-meter diameter, carbon-fiber mega-turbines of today, the two share a common history and the same uncertain future. 

Those easily recognizable three-blade lift turbines are by far the most popular choice for modern wind technology. They work on the same principles as an airplane wing, slicing through the air to generate electricity for the grid. Since the 1980’s the industry’s attention has centered on using wind power to replace thermal power and reduce green house gas emissions. Many countries including the United States, China, Germany and Australia want to draw an average of 30% of electricity from renewable sources in the next two decades. Wind turbines are often the technological solution of choice for this task. 

This focus caused a steady increase in the size of three-blade wind turbines from 20 kilowatts in 1980, to over two megawatts today. The trend is expected to continue in that direction, so much so that Morphocode, an architectural firm, designed an offshore wind turbine with a loft-style apartment built into the nacelle (the box behind the blades) for the technicians to live in, so they don’t need to be ferried back and forth from land. 

This ‘bigger is better’ trend isn’t a flight of fancy, but a default in innovation. Early on in the wind turbine race, it became apparent that three-blades are the most cost-effective compared to efficiency – you get the most electricity for your dollar. This resulted in enormous amounts of engineering on everything from the design of the blade tips, to how the tower is anchored into the ground or seafloor. Three-blades are possibly some of the most engineered pieces of machinery on the planet and can be found almost everywhere there are favorable wind conditions. 

 


 

The same features that make them so efficient also determine their limitations: three-blades can only operate in wind speeds between an average of 10km/hour to 90km/hour, they require a steady wind stream, not gusts, and are prone to breaking apart during adverse weather, like the wind farm in Dunhobby, Scotland that torn itself apart near an elementary school. The swift movement of the blades themselves has caused noise pollution problems and the airspace beacons can be distracting for people living near the farms.  

The flaws caused people to look for alternative technologies for environments where three-blades are not optimal. The alternatives fall into two broad categories: Horizontal Axis Wind Turbines (HAWTs) and Vertical Axis Wind Turbines (VAWTs). Envison Energy is currently testing a two-blade HAWT in Denmark to see if the less-stable but more cost-effective design is viable. Another popular wind turbine design, this time a VAWT, that has also been around for centuries is the Darrieus wind turbine. These have blades that resemble an eggbeater and are related to the Savonius wind turbine. These designs rely on drag rather than lift to move the blades and are sometimes called ‘impulse’ turbines. WindFlo built a large Darrieus turbine farm in Cameron Ridge, California in the 1980’s, but the site was slowly decommissioned because of structural joint failures. Somewhat like alternative music, these alternative wind turbines were not inherently popular, because they still require 7km/h wind speeds to start generating power and breakdown more easily. However, a promising 2010 study done at Caltech found that if the alternative turbines are configured correctly, they could generate just as much power as a three-blade farm.   

The struggle to find alternative wind technologies has begun to intensify in the last few years. Many countries have sustainability milestones coming up in the next few years and while the first 80% of a goal in relatively easy to meet with existing technologies, the last 20% get exponentially more difficult. The last minute scuffle has led to a variety of innovations, each making their way through testing and on to the market. For example, Kyushu University in Japan is designing a project called WindLens, which uses a five-blade lift turbine, mounted of a floating platform. Because the five blades are structurally weaker, they placed a supportive ring around the outside to both support the blades and channel the wind. 

Saphon Energy created a quirky bird-friendly turbine, which uses a dish instead of blades to capture wind energy by wobbling back and forth, in perpetual motion. SheerWind is behind the behemoth INVELOX wind tunnel/wind turbine in Minnesota, which uses a giant funnel-shaped tower to capture wind and direct it through generators at the bottom. 

Mitsui, also in Japan, designed a hybrid wave-wind turbine that incorporates both a Darrieus and a Savonius turbine, which they hope will generate enough power for 300 homes.  The race is still on for a design that is suitable to be mounted on rooftops, for on-site generation in cities and residential areas.  

 


 

The focus on three-blade technology has let wind turbine innovation fall to the wayside, and the lack of new technologies currently available makes it appear that the industry hit an innovation wall. A 2013 wind technology review found that the lack of innovation is not due to inferior technology, but simply a lack of research. It is possible for alternative technologies to be just as efficient and cost-effective as their three-blade relatives, but up until now, there has been no serious motivation to conduct the research.  

As demand for alternative technologies grows and sustainability goals become increasingly difficult to reach, the technologies currently percolating away in research and development will begin to make their way onto the market – and in some cases on a rooftop or backyard near you – meaning that over the next 20 years, when the pressure is really on, we might just see a plethora of innovation. 

 

 

Sources:

M.R. Islam, S. Mekhilef, R. Saidur, Progress and recent trends of wind energy technology, Renewable and Sustainable Energy Reviews, Volume 21, May 2013, Pages 456-468, ISSN 1364-0321, http://dx.doi.org/10.1016/j.rser.2013.01.007.

(http://www.sciencedirect.com/science/article/pii/S1364032113000312)

http://morphocode.com/work/arch/wind-turbine-loft/ 

http://www.riam.kyushu-u.ac.jp/windeng/en_aboutus_detail04_02.html  

http://sheerwind.com/about 

http://www.cbsnews.com/8301-205_162-57584292/worlds-first-wind-current-power-system-to-be-installed-off-japanese-coast/ 

http://qualenergia.it/sites/default/files/articolo-doc/FLOWE_PPT_Dec2010.pdf

http://www.telegraph.co.uk/earth/energy/windpower/10285964/Wind-turbine-destroyed-by-wind.html