Vertical axis wind turbines (VAWTs) appear to be making a comeback after a few dormant decades, but it’s unclear how much legs the somewhat maligned technology will have in the market. VAWTs are most commonly known in the United States from their days during the 1970s to the early 1990s in California, when Sandia National Laboratories and several private companies worked together to design and deploy a number of 500 kW-600 kW utility-scale VAWTs in California. The units worked fairly well, even if not as well as expected, for a number of years. But they ultimately ran into mechanical problems that stifled their commercial viability. By that time, interest had largely shifted to today’s more common three-bladed horizontal axis wind turbine (HAWT) designs, and the industry has never looked back.
VAWTs do potentially offer advantages over HAWTs, including producing power with less wind so they can be located closer together and closer to the ground for easier maintenance and installation. There are at least 28 active VAWT manufacturers in the world today, primarily producing less than 10 kW units intended for use in urban and building-integrated settings. Yet, many companies in this sector, such as Helix Windpower and Windspire, have faced significant financial challenges. Small wind turbines in general have faced increased scrutiny, as there are many cases of both VAWTs and HAWTs not performing as advertised in the urban environment. The establishment of the Small Wind Certification Council has been a major step forward for a small wind industry that is looking to regain credibility. Still, only five small wind turbines are currently certified by the council – all HAWTs.
These challenges did not, however, prevent the largest building-integrated VAWT installation in the United States from coming online in June 2012. It uses 18 4.5 kW Venger Wind V2 turbines on the roof of the Oklahoma Medical Research Foundation. The V2 wind turbines are 18.5 feet tall and are designed to start producing electricity at winds of 8.9 mph, well below Oklahoma City’s annual wind speed average, according to Venger Wind.
Packing Them In
Making inroads in the utility-scale market is a challenging task for VAWTs, given the formidable competition from incumbent manufacturers that have a long history of commercial viability and strong technical performance. There is strong, though relatively limited, potential in the medium wind turbine market segment (100 kW-900 kW range) related to rural areas, islands, community wind, schools, and other distributed wind applications. No known commercially available VAWT product currently exists in that power range – Italy’s Ropatec offers the largest known VAWT unit at 20 kW. But a number of universities and companies are taking a closer look at VAWT technology and applications and are seeking to learn from others’ successes and failures.
A Caltech study that analyzed the performance of six VAWTs more tightly packed together found that they produced 21 to 47 watts of power per square meter of land area, compared to just 2 to 3 watts per square meter from a similarly sized HAWT farm. Shanghai Aeolus Windpower Technology (SAWT) currently offers less than 10 kW VAWTs, but has stated plans to develop 50 kW and 1 MW units. Sandia National Labs received a $4.1 million grant in June 2012 to reevaluate VAWTs, including their potential for offshore applications – an opportunity that Japanese, Korean, and Chinese researchers and companies are also examining.
Finally, high-profile projects at Adobe and the Lincoln Financial Field (home of the NFL’s Philadelphia Eagles) continue to drive interest in VAWTs. But only actual performance details over time will determine if the resurgence of VAWT interest is based on concrete technical improvements or hype.