Rooftop Wind Power in Cities is Here

In 2003, just twelve pioneering renewable energy years ago, multiple wind energy innovators in the USA and worldwide, all seemed to see the coming confluence of technical breakthroughs that could bring on a revolution in electric wind power technology. That confluence continues today with little media notice. Primarily in U.S. cities like Chicago, New York City, Los Angeles, and San Francisco, wind power experimenters recognized a platform from which they could build and launch the next generation in Vertical-Axis Wind Turbine (VAWT) electric power technology. 

Wind experimenters, worldwide, had discovered that vertical-axis wind turbines were quite different from horizontal-axis (propeller-type) wind turbines due greatly to the research done by Gary Johnson, PhD.; a professor of electrical engineering at Kansas State University (KSU). Under a 1972 research grant from the U.S. Energy Research & Development Administration (ERDA); the predecessor to the U.S. Dept. of Energy, Dr. Gary Johnson did testing, analysis, and power graphs for the various wind machines in operation at the time, including electric generators and water-pumping machines. His graphs of efficiency (Figure 1) helped establish the status of the different wind turbine technologies.

       

Figure 1                                                                         Figure 2

 

A vital publication error

It is important to note the measured efficiencies of the vertical-axis wind turbines tested by Dr. Gary Johnson in 1972 (Figure 1). The Savonius rotor (S-type VAWT) measured at 30% efficiency peak, and the Darrieus rotor (Blade-Type VAWT) measured at over 35% efficiency peak. High-speed, two-blade propeller-type wind turbines measured over 45% efficiency peak, and the traditional American multi-blade type “water pumper” barely reached a 15% efficiency peak. But, when ERDA sent this chart out for publication, a major change had been made! A graphic artist had mistakenly made a shift in labels! (Figure 2) Now, the more inefficient American multi-blade rotor was labelled at 30% peak efficiency and the Savonius rotor was shown to be only 15% efficient; switched from Dr. Johnson’s multi-blade rotor curve. In spite of Dr. Johnson’s many phone calls and letters to ERDA, and to the many publishers of this wrongly labelled graph, the wrong power curves stuck, creating a sense of inefficient ‘S-type’ rotors, which remains to this day.

 

The results were the proof

But, wind power experimenters at Northwestern University were building and now getting 30%  (not 15%) efficiencies from typical ‘S-shaped’ rotors and nearly 35% peak efficiencies when the ‘S’ profile had been twisted into a helix. In Holland, at Delft University of Technology, a 3-bladed Darrieus rotor with twisted helical blades got close to 40% peak efficiency and was starting up in slower winds than previous straight-bladed or hoop-bladed Darrieus rotors from the 1970s. All this was happening in conjunction with the electronic breakthroughs occurring with the super magnet generators and super-efficient, grid-tied power inverters. By 2003, new VAWT patents were being filed and the growth in VAWT startups had begun worldwide.

 

Acceptance soon came

By 2005, many prop-type HAWT manufacturers began to complain about the unreal performance of the new VAWT machines and showed the public the wrongly labelled ERDA graphs as evidence. But as more and more VAWTs of different kinds found acceptance with their 30% and better power production and capacity to receive building permits in suburbs and cities where HAWTs were banned, the tide began to turn. Why did these VAWTs receive better acceptance in suburbs and cities?

 

VAWTs, with their profiles that can take winds from all directions at once; and that can work well in the turbulent winds around buildings and trees, could operate where HAWTS needing steady, non-turbulent, single-direction winds could not;

 

It is for these reasons and others, that VAWT turbines of all profiles have gained acceptance and building permits for rooftop installations in cities and suburbs where few HAWTs have. 

 

As of 2015, there seems to be three main categories of rooftop VAWT technology:

 

Helical ‘ONLY’ VAWTs can become an architectural feature for a modern building and operate year-long in supplying both power production as well as an interesting visual aesthetic to a unique facility. It is probably noticed by many who work at this large medical research facility, (Image 1) that the helical turbines have qualities quite similar to those of the DNA molecule.

 

 

 

Bladed ‘ONLY’ VAWTs (Image 2) can also become an architectural feature and operate year-long in supplying renewable clean power to a unique facility. These helically- shaped, bladed machines operate as quietly as the helical only systems, with a little more lift, and efficiencies closer to 40%. Most VAWT manufacturers and suppliers also have longer warrantee times and lower maintenance schedules than non-VAWT machines.

                                                                                                                           

 

 

 

Helical & Bladed ‘Hybrid’ VAWTs (Image 3) combine the best aspects of the Helix and Darrieus Bladed geometries. They can reach 40% efficiency peaks, become architectural features for a modern building, and operate year-long in supplying both power production and interesting visual qualities to a unique facility. Due to low/no vibrations coming from these machines, their unique stands can support cantilevered solar arrays thus making them hybrid-hybrids in producing clean renewable energy.                              

                  

It is evident the rooftop VAWT revolution is here; turning the rooftops of American cities into aesthetically pleasing, clean energy generating powerhouses.

 

 

William Becker is President and CEO of Aerotecture International Inc. located just south of Chicago.

 

Aerotecture International, Inc. | www.aerotecture.com