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. 
  • Powerful new ‘rare earth super magnets’ became available and were helping build 96% efficient generators, alternators and electric motors;
  • Design software for the engineering needed to ‘custom build’ powerful, high-efficiency, yet low RPM generators and alternators had also arrived and were being successfully sold and used;
  • Grid-Interactive electric power inverters were being manufactured in Germany and Italy that could hook up solar and small wind turbines to the utility grid without the need for batteries; and
  • Quiet, low-RPM vertical-axis machines were getting urban/suburban building permits where noisier horizontal-axis ‘propeller-type’ wind electric turbines (HAWTs) were not.
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;
  • VAWTs work at lower spin rates and therefore create less noise than the higher RPM HAWTs. Less noise is a major factor in being accepted in densely populated towns and neighborhoods;
  • VAWTs, due to their lower RPMs, have less vibration transferred to a supporting tube tower or supporting stand, making them much more compatible with being mounted on buildings;
  • Some find the aesthetics of VAWTs more compatible with the architecture of modern buildings on which they might be mounted. Architects in particular seem to like VAWTs, but not HAWTs; and
  • Maybe, most importantly for safety. It appears that VAWTs, particularly helical turbines, have the inherent capacity not to overspin, even in storm winds and if lightning has knocked out any electronic braking capability. This is a special quality reserved to non-bladed wind turbines. The makers of helical VAWT machines can guarantee no over-spinning, where other manufacturers cannot. Also, most helical-type turbines don’t spin faster than 500 RPM, even in winds over 60 mph. It is at over 650 RPMs that spinning fans and turbines of all kinds start to become transparent to the eyes of birds, bats, and other wildlife. Because most VAWTs do not spin up to transparency, they can be seen before doing mortal damage to wildlife. This is of particular importance for turbines placed on tall buildings.
 
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
 

Volume: July/August 2015