Sustainable energy, out of thin air …

Back in 2011, a local entrepreneur was impressed by the scale of the European wind farm industry; in Germany in particular, which is considered one of the leading wind turbine and wind energy producers in the world. He saw the potential for implementing the same industry in South Africa, but on a larger (although smaller) scale …

After six years of research and development, Rolf Seeliger designed a folding, twin-rotor turbine system. Flying in the face of the “bigger is better” perception in the wind energy sector, his 3 kW prototype stood a mere six metres high and appeared to be the solution to the global wind turbine/farm challenge.

“When you see the standard turbines from a distance, you cannot appreciate the scale of each unit; some with tower heights of 100 m,” he says. Putting that into perspective, each (traditional) mast stands the height of a thirty-story building, with blades measuring an astounding 60 m or more.

Seeliger saw an opening in the green energy market for more compact, high-ef?ciency wind turbines – with the associated cost bene?ts of transporting and installing smaller components and units. In 2011, with international patents pending, his first machine was launched with the 3 kW technology, fully up-scalable to megawatt utility capacity. It met with huge international interest and talk of manufacturing in Germany followed.

But that was in 2011, and he knew that he could improve the design before launching it into the global energy market.

Since then, while Seeliger’s invention has continued to whet the international market’s appetite, he has refined and modified the wind turbine substantially, with numerous patents pending on the enhanced design.

The improved turbine remains a folding rotor system, requiring no blade dismantling, allowing for complete factory assembly. It is delivered ready for installation and operation, making it a plug-and-play system for the end-user.

The innovative blade design makes use of biomimicry, which, simply put, means that through observation of nature, the blade is modelled on biological forms and processes. The end product results in high rotor-blade torque, through vortices generated on its surface and airflow compression.

The rotor-blade surface area can measure up to an astounding 50 percent – relative to the rotor-swept area – in comparison to conventional blades, which have a surface area of five to 10 percent. Seeliger elaborates: “In the design, the biggest blade-surface areas are positioned towards the centre of the rotor-swept area, resulting in greater kinetic power extraction, giving the rotors smaller diameters than conventional rotors, yet affording them substantially more blade-surface area.”

Despite the significantly reduced blade lengths, the design enables the optimum amount of kinetic energy to be harvested, and achieves exceptional rotor torque – with almost noiseless operation across all wind speeds, making them ideal for urban and inner city areas. In the latter case, building rooftops are ideally suited to position these turbines, owing to substantially smaller rotor diameters and the multiple stackable array system, requiring lower overall mast heights.

According to Seeliger: “Counter rotating wind turbine systems eliminate any gyroscopic effect and can be con?gured with twin, quad or more rotors to suit the prevailing wind conditions in any given region.”

The vastly remodelled turbine is configured with four counter-rotating rotors: two facing up-wind and two facing down-wind. The variant rotors can be configured with four-, six- or eight-blade rotors for very low start-up speeds, < 1,5 m/second, a variation on an existing patent.

The low inertia, high-ef?ciency rotors are minimally affected by turbulent air?ow, compared to conventional wind turbines.

The passive rotor tilt-furling system (reduction of the rotor angle against air?ow) allows for continuous operation, with no minimum cut-out speed, regardless of wind conditions. The passive rotor steering ensures that the machine is not put under undue stress. The specially designed rotor configuration offers substantially lower costs per kilowatt output, resulting in an increased yield of 50 to 60 percent.

Although the entire transformable and transportable unit requires no foundations, other than earth anchors to fix it into position, the system is also suitable for more permanent applications.

In addition, the technology is scalable for megawatt turbines, for use in both onshore and offshore applications including: agriculture; disaster-crisis areas; emergency power; irrigation; desalination; water treatment; large construction sites; pipeline construction; harbour applications; decontamination requirements and many more applications, as well as urban use. “Smaller rotor-diameter wind turbines could also be used as in?ll turbines in existing wind farms, thereby utilising the existing infrastructure and reducing wind farm costs further,” Seeliger adds.

The rotor blades can be utilised for both horizontal- and vertical-axis turbines and hybrid combinations, with integrated solar PV and fuel cells also possible.

Additionally, maintenance is carried out by the end-user, as the machine can be brought down to ground level within
15 minutes and lubrication and blade cleaning can be undertaken with minimal, if any, safety risks to personnel. Thereafter, the machine can be brought back into operation, resulting in substantial ongoing maintenance cost saving over the long term. All electronic components come pre-installed in the transport unit, with a professional connection to the grid being the only additional requirement.

Other features

With the reduced size of the unit, there is significantly less material used for the rotor blade in the manufacturing process, with up to 50 percent saving over the traditional blades. “The approach is that the greater the power output required from a wind turbine, the bigger the rotor diameter must be,” Seeliger adds, emphasising the reduced dimensions of his machine.

The overall construction cost is between 30 and 40 percent less than that of conventional turbines, and the unit supplies substantially higher and more constant energy output per annum than its traditional counterpart.

With further testing and tweaking in progress, it is anticipated that production of the units will commence in early 2015, in Germany, with a possible market in South Africa.