Wind Energy Challenge: Google Raises the Hub

Posted on July 27, 2010

Posted By: Harry Valentine

Topic: Wind

Internet search engine Google provided an estimated $10 million to a wind energy research group to develop a technology that could convert wind energy to massive amounts of electrical energy at competitive costs. Several entrepreneurs, organizations and groups are working toward such an objective and all agree that there is merit in accessing the more powerful winds that blow at higher elevations. One group seeks to connect high-altitude winds to ground-level electrical generators while another group seeks to carry the electrical generation equipment aloft, in the air stream.

In this regard, Google's energy chief literally "raised the hub" by commenting on the merit of mounting turbines on towers with hubs at elevations of 200m or 656-feet. For many years the hubs were placed at an elevation 80m or 262-feet with newer towers placing the hub at 100m (328-feet) and up to 128m (420-feet). Wind velocities are respectively 1.25 and 1.6-times the velocity at 80m elevation. While placing hubs at an elevation of 200m may seem daunting, there may be potential to borrow precedent from the bridge building industry.

Cable Suspended Turbines:

There has been recent research on installing suspension bridge type cable systems across windswept valleys and ocean inlets to carry turbines at locations where predominantly unidirectional winds blow. Such is the case in the southern Andes Mountains (southern Chile), the fiords of Norway and the Western Ghats of India during the summer monsoon. The boundary layer effect causes wind to interact with nature of the terrain, often "steering" winds into the valleys where the channel effect guides the wind through.

While cable systems derived from suspension bridge design have potential to carry multiple levels of groups of lateral-axis turbines across valleys, they limited to valleys that are often less than 2000m (6500-feet) across. Cable-based-windlass drive mechanisms may connect groups of turbines that rotate in the same direction at different elevations and drive into a single electrical generator. Such an approach promises to reduce the cost of generators and towers that are related to wind power.

An alternate cable-suspended wind technology combines aerial tramway and ski lift cable technology. Wind pushes cable-mounted airfoils in a loop back-and-forth across a valley and drives electrical generators mounted near the valley walls. Several research people are undertaking further research to develop such a concept. A cross-sectional area of wind of 5000-feet in width by 200-feet in height, blowing at 30mi/hr (50Km/hr) could generate a peak output of 46MW at 35% conversion efficiency with over 150MW of peak output in a wind of 45mi/hr.

Curved Span on Towers:

A revolutionary new design of bridge was recently opened to traffic in France and involves a curved span placed at an elevation of 780-feet or (237m) crossing a windswept valley. Tension cables installed inside the rectangular cross section maintain a compressive load across the curved span that is held aloft of comparatively slender bridge posts. The curved span is built into the valley walls on both sides and provides fore-and-aft stability and lateral stability to the bridge posts through a firm connection.

While bridge posts and wind towers differ greatly in design, there may be potential to borrow design precedents from one and apply it to the other. Example, 2 x offshore islands that are 2 to 3-miles apart may each protrude to a height of over 300m from the sea or a lake. The water between them may be sufficiently shallow to install towers for wind turbines and winds may be favorable. There may be potential for structural engineers to seek ways by which to combine a curved span structure with wind towers placed between the 2-islands, to increase the elevation of turbine hubs.

Wind velocity may increase by a factor of 1.7 to 2.2 over the velocity at an elevation of 80m (262-feet), with potential for the same diameter of wind turbine to generate 5 to 10-times the power output. For wind power generation, 2-curved rows of box-shaped trusses that connect the between the towers would form the spans that would be secured into islands or valley walls on either side. The trusses would be secured at 2-levels to each tower and be designed to manage tensile as well as compressive loads. Diagonal trusses would connect at 2-levels between the towers of the 1st and 2nd row.

The combination of the box-shaped trusses that form the curved spans and similar diagonal bracing trusses would duplicate the curved bridge span. The design would provide the lateral and fore-and-aft stability that would strengthen the towers against buckling and flexing. An offshore wind farm built using such technology could involves 50-turbines of 20MW to30MW each with hubs placed at elevations of over 200m. The array could generate a peak output of some 1000MW to 1500MW of output at lower costs than independently built towers.

The towers connected to and stabilized by a curved span may also carry vertical-axis turbines, with the potential to install groups of multiple lateral-axis turbines that drive into a generator above and blow the curved span. The vibrations generated by the lateral-axis turbines may mimic the vertical and lateral vibrations generated by a freight train crossing over a bridge. There may be scope to install a combination of tower mounted (axial-flow or vertical axis) and span mounted (lateral-axis) turbines to increase power output at competitive costs.

Conclusions:

Future energy markets will likely demand technology that can generate electric power at competitive market prices and free from government subsidy. On this front, there is potential to develop terrain enhanced tower-mounted turbines that place hubs at elevations of 200m to 300m and incorporate turbines of 20MW to over 30MW output. While the curved span offers a method by which to stabilize towers and allow them to be built to greater height, there is also potential to use tension cable systems secured to valley walls to provide structural support to higher towers that are placed in windswept valleys.

There will likely be further development on turbines that dispense with the tower and that may be carried entirely by tension cable suspension systems for operation in windy valleys and ocean inlets. Several groups that are working at refining competing airborne wind power technologies that involve airborne and ground level electrical generators have already built and tested prototypes. The work of increasing power output while reducing the cost of wind power will continue, with the likelihood of breakthroughs also occurring in tower-mounted turbine technology.

Authored By:

Harry Valentine

Harry Valentine holds a degree in engineering and has a backround in free-market economics. He has undertaken extensive research into the field of transportation energy over a period of 20-years and has published numerous technical articles on the subject. His economics commentaries have included several articles on issues that pertain to electric power generation. He lives in Canada and can be reached by e-mail at harryc@ontarioeast.net .

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Comments

August, 02 2010

Ferdinand E. Banks says

The United States is a democracy, and so GOOGLE has every right to be dumb - dumber than stupid, in fact. Why didn't some of that ten million come to me. I need money too. I want to play a lot of indoor tennis this year, spend quality time in Paris, visit Vienna and Venice with my wife - who inexplicably hasn't been to those cities, and I need some new clothes. In fact if I get a chance to teach energy or mathematical economics the coming academic year, I think that I'll wear a zoot suit during my lectures.

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August, 03 2010

KENNY MAGERS says

This approuch is not new but gaining some thought, Its well known that tall structures have also up drafts with high inner structure winds like a small tornado! letts think of how a cone shape structure open at base on stliks. then wind then incresses as it rizess to the top where jet type fans? think of the power produceed. The systems in development stage 2 construction phase that does just that. Its called RENEWABLE (THERMAL)=WIND POWER THE ENERGY POWER SOURCE this systems combine 8 natural techs & 6 man made thermal transfure systems in 1 structure. The height is what makes it a better less costly approuch for nature. Get involved with our planets' health. kennynabb6@win.net Get the facts for your own mind expanding with information that can make a better way to think about GREEN ENERGY

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August, 04 2010

Don Hirschberg says

While the design of blades and hardware determines what percentage of wind kinetic energy becomes electrical energy the maximum is elegantly simple and fixed. KE = 1/2 m v^2 That is, kinetic energy equals one half the mass (of air passing, say per second) times the velocity of this mass of air squared, in consistent units. That's it. Period. This is high school physics - at least when I went to highschool.

Since the mass of the intercepted air is directly proportional to the air velocity of the air flow then KE is proportional to v^3. Putting a wind turbine where it gets higher velocity wind certainly increases its possible name plate rating. But it cuts both ways. If a wind turbine is designed and rated for 30 mph wind it can produce only 1/8 th as much with 15 mph wind..

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August, 05 2010

Malcolm Rawlingson says

Ahhhh the sheer inconvenience of physics Don. Of course the majority of alternative energy enthusiasts have degrees in Social Science, Philosophy or Law which is why they do not have a clue what you're talking about.

They think as long as the turbine blades are going around the wind turbine is operating at full power. How can you expect them to understand how it REALLY works. You lost most at the word percentage and the rest at the word kinetic. These folks are blissfully unaware of the equations governing energy.

And - Kenny - great idea but what do we do with all those nasty old rectangular boxes we have built by the million around the world. Who is planning to knock that lot down and build super efficient wind cones. Good idea but there is a real world out there that thinks round buildings are rather impractical that is why they build them square. I would also remind you that this is not a new idea. The very principle is used in cooling towers of inland steam generating stations. But there are no people living or working in these structures.

Malcolm

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August, 06 2010

Don Hirschberg says

While it is not at all clear, I think Kenny is talking about the effects of a chimney and of the venturii. The chimney works because the column of gases in the chimney (stack, flue, etc.) weighs less than a column of air of the same height. (The taller the stack the better it "draws". (It doesn't actually draw or suck, it is pushed.). If it didn't, your fireplace flue gases would as soon discharge into the room as go up the chimney.

We used to use the perfume atomizer to explain the venturi and the carburetor. One was on my lady's bureau and the other in every car. How many today know about carburetors or perfume atomizers? So today the venturi is perhaps best illustrated by the cooling towers so often associated by the media's pictures of nuclear plants - and I'd guess in the public mind as nuclear reactors.

A venturi has big hips and a small waist. Since the same amount of stuff goes in as comes out the velocity must increase as it passes through the waist. No energy is created only converted by trading potential energy (decreased pressure) to kinetic energy ( increased velocity)..

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August, 07 2010

Malcolm Rawlingson says

Thanks for the lucid explanation Don. A city made of those would look different wouldn't it. I guess we would all have to get used to curved furniture. Re-tooling all the office furniture manufacturers should only cost a few billion. I wonder how you would get the elevator shafts through the narrow bit.

Might be good as a physics experiment but seems a tad impractical to me...but then I like rectangular buildings and furniture that fits into the corners. Just old fashioned I guess.

Malcolm

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