# Efficient ground based wind energy



## begreen (Jan 11, 2015)

I love the simplicity of this concept. It appears to test well, demonstrating significant efficiency improvements.
http://sheerwind.com/
http://sheerwind.com/


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## woodgeek (Jan 11, 2015)

Sadly, the power density of wind goes like Area*speed^3 no matter how you collect it.  You can use a funnel to increase the speed while decreasing the area, resulting in a smaller turbine, but you will not gain energy in process.  For a given power, the funnel on this thing has the be the size of the swept area of a regular turbine, and the generator is still the same (and currently a significant portion of the expense).  The traditional form uses a lot less material than this monster, and thus is probably a lot cheaper in the end.  And to my eyes more attractive than a funnel tower of the same collecting area.

This is the same reason why vertical axis machines and some other geometries never scaled up well either.

Lest you think me a total wet blanket, I DO like airborne wind power, like kite power, or the things in Big Hero 6.


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## begreen (Jan 11, 2015)

The field data appears to demonstrate a significant improvement over the same free-stream turbine in identical conditions. 
http://sheerwind.com/technology/field-data


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## woodgeek (Jan 11, 2015)

The fact that the wind speed is increased is not surprising....but the energy content of the wind collected is not increased by passing it through a venturi, its slightly faster wind over a smaller area.


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## begreen (Jan 11, 2015)

Slightly? They are stating a 400% increase in windspeed at 10mph input,  but you seem to doubt that?


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## woodgeek (Jan 11, 2015)

Testing the same turbine in free air and behind a giant funnel, the funnel will yield more energy.  Testing the funnel + small turbine against a free rotor turbine with the same collecting area....at best same energy output.


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## begreen (Jan 11, 2015)

I am wondering over the lifespan if there are greater advantages to their system. Lower maintenance costs and ground based maintenance seem obvious, but maybe lower avian kill count too?


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## peakbagger (Jan 11, 2015)

The laws of physics still apply and the design has significant friction loss that a standard wind turbine doesn't. Sure Q=AV applies Flow= Area*velocity. Reduce the cross sectional area and the velocity increases but the flow is the same. Friction loss varies roughly by the square of velocity. so the higher velocity, the more friction loss. Friction loss is lost power that that the turbine doesn't capture.


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## Ehouse (Jan 12, 2015)

Woodgeek and peakbagger, I bow to your technical prowess but I have a couple of questions.  I've been working part time at a trout hatchery built in the '30's that does amazing things with water and gravity.  I was reading a tech manual about flow of impounded water through flumes and over weirs with various aperture shapes, orientations and run configurations.  I know water dynamics do not translate directly to air dynamics but there are some similarities.  One thing they talk about is approach velocity causing turbulence and back eddys, which can be lessened with a winged entry for a flume or weir, or a funnel for a stand pipe.  This set up claims to be omnidirectional and able to operate at wind speeds of 2MPH, while a conventional setup would need around 5 to 7MPH.  Gravity could bolster wind force with a temperature differential and a siphon effect could come into play.  With a venturi, flow remains the same.  What about torque?  What If it's driven by a sympathetic vortex flow rather than merely impacted by a strait slug of wind?  The Bumble Bee can't fly either.


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## woodgeek (Jan 12, 2015)

Conventional turbines could be designed to cut in at 2 mph, but since the energy goes like v^3, the available power at 2 mph is only 3% what it is at 7 mph, or 0.1% what it is at 20 mph.  So turbines are designed to maximize annual energy delivered, not for low cut-in.


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## peakbagger (Jan 12, 2015)

Bummer that folks don't have access to Home Power Magazine. There was an excellent article about 3 or 4 issues ago on wind power fundamentals. Read that and it would explain fairly quickly why this concept is not going to be more efficient than a standard wind turbine.


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