Page 20 - North American Clean Energy March April 2015

wind power

Image 1. (Far Left)
Ducted turbine
design concept for a
rural community (by

Vendula Andrs)

Image 2. (Left) CFD
model showing how
wind speed increases

Turning Technology Upside Down

The power of controlling the wind

By Steve Faber

REVOLUTIONARY FOR ITS TIME, agriculturists in the 1900s implemented age-old windmill turning the turbines in the direction of the wind to better capture it. But, these systems
technology for pumping water and running mills. In the 1940s, the irst megawatt turbine do contribute to added costs, failure rates, and turbine downtime.

was built with 75-foot blades, weighing in at 240 tons. It wasn’t until the late 1970s, how- As the speed of the wind cannot be controlled any more than the direction, the result
ever, with the fossil fuel crises that wind turbines began to ind their way across the globe.
has been enlarging blade sizes and tower heights, so as to gain access to smoother wind
In the last two decades, manufacturers have incrementally improved the technology be- speeds. Two factors control the electric power generated by horizontal-axis wind turbines:
hind these turbines. In particular, conventional, horizontal-axis wind turbines have been free-stream wind speed and blade radius. Because of these two parameters, along with the

ine-tuned to gain more and more energy output. hese improvements have resulted in fact that wind cannot be controlled, the tower height and blade sizes have grown exten-
turbines with larger blades, adjustable pitch, and taller towers that require more land.
sively.
As the size and height of turbines and towers increase—nowadays, often reaching be- Manufacturing, logistics, installation, and maintenance challenges and cost efects
yond 490 feet—the cost of wind-generated power continues to exceed the cost of power at these heights are forcing blade sizes to reach their limits. Furthermore, pitch control

generated by hydropower plants, coal, and natural gas.
systems have been added to help reduce wind loads when wind speeds are higher than 25
mph. However, even a pitch control can no longer be an efective adjustment at high wind
Comparing cost & output
speeds, and turbines simply shut down at wind speeds of about 55 mph.
Measuring output (or capacity factor) is an important factor inluencing the inancial viabil-

ity of a power plant. Capacity factor is deined as the percentage of the year a turbine gener- Controlling the wind
ates its nameplate power. his capacity factor of wind turbines ranges from 25% to 40%.
So, what if it was possible to control wind speed and direction? his is one of the questions
hese large systems require a minimum of nine miles-per-hour (mph) winds (i.e. cut-in that led researchers on a new path to try just that. In recent years, a new concept in wind
speed) to begin turning, and 25 mph to produce nameplate power. In addition to low-ca- power application was developed that outperforms traditional wind turbines of the same

pacity factors (less than 40%), wind turbines are often subject to excessive downtime due diameter and aerodynamic characteristics, while under the same wind conditions. he
to repair, failure, and service maintenance. Due to the size of today’s towers, these costs technology has been shown to deliver higher outputs, at a reduced cost.
are comparatively high in expense and in time. Often repairs can take two to three weeks he concept is simple: eliminate tower-mounted turbines, with their large rotational

to complete, which adds up in terms of lost power.
blades, and replace them with smaller, faster blades. his concept advances wind power
Another major factor inluencing the cost and output of a turbine is the lack of control generation the same way jet engines replaced or advanced prop airplanes. Jet engines sim-
over the source of energy—in this case, wind. However, technology has come a long way ply traded speed with prop size. he concept of capturing and accelerating wind does the
and rather than controlling the source of the energy, engineers have attempted to control same to the large wind turbines of today. Plus, the new technology ofers an added beneit

the equipment. Massive yaw systems have been implemented in modern-day turbines,
of being safely installed inside a tube structure at ground level. Safety, in terms of heights
and fall protection, is no longer an issue.
To break it down, this technology includes capturing wind at the top of a funnel struc-
ture, which tapers downward like a hopper, funneling wind in a series of pipes that also

accelerate and squeeze it (much like a hydro dam accelerates water). A Venturi chamber
works on increasing the dynamic pressure, ultimately, increasing the velocity of a wind.
With wind accelerated and funneled to ground level, it can safely be converted to electrical
energy by turbine-generators securely covered on the ground.

his concept controls the wind, as speed and direction are managed inside the Venturi.
he turbine also only receives wind in one direction and, therefore, doesn’t require a costly
yaw system. As wind speeds can be controlled and maintained at optimum levels, herein,
no blade pitch control is required. Wind speed is harnessed and maintained at the speed

that results in the maximum power output. his technology operates very much like cruise
control in passenger cars. In this case, the turbine runs on cruise control.

Concept challenges

225 kW turbine nacelle prepared for shipping from Halus facility.
With all new technologies come skeptics with opposing views, so education is key. In the
past, ducted turbines haven’t made signiicant headway in the wind industry. Despite
The leader in remanufactured wind turbines. mainly positive performances, questions arose related to their technical implementation
Vestas 90, 108, 120, 225, 500, 600 kW in stock.
and inancial viability. Ducted turbines have to be placed at a certain height, for instance,
HALUS
Turbine supply which can increase their technical complexity and add to their costs. Another technical is-
POWER SYSTEMS
Design/build (510) 278-2212 sue involves the implementation of a mechanism design, which allows for self-alignment
Bondable
www.halus.com
of large-scale ducted turbines in the direction of the wind.

20 nacleanenergy.com
MARCH/APRIL 2015