[permaculture] Maglev wind turbines
dwoodard at becon.org
Fri Dec 14 07:40:16 EST 2007
This has to be either a scam or the product of mass self-delusion on the
part of the people involved.
1. "1000 times more efficient"
The theoretical limit of efficiency of extraction of the power in the
wind is 16/27 or about 59.3%, established by Dr. Betz in the 1920's.
Conventional large wind turbines reach a maximum of about 47% efficency
at their most efficient windspeed, averaging 30-40% over a range of
windspeeds.. Small wind turbines tend to be somewhat less efficient.
On the face of it the "developers" are claiming to extract roughly 300
times more power from the wind than it contains. Maybe they mean
something else by "efficiency." Why don't they say what it is?
2. The quoted cut-in windspeed is 1.5 metres per second, 3 knots, 3.45
miles per hour. Some conventional wind turbines reach their rated power
at windspeeds of 12 m/s, 24 knots, 27.6 miles per hour. The power in the
wind varies as the cube of the windspeed so if the Maglev wind turbine
reaches its rated power at 12 m/s it would deliver 1/512, 0.2% of its
rated power at cut-in (start-up) windspeed. This is a negligible amount
of power in relation to the cost of any wind energy converter, and that
is why wind turbines are designed to start at typically 3-4 m/s or about
9 miles per hour, with maximum efficiency at a somewhat higher
windspeed, somewhat below the windspeed for rated power.
The developers are claiming as an advantage, something that is pointless
3. From the sketch, the Maglev wind turbine is a vertical axis machine
with a great many blades. From known principles of wind turbine design,
the large number of blades would lead to a reduced efficiency. Vertical
axis wind turbines tend to suffer large force reversals on the blades
with each rotation giving high fatigue loads and short blade life.
Vertical axis wind turbines tend to be hard to design for speed
limitation to limit stress in high windspeeds, yet this is essential for
economy and safety.
Many designs of vetical axis wind turbine have been built and tested.
One type was installed in dozens in California in the 1980's. Hard
experience of relative reliability and price competition has led to the
domination of horizontal axis designs.
"Would last 500 years"
Even conventional horizontal axis wind turbines at large sizes schedule
blade replacements every 10 years due to fatigue loads. Generators are
rewound at intervals of 10 years. A life of 500 years would require
large innovations in more than bearings.
4. Relative cost
Conventional large wind turbines tend to cost $1500-$2500 per rated
kilowatt installed. Vertical axis turbines normally use more materials
and cost more than conventional horizontal axis types. As far as I can
make out the estimated cost of the big Maglev turbine is something like
$50 per rated kilowatt, for something that presumably would be made in
about 1/1000 the numbers of conventional types and would not benefit
from mass production to anything like the same extent. I don't believe it.
5. The bearing
I require to be convinced that a permanent-magnet bearing would
necessarily be friction-free, long-life and superior in cost to
conventional types. Nothing is said about the details, but it's
supposedly the key to the whole design.
For the implied power production the large Maglev turbine would have to
intercept the wind over a cross section area of some like 4 million
square metres. Given the proportions in the drawing this would mean a
height of say 2800 metres (~9000 feet) and a diameter of around 1400
metres (~4500 feet). Machines tend to develop new problems when scaled
up, and this was why big horizontal axis wind turbines of 80-120 metres
rotor diameter were not successful until developed over several
generations of steadily increasing size, over 20-30 years, with each
generation produced in quantity to get the bugs worked out.
I'm not surprised that initial production plans propose machines of 5
kilowatts or less rated power, suitable for one house. Then one
encounters the problem of where to mount them with the usual problems of
small vertical axis machines - it's hard to mount them high where the
wind is strong and smooth. If you mount them on a building not only is
the wind weak and turbulent (producing high stresses and short life) but
vibrations tend to be transmitted into and through the building.
Rotating machines vibrate, it's hard to avoid.
Nothing is said about what has been built to this design, under what
circumstances and over what period it has been tested, and what the
results were. These are crucial points. Why aren't they mentioned?
This announcement has "scam - hold on to your wallet - flee"
written all over it.
For some reason wind power seems to attract scam artists and deluded
inventors. This is just the latest in a long series. It won't be the last.
If you want to learn solid information about wind turbines, read the
books by Paul Gipe and Hugh Pigott, listed on their websites
also the website
St. Catharines, Ontario, Canada
Keith Johnson wrote:
> First time I've heard about these....one imagines that if they can be
> made large, they could also be made smaller.
> We've seen a couple innovative wind power solutions pop up, but none
> that claim to offer the benefits of maglev wind turbines, which use
> full-permanent magnets to nearly eliminate friction by "floating" the
> blades above the base. According to developers, the technology is
> capable of scaling to massive sizes, with a proposed $53M turbine able
> enough to replace 1000 traditional windmills and power 750 thousand
> homes. Additional benefits include the ability to generate power with
> *winds as slow as three miles per hour*, operational costs some 50
> percent cheaper than windmills, and an estimated lifespan of 500 years.
> That all sounds great, but the real proof will come when these things
> get put to use, which may happen sooner than you'd think: Development is
> proceeding rapidly in both the US and China, with Chinese power company
> Zhongke Hengyuan Energy Technology currently building a $5M factory to
> produce the turbines in capacities from 400 to 5,000 watts.
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