DougS comments hereon:
======================
Gordon said: "Doug,
you are incorrect in saying that the cable drive causes additional
forces on the lifter kite. As I said before, activating the drive only
redistributes the forces on both sides of the pulley. Additional forces
only occur if the return side has zero tension."
***Doug Replies:
Exactly, and the return side has zero tension when the wind gets
weak. You have to counter that downward pull with
SOMETHING. You're saying you have countered it with a kite, which
is fine, but that means the kite must lift not only itself, but also
the rest of the apparatus, PLUS countering any downward pull, so to
make power, you need to make the kite bigger. Once you start
making power, if your rotors don't pull upward hard enough, the kite
must make up the difference, so the kite has to be bigger than it
otherwise would. SOMETHING has to counter that downward pull, and since
the goal is to keep everything aloft, the downward pull works against
that. What weighs more, a generator or the return side of the
tether? Besides that, if you use a generator, you can use smaller
kite. So I don't think it holds water to say the downward pull is
not a factor. It is a main factor. It means you have to
make your kite bigger to handle it. You seem to be saying "NO, I
already MADE the kite bigger", but why did you have to make it
bigger? To fight that downward pull. So it seems that we
agree: To fight that downward pull requires more kite. At some
point, the wind dies down and the whole thing comes down. Also,
there may be some lighter winds where you COULD make power IF not for
that downward pull. So using downward pull to transmit power to
the ground raises your cut-in speed, throwing away energy.
Another way to look at it is Joe's point several months ago which he
phrased as what percentage of the energy is used to keep things aloft
versus making power (Joe included kite lift as "energy" and he has a
point that it does require structure and materials that COULD be used
to make power.)
Gordon said: "The
lifter kite is the equivalent of the tower in a conventional wind
turbine. (Considerably cheaper because there is no base, structure or
generator)."
***Doug Replies: Not really, when the wind stops, the tower is still there, while the kite falls to the ground.
Gordon said: "The lifter kite(s) must be large enough to maintain positive tension in the return side of the pulley system."
***Doug Replies:
Bingo, the kite MUST BE large enough - you call it maintaining positive
tension, I call it countering the downward pull - same thing.
Gordon said: "The lifter kite does not compete with the rotors for wind energy."
***Doug Replies:
Well it competes for a budget to build it, and it takes material, has
weight, and occupies what COULD be "swept area", so it becomes one more
case of "there is no free lunch".
Gordon continues: "In comparing the cable drive rotor system with a conventional ST system we have the following advantages:
* More energy output due to higher winds at altitude.
* Less expensive structure. Lifter kite and tether vs tower and support wires.
* Easier maintenance of generator/motor due to ground-gen.
*
Retraction and storing the device prevents possible damage to rotors
and generator overload during high wind and storm
conditions. ~ Gordon"
***Doug replies:
Well like I've told certain people on here, there's no specific
requirement that SuperTurbine(R) is based on the ground or a tower per
se. SuperTurbine(R) is a versatile concept that can be located
anywhere, with a generator at any altitude - it is a broad
concept.
I
can tell you, over the years, I've seen hundreds of crackpot wannabe
inventors fixated on placing the generator on the ground, never
considering, for example that any tower robust enough to counter rotor
thrust has no problem supporting a generator. Probably the most
common theme I've seen is substituting a compressor for the generator,
and running a groundgen on the compressed air. The only hole in
that is: "Who said compressors are ighter than generators in the first
place?" All they really did is make the system heavier, more
expensive, and twice as complicated, not to mention far less efficient,
but they were too busy patting themselves on the back for being "a
genius" to notice such "minor" details.
Other
crackpots prescribe a hydraulic pump - same basic idea, just as heavy
as a generator, more complicated system, more expensive, plus less
efficient.
You STILL need a generator, but you've added a compressor or hydraulic pump.
You
cited easier maintenance of the generator at ground level - this
implies the wind never dies and your kite remains aloft forever, so you
can never get at the generator. In reality, the wind usually does
not last more than one day at most. You can do maintenance
anytime the wind dies and the craft lands. So that reason is not
valid. Consider the following:
Another
very common "Professor Crackpot" idea is to run a driveshaft all the
way down the tower, complete with carrier bearings etc. for the luxury
of locating a generator at the ground, instead of the top. More
material, more complication, more expense, all the fight the phantom
demon of the imaginary problem that the generator is just too darn
heavy to be supported by that big, strong tower.
In
the case under examination, we COULD place a generator up there in the
sky, but instead we substitute a large pulley, which has weight and
cost and friction, and we double the total tether length, which costs
money and adds weight that must be lifted by the kite, and the tether
must be a little stronger now, to handle that extra pull from the kite
that must be larger to keep it taut, and both upper and lower wheels
lose some power to inefficiency.
So,
in the end, there is no free lunch in wind turbine design. You
will have to use more material, and the kite must be bigger to handle
that extra downward pull, so I'm glad we agree on that. I'm
trying to actually figure out what it is we don't agree on. I
don't think there is anything. It sounds like you started
out with the traditional "Doug is wrong" so commonly seen on this list,
but then explained that you actually agree with what I said: It will
take more upward pull to counter that downward pull, so you need a
bigger kite. And then you have the extra tether weight. If
you thought you needed one mile of tether and it weighs a ton, now you
have two miles of tether and it weighs 2 tons, and that is before it
starts adding that extra downward pull. So yes, that kite keeps
getting bigger and bigger.
Besides
that, I think it is a great idea, and the fact that nobody is building
anything remotely resembling it, even in its most basic functionality,
is part of the mountain of evidence that:
"There ARE NO serious teams in AWE."
:)))
~~ DougS
