The three drawings for the following document from John V. Mizzi
are in a PDF served at
http://www.energykitesystems.net/JohnVMizzi/gtdrawings.pdf
GOSSIMER TITAN
a titan of energy
over
deep water away
from congested shores
giant gossimer wings
caress the wind
offering our lifeblood
KEY CONCEPTS
*
Counter-intuitive approach to implementing very large deep water
offshore wind energy conversion systems by focusing on minimal life
cycle costs.
*
Making this work depends on consideration of all phases of system life
from pre-deployment to operation and maintenance to decommissioning.
*
Inherent to system design is loose subsystem coupling to permit
separate optimization of subsystem parameters resulting in better
overall system outcomes.
INTRODUCTION
Evaluation of computer models should point the way to an ideal size and type for this
WECS by relating various component subsystem parameter tradeoffs. Conceptually it is a giant
system, while the airfoils are ethereal in appearance.
The
concept calls for a tethered system using two airfoils. The IP basis
for this concept is US patent number 6555931 as well as US patent
number 8395271. This system is designed specifically for deep water
offshore deployment with the aim of minimal lifecycle cost for
generation of electricity or equivalent energy as desired. While energy
storage is not addressed directly, this concept is as compatible with
such considerations as other WECS designs commonly considered.
This
short paper will present an overview of some preliminary ideas to be
explored by appropriate models and then, if any pass muster, by
physical small scale models and further evaluation.
DESIGN SUMMARY
Gossimer Titan will be described in summary as well as by specific designs suggestions as in the attached figures.
The
arguments for the use of a tethered wind energy conversion system
(WECS) for deep water offshore deployment are presented in the
Background section of US patent 8395271 entitled,
Pass-Through PTO Mechanism for Renewable Energy Systems. Not least of
these reasons is the elimination of the tower structure.
Very
strong ropes of UHMWPE or aramid fibers have been manufactured now for
over half a century. More current developments as offshoots of DOD or
NASA projects have exceeded their performance. Current research such as
the use of silica nano fibers may also contribute to improved tether
and/or airfoil fabrics for Gossimer Titan.
Although
not limited to generating electricity, this WECS design will be
described as such in this introductory paper. One can envision a
closely analogous system that primarily compresses air; this would be a
natural to integrate with deeply submerged energy storage bags.
As
described in patent 6555931, this is a two-airfoil design of the
long-stroke (perhaps over 1000') variety. Simply put, while one airfoil
is harvesting wind energy, the other can be rewound (ie.- in a
parasitic mode); both airfoils are connected to a single generator. In
this manner, the duty cycle of the generator is greatly enhanced above
the 50% mark. The single large generator may be a candidate for a
superconducting design which may not be cost-effective for one operated
by a single airfoil with less than 50% duty cycle.
Note
that size and weight of the mechanical and electrical devices is of
little consequence to Gossimer Titan as compared to the situation
inside the nacelle of a typical modern wind turbine. The parts and
subsystems can be optimally configured on a floating platform for
function as well as ease of service. This permits the use of lower cost
materials that would surpass the weight and/or size constraints of
nacelle placement.
The
use of a pass-through PTO mechanism as opposed to a power drum or
capstan for tether handling can either eliminate or at least simplify
the gearbox.
The
airfoils can be separately optimized and easily integrated with the
rest of the WECS. A two section hybrid airfoil design for Gossimer
Titan is suggested. It has a very large area drag section for
generating pull simply “before the wind” with a separate lift airfoil
section which can be an air-buoyant element. The drag section can be
“opened” and “closed” directly by wind energy to facilitate the
transitions from and to energy harvesting mode greatly reducing the
“local” energy required at the airfoil. This “local” energy can be
simply harvested locally eliminating the need for conductive tethers.
Much airfoil design will depend on life-cycle cost/performance
considerations.
A mechanical schematic design for anchor and floating platforms is also presented for consideration.
SPECIFIC DESIGN SUGGESTIONS
Figure
1 shows a top view of a mechanical layout for the generating equipment
(on an anchored floating platform) of Gossimer Titan. If you refer to
figure 13 of patent 8395271 and the descriptive text toward the end of
the Detailed Description section, you would realize that figure 1 of
this document is a merging of two PT-PTO subsystems of the patent’s
figure 13 to drive a single generator 138. Each PT-PTO handles one of
the two hybrid airfoils. This is just a high level schematic
representation, but it should describe the general intent.
Figures
2 and 3 describe the suggested airfoil design which is a hybrid pair
with a lift airfoil and a separate drag airfoil. The general design
avoids the problem of air abrasion encountered by smaller “high
efficiency” airfoils sweeping large areas at high speeds in figure-8
patterns as used in other tethered WECS. Figure 2 shows a hybrid
airfoil in its energy harvesting configuration. The drag airfoil is
shown as a parachute structure of very light but reinforced canopy
material with multiple canopy lines emanating from a bridle; this is a
tension loaded design. The entire canopy can be permitted to rotate
around the central rod to prevent canopy line entanglement by
adding a bearing at the bridle as well as at the canopy latch plate at
the rod end stop. The main tether which produces the pull for the
energy conversion is attached to the powered bridle winch housing The
lift airfoil is a high lift/low drag shape which adds some lift to the
main drag airfoil. This lift airfoil can be morphed into a hydrogen
inflatable structure to keep the drag canopy out of contact with the
ocean surface even in still no-wind conditions. Alternatively,
occasional contact with water surface can be designed to be acceptable.
The rewind motor pull force should be sufficient to keep the hybrid
airfoil aloft even in a dead calm. Another function of the lift airfoil
is to steer the two hybrid airfoils laterally away from each other so
as to prevent touching or tangling of tethers especially as the two
airfoils pass each other, one outgoing and the other incoming.
Figure
3 shows the de-powering or “rewind” configurations of the drag airfoil.
These configurations produce low pull on the tether due to the
small area crossection presented to the wind. To start this mode, the
bridle is signaled to release from the bridle latch plate (one can
imaging a solenoid latch release). The wind should blow the canopy
forward pulling the bridle along the central rod to latch onto the
canopy latch plate while the canopy flies loosely forward. At this
point, the rewind motor can be engaged to rewind the main tether of
this airfoil. The bridle winch is now started; this uses the locally
harvested stored energy. The winch winds back the bridle winch line
thereby moving the “closed” canopy back up the central rod by moving
the combined bridle and attached canopy latch plate. This action keeps
the canopy closed while moving it back so that the bridle now also
latches onto the bridle latch plate at the winch housing. When a signal
is received, the canopy latch plate is released from the bridle; the
wind blows the canopy “open” to restart the energy harvesting phase as
depicted in figure 2. Thus the only electrical energy expended at the
airfoil is to power the unlatch “solenoids”, the signal communications
receiver, and the winch moving a closed canopy a short distance.
Obviously, the opening of one airfoil is coordinated with the closing
of the other but the triggers may not be simultaneous for
maximizing harvested energy.
Figure
4 is a high level mechanical schematic of the various parts of the
anchor system and a populated equipment platform. No attempt at
actually showing the support platform shape nor the hundreds of missing
details (such as waterproofing and housings) has been made. The main
purpose of figure 4 is to show a possible relationship between a
submerged anchor platform and a surface floating equipment platform as
joined by a hollow attachment column for Gossimer Titan.
The
buoyant submerged anchor platform is anchored to the sea bottom by
weighted cables; alternatively the cables can be actually attached to
the seabed via simple robotic mechanisms. It has floatation elements
(F) to position it in a level attitude several feet below the surface
of the water. A gimbal mount or spherical bearing in the center of the
anchor platform is attached to the bottom end of the hollow attachment
column. This attachment prevents the hollow column from moving
laterally and from rotating; it is, however, permitted to tilt.
The
top end of the hollow attachment column rises through a hollow platform
riser attached in some central region (not necessarily the
geometric center) of the floating equipment platform. Since the
equipment platform will move vertically with the tides and with swells
as well as tilt with wave motion and tether pull variations, the
distance between the bottom of the equipment platform and the top of
the anchor platform will vary. The top distal end of the hollow
attachment column is rigidly attached to a column cap (and slip ring
mount) in the shape of an inverted cylindrical cup. This is able to
ride on the outer surface of the platform riser due to an internal
bearing sleeve attached to the column cap. The vertical travel
capability should keep the column cap from hitting the top surface of
the equipment platform at its lowest elevation from the seabed; as
well, it should also keep the column cap from losing contact with the
top of the riser at the highest platform elevation. The internal
bearing sleeve also permits the equipment platform to rotate relative
to the column cap (which is constrained from rotating due to its
attachment to the hollow attachment column). In this way, the
equipment platform can simply rotate on the water surface to align
itself with the pull forces from the airfoil attached tethers and
follow the possibly shifting winds. To accommodate this relative
rotation and maintain electrical attachment to equipment on the
platform, slip rings mounted on the outer surface of the column cap are
used with slip ring shoes which rotate with the platform and which are
permitted movement along the column cap to maintain contact during
rotation, vertical movement, or tilting of the equipment platform. Note
that the submarine cable to off-load the electrical output is guided
through the hollow attachment column and electrical connections at its
top distal end are made to the slip rings. The slip ring shoes are
connected to platform equipment through flexible cables.
These design suggestions are “talking points” to give some gravitas to the general concept of Gossimer Titan.
John V. Mizzi, P.E.
Poughkeepsie, NY
22 FEB 2013
