Aeronautics and astronautics – Kites
Reexamination Certificate
2001-08-29
2003-02-25
Jordan, Charles T. (Department: 3644)
Aeronautics and astronautics
Kites
C244S030000, C244S033000
Reexamination Certificate
active
06523781
ABSTRACT:
BACKGROUND—FIELD OF INVENTION
The field of this invention relates to devices that produce useful work from wind energy, and more specifically devices that extract energy from the wind using tethered kite structures.
BACKGROUND—WIND ENERGY
Collecting energy from the wind has been well know for more than 1000 years. However, nearly all wind energy has been collected near the ground. In recent years several designs have been proposed to take advantage of wind at higher elevation. The advantage of using high elevation wind is two-fold. First, wind speed is greater because boundary layer effects at the surface have less effect at high elevation. Second, there is a much greater volume of air flowing above 300 feet than below this elevation. In general, wind speeds increase with increasing elevation, however, the relationship is not always stable and can be much higher at night due to uncoupling of the air stream. According to the National Weather Service, average wind speed in the US is three times faster at 853 feet than at 15 feet.
Estimating total wind energy is difficult because not all available wind is economical to capture, plus, there is no consensus from the scientific community on exactly how much total available wind energy there is. Estimates of total wind energy is placed somewhere between 0.25 percent and 3.0 percent of the total solar radiation intercepted by the earth (Solar total=10
18
kWh/year, 1% Solar Total=10
16
kWh/yr). It is estimated that a practical wind energy of 20×10
12
kWh/year could be recovered over strategic land areas, and would represent a 4% land utility and 23% capacity factor for standard wind turbines. This translates into a savings of 100 million barrels of oil per day, should all this potential be exploited. The proposed Lift-Mode Linear Wind Turbine (or simply Linear Turbine or Lift Turbine), has far more wind energy available to it than a standard wind turbine. This is because can it operate economically in very low wind speeds, and can collect energy from the wind well above 300 feet elevation, and possibly to 3,000 feet, with similar heights over water. Since wind energy increases with the cube of air speed, higher elevation wind would have a much greater mean energy density than wind near the ground, and have a much greater volume of air available to it. The Linear Turbine is also well suited to operation at sea because of its low center of gravity and very low turning moment. The result is that wind energy available to a Linear Turbine is enormous. For comparison, world energy usage is 400×10
15
Btu per year or about 1.2×10
14
kWh/year including coal, oil, and gas. A conservative estimate of wind energy available between 300 and 3,000 feet elevation is 10
15
kWh/year or about 10% of the total available wind energy. Most of this wind is high energy density (above 300 W/m
2
), and viscose interactions within the air flow would allow drag effects to recover wind energy well above 3,000 feet as multiple systems slow the entire air stream. If 10% of this available energy was recovered (10
14
kWh/yr), there would be enough energy to displace nearly all current world energy usage.
SUMMERY
The linear wind-turbine disclosed here has many advantages over all other wind generation system. The power density of the disclosed invention is over a hundred times greater than other prior art self-erecting wind energy systems. Systems such as those disclosed by inventors Carpenter, Lois, Loeb, Ockels, and Payne all operate at below ambient wind speed, and would produce 100 times less power than the Applicant's linear wind-turbine of similar size. Though the high-speed systems disclosed by Loyd and Payne use high-speed flight to capture wind energy, they do it in such a way that makes them unworkable by placing large-complicated machinery in its air vehicle or using pulley systems that make control nearly impossible.
The Applicant's linear wind-turbine system operates under novel physical principles and is the only known example of a greater-than-ambient-wind-speed energy device that collects wind energy by movement in the AXIAL direction. The AXIAL direction being defined as the direction perpendicular to the airfoil's flight direction (not including the AXIAL movement itself), in the same plane as the LIFT and DRAG force vectors. For the special case where the airfoils rotate about a fixed point (see ground station
30
in FIG.
2
), the AXIAL direction is in the same direction as the radial vector in spherical coordinates with its vertex centered at the fixed point (pivot point of control lines in ground station
30
). For other non-spherical systems, such as Payne's design U.S. Pat. No. 3,987,987, the AXIAL component is simply the component of LIFT perpendicular to the airfoil's flight path which does no work in Payne's design. AXIAL wind-turbines represent a completely new way of collecting wind energy. The combination of AXIAL energy collection and high-speed operation, provide the linear wind-turbine system with advantages that no other system can match, i.e. extremely light-weight devices, simple flight controls, and very-high power density.
Snow and ice would stop any low power wind kite system, but the disclosed design has the high power density that can handle nearly any adverse weather. Other advantages include high elevation operation which makes available the collection of energy from a much larger percentage of the total wind energy on Earth. Expensive components of the Linear turbine remain on the ground and protected, only the airfoils are exposed, with all heavy components of the system placed on the ground. This allows buoyant airfoils to be used. Also, because of the very low center of gravity for the system, it can easily be placed at sea with the addition of a few control systems to compensate for the added rocking motion of the platform due to waves. Since the control system is already designed to handle a wide range of control line movement, making the flight control system insensitive to rocking and rolling of the ground station (sea station) is relatively straightforward. The design allows easy lowering the buoyant kites by either reeling them in or by controllably flying the kites to the ground for easy replacement or repair.
PRIOR ART
Many lighter-than-airships have been proposed for collecting this energy; but lifting an entire windmill and generator into the sky is expensive at best. These large airships are also susceptible to damage even in mildly strong winds making this type of system an extremely uneconomical method of collecting the wind energy.
Lois U.S. Pat. Nos. 3,924,827 & 4,076,190, Loeb U.S. Pat. No. 4,124,182, and Carpenter U.S. Pat. No. 6,254,034 B1 disclose devices for collecting wind energy using airfoil wings which produce drag for playing in and out a line attached to a pulley. While these inventions look similar to the Applicants invention, they are in fact missing key structures needed to allow the approximately 100 fold increase in power density that the Applicant's invention provides. Lois, Loeb and Carpenter use drag wind force on the kites (airfoil, wing, aircraft) to produce power, with lift coming from wind flowing around the kite. Lois, Loeb and Carpenter all realize maximum power at kite speeds equal to approximately one-third the wind velocity. These kite designs operate due to drag forces from direct wind resistance created by the wing. This operating criteria greatly limit the amount of energy collected because the kite must move generally in the direction of the wind. Carpenters design attempts to maximizes this drag by placing the airfoil (aircraft) at an angle-of-attack just beyond aerodynamic stall where turbulent airflow around the kite (aircraft) would create significant drag (called lift by Carpenter) to force the kite to move downwind. The Applicants invention on the other hand operates the airfoil (kite) at high-speed, with its airfoil moving substantially perpendicular to the wind stream (Lois, Loeb and Carpenter
Holzen Stephen A.
Jordan Charles T.
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