Patent Application
20100303623
With the current climate change crisis and energy demand rising, the world is looking for wind power to provide a bigger share of the energy demand. Wind energy is widely available but is a dilute form of energy. Turbine blades have to be large to catch enough kinetic energy from the low density air medium. Energy production is also an economic investment; the bottom line for the success of any wind turbine design, is the cost to power produced ratio ($/kwh).
It is the object of this patent to design a wind wheel style turbine that give a better cost to power ratio ($/kwh) than all the presently available WTG's (Wind turbine generators) by a wide margin. This is achieved through a design that is lighter in weight, uses less expensive materials, easier to manufacture, and at the same time has more mechanical efficiency through minimized losses of energy to air friction, and maximization of lift generated by the wings or the blades.
Wind turbines are of the horizontal or vertical shaft type. Previous vertical shaft turbine designs proved uneconomic and achieved limited success. Common horizontal axis turbine designs have the blades in a self supporting cantilever style (The most common design), or can be supported at the edges by a rim (a wind wheel). The former is the most common wind turbine technology; it is the horizontal axis upwind 3bladed design pioneered by Danish companies, and used all over the world. The later had seen a few patents granted, but had never been utilized on a commercial scale. We propose to use the later type, rather than the former. The deficiencies of the first type will be outlined, as well as the deficiencies in the second, then we show how we remedied these deficiencies in our new invention.
Conventional WTG's use upwind 3 cantilevered blades connected to a low speed horizontal shaft that drives a high ratio gear box that delivers to a high speed [1500-1800 rpm] generator with the same grid frequency.
1—The high center of gravity and the tower cost: This configuration concentrates a lot of the massive components heavy steel hub, nacelle, heavy yaw drive and slew ring, on top of the tower [High Center of Gravity]. This requires the tower to be highly rigid to resists the swinging action of the massive inertia on top of it moved by the wind forces. Our design uses much lighter power transmission components and blades, located half way up the tower height, thus lowering the overall center of gravity of the turbine, allowing a less rigid design, able to bend in excessive wind, and thus is a less expensive tower.
2—The cantilevered blades: The unsupported cantilevered blade configuration, requires a heavy blade root section, to resist the high wind loads on a blade that is 60 m long or more. The root of the blade has to be of exceptionally large cross section to counter the high bending moment, especially if the blade is a variable pitch design. The material of the blade also has to be highly resistant to fatigue. These factors combined narrows the choice of materials to expensive fiber reinforced composites. These also require a very expensive and accurate die to manufacture a 60 meter long blade. Our design uses a conical wind wheel configuration where the blades are supported at the tips by a circumferential ring supported by tension elements or wires, which reduces the bending loads at the blade roots, allowing a lighter section, and other choice of materials of construction.
3—Rotor rpm and the high blade tip velocity: Because the generator has to rotate at 1500-1800 rpm's, and there are economic and practical limits for the gearbox ratio used, there is a minimum rotational speed for the rotor blades that the designer cannot go below. The average current operational speed is 18 rpm for an 80 meter diameter turbine blade. Unfortunately, the tip speed is still fairly high (around 70 m/s) resulting in high frictional [drag] losses to the air. Additionally, the resultant angle of attack between the blade and the wind is very shallow at this tip velocity, which reduces the generated rotational force component. Rotational power from the blades becomes only a small fraction of the total wind power. Therefore, the lower the rotational velocity of the rotor, the more power captured form the wind, and the lower the energy losses at the tip of the blades, which is exactly what we intend to do in our design, without the price offset of a large reduction ratio gearbox.
4—The heavy powered Yaw system: Up wind configuration of such large diameter rotors requires extremely strong and precise yaw ring and ring drive; usually two or four opposite yaw drive gears that rotate the giant nacelle/rotor, against the tremendous gyroscopic forces. Once properly directed facing the wind, the opposite yaw drives lock against each other to take up the slew ring gears' backlash. Due to these factors and complications, the yaw drive/slew ring system cost is a considerable portion of the total cost of a large WTG. Our design requires no slew ring or yaw drive system to orient the turbine into the wind, further reducing the overall cost.
5—Blade pitch system: Similarly, High bending moment of the cantilevered blades, requires a precise and expensive yaw system for each individual blade. Our design uses a new system that does not require a slew ring/yaw drive gear to vary the blade pitch angle.
Several Windwheel patents were presented in the past but not one proved successful, and never brought to production: for the following reasons:
All the above wind wheel designs have two limitations; First, they use near ground supported power take off carriage thus there wind wheel operation is confined to a certain height near the ground. Second, They have up wind positive yaw systems.
The first limitation severely restricts the maximum power that can be captured, because the power drawn is proportional to the cube of the wind speed which in turn decreases as the hub height above ground is decreased. The second limitation adds the cost of the positive yaw system to the total cost of the wind wheel. Our design permits the wind wheel to be installed high above a tower, capturing more of the kinetic wind energy at any specific location. Additionally, our design permits a down wind configuration thus will not require a yaw system at all.
A slowly rotating wind wheel rotates about a shaft supported on a high tower. The semi flexible sails catch the wind and provide rotational force. The rotational force forces the rim to rotate. The shaft supporting the rim is fixed on top of a two piece tower that has bearings to allow the upper half to rotate freely facing the wind direction. Generators are fixed to upper tower and their rubber wheels press against the rim, thus getting the rotational energy from the rim, and transferring it to the generators. Energy is produced inside generators.
The Rim, Hub, and Spokes:
Our design consists of a very large diameter rim (9) connected to a hub (14). The hub (14) and the rim are connected by a multitude of poles or spokes(7). These spokes may be supported by tensile elements or wires(8) at an angle to the spokes on the upwind side of the spokes. The tensile elements thus bear all the large horizontal force generated by the wind, and thus reducing the bending at the spoke root to a minimum. Some of the spokes or poles go through the sails (the lift generating surfaces) (11) chord or the blade's chord and is connected to it such that when the spokes rotate along their longitudinal axis, the sail's angle of attack changes accordingly. The connection between the spokes (10) and the rim or the hub, can be very simple bushings, or a flexible material that allows a certain measure of twist, similar to the root support of a windsurf sail. A slew ring on the wing root is not required. The rim supported by the spokes, with the wings or sails in between, and the wires taking all the horizontal forces of the wind is a very light weight yet structurally stronger design than the cantilevered blades design previously used on upwind wind turbines. It is able to resist very high wind forces, with a very low cost, and ease of manufacturability.
The Wings:
The wings (wind catching sail or blades) (11) other wise called the generating surfaces can be manufactured of aluminum or wood, or like early airplanes with airfoil ribs, covered with canvas or any flexible tension bearing sheets material. The airfoil ribs (12), define the shape of the wing, thus dictating the amount of lift (and drag) generated. No composite material is necessarily required, and the wing sections can be fairly thin as they are supported at both ends, and very slowly rotating, thus improving their lift to drag ratio.
Single or Double Sails:
As an alternative embodiment the wings or blades (11) can be a single or double sheet sails. Inside the sails, airfoil shaped rods (12) can be embedded, thus supporting the flexible material and giving it a shape closely approximating an airfoil shape. This is a cheaper and lighter alternative to a rigid wing, albeit with less efficiency. A good cost to efficiency trade off.
The AOA Changing Mechanism:
This consists of a solid element across the chord of the wing called the beam (6). This solid element is rigidly connected the spoke or the pole carrying the wing, and connected to the wing in one or several points along its length. In the case of using flexible sails, this element is also used to stretch the sails. The solid element can have any section shape that resists bending. The beam is rotated by pulling it with a tensile element or a wire rope (20). Each of the wings' beams is connected by a wire rope that rolls/hinges on a roller (21) fixed to the next spoke (7). The wire ropes run through the spokes to a central point in the hub. All the ropes are pulled together with a control mechanism (22), which can be a spring loaded mechanism, or a fluid actuated pressurized cylinder, or an electrical actuator mechanism. In case of using a fluid actuated cylinder, the fluid pressure inside the cylinder governs the pull of the all the ropes, thus furling the wings in excessive wind speeds, or adjusting to the optimum angle of attack desired to give the best lift relative to the wind speed. The amount of pull on the tensile element regulates the angle of attack of the wings or sails
The Power Take Off Wheels:
These are small diameter friction wheels (14) or gears pressing on opposite sides in contact with the rim (9). When the rim rotates, it causes the wheels to rotate. These wheels are much smaller in diameter relative to the outer rim. Even when the rim rotates very slowly, the wheels rotate at a much greater rpm than the rim—close to the required speed of the electrical generator which is 1500 rpm—thus requiring a very small reduction gearbox if any is needed. The wheels are directly connected to energy converters (15) like electrical generators, pumps, or frictional heat generators that convert the rotational energy of the wheels into useful work, in the form of electricity, heat, or fluid pressure, useful for many commercial processes as well as electricity generation. The energy converters (15) are supported by a support beam (16)
The Tower:
The tower consists of two concentric columns. There are two anti friction bearings (2), or ball/roller bearings; one located on the upper tip of the lower inner column (1), and the other connected inside the lower tip of the upper column (4). The stationary shaft (5) is fixed to the upper tower (4), such that the outer rim lowest part does not go lower than the lower tip of the upper tower, or such that the power takeoff wheels are supported by the lower part of the upper tower, and they rotate with it maintaining the contact with the outer rim.
The Cable or Hoses Anti-Twist Mechanism:
If using generators, cables will run inside the tower. Because the upper tower (4) rotates freely around its longitudinal axis, thus a power transfer slip ring (3) will be utilized to avoid over twisting and damaging the power and control cables. Slip ring devices with the required current and voltage capacities are commercially available, and affordable. If the wind wheel is used to drive gas compressors or hydraulic pumps, a hydraulic distributor similar to the ones used inside the slew ring of rotating hydraulic excavators or other hydraulic construction equipment, will be used to avoid twisting and damaging the hydraulic high pressure hoses if the wind wheel upper tower makes a few full revolutions.
In another option, a chain or brake mechanism can be used to limit the number of full revolutions the wind wheel complete around its longitudinal axis. An alarm is sounded if the safe limit of the cables/hoses is reached, prompting manual untwisting action to be initiated. This is a low budget way to further save the cost of the slip rings, especially if the wind wheel is operating in an area where the wind will very rarely change direction in a way to cause the wind wheel to rotate several full revolutions.
