STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
None.
NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT
None.
BACKGROUND
According to the U.S. Department of Energy, modern, wind-driven electricity generators were born in the late 1970′s. See “20% Wind Energy by 2030,” U.S. Department of Energy, July 2008. Until the early 1970s, wind energy filled a small niche market supplying mechanical power for grinding grain and pumping water, as well as electricity for rural battery charging. With the exception of battery chargers and rare experiments with larger electricity-producing machines, the windmills of 1850 and even 1950 differed very little from the primitive devices from which they were derived. As of July 2008, wind energy provides approximately 1% of total U.S. electricity generation.
As illustrated in FIG. 1, most modern wind turbines typically have 3-bladed rotors 10 with diameters of 10-80 meters mounted atop 60-80 meter towers 12. The average turbine installed in the United States in 2006 can produce approximately 1.6 megawatts of electrical power. Turbine power output is controlled by rotating the blades 10 around their long axis to change the angle of attack (pitch) with respect to the relative wind as the blades spin around the rotor hub 11. The turbine is pointed into the wind by rotating the nacelle 13 around the tower (yaw). Turbines are typically installed in arrays (farms) of 30-150 machines. A pitch controller (for blade pitch) regulates the power output and rotor speed to prevent overloading the structural components. Generally, a turbine will start producing power in winds of about 5.36 meters/second (12 miles per hour) and reach maximum power output at about 12.52-13.41 meters/second (28-30 miles per hour). The turbine will pitch or feather the blades to stop power production and rotation at about 22.35 meters/second (50 miles per hour).
In the 1980s, an approach of using low-cost parts from other industries produced machinery that usually worked, but was heavy, high-maintenance, and grid-unfriendly. Small-diameter machines were deployed in the California wind corridors, mostly in densely packed arrays that were not aesthetically pleasing in such a rural setting. These densely packed arrays also often blocked the wind from neighboring turbines, producing a great deal of turbulence for the downwind machines. Little was known about structural loads caused by turbulence, which led to the frequent and early failure of critical parts. Reliability and availability suffered as a result.
A dominant factor driving development of wind turbine technology is a desire for increased power production. Where wind turbines are intended to reduce carbon emissions that would otherwise occur from the burning of fossil fuel, high power output means a greater reduction in carbon emissions. Increasing power production typically reduces cost of generation of electricity by allowing fixed costs to be spread over a larger amount of variable power production.
One factor affecting the power output from a wind turbine is rotor size. In a typical, 3-bladed, horizontal axis wind turbine, the amount of energy available to be captured depends on the sweep area of the rotor blades. The greater the sweep area, the greater the potential amount of energy in the wind that could be captured. As of August 2009, rotor blades may exceed 100 meters in length.
Another factor affecting the power output from a wind turbine is efficiency, that is, the percentage of available power in a given cross section of wind that the turbine actually captures. It is generally believed that horizontal axis wind turbines that have their axis of rotation parallel to the direction of the prevailing wind have better efficiency than transverse-axis wind turbines. So-called “horizontal axis” wind turbines have rotors with an axis of rotation that is horizontal (i.e., parallel to the earth's surface) and typically parallel to the direction of the prevailing wind. So-called “vertical axis” wind turbines typically have rotors with an axis of rotation that is vertical (i.e., at right angles to the earth's surface) and typically perpendicular to the direction of the prevailing wind. Wind turbines that have rotors with an axis of rotation perpendicular to the direction of the prevailing wind are often called “transverse axis” wind turbines, regardless of the orientation of their axis of rotation.
SUMMARY
An object of the invention is to provide a wind turbine for deployment in high-visibility areas. Other objects of the invention include:
- 1. providing a transverse axis wind turbine; and
- 2. providing a wind turbine with integrated photovoltaic cells.
These and other objectives are achieved by providing a transverse axis wind turbine with a visual envelope suggestive of a flame. Blades of the wind turbine preferably have a curvilinear envelope that tapers near a tip end and wrap around the axis of rotation. The cross section of such a wind turbine typically would be smaller than that of a wind turbine with a rectangular cross section having the same maximum width and height. A preferred wind turbine includes an electric generator and may optionally include photovoltaic cells that store energy in a battery, capacitor, or other storage device. A preferred wind turbine also includes a connection for transmitting electrical power.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
Reference will be made to the following drawings, which illustrate preferred embodiments of the invention as contemplated by the inventor(s).
FIG. 1 illustrates a prior art wind turbine.
FIG. 2 is a side view of a decorative wind turbine.
FIG. 3 is a top view of the wind turbine if FIG. 2.
FIG. 4 is a cut-away side view of the wind turbine if FIG. 2 illustrating a location of an electrical generator.
FIG. 5 is a side view of a blade for a decorative wind turbine.
FIG. 6 is a perspective view of a decorative wind turbine with a mount bearing photovoltaic cells.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 2 is a side view of an exemplary, decorative wind turbine. Visually, a preferred turbine has an overall appearance suggestive of a candle or other flame. This can be accomplished by providing a vertical axis rotor with a bottom end (along the axis of rotation) having a generally wider visual cross section, a top end having a generally narrower visual cross section, and a curvilinear envelope. The widest visual cross section may be in the middle. For purposes of description, an exemplary turbine will be described as having a base end and a tip end with an implication that the turbine frequently will be oriented with the tip end up and the bottom end down to be suggestive of the way a candle or other flame often has a wider base, an even wider center, and a narrower tip than the both. This orientation is not required. The visual cross section may broadest in the middle, but preferably tapers to a relatively narrow tip.
Structurally, an exemplary turbine includes a rotating part (rotor) and a fixed part. The rotating part includes blades 20a, 20b, 20c, 20d and, optionally, a rotating housing 22. The blades 20a, 20b, 20c, 20d preferably attach at their root (base) ends to a rotational housing 22. The blades 20a, 20b, 20c, 20d may connect together at their tip ends through a cap or fineal 27. (The term “fineal” is used here to mean any structure—preferably but not necessarily decorative—used to join tips of blades. A fineal may alternately be a plate or other shape.) FIG. 2 illustrates a turbine with four blades, but differing numbers of blades may be used. The fixed part of the turbine usually will include a base 24 and, optionally a fixed housing. The base 24 may include a central post 25 and a disc-shaped horizontal plate 26, though other supporting arrangements may be used.
Aerodynamically, the blades 20a, 20b, 20c, 20d are adapted to rotate about a central axis that extends from the cap or fineal 27 to a centroid of the housing 22. The blades 20a, 20b, 20c, 20d and cap or fineal 27 preferably provide sufficient structural strength that no central axel is required. Frequently, the axis of rotation will be perpendicular to the ground, and blades will be adapted to rotate in the presence of a wind traveling in a direction parallel to the ground, making it a so-called transverse axis wind turbine. In a preferred embodiment, the blades 20a, 20b, 20c, 20d, housing 22, and cap or fineal 27 are joined together and rotate as a single unit. Alternately, the blades may couple to a non-rotating housing or other structure through a bearing.
When viewed from the side as in FIG. 2, the blades 20a, 20b, 20c, 20d have a visual envelope that is not rectangular. The envelope can be thought of as the outline of the silhouette, the shadow the blades would cast on a wall, or in mathematical terms, as an outline of a projection of the blades onto a plane parallel to the axis of rotation. In the example of FIG. 2, the envelope is curvilinear, which here means that at least a portion of the envelope is curved rather than a straight line. The envelope has a height denoted in FIG. 2 as line segment H-H. The envelope has maximum width at points denoted in FIG. 2 as arrows MW. The area of the envelope is less than the area of a rectangle of the same height and maximum width. The curvilinear envelope reduces the cross section of wind that engages the turbine blades, which in turn reduces the total amount of power that potentially could be captured when compared to a turbine with a rectangular envelope of equal height and maximum width. The minimum width of the envelope at the tip may be less than 50%, 25%, or even 10% of the maximum width depending: on the number of blades; the overall height, width, and other dimensions of the turbine; and other factors.
FIG. 3 is a top view of the wind turbine of FIG. 2 showing a view of blades 20a, 20b, 20c, 20d, housing 22, base plate 26, and cap or fineal 27. FIG. 3 designates two points 28, 29 along the leading edge of one of the blades 20a. The leading edge of the blade 20a attaches at its tip to the cap or fineal 27 at a first point 28. The leading edge of the blade 20a attaches at its base to the housing 22 at a second point 29. In FIG. 3 it can be seen that the point of attachment to the cap or fineal 27 is advanced approximately 90 degrees around the central axis of rotation. The degree of advancement may be 45 degrees, 90 degrees, or more than 180 degrees depending on the number of blades, the overall turbine geometry, and other factors. The degree of advancement may mean that different portions of the blade engage with the wind at different times to cause a torque to rotate the rotor. This has an effect of smoothing out the torque over time when compared to transverse axis turbines with straight blades. In such straight-bladed turbines, torque impulses are more discrete as an individual blade moves into and out of its orientation of maximum torque.
The term “leading edge” here is used here only as a convenient point of description to refer to the point of attachment. It is the side of the blade facing into the direction of the prevailing wind when on the downwind part of its rotational cycle. When the blade is on the downwind part of its rotational cycle, the “leading edge” would be facing opposite the direction of the blade's travel. The term is not intended to require the blade to operate at any particular velocity relative to the prevailing wind. Where the point of attachment of the tip is greater than 180 degrees, one portion of the blade may be on an upwind leg while another portion of the leg may be on the downwind leg of rotation. The leading edge may be identified by choosing any portion of the blade while on the downwind leg.
As can be seen in FIG. 2, the advancement of the point of contact at the blade tips contributes to a visual appearance suggesting a flame. FIGS. 1 and 2 also illustrate that the blades 20a, 20b, 20c, 20d become narrower toward the tip, which further contributes to the visual appearance of a flame.
FIG. 4 is a cut-away side view of the wind turbine of FIG. 2 illustrating a location of an electrical generator 30. The generator 30 preferably has a rotor coupled through a flange 31 to the rotational housing 22 or other rotational structure that in turn couples to the blades 20a, 20b, 20c, and 20d. The generator 30 preferable has a stator coupled through a casing mount 32 to the central post 25 or other non-rotating structure. The housing 22 is clear to rotate with the blades 20a, 20b, 20c, 20d without interference from the casing mount 32 or other fixed structure. The generator 30 preferably has bearings sufficient to support the axial (weight) load and lateral (side) stresses of the blades 20a, 20b, 20c, 20d and other rotational components. The housing 22 preferably is weatherproofed to shield the rotor and other electrical components, such as electrical storage device, fuses, wiring, connectors, etc., from rain and other elements.
FIG. 5 is a side view of a blade 40 for a decorative wind turbine. The blade has a root end 41 and a tip end 42. The blade also has a leading edge 43 and a trailing edge 44. The blade chord (cross section taken in a direction from the leading edge to the trailing edge) is wider at the root end 41 than at the tip end 42. When viewed in a static position as in FIG. 5, it can be seen that blade has a twist along its length from the base end 41 to the tip end 42. The orientation of a blade chord at the tip end 42 is advanced around the axis of rotation relative to the orientation of a chord at the base end 41.
FIG. 6 is a perspective view of an alternate, decorative wind turbine integrated with photovoltaic cells 53. Here, the photovoltaic cells 53 attach to a top surface of a base plate 54. The base plate 54 couples to a mount 55, which may be a hollow cylinder adapted to fit onto a cylindrical post (not shown). A set screw 56 locks the mount 55 to the post. The mount may attach to the base plate 54 with reinforcing brackets 57, welds, or other attachments. Other mounts may be used according to installation site. For example, the mount may be made integral to fence posts, lamp posts, or any other object.
In the embodiment of FIG. 6, the housing has two parts. A domed top part 51 a couples to and rotates with the blades 50a, 50b, 50c, and 50d. A cylindrical bottom part 51b couples to the base plate 54 and remains stationary. The top and bottom parts couple to one another through a bearing. A generator (not shown) is located within the housing 51a, 51b. The generator rotor couples to the housing top part 51a. The generator stator couples to the housing bottom part 51b. The cap or fineal 52 of this embodiment is a disc.
The embodiments described above are intended to be illustrative but not limiting. Various modifications may be made without departing from the scope of the invention. The breadth and scope of the invention should not be limited by the description above, but should be defined only in accordance with the following claims and their equivalents.
Patent Application
20100140950
