FIELD OF THE INVENTION

This invention relates to wind energy.

In particular this invention relates to a device for harnessing wind energy.

DEFINITIONS OF TERMS USED IN THE SPECIFICATION

The expression 'betz limit' or 'betz law' states no turbine can capture more than 59.3 percent of the kinetic energy in wind.

The expression 'venturi' in this specification is used to mean a tubular apparatus of varying cross section. A tapering constriction at intervals causes an increase in the velocity of flow of a fluid and a corresponding decrease in fluid pressure. The fluid velocity must increase through the constriction, while its pressure must decrease due to conservation of energy. The gain in kinetic energy is balanced by a drop in pressure.

These definitions are additions to those expressed in the art.

BACKGROUND OF THE INVENTION AND PRIOR ART

As the cost of oil and other fuels rises, the power needs of mankind are becoming costly. Wind energy is one of the many available clean and natural sources of power. Equipment for harnessing wind energy is known. Windmills have been in use for many centuries and were used to harness kinetic energy of moving air. With the discovery of steam engines, internal combustion engines and electricity, the windmills were slowly replaced as a means for garnering nature's energy. The traditional wind mills operate at very low efficiency as only a part of the moving air is swept by the vanes of a wind mill.

Burning of fossil fuels and generation of green house gases harmful to the environment has led to a renewed interest in the use of clean energy sources like wind and solar power. This has led to development of more wind energy harnessing equipment. As the direction of the wind and its velocity are not controllable, it is a common practice to locate the harnessing equipment in regions which have naturally occurring stable wind patterns. This leads to the problem of having to harness wind energy in remote locations and then transmitting the generated power to other locations. To be commercially viable, this type of generation has to be on a large scale necessitating huge investments in remotely located wind turbine farms and distribution equipment.

US Patent US4134707 discloses a wind turbine apparatus with discrete segments which can be added to incrementally increase the driving force and power generation of the machine. One of the side walls along with the rotor defines a venturi to enhance the apparent wind speed. This arrangement though efficient, has a limitation because of its arrangement. The requirement of increased power generation increases the height of the assembly and hence such an arrangement is only possible in locations where space and height is not a restraint.

Further, US patent US4143992 discloses a convergent intake duct with a radial outflow opening through which air accelerated in the duct impinges on airfoil shaped vanes to induce rotation of the rotor on which the vanes are mounted. The duct is formed internally of a tubular airfoil body so that a low pressure region formed on the trailing edge portion of the external airfoil surface increases the pressure differential across the vanes in the radial direction of outflow of the air from the duct. This arrangement aims to reduce frictional losses as well as structural problems with respect to design of blades and ducts. However, the design is not flexible enough to cater to varying demands of power.

Again, US patent application US2007138797 discloses systems and methods of improving the power production capability of a wind farm. As such the arrangement in this disclosure is suitable only for large scale power generation where a large area can be devoted to such an arrangement. Moreover, the need for varying sizes of turbines in accordance with the disclosure increases the inventory and is not conducive to small scale power generation.

US patent application US20080061559 discloses a method for converting kinetic energy of air into electrical energy by allowing the air flow to pass through a convergent or convergent-divergent nozzle, which accelerates the air. The turbine is placed within the nozzle to convert the kinetic energy of the airflow into mechanical energy that is further transformed into electrical energy. This arrangement however involves coaxial shafts for the motor and alternator which could lead to alignment and frictional problems and also add to the material cost. It also lacks flexibility in meeting with an increase or decrease in demand of power.

In view of the above deficiencies in the conventional wind energy harnessing devices there exists a need for developing a better and more suitable equipment to harness wind energy with less installation cost and high output efficiency which can operate in low wind velocity regions and under varying weather conditions.

OBJECTS OF THE INVENTION

One object of the invention is to provide a device for harnessing wind energy.

Another object of this invention is to provide a device for harnessing wind energy that is less capital intensive.

Yet another object of this invention is to provide a device for harnessing wind energy that is suitable for low wind velocity regions.

Another object of this invention is to provide a device for harnessing wind energy that is operable at ground level.

Yet another object of this invention is to provide a device for harnessing wind energy that is easy to install.

Another object of this invention is to provide a device for harnessing wind energy that is easy to maintain.

Yet another object of this invention is to provide a device for harnessing wind energy that is operable under varying weather conditions. SUMMARY OF THE INVENTION

In accordance with a preferred embodiment of the present invention, there is provided a device for harnessing wind energy to provide power to a load, said device comprising:

- a source of AC power connected to an AC motor;

- duct adapted to channelize wind energy;

- a first rotor vane unit connected to the shaft of said AC motor using a belt and pulley arrangement, said rotor vane unit being positioned and supported on a shaft positioned along the axis of said duct; and

- a plurality of rotor vane units each connected to the shaft of an alternator using a belt and pulley arrangement, said rotor vane units being positioned and supported on a shaft positioned along the axis of said duct and faces said first rotor vane unit.

Typically, in accordance with this invention, said duct comprises a plurality of duct sections of uniform cross section connected with flanges.

Typically, in accordance with this invention, said duct is a plurality of Venturis connected with flanges.

Typically, in accordance with the invention, there is provided a device to harness wind energy, said device being adapted to operate on wind power derived as 0.5 x Swept area x Air density x (velocity) ³ . In accordance with a preferred embodiment of the present invention, there is provided a method for harnessing wind energy to provide power to a load, said method comprising the following steps:

- supplying power to an AC motor;

- sucking air into a duct;

- increasing the velocity of the sucked air;

- converting kinetic energy of the moving air to mechanical energy;

- converting the mechanical energy to electrical energy;

- supplying part of the generated electrical energy to the AC motor; and

- , supplying electrical energy to a load.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS

The invention will now be described in accordance with the accompanying drawings, in which:

FIGURE 1 illustrates a sectional elevation of a device for harnessing wind energy in accordance with the present invention;

FIGURE 2 illustrates a sectional elevation of a device for harnessing wind energy in accordance with another embodiment of the present invention; and

FIGURE 3 illustrates a graph representing the relationship between rated power output and motor HP providing the input power in accordance with the present invention. DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The invention will now be described with reference to the embodiments shown in the accompanying drawings. The embodiments do not limit the scope and ambit of the invention. The description relates purely to the exemplary preferred embodiments of the invention and its suggested applications.

The present invention envisages a device for harnessing wind energy. Prior art has disclosed various means for harnessing wind energy in the quest for finding alternative sources of power. However, the known art has not been able to completely utilize the available wind resource and as such has not been very efficient. The amount of kinetic energy of the wind actually getting converted to power is very less because of the limited contact between the flowing wind and the turbine blades. Moreover, in areas with low wind power, this situation is aggravated and it is difficult to convert the available wind power into useful energy. The present invention takes care of this deficiency in the prior art and boosts the kinetic energy of the available natural wind in order to have a more efficient device for power generation.

Betz limit and the following two formulae form the basis of the design of the device in accordance with the present invention.

Formula 1 : Wind power = 0.5 x Swept area x Air density x (velocity) ³ where

Wind power is the power in watts (joules/second) of the wind, Swept area is the area swept by the rotor blades in square meters, Air density is about 1.23 kg/m ³ at sea level and Velocity is the wind speed in meters/second. Formula 2: Motor HP = CFM x static pressure (inches)

(6356 x static fan efficiency) where

Motor HP is the input power drawn by the motor, and CFM is Cubic feet per minute - a non-SI unit of measurement of the flow of a gas or liquid that indicates how much volume in cubic feet passes by a stationary point in one minute.

FIGURE 1 illustrates a sectional elevation of a device for harnessing wind energy in accordance with the present invention and is referenced generally by numeral 100.

The device 100 in accordance with an embodiment of the present invention comprises a duct of uniform cross section 10 supported on a base 12 and provided with support elements 14. The duct is provided with a flange 42 at the rim of the duct sections for ease of assembly. A rotor vane unit 16 is connected to the shaft of an AC motor 18 using a belt 44 and pulley 40 arrangement. The rotor vane unit 16 is positioned and supported on a shaft 46 positioned along the axis of the duct 10. The arrangement and functioning of the device 100 is described using one alternator. However, the number of alternators can be increased depending on the power of the motor 18. An alternator 20 is connected to a rotor vane unit 26 through a belt 44 and pulley 40 arrangement. The rotor vane unit 26 is also positioned and supported on a shaft 38 and faces the rotor vane unit 16. The belt 44 and pulley 40 arrangement provided at the motor end transmits the rotational energy of the motor 18 to the rotor vane unit 16 and that at the alternator end provides the drive for the alternator 20 through the rotor vane unit 26.

To start the operation of device 100, the motor 18 is supplied with power from an external source of AC power to initiate the rotation of the rotor vane unit 16. Wind blowing at a low speed is inducted into the duct 10 though an opening 32. Rotation of the rotor vane unit 16 connected to the motor 18 results in a suction effect and increases the velocity of the moving air current. This air moving with increased velocity in turn drives the rotor vane unit 26 connected to the alternator 20 and acts as a prime mover for the alternator 20. The alternator 20 converts the mechanical energy to electrical energy which can be supplied to an external load. Air inducted into the duct 10 exits through an opening 36 after passing over the rotor vane unit 26.

FIGURE 2 illustrates a sectional elevation of a device for harnessing wind energy in accordance with another embodiment of the present invention and is referenced generally by numeral 200.

The device 200 in accordance with another embodiment of the present invention comprises a venturi 10 of varying cross sections supported on a base 12 and provided with support elements 14. The venturi is provided with a flange 42 at the rim of the duct sections for ease of assembly. A rotor vane unit 16 is mounted on the shaft of an AC motor 18 and is positioned and supported along the axis of the venturi 10. The arrangement and functioning of the device 200 is described using three alternators. However, the number of alternators can be increased or decreased depending on the power of the motor 18. Three alternators 20, 22 and 24 are connected to rotor vane units 26, 28 and 30 respectively. The rotor vane units 26, 28 and 30 are positioned and supported on the axis of the venturi 10. The rotor vane unit 16 connected to the motor 18 faces in a direction opposite to that of the rotor vane units 26, 28 and 30.

To start the operation of device 200, the motor 18 is supplied with power from an external source of AC power to initiate the rotation of the rotor vane unit 16. Wind blowing at a low speed is inducted into the venturi 10 though an opening 32. Rotation of the rotor vane unit 16 connected to the motor 18 results in a suction effect and increases the velocity of the moving air current. This air moving with increased velocity drives the rotor vane unit 30 connected to the alternator 24 and passes through the constriction in the venturi which further increases the velocity of the wind and drives the rotor vane unit 28 connected to the alternator 22. At this stage, the rotor vane unit 16 mounted on the shaft of the motor 18 rotating at its rated speed increases the velocity of the moving air current. Finally the induced air passes over the rotor vane unit 26 connected to the alternator 20 and the vanes of the rotor unit 26 rotate at a high speed. The alternators 20, 22 and 24 convert the mechanical energy to electrical energy which can be supplied to an external load 34. Air inducted into the venturi 10 exits through an opening 36 after passing over the rotor vane units 16, 26, 28 and 30.

Increasing the horsepower (HP) of the motor and / or increasing the number of alternators connected can result in an increase in the power output such that under optimal working conditions, the motor 18 need not be supplied with external power to maintain sustained power output from the alternator(s). Part of the power produced by the alternator(s) is supplied to the motor 18 and the residual power is supplied to the external load. However, with continued operation there is mechanrcal wear and tear and heat is generated, thereby reducing the efficiency of the device and a greater percentage of the generated power will be used up for maintaining said rotation. In order to sustain continuous power generation, the present invention envisages replacement of the worn out parts and thereby ensuring continued operation of the device.

Although the devices 100 and 200 have been described with reference to AC power, the same can also be extended to DC source of power.

FIGURE 3 illustrates a graph representing the relationship between rated power output and motor HP providing the input power in accordance with the present invention.

The values for Motor HP Vs Rated Power Output (HP) based on the aforementioned formulae are as tabulated below:

As can be seen from the graph illustrated in FIGURE 3, the threshold is reached at about 23 HP beyond which the power output exceeds the power input.

This graph is a theoretical representation of the power generated in a pipe of a predetermined diameter. However, in practice, beyond a certain value of wind speed, the power output will plateau. In order to further increase the power output, certain changes such as increasing the diameter of the pipe is required.

TECHNICAL ADVANCEMENT

The power generation device as described in this invention has several technical advantages including but not limited to the realization of:

• a consistent source of power;

• a device that is less capital intensive;

• a device operable in low wind velocity regions;

• a device operable at ground level;

• a device that is easy to install;

• a device that is easy to maintain; and

• a device that is operable under varying weather conditions.

While considerable emphasis has been placed herein on the particular features of this invention, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiments without departing from the principle of the invention. These and other modifications in the nature of the invention or the preferred embodiments will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.