WO2012167015A2

WO2012167015A2 - Offshore hybrid wind-wave power plants

Info

Publication number: WO2012167015A2
Application number: PCT/US2012/040369
Authority: WO
Inventors: Gregory M. MATZAT
Original assignee: Alternative Current Corp.
Priority date: 2011-06-03
Filing date: 2012-06-01
Publication date: 2012-12-06
Also published as: WO2012167015A3

Abstract

Disclosed is an offshore hybrid wind-wave power plant, which includes, inter alia, a base substructure that has a tubular support element that defines an internal chamber. At least one water inlet is formed in the base substructure and is positioned below mean water level such that a water column level within the internal chamber oscillates with each passing wave. The offshore hybrid wind-wave power plant of the present invention also includes a wind turbine for generating wind power. The wind turbine is supported by a tower structure that extends vertically from the base substructure. Moreover, a generator is operatively associated with the internal chamber defined in the base substructure such that the generator creates power based on the oscillating water column within the base structure.

Description

OFFSHORE HYBRID WIND-WAVE POWER PLANTS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of the following U.S. Provisional

Application No.: 61/493,062, filed April 22, 2011, the contents of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0002] The subject invention is directed to hybrid systems and methods for generating energy from wind and wave power, and more particularly, to offshore wind-wave power plant constructions, and still more particularly, to power plant constructions that includes a wind turbine and a wave power generation apparatus associated with the foundation/structure used to support the wind turbine offshore.

2. Background of the Related Art

[0003] Renewable energy resources such as solar power, wind power and wave power are seen as beneficial in reducing the risks of atmospheric pollution and change to the earth's climate which may arise from the extensive use of fossil fuels, and also in reducing dependence on fuel resources which may become expensive or scarcer in future.

[0004] Ocean waves are one of the most abundant sources of renewable energy, and provide a much larger energy density than either wind or solar power. However it has not been found easy to harness wave power; this is partly because any device suitable for extracting wave power from the open sea must be sufficiently strong to withstand storms in which the wave power is much greater than normal. [0005] There are five primary types of wave energy converter (WEC) designs: point absorbers, attenuators, overtopping devices, oscillating wave surge converters and oscillating water columns. The marine environment in which WECs must operate is harsh. Existing WEC designs typically involve a structure that is submerged and/or a float, making them susceptible to corrosion, biofouling and damage due to storm waves.

[0006] The oscillating water column (OWC) has become a very popular method of converting wave energy into electrical power, whether as a shore-based device, such as that disclosed in U.S. Patent No. 5,191,225 to Wells or a floating device, such as that disclosed in U.S. Patent Application Publication No. 2010/0025996 to Edwards et al. The disclosure contained in each of these patent publications is incorporated herein by reference.

[0007] In operation, the water level oscillates up and down within a water column as the crests and troughs of the waves pass through the water column. If this oscillating water level is made to take place in a structural column opened at both ends, the air column above the water oscillates in a similar manner and, thus, wave energy is thereby converted into low pressure, high volume air flow. Energy is then extracted from the moving air by a self- rectifying Wells turbine, for example, in which rotation is unidirectional regardless in which axial direction air is flowing. In essence, the Wells turbine is essentially operated as a wind or aero turbine. The working interface is therefore between water and air, and air and rotor blades. The turbine reacts to the low pressure air stream which is far less destructive than directly absorbing the powerful impact force of sea waves. The efficiency of energy transfer between the wave and the air is high if not total whilst the energy transfer efficiency at the air/rotor blade is very much dependent upon good design and efficient management of the energy transfer itself. [0008] A disadvantage of many prior offshore wave power generation designs, such as the PowerBuoy® by Ocean Power Technologies (OPT) Corporation or the design disclosed in and U.S. Patent No. 6,766,643 is that they include moving parts which are in contact with the seawater and therefore are very susceptible to corrosion, fouling and failure. For example, in the PowerBuoy® design, which is illustrate in Figs, la and lb, annular float 10 bobs up and down with the waves around a mostly submerged support structure 20, working an internal plunger 30 that is connected to a hydraulic pump. The joints 25a-c which connect the float 10 to the support structure 20 and plunger 30 are in frequent contact with the seawater and therefore, are susceptible to corrosion and failure.

[0009] Other designs such as the one disclosed in U.S. Patent Application

Publication No. 2010/0025996, which is herein incorporated by reference, include a floating platform or support structure which is not capable of surviving large storm waves.

[00010] Therefore, there is a need for a system for harnessing offshore wave energy which is simple to manufacture, cost effective, can survive large storm waves, requires a minimal amount of maintenance and can be readily adapted to existing offshore wind power plant constructions.

SUMMARY OF THE INVENTION

[00011 ] The present invention is directed to an offshore hybrid wind-wave power plant, which includes, inter alia, a base substructure that has a tubular support element that defines an internal chamber. At least one water inlet is formed in the base substructure and is positioned below mean water level such that a water column level within the internal chamber oscillates with each passing wave. Those skilled in the art will readily appreciate that the number of tubular support elements, internal chambers and water inlets can vary without departing from the inventive aspects of the present disclosure. For example, depending on the type of substructure used in the design, the number of internal chambers which contain an oscillating water column used for wave power generation, can be increased or decreased based on for example the number of support legs used in the substructure.

[00012] The offshore hybrid wind- wave power plant of the present invention also includes a wind turbine for generating wind power. The wind turbine is supported by a tower structure that extends vertically from the base substructure. Moreover, a generator is operatively associated with the internal chamber defined in the base substructure such that the generator creates power based on the oscillating water column within the base structure.

[00013] In a preferred embodiment, the offshore hybrid wind- wave power plant of the present invention further includes a foundation element for securing the base substructure to sea bottom.

[00014] It is envisioned that the base substructure can be, for example, a monopile structure, a jacket structure, a tripod structure, or a gravity base structure.

[00015] In an embodiment of the present invention, the oscillating water column compresses and expands air contained within the internal chamber formed in the tubular support element of the base substructure and the compression and expansion of the air is used to move a piston element associated with the generator.

[00016] Preferably, the offshore hybrid wind- wave power plant further includes an air duct in communication with the internal chamber defined in the base substructure. In certain constructions the generator includes a piston positioned with the air duct and piston driven gearbox. [00017] Alternatively, the generator can include a bi-directional turbine or a pneumatic power generator operatively associated with the internal chamber. It is envisioned that the bi-directional turbine can be a Wells turbine.

[00018] As will be readily appreciated, the preferred embodiments of the present invention are more cost effective than prior art designs/constructions because they leverage the structure and infrastructure of existing offshore wind farms, taking advantage of their foundation structure and electrical grid.

[00019] These and other features and benefits of the subject invention and the manner in which it is assembled and employed will become more readily apparent to those having ordinary skill in the art from the following enabling description of the preferred embodiments of the subject invention taken in conjunction with the several drawings described below.

BRIEF DESCRIPTION OF THE DRAWINGS

[00020] So that those skilled in the art to which the subject invention appertains will readily understand how to make and use the systems and methods of the subject invention without undue experimentation, preferred embodiments thereof will be described in detail hereinbelow with reference to certain figures, wherein:

[00021] Fig. 1A provides an elevation view of the Ocean Power Technologies (OPT)

PowerBuoy®;

[00022] Fig. IB provides a perspective view showing the PowerBuoy® offshore;

[00023] Fig. 2A provides a side elevational view of a typical monopile structure design; [00024] Fig. 2B provides a side elevational view of a typical gravity base structure design;

[00025] Fig. 2C provides a side elevational view of a typical jacket structure design;

[00026] Fig. 2D provides a side elevational view of a typical tripod structure design;

[00027] Fig. 3 provides a side elevational view of a first embodiment of the hybrid wind-wave power plant of the present invention;

[00028] Fig. 4 is an enlarged elevation view of the lower portion of the hybrid wind- wave power plant of Fig. 3;

[00029] Fig. 5 is an enlarged elevation view of the lower portion of a hybrid wind- wave power plant which has been constructed in accordance with a second embodiment of the present invention; and

[00030] Fig. 6 is an enlarged elevation view of the lower portion of a hybrid wind- wave power plant which has been constructed in accordance with a third embodiment of the present invention.

[00031] These and other aspects of the subject invention will become more readily apparent to those having ordinary skill in the art from the following detailed description of the preferred embodiments of the invention taken in conjunction with the drawings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[00032] Disclosed herein are detailed descriptions of specific embodiments of the systems and methods of the present invention for generating energy from wind and wave power. It will be understood that the disclosed embodiments are merely examples of ways in which certain aspects of the invention can be implemented and do not represent an exhaustive list of all of the ways the invention may be embodied. Indeed, it will be understood that the systems, devices, and methods described herein may be embodied in various and alternative forms. The figures are not necessarily to scale and some features may be exaggerated or minimized to show details of particular components. Well-known components, materials or methods are not necessarily described in great detail in order to avoid obscuring the present disclosure.

[00033] Figures illustrating the components show some elements that are known and will be recognized by one skilled in the art. The detailed descriptions of such elements are not necessary to an understanding of the invention, and accordingly, are herein presented only to the degree necessary to facilitate an understanding of the novel features of the present invention.

[00034] An advantage of the present invention is that the wave power generation systems disclosed herein can be integrated into any type of offshore wind turbine support structure. For example the wave power generation systems are readily adaptable to existing support structure designs such as: a monopile structure (Fig. 2A); a gravity base structure (Fig. 2B); a jacket structure (Fig. 2C); and a tripod structure (Fig. 2D). The embodiments discussed in detail below are associated with a monopile substructure, but those skilled in the art will readily appreciate that other substructures, such as those shown in Figs. 2A-2D can be used without departing from the inventive aspects of the present disclosure.

[00035] Referring now to Figs. 3 and 4 in which there is illustrated a first embodiment of the offshore hybrid wind-wave power plant of the present invention which has been designated by reference numeral 100. Hybrid power plant 100 includes a monopile base substructure 110 that has a tubular support element 112 that defines an internal chamber 116. In the embodiment illustrated in Fig. 3, the monopile substructure 110 is secured to the sea bottom and surrounded by scour protection 122.

[00036] A plurality of water inlets 118 are formed in the wall of the base substructure

112 and are positioned below mean water level or the sea surface. The water inlets allow sea water to flow in and out of the internal chamber 116. As a result, the level of the water column within the internal chamber 116 oscillates with each passing wave.

[00037] As indicated previously, the number of tubular support elements, internal chambers and water inlets can vary without departing from the inventive aspects of the present disclosure. For example, if the substructure is of the jacket type as shown in Figure 2C, each support leg could include an internal chamber for containing an oscillating water column used for wave power generation. Alternatively, the support legs could be enclosed with a skirt (extending above and just below the water line) which creates a large internal chamber for containing an oscillating water column used for wave power generation.

[00038] Hybrid power plant 100 also includes a wind turbine 130 for generating wind power. The wind turbine includes, among other elements, a rotor 134 and is supported by a tower structure 136 that extends vertically from the base substructure 112. In the embodiment disclosed in this figure, the tower structure 136 is connected to the substructure 112 using a transition piece and grout can be used to seal the connection and prevent air from escaping from within the interior chamber 116.

[00039] A wave power plant or wave power generating system 140 is operatively associated with the internal chamber 116 defined in the base substructure. As shown, power generating system 140 is positioned within the tower structure 136 which protects it from the harsh environment. However, if necessary, certain components of the wave power generating system 140 could be located on the tower exterior. [00040] As shown in Fig. 4, wave power generating system 140 includes a gearbox and generator 142, a piston assembly 144, an air duct 146, a pressure sensor 148 and a motorized valve 150. Wave power generating system 140 uses the oscillating water column within the base structure 112 to create electrical power. As the water column oscillates within interior chamber 116, the air within the chamber 116 and duct 146 is compressed and expanded and moves in and out of duct 146 causing the piston assembly 144 to drive gearbox and generator 142. Motorized valve 150 is controlled by pressure sensor 148 and opens intermittently to adjust the pressure inside the internal chamber 116 and air duct 146 to synchronize the piston stroke with the mean water level which may change as a result of tides and other factors.

[00041 ] As can be readily seen, wave power generating system 140 can be integrated into any offshore wind turbine base, including designs which use a floating base or platform. It may be desirable to increase the size (e.g., diameter) of certain base designs in order to increase wave, and therefore, energy capture.

[00042] Referring now to Figs. 5 and 6 which illustrate a second and a third embodiment of the offshore hybrid wind-wave power plant of the present invention which have been designated by reference numerals 200 and 300, respectively. Hybrid power plants 200 and 300 are similar in structure and operation to power plant 100 and similar structural elements have been designated using like reference numerals.

[00043] Like hybrid power plant 100, power plant 200 includes a monopile base substructure 210 that has a tubular support element 212 that defines an internal chamber 216. The monopile substructure 210 is secured to the sea bottom and surrounded by scour protection 222. A plurality of water inlets 218 are formed in the wall of the base substructure 212 and are positioned below mean water level or the sea surface and the level of the water column within the internal chamber 216 oscillates with each passing wave. Hybrid power plant 200 also includes a wind turbine (not shown) for generating wind power. Like before, the wind turbine includes, among other elements, a rotor and is supported by a tower structure 236 that extends vertically from the base substructure 212.

[00044] However, unlike power plant 100, which includes a piston assembly, hybrid power plant 200 utilizes a bidirectional turbine 260 to generate electrical power from the oscillating water column contained within interior chamber 216. Additionally, the air duct 246 is not sealed, but is open to the exterior and allows air to flow from within the interior chamber to the exterior and vise versa. A Wells turbine as described in U.S. Patent No. 5,191,225, which is incorporated by reference, could be used as the bidirectional turbine 260.

[00045] Wells turbines which are driven by the pressurized air escaping from or entering the air duct as the water rushes in and out of the interior chamber. The Wells turbine converts bi-directional airflows between wave chamber and atmosphere into unidirectional bursts of torque in the coupling of the electrical generator. Moreover, during lulls in the sea or when the air velocity drops to zero during twice-per-wave flow reversal, the Wells turbine needs little power to stay rotating. Simplified Wells turbines employ a set of fixed pitch blades and whilst these provide a generally very positive contribution to the creation of electrical energy the range of wave, and therefore airflow, conditions over which a fixed blade Wells turbine operates with reasonable efficiency is severely limited by blade stall. Typically, Wells turbines use symmetrical profile blades with their chords in the plane of rotation and often produce positive torque only for angles of incidence between 2 and 13 degrees. [00046] Unlike the previously described embodiments, hybrid power plant 300 the wave power generating system 340 uses a liner generator to create electrical power from the oscillating water column. As shown in Fig. 6, wave power generating system 340 includes a linear generator 342, a piston assembly 344, an air duct 346, a pressure sensor 348 and a motorized valve 350. As before, wave power generating system 340 uses the oscillating water column within the base structure 312 to create electrical power. As the water column oscillates within interior chamber 316, the air within the chamber 316 and duct 346 is compressed and expanded and moves in and out of duct 346 causing the piston assembly 344 to reciprocate linearly and drive generator 342. Motorized valve 350 is controlled by pressure sensor 148 and opens intermittently to adjust the pressure inside the internal chamber 316 and air duct 346 to synchronize the piston stroke with the mean water level which may change as a result of tides and other factors.

[00047] Those skilled in the art will readily appreciate that other power generating systems, such as for example, a pneumatic power generator, can be used which are capable of converting the changes in air pressure and/or air flow rate caused by the oscillating water column within the base structure 112 to create electrical power.

[00048] Advantages of the above describe hybrid wave- wind power plant

embodiments include the fact that none of the moving parts or machinery used are submerged or exposed to water, greatly reducing maintenance and improving reliablility. The disclosed systems can also work in relatively small wave environments, as the air duct functions to increase the speed of the air relative to the airspeed within the internal chamber. Additionally, the disclosed systems minimize the initial and maintenance costs by utilizing the structure of offshore wind turbines and their grid connections with minimal

modifications.

Claims

What is Claimed is:

1. An offshore hybrid wind-wave power plant, comprising: a) a base substructure that includes a tubular support element that defines an internal chamber and having at least one water inlet formed therein which is positioned below mean water level such that a water column level within the internal chamber oscillates with each passing wave; b) a wind turbine for generating wind power which is supported by a tower structure that extends vertically from the base substructure; and c) a generator operatively associated with the internal chamber defined in the base substructure such that the generator creates power based on the oscillating water column within the base structure.

2. An offshore hybrid wind- wave power plant as recited in claim 1, further comprising a foundation element for securing the base substructure to sea bottom.

3. An offshore hybrid wind- wave power plant as recited in claim 2, wherein the base substructure is a monopile structure, a jacket structure, a tripod structure, or a gravity base structure.

4. An offshore hybrid wind-wave power plant as recited in claim 1, wherein the oscillating water column compresses and expands air contained within the internal chamber formed in the tubular support element of the base substructure and the compression and expansion of the air is used to move a piston element associated with the generator.

5. An offshore hybrid wind- wave power plant as recited in claim 1, further comprising an air duct in communication with the internal chamber defined in the base substructure.

6. An offshore hybrid wind- wave power plant as recited in claim 5, wherein the generator includes a piston positioned with the air duct and piston driven gearbox

7. An offshore hybrid wind- wave power plant as recited in claim 1, wherein the generator includes a bi-directional turbine operatively associated with the internal chamber.

8. An offshore hybrid wind-wave power plant as recited in claim 7, wherein the bidirectional turbine is a Wells turbine.