GB2575336A

GB2575336A - Subsea energy generation assembly utilising wave energy

Info

Publication number: GB2575336A
Application number: GB1902023.9A
Authority: GB
Inventors: King Lee
Original assignee: Hydro Wind Energy Ltd
Current assignee: Hydro Wind Energy Ltd
Priority date: 2019-02-14
Filing date: 2019-02-14
Publication date: 2020-01-08
Anticipated expiration: 2039-02-14
Also published as: GB2575336B; GB201902023D0

Abstract

An energy generation system 100 for harnessing wave energy and potential energy stored in water under subsea hydrostatic pressure, comprises buoy 114, which may be a ship or barge disposed on a surface 102 of water 104, which may be a sea, ocean or lake. A pulley wheel, or the like 112 may be located on the buoy. Pressure vessel 116 is submerged in the water and has a body of pressurised air (Fig 2, 130) inside it. The vessel is operated, by lowering it to a pre-set depth allowing water to enter through an inlet 126 when hydrostatic pressure on the vessel exceeds the pressure of air in the vessel. Incoming water turns inlet turbine 132. Movement of the buoy due to wave action also alters the depth of the vessel. Water exits the vessel via outlet 128 as it rises and hydrostatic pressure drops. Air pressure in the vessel pushes water out. The winch 120 may be used to raise and lower the vessel and is also used to tension tether 122 acting to keep the pressure vessel and buoy in relative positions.

Description

AN ENERGY GENERATION SYSTEM USING WAVE ENERGY, BUOYANCY OF AIR AND POTENTIAL ENERGY STORED IN WATER UNDER SUBSEA HYDROSTATIC PRESSURE

TECHNICAL FIELD

The present disclosure, generally, relates to energy generation and more particularly relates to an energy generation system harnessing wave energy and potential energy stored in water under subsea pressure.

BACKGROUND

Our dependence on fossil fuels is causing many of the environmental problems the world faces today. There has been a substantial increase in the number of power systems, which use renewable energy sources, such as water, wind, and solar. There is a need for more renewable power systems to ensure security of supply over the coming decades and counter the global environmental crisis. It has been observed that every year, all over the world, the generation capacity of the power systems using renewable energy sources is increasing. The power systems are challenging to operate as there must a precise balance between supply and demand, at all times. Since, it is impossible to forecast the power demands with precision, the power systems must always be flexible. Also, the power generated by these power systems is intermittent. The intermittent renewable power from renewable energy makes it more difficult to vary output, and rises in demand do not necessarily correspond to rises in renewable energy generation. Owing to the above-mentioned facts, widespread adoption of such power systems is often limited. There is a requirement for sources of energy that can produce energy on demand, called dispatchable sources. The power generated from offshore resources is not reliable over short periods of time due to the intermittent and non-dispatchable nature of these sources. One solution to this limitation is an energy storage system, but such energy storage systems are not economical enough to offset the extra costs incurred in installation and maintenance. Further, the current energy storage systems require expensive materials and manufacturing process.

Although wave energy is fairly consistent in the long run, short term capacity fluctuations prohibit wave power from replacing dependable fossil-fuel based energy generation systems. This limitation could be overcome if the energy harvested from wave power could be cost effectively stored temporarily and released when required. Typically, in pumped water storage, the energy is stored by pumping water up from a low reservoir into an elevated reservoir. The energy is extracted from such a system by allowing the water to flow from the elevated reservoir back into the low reservoir via turbines that spin generators, generating electricity. This requires construction of pipelines to connect pumps and turbines, making the pumped water systems costly to build and maintain. To date, there are no pumped water energy storage systems that are economical, scalable, and deployable in a wide variety of locations. A desirable energy storage system must take into account power rating, storage duration, frequency of charge and discharge, efficiency and response time, and site constraints that determine power and energy density requirements.

Therefore, there is a need in the art for an efficient, durable, and cost-effective energy generation system, which ameliorates all or some of the deficiencies of the prior art or at least provides a viable alternative.

SUMMARY

According to a first aspect of the present disclosure, there is provided an energy generation system for using wave energy and potential energy of subsea pressure, the system comprising a buoy disposed on a surface of a water body, a pulley wheel disposed on the buoy, a pressure vessel submerged in the water body, the pressure vessel having air, a water inlet, a water outlet and a hydroelectric turbine, a winch mechanism, a tether engaged with the pressure vessel and the winch mechanism, through the pulley wheel. Further, the buoy is configured to move in a vertical direction on the surface of the water body during passing of the waves generated in the water body. Further, the pulley wheel is configured to transmit the vertical motion of the buoy to the pressure vessel. Further, the water inlet is configured to allow water of the water body to enter into the pressure vessel, when a hydrostatic pressure of the water in the water body exceeds a pressure of the air inside the pressure vessel. Further, the water outlet is configured to allow the water of the water body to exit out of the pressure vessel, when the pressure of the air inside the pressure vessel exceeds the hydrostatic pressure of the water in the water body. Further, the hydroelectric turbine is configured to harness electrical energy from a hydrodynamic flow of the water, into the pressure vessel at a predetermined initial depth. Also, the winch mechanism is configured to adjust tension in the tether.

In accordance with an embodiment of the present disclosure, the winch mechanism comprises a winch attached to a deadweight anchor provided on a bed of the water body, the winch being configured to reel-in and reel-out the tether, in order to adjust the tension in the tether.

In accordance with an embodiment of the present disclosure, the tether is one of a group comprising nylon rope, nylon webbing, wire cable, chain and carbon nano-tube based cabling.

In accordance with an embodiment of the present disclosure, the system further comprises a counterweight attached to the tether, wherein the counter weight is configured to provide additional tension to the tether.

According to a second aspect of the present invention, there is provided a method for using wave energy and potential energy of subsea pressure, the method comprising steps of disposing a buoy on a surface of a water body, such that the buoy moves in a vertical direction on the surface of the water body, during passing of the waves generated in the water body, submerging a pressure vessel having air, to a predetermined initial depth in the water body, allowing water of the water body to enter into the pressure vessel, harnessing electrical energy from a hydrodynamic flow of the water into the pressure vessel, at the predetermined initial depth, transmitting the vertical motion of the buoy to the pressure vessel and allowing the water of the water body to exit out of the pressure vessel.

In accordance with an embodiment of the present invention, the method further comprises a step of adjusting tension of the tether.

In accordance with an embodiment of the present invention, the method further comprises a step of providing additional tension to the tether.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may have been referred by embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments.

These and other features, benefits, and advantages of the present disclosure will become apparent by reference to the following text figure, with like reference numbers referring to like structures across the views, wherein:

Fig. 1 illustrates an exemplary environment of an energy generation system to which various embodiments of the present disclosure may be implemented;

Fig. 2 illustrates a state of an exemplary energy generation system during a filling process, in accordance with an embodiment of the present disclosure;

Fig. 3 illustrates a state of the energy generation system during a lifting process, in accordance with another embodiment of the present disclosure; and

Fig. 4 illustrates a method for generating electrical energy by using wave energy and potential energy of subsea pressure, in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION

Detailed embodiments of the present disclosure are described herein; however, it is to be understood that disclosed embodiments are merely exemplary of the present disclosure, which may be embodied in various alternative forms. Specific process details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present disclosure in any appropriate process.

The terms used herein are for the purpose of describing exemplary embodiments only and are not intended to be limiting. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” or “comprising” when used in this specification, do not preclude the presence or addition of one or more components, steps, operations, and/or elements other than a mentioned component, step, operation, and/or element.

The present disclosure may be embodied in a variety of different forms and, example embodiments are provided merely to be illustrative. Among other things, for example, the present disclosure may be embodied as methods, devices, components, or systems. Accordingly, embodiments may, for example, take the form of hardware, software, firmware or any combination thereof (other than software per se). Although the exemplary embodiments will be generally described in the context of software modules running in a mobile device, those skilled in the art will recognize that the present disclosure also can be implemented in conjunction with other program modules for other types of computing environments. For example, execution of the program modules may occur locally in a stand-alone manner or remotely in a client/server manner.

The embodiments of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, which form a part hereof, and which show, by way of illustration, specific example embodiments. The following detailed description is not intended to be taken in a limiting sense.

Figure. 1 illustrates an exemplary environment of an energy generation system 100 to which various embodiments of the present disclosure may be implemented. In a preferred embodiment, an energy generation system 100 is installed beneath a surface 102 of a water body 104. The energy generation system 100 is electrically connected to an onshore unit 106, via an export electrical cable 108. The energy generation system 100 is installed in the water body 104 in such a manner, that the energy generation system 100 is partially floating along the surface 102. The water body 104 may embody a sea, an ocean, or the like. The energy generation system 100 includes a pulley wheel

112, a buoy 114, a pressure vessel 116, a winch mechanism 118, the export electrical cable 108, a tether 122, and a counterweight 124. The pulley wheel 112 is disposed on the buoy 114. The buoy 114 can also be referred to as a floating barge or a floating structure. The buoy 114 is disposed on the surface 102 of the water body 104, such that the buoy 114 moves in a vertical direction on the surface 102 of the water body 104 during passing of the waves generated in the water body 104. The buoy 114 moves in tandem with a motion of a plurality of sea waves, resulting in an upward motion and a downward motion of both the buoy 114 and the pressure vessel 116. The buoy 114 uses rise and fall of the sea waves to mechanically lift the pressure vessel 116.

The pressure vessel 116 is submerged in the water body 104. The pressure vessel 116 is connected to the pulley wheel 112 via the tether 122. The pressure vessel 116 is configured to be lifted vertically up by the movement of waves. In a preferred embodiment, the pressure vessel 116 is made of steel with a mass of 603,400 kilograms with a volume of approximately 502 cubic meters. The pressure vessel 116 is structured and configured to remain submerged at a predetermined initial depth D in the water body 104. The pressure vessel 116 includes a water inlet 126, a water outlet 128, air 130, a hydroelectric turbine 132, and a generator (not shown). The water inlet 126 is configured to allow water of the water body 104 to enter into the pressure vessel 116, when the hydrostatic pressure of the water in the water body 104 exceeds a pressure of the air 130 inside the pressure vessel 16 at an initial predetermined water depth. The water outlet 128 is configured to allow the water of the water body 104 to exit out of the pressure vessel 116, when the pressure of the air 130 inside the pressure vessel 116 exceeds the hydrostatic pressure of the water during lifting. The water inlet 126 is positioned in way that the water entering the pressure vessel 116 is directed at the hydroelectric turbine 132. The hydroelectric turbine 132 is configured to harness electrical energy from a hydrodynamic flow of the water into the pressure vessel 116. The hydroelectric turbine 132 is coupled to the generator (not shown). The generator (not shown) is configured to convert the mechanical energy into the electrical energy.

The pulley wheel 112 is connected to the pressure vessel 116 via the tether 122. The tether 122 is one of a group comprising nylon rope, nylon webbing, wire cable, chain, and carbon nano-tube based tether 122. The pulley wheel 112 is configured to transmit the vertical motion of the buoy 114 to the pressure vessel 116. The pulley wheel 112 guides the tether 122 to the pressure vessel 116 and secures the pressure vessel 116 in place in a submerged position. The tether 122 is engaged with the pressure vessel 116 and the winch mechanism 118, through the pulley wheel 112.The tether 122 is connected to, and wound on, the pulley wheel 112. One end of the tether 122 is connected to the pressure vessel 116 and other end of the tether 122 is connected to the winch mechanism 118, while engaged with the pulley wheel 112 in-between the pressure vessel 116 and the winch mechanism 118. Further, the counterweight 124 is attached to the tether 122. The counterweight 124 is configured to provide additional tension during slacking of the tether 122.

The winch mechanism 118 is connected to the pulley wheel 112 via the tether 122. In accordance with an embodiment of the disclosure, the winch mechanism 118 comprises a winch 1182 mounted on a deadweight anchor 120, which is anchored to the floor 110 of the water body 104. The winch mechanism 118 is configured to adjust tension in the tether 122. In that manner, it is envisaged that the winch 1182 is a motorized winch configured to automatically reel in and reelout the tether 122 in order to adjust the tension in the tether. In other words, the winch mechanism 118 aids to maintain depths of the pressure vessel 116 via the tether 122 which engages with the pulley wheel 112.

Figure 2 illustrates a state of the exemplary energy generation system 100 during a filling process, in accordance with an embodiment of the present disclosure. As shown in figure 2, during the filling process of the energy generation system 100, the pressure vessel 116 is submerged to the predetermined initial depth D. The buoy 114 moves in tandem with motion of the sea waves, resulting in movement of both the buoy 114 and the submerged pressure vessel 116, in the vertical direction (an upward motion and a downward motion). In a preferred embodiment, the predetermined initial depth D is 100 meters. However, it may be contemplated that the pressure vessel 116, tethered on the buoy 114, can be extended and operated at any initial depth. Since pressure is arbitrarily considered to be energy density per volume, the deeper the pressure vessel 116 is submerged the greater the pressure, the higher the capacity for energy storage with the same volume of pressure vessel 116. For example, at the predetermined initial depth of 100 m, the pressure vessel 116 contains approximately 502 cubic meters (m³) of the air 130 at a pressure of 200 kilo Pascal (kPa). The pressure vessel 116 is negatively buoyant by 450 kg once fully submerged in the water body 104. The floating buoy 114 holds the pressure vessel 116 in place once submerged on the pulley wheel 112 wheel to the predetermined initial depth D.

At the predetermined initial depth D of 100 meters (m), the hydrostatic pressure in the water body 104 is approximately 1106kPa. Hence, a pressure difference is created between the air inside (pressure of the air 130 inside the pressure vessel 116, that is, 200 kPa) and the hydrostatic pressure at 100m (that is, approximately 1106 kPa). Once the inlet 132 is opened the pressure difference causes the water to flow into the pressure vessel 116 via the water inlet 126 and generates electricity through the hydroelectric turbine 132. This floods the pressure vessel 116 and results in compression of the air 130 inside the pressure vessel 116 to a small pocket of volume 90m³ and filling a remaining volume of 412m³ with the water. Once the pressure vessel 116 is filled with water, the buoyancy and weight of the energy generation system 100 alters (that is, the pressure vessel 116 becomes negatively buoyant by 450 tons), and energy generation is stopped. This increases the draft line of the buoy 114, countering the increase in weight. The pressure vessel 116 further sinks in the water body 104 beyond the predetermined initial depth D of 100m. When the pressure vessel 116 sinks in the water body 104, the tether 122 reels-out from the winch 1182, passes over the pulley wheel 112, and holds the pressure vessel 116 in place.

In an embodiment, the energy generation system 100 may be charged and discharged depending on demand. Further, monitoring of grid demand can be used to control when to charge and when to discharge the energy generation system 100. Charging of the energy generation system 100 occurs during the lifting process and discharge or energy generation occurs during the filling process at the predetermined initial depth D.

Figure 3 illustrates a state of the exemplary energy generation system 100 during the lifting process, in accordance with an embodiment of the present disclosure. In Figure 3, the pressure vessel 116 is shown to be at a depth which is lesser than the predetermined initial depth D. In an exemplary embodiment, the depth Dt is 10m. The buoy 114 uses the rise and fall of swells in the sea waves to gradually lift the pressure vessel 116 to the depth Once a crest of the sea wave is reached, the pulley wheel 112 locks the tether 122 connected to the pressure vessel 116. As the sea wave drops in height and reaches a trough, the winch mechanism 118 collects and locks in any loose tether 122. The counterweight 124 provides additional tension for the loose tether 122 to be collected by the winch mechanism 118. During the lifting process, water is allowed to flow out of the pressure vessel 116. As the water escapes, the compressed air pocket inside the pressure vessel 116 continuously expands, until the hydrostatic pressure is equalized with the pressure of the air 130 at each depth. Once the water is removed with air 130 left inside at 200 kPa, the water at 10m depth Dt and the air 130 are at hydrostatic equilibrium. The water outlet 128 is closed and the pressure vessel 116 maintaining negative buoyancy with only air 130 inside is again allowed to sink to the predetermined initial depth D and the energy generation system 100 is reinstated for a new cycle.

Figure 4 illustrates a method 400 for generating electrical energy by wave energy and potential energy of subsea pressure, in accordance with an embodiment of the present disclosure. At step 402, the buoy 114 is disposed on the surface 102 of the water body 104. Further, the pulley wheel 112 is disposed on the buoy 114. At step 404, the pressure vessel 116 is submerged in the water body 104 at the predetermined initial depth D. The pressure vessel is contains the air 130. The pressure vessel 116 is positioned in the water body 104 using the pulley wheel 112 disposed on the buoy 114. The depth of the pressure vessel 116 is maintained using the tether 122, which reels in and reels out from the winch 1182 and engages with the pulley wheel 112. At step 406, the water inlet 126 opens and allows the water to enter into the pressure vessel 116, as the hydrostatic pressure of the water in the water body 104 exceeds the pressure of the air 130 inside the pressure vessel 116 at the predetermined initial depth D. This floods the pressure vessel 116, resulting in compression of the air inside the pressure vessel 116 to the small pocket of volume 90m³ and filling the remaining volume of 412m³ with water.

At step 408, the electrical energy is harnessed from the hydrodynamic flow of the water, into the pressure vessel 116 at the predetermined initial depth D. This is done only when water flowing into the pressure vessel 116 impinges on the hydroelectric turbine 132 and force of water rotates the hydroelectric turbine 132. The hydroelectric turbine 132 thus converts moving water into mechanical energy. The mechanical energy of the rotating hydroelectric turbine 132 rotates the generator (not shown) coupled to the hydroelectric turbine 132. The rotation of the generator (not shown) converts the mechanical energy into electrical energy. This results in generation of electricity, which is then transferred to the export electrical cable 108. The buoy 114 moves in the vertical direction on the surface 102 of the water body 104 during passing of the waves generated in the water body 104.

At step 410, the vertical motion of the buoy 114 is transmitted to the pressure vessel 116. In accordance with an embodiment, the tension of the tether 122 is adjusted by the winch mechanism 118. In other words, the tether 122 is reeled in by the motorized winch 1182 to adjust the tension in the tether 122 during the vertical motion of the buoy 114. Further, in accordance with an embodiment, the additional tension is provided by the counterweight 124. Therefore, the pressure vessel 116 is lifted by each wave height (crest) thereby making the buoy 114 to gradually lift the pressure vessel 116 upwards. At step 412, as the pressure vessel 116 is being lifted, the water outlet 128 allows the water of the water body 104 to exit out of the pressure vessel 116, when the pressure of the air 130 inside the pressure vessel 116 exceeds the hydrostatic pressure of the water in the water body 104, during the lifting process. In a preferred embodiment, upon the lifting process, the pressure vessel 116 is brought to the depth of 10 m, where the water at 10m depth and the air 130 are at hydrostatic equilibrium.

The embodiments of the system and the method offer a number of advantages. The energy generation system 100 is based on combining subsea pressure in the form of hydro energy with wave power to generate zero carbon emissions electricity. This energy generation system 100 harnesses wave power using the buoy 114. The pressure vessel 116 and water under hydrostatic pressure is used to store that energy for on-demand dispatchable power generation through the hydroelectric turbine 132. The energy generation system 100 generates zero carbon emissions electricity from renewable energy sources. The energy generation system 100 reduces cost of generating electrical energy from renewable energy sources. The energy generation system 100 turns a nondispatchable power source (wave) into a subsea hydro dispatchable power source (subsea hydro). Further, the energy generation system 100 eliminates carbon emissions by generating electrical energy from wave power but does this indirectly through the buoyancy of the air 130. Moreover, the energy generation system 100 avoids or levels out intermittent nature of the renewable energy sources, thereby increasing the capacity factor of wave energy. The energy generation system 100 also has the ability to store the electrical energy for ondemand supply. The energy generation system 100 exhibits the highest electrical energy conversion efficiency of approximately 85% to 90%. Additionally, the energy generation system 100 is totally offshore and can be installed in deep waters. The energy generation system 100 operates as an environmentally benign technology since the energy generation system 100 uses only floating buoys and subsea water pressure. This energy generation system 100 acts as an energy generation system 100 as well as energy storage system to solve issues such as, intermittency of renewable energy sources, load balancing, reserve capacity, and/or peak-shaving.

The terms and descriptions used herein are set forth by way of illustration only and are not meant as limitations. Examples and limitations disclosed herein are intended to be not limiting in any manner, and modifications may be made without departing from the spirit of the present disclosure. Those skilled in the art will recognize that many variations are possible within the spirit and scope of the disclosure, and their equivalents, in which all terms are to be understood in their broadest possible sense unless otherwise indicated.

Various modifications to these embodiments are apparent to those skilled in the art from the description and the accompanying drawings. The principles associated with the various embodiments described herein may be applied to other embodiments. Therefore, the description is not intended to be limited to the embodiments shown along with the accompanying drawings but is to be providing broadest scope of consistent with the principles and the novel and inventive features disclosed or suggested herein. Accordingly, the disclosure is anticipated to hold on to all other such alternatives, modifications, and variations that fall within the scope of the present disclosure and appended claims.

Claims

1. An energy generation system (100) for using wave energy and potential energy of subsea pressure, the system (100) comprising:

a buoy (114) disposed on a surface (102) of a water body (104);

A pulley wheel (112) disposed on the buoy (114);

a pressure vessel (130) submerged in the water body (104), the pressure vessel (116) having air (130), a water inlet (126), a water outlet (128) and a hydroelectric turbine (132);

a winch mechanism (118);

a tether (122) engaged with the pressure vessel (116) and the winch mechanism (118), through the pulley wheel (112);

wherein the buoy (114) is configured to move in a vertical direction on the surface (102) of the water body (104) during passing of the waves generated in the water body (104);

wherein the pulley wheel (112) is configured to transmit the vertical motion ofthe buoy (114) to the pressure vessel (116);

wherein the water inlet (126) is configured to allow water of the water body (104) to enter into the pressure vessel (116), when a hydrostatic pressure of the water in the water body (104) exceeds a pressure of the air (130) inside the pressure vessel (160);

wherein the water outlet (128) is configured to allow the water of the water body (104) to exit out of the pressure vessel (116), when the pressure of the air (130) inside the pressure vessel (116) exceeds the hydrostatic pressure of the water in the water body (104);

wherein the hydroelectric turbine (132) is configured to harness electrical energy from a hydrodynamic flow of the water, into the pressure vessel (116) at a predetermined initial depth; and wherein the winch mechanism (118) is configured to adjust tension in the tether (122).

2. The system (100) as claimed in claim 1, wherein the winch mechanism (118) comprises a winch (1182) attached to a deadweight anchor (120) provided on a bed (110) of the water body (104), the winch (1182) being configured to reel-in and reel-out the tether (122), in order to adjust the tension in the tether (122).

3. The system (100) as claimed in claim 1, wherein the tether (122) is one of a group comprising:

nylon rope;

nylon webbing;

wire cable;

chain; and carbon nano-tube based tether.

4. The system (100) as claimed in claim 1, further comprising a counterweight (124) attached to the tether (122), wherein the counterweight (124) is configured to provide additional tension to the tether (122).

5. A method (400) for using wave energy and potential energy of subsea pressure, the method comprising steps of:

disposing (402) a buoy (114) on a surface (102) of a water body (104), such that the buoy (114) moves in a vertical direction on the surface (102) of the water body (104), during passing of the waves generated in the water body (104);

submerging (404) a pressure vessel (116) having air (130), to a predetermined initial depth in the water body (104);

allowing (406) water of the water body (104) to enter into the pressure vessel (116);

harnessing (408) electrical energy from a hydrodynamic flow of the water into the pressure vessel (116), at the predetermined initial depth;

transmitting (410) the vertical motion of the buoy to the pressure vessel (116); and allowing (412) the water of the water body (104) to exit out of the pressure vessel.

6. The method (400) as claimed in claim 5, further comprising a step of adjusting tension of the tether (122).

7. The method (400) as claimed in claim 5 or 6, further comprising a step of providing additional tension to the tether (122).