GB2587113A

GB2587113A - System and method

Info

Publication number: GB2587113A
Application number: GB2016313.5A
Authority: GB
Inventors: Stephen Baross John
Original assignee: AXIS ENERGY PROJECTS Ltd
Current assignee: AXIS ENERGY PROJECTS Ltd
Priority date: 2015-06-02
Filing date: 2015-06-09
Publication date: 2021-03-17
Anticipated expiration: 2035-06-09
Also published as: GB2542548A; GB202016313D0; GB2542548B; GB2587113B; GB201510000D0; GB201509527D0

Abstract

A combined wind and wave energy converter system comprises a buoy 20 attached to an anchor 60 by a plurality of tethers 50, which apply a mooring load in a primarily vertical direction, i.e. a tension leg mooring system. The wave energy converter 30 may be an oscillating water column OWC device. The anchor 60 is preferably a modular gravity base anchor. This system may be suitable for installation in a range of water depths.

Description

SYSTEM AND METHOD

The present invention relates to an energy converter system and method of installing an energy converter system.

Renewable energy sources such as wind and wave are increasingly important as governments and industries try to de-carbonise energy production. There are however many engineering and environmental challenges to address if the output from these renewable energy sources is to be increased.

For wind power, there is limited space on land for installing large wind farms. The focus is therefore increasingly turning to offshore sites. These offshore sites address some of the disadvantages of onshore sites but have historically needed to be in shallow water near the coast and with seabed soils that are suitable for the necessary foundations, so that the base of the wind powered generators can stand on the seabed.

Offshore, deepwater sites move the wind powered generators away from the coast but the wind powered generators can then typically not stand on the seabed. Using decommissioned oil and gas platforms has been suggested as one possible solution.

In accordance with a first aspect of the present invention there is provided an energy converter system, the system comprising: a buoy attached to an anchor by a tether; a wind powered generator; and a wave powered generator; wherein the wind powered generator and the wave powered generator are attached to the buoy.

It may be an advantage of the present invention that in use, the wave powered generator removes some of the energy transferred from the water to the buoy. The energy may be derived from waves, swell and/or currents. Removal of energy transferred from the water to the buoy typically means in use, the buoy and therefore the wind powered generator moves less relative to the surface of the water. If the wind powered generator move less relative to the surface of the water, it may be more stable and/or may be more energy efficient, that is more wind energy can be converted to electrical energy.

It may also be an advantage of the present invention that the combination of wind and wave power generation increases the generating capacity of the system compared to separate wind and wave powered generators. Also, the wave powered generator can continue to generate power when there is no or little wind for the wind powered generator. This may improve the commercial viability of the system.

The wind powered generator is typically an aerofoil-powered generator. The wind powered generator may be a horizontal-axis wind turbine (HAVVT) or a vertical-axis wind turbine (VAVVT).

The wave powered generator is typically an Oscillating Water Column (OWC) device. The Oscillating Water Column (OWC) device typically generates energy from the rise and fall of water, normally in the form of waves. The wave powered generator may be a Wells Turbine. The wave powered generator may be referred to as a Wave Energy Converter (VVEC).

The wind powered generator and the wave powered generator are typically used to generate electricity.

There may be more than one tether, typically a plurality of tethers. The tether(s) between the buoy and anchor may be tensioned using a winch and/or a strand jack. The winch and/or strand jack may be in the buoy. In use the tether(s) may be tensioned. The amount of tension in the tether(s) may be adjustable.

The buoy typically provides a platform for the wind powered generator. The wave powered generator may be attached to and/or arranged on an outer surface of the buoy.

It may be an advantage of the present invention that the energy converter system can be installed in deep water.

The system provides a combined wave energy and wind energy converter suitable for use in deep water environments, the system being configured to maximise electricity generation per installed unit. Furthermore, the system is easier to install compared with existing floating wind turbines due to the anchor and tether arrangement.

Optionally, the buoy may be configured to house elements of the wave energy converter unit, including the winch(s) and/or strand jacks, in a lower portion of the buoy in order to lower the centre of gravity of the buoy. A benefit of lowering the centre of gravity of the buoy is that the buoyancy element is more stable and provides a more stable platform for the wind turbine.

Optionally, the buoy may further comprise ballast. The ballast may lower the centre of gravity of the buoy. The ballast may be a fluid, typically water, normally seawater. The ballast may be stored in one or more tanks. The one or more tanks may be in the buoy. When the ballast is a fluid, typically water, normally seawater, the ballast may be pumped into and/or out of the one or more tanks to control the centre of gravity of the buoy, the buoyancy of the buoy and/or control the position of the buoy in the water.

The energy converter system may comprise more than one, typically a plurality of buoys, anchors, tethers, wind powered generators and wave powered generators. Each buoy, anchor, tether, wind powered generator and wave powered generator may be referred to as a subunit. There may be 3 or more, typically 5 or more, may be 10 or more subunits in each energy converter system. The more than one, typically a plurality, of subunits may be referred to as an array.

The more than one, typically a plurality of subunits may be arranged to form at least a partial perimeter around a standard wind powered generator or plurality of standard wind powered generators. The more than one, typically a plurality of subunits may be arranged to form at least two partial perimeters around a standard wind powered generator or plurality of standard wind powered generators. The standard wind powered generator(s) may be attached to the seabed or may be floating.

It may be an advantage of the present invention that the wave powered generator removes some of the energy of the surrounding water. The energy may be derived from waves, swell and/or currents. Removal of energy from the surrounding water normally reduces the energy of the corresponding and/or nearby waves and/or typically means in use, the loading on the foundations of a proximate standard wind powered generator are reduced. The standard wind powered generator may therefore be in a more stable environment.

It may be an advantage of the present invention that the buoy, anchor and tether reduce the environmental impact of the energy converter system compared to a standard wind powered generator attached to the seabed by piling. It may also be an advantage of the present invention that because the energy converter system has a buoy, anchor and tether, it is portable. The portability of the system means it can be commissioned and/or repaired in calmer and/or shallower waters compared to its installation site. These waters may be referred to as inshore waters. The portability of the system may mean it can be located at an optimum site that is not determined by water depth.

The buoy, anchor and tether may be referred to as a mooring. The buoy, anchor and tether may be a taut mooring. The buoy, anchor and tether are typically suitable for installation in any depth of water and/or on any seabed soil conditions. It may be an advantage of the present invention that the system is therefore suitable for mass production and that this will reduce production costs. It may alternatively or additionally be an advantage of the present invention that the system can be installed at a site that optimises the wind and/or wave conditions, not dependent on the water depth or seabed conditions.

The buoy, anchor and tether comprising the mooring are typically arranged to reduce the vertical, horizontal and/or roll motion of the buoy, thereby making the buoy more stable.

The anchor may be a modular gravity base anchor.

The system may have a smaller footprint compared to a standard and/or conventional wind powered generators. The system may have a smaller footprint when the buoy, anchor and tether are a taut mooring compared to, for example, a compliant mooring. The smaller footprint of the taut mooring may mean that two systems can be positioned closer together than standard and/or conventional wind powered generators and/or a system using a compliant mooring.

A compliant mooring typically has an array of catenary anchor legs.

It may be an advantage of the present invention that a system with a smaller footprint is more easily negotiated by, for example, fisherman.

In accordance with a second aspect of the present invention there is provided a method of installing an energy converter system, the method comprising the steps of: attaching an anchor to a buoy using a tether; attaching a wind powered generator and a wave powered generator to the buoy; at least partially submerging the buoy; locating the anchor on a seabed; and tensioning the tether to control the position of the buoy relative to the anchor.

It may be an advantage of the present invention that the method of installation can be used in any depth of water. This may mitigate the need for changing the method of installation when the depth of water changes.

The steps of the method of installing an energy converter system according to the second aspect of the present invention may be in any order. The steps may be in the order presented. Alternatively the steps may be as follows: attaching a wind powered generator and a wave powered generator to a buoy; locating an anchor on a seabed; at least partially submerging the buoy; attaching the anchor to the buoy using a tether; tensioning the tether to control the position of the buoy relative to the anchor.

The seabed is typically at the bottom of deep water. The deep water is normally more than 50m deep, usually more than 100m deep. The deep water may have a depth of from 50 to 120m. The step of tensioning the tether usually includes using a winch and/or strand jack to shorten the tether. The tether is typically wound onto a drum of the winch. The winch is usually mounted to the anchor or the buoy. A first winch or strand jack may be mounted to the anchor and a second winch and/or strand jack may be mounted to the buoy.

In an alternative embodiment the step of tensioning the tether includes using fluid, typically water, normally seawater to raise the buoy relative to the seabed and/or the anchor. The method may further include the step of adding and/or pumping fluid, typically water, normally seawater into the buoy and/or tanks on or in the buoy.

The method may include pumping and/or draining fluid out of the buoy and/or the one or more tanks in or on the buoy to reduce the mass of the buoy. This in turn will typically make the buoy more buoyant, thereby raising the buoy relative to the surface of the water, seabed and/or anchor and thereby increasing the distance between the buoy and the anchor and tensioning the tether. The position of the buoy in the water relative to the surface of the water and/or the seabed may be referred to as the depth of the buoy. The step of pumping and/or draining fluid out of the buoy and/or the one or more tanks in or on the buoy may be referred to as venting.

When using fluid to control the position of the buoy in the water relative to the surface of the water, the seabed and/or anchor and thereby using fluid in the step of tensioning the tether, the tether is typically a fixed length. It may be an advantage of the present invention that a fixed length tether negates the need for a winch and/or strand jack to shorten the tether. This typically simplifies the system and thereby typically improves the reliability of the system.

A Remotely Operated Vehicle (ROV) may be used in the step of attaching the anchor to the buoy using a tether. The ROV may be used to attach the tether to the anchor.

The step of at least partially submerging the buoy typically includes partially submerging the buoy in water, normally seawater.

The system is typically commissioned and/or repaired in inshore waters before being towed out to an installation site. This may avoid the need for complex offshore installation operations in areas where wind and waves can be extreme and/or are less predictable. In the event of breakdown, for example failure of a blade of the wind generator, the system can be disconnected from the anchor and towed back inshore for repair.

When the system is being towed, the tether is normally disconnected from the anchor and/or buoy.

Fluid, water and/or seawater may be used to control the position of the buoy relative to the surface of the water, seabed and/or anchor when the system is being commissioned and/or repaired in inshore waters before being towed out to an installation site.

The optional features of the first aspect of the present invention can be incorporated into the second aspect of the present invention and vice versa.

An embodiment of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which: Figure 1 is a schematic view of the energy converter system; Figure 2 is a cross-sectional view of the buoy and wave powered generator; Figure 3 is a schematic view of the anchor and tether; Figure 4 is a plan view of the buoy, wind powered generator and multiple wave powered generators; and Figure 5 is a schematic view of an array of the energy converter systems and a wind farm of standard wind powered generators.

Figure 1 shows an energy converter system 10. The system includes a buoy 20 attached to an anchor 60 by a tether 50. There is a wind powered generator 40 and a wave powered generator 30. The wind powered generator 40 and the wave powered generator 30 are attached to the buoy 20. The anchor 60 sits on the seabed 70. The buoy 20 floats at the surface of the water 80, partially submerged.

The buoy 20 is a buoyant structure made from concrete. It may be a concrete caisson. The buoy 20 has a density lower than water and is thus buoyant in water. In alternative embodiments the buoy 20 is made of a composite material or steel.

Two wave powered generators 30, shown in more detail in Figure 2, are attached to the buoy 20.

The buoy 20 provides a platform for the wind powered generator 40, also referred to as a wind turbine. The wind powered generator 40 comprises a tower on which at one end is a rotor shaft and generator. The wind powered generator 40 is fixed to the buoy at the opposing end of the tower. The generators 24 (as shown in Figure 2) of the wind powered generator 40 and wave powered generator 30, are housed in the buoy 20 to reduce the mass of the wind powered generator 40 and thereby lower the centre of gravity of the system 10.

There are two tethers 50. The tethers are steel cables. The system is designed such that any one tether can fail without loss of station keeping and such that individual tethers can be removed and replaced if required.

The system 10 is configured to maximise the stability of the buoy 20 in order to provide a stable platform for the wind powered generator 40. By providing a stable platform for the wind powered generator 40, the stability and associated restricted motions of the buoy 20 in turn make the buoy 20 suitable for installation of wave powered generators 30 The wind powered generator 40 is a horizontal-axis wind turbine (HAVVT). The wave powered generators 30 are Wells Turbines.

The wave powered generator 30 contributes to the overall stability of the system 10.

This is because the wave powered generator 30 converts at least some of the wave energy of the water to electrical power, thereby reducing the kinetic energy of the surrounding water. The degree of stability can be tuned to minimise the shock loading effect of blades of the wind powered generator 40, also referred to as a wind turbine, have on the buoy. This reduces fatigue loadings on the system 10 and on bearings (not shown) in the wind powered generator 40.

Figure 2 shows the buoy 20 in more detail. The buoy 20 includes two winches 22 that are used to shorten and thereby tension the tethers 50. In an alternative embodiment the winches are strand jacks. When the buoy 20 is in the right position relative to the water level 80, the tethers 50 are locked in place so that the length of the tethers is fixed. The tension on each tether is in the region of several hundreds of tonnes.

The wave powered generators 30 are located lowermost when the buoy 20 is in the water. This lowers the centre of gravity of the buoy 20 and thereby improves the stability of the buoy. The generators (not shown) of the wave powered generators 30 are located inside the buoy 20.

The wave powered generators 30 are attached to the outside of the buoy 20 and are therefore easily accessible for maintenance and repair.

The stability of the buoy 20 is important for the efficiency of the system 10 as a whole. The buoy 20 can be further provided with ballast (not shown) to further lower its centre of gravity.

Figure 3 shows the anchor 60 in more detail. The mooring load of the system 10 comprising buoy 20, wind powered generator 40 and wave powered generator 30 is primarily vertical and the anchor 60 is a modular Gravity Base Anchor (GBA). Modular Gravity Base Anchors are large and heavy. The wind powered generator 40 has an output of equal to or greater than 6MW. The Gravity Base Anchor therefore has a total submerged weight of between one and two thousand tonnes.

The Modular Gravity Base Anchor 60 is re-useable and comprises a steel base 68 accommodating a number of reinforced concrete blocks 62, 64, 66. The steel base 68 has a number of posts (not shown) which are used to guide the concrete blocks 62, 64, 66 into position. The blocks 62, 64, 66 are designed to stack on top of each other.

Male and female connectors (not shown) on adjacent blocks 62, 64, 66 provide couplings between the blocks. The Modular Gravity Anchor 60 is installed offshore and at the end of the life of the anchor, the blocks 62, 64, 66 are easily lifted from the base 68 and the base lifted back to surface for decommissioning and/or re-use.

Another advantage of the Modular Gravity Base Anchor 60 may be that there is no piling necessary for its installation. No piling means no noise pollution from piling. The Modular Gravity Base Anchor 60 typically has only a limited environmental impact on the seabed.

The Modular Gravity Anchor 60 is designed to facilitate installation of a large anchor without the need for a heavy lifting vessel. Individual lifts are tailored to the lifting weight limit of the chosen installation vessel crane so that an anchor 60 of any submerged weight can be built up within the constraints of the size of the installation crane.

The base 68 of the anchor 60 is provided with a skirt. The skirt extends below the base 68 and helps to mitigate the likelihood of the anchor 60 moving relative to and/or sliding over the seabed 70. The depth of the skirt is designed to take into account local geotechnical and metocean conditions. The anchor 60 can be installed without diver intervention.

Connectors (not shown) on the anchor 60 provide attachment points for the tethers 50.

The tethers 50 are attached to the connectors using a Remotely Operated Vehicle (ROV). The connectors articulate so to provide movement of the tethers 50 relative to the anchor 60.

Figure 4 shows a plan view of the buoy 20, wind powered generator 40 and multiple wave powered generators 30.

Figure 5 shows a schematic view of an array 90 of the energy converter systems 10 and a wind farm 92 of standard wind powered generators 94.

Modifications and improvements can be incorporated herein without departing from the scope of the invention.

CLAUSES

1. An energy converter system, the system comprising: a buoy attached to an anchor by a tether; a wind powered generator; and a wave powered generator; wherein the wind powered generator and the wave powered generator are attached to the buoy.

2. An energy converter system according to clause 1, wherein the wind powered generator is an aerofoil-powered generator.

3. An energy converter system according to clause 1 or clause 2, wherein the wind powered generator is a horizontal-axis wind turbine (HAVVT) or a vertical-axis wind turbine (VAVVT).

4. An energy converter system according to any preceding clause, wherein the wave powered generator is an Oscillating Water Column (OWC) device.

5. An energy converter system according to any preceding clause, wherein the wave powered generator is a Wells Turbine.

6. An energy converter system according to any preceding clause, wherein the system comprises a plurality of tethers, the tethers between the buoy and anchor tensionable using a winch or a strand jack.

7. An energy converter system according to clause 6, wherein the winch or strand jack is in the buoy.

8. An energy converter system according to clause 7, wherein the winch or strand jack is housed in a lower portion of the buoy to lower the centre of gravity of the buoy.

9. An energy converter system according to any preceding clause, wherein the buoy further comprises ballast, the ballast lowering the centre of gravity of the buoy.

10. An energy converter system according to clause 9, wherein the ballast is seawater.

11. An energy converter system according to clause 10, wherein the buoy comprises one or more tanks, the seawater pumpable into or out of the one or more tanks to control the centre of gravity of the buoy or control the position of the buoy in the water.

12. An energy converter system according to any preceding clause, wherein the buoy, anchor and tether are arranged, in use, to reduce the vertical, horizontal or roll motion of the buoy, thereby making the buoy more stable.

13. A method of installing an energy converter system, the method comprising the steps of: attaching an anchor to a buoy using a tether; attaching a wind powered generator and a wave powered generator to the buoy at least partially submerging the buoy; locating the anchor on a seabed; and tensioning the tether to control the position of the buoy relative to the anchor.

14. A method of installing an energy converter system according to clause 13, the method including the step of pumping or draining the seawater out of the buoy or one or more tanks in the buoy to reduce the mass of the buoy, thereby tensioning the tether.

15. A method of installing an energy converter system according to clause 13 or clause 14, wherein a Remotely Operated Vehicle (ROV) is used in the step of attaching the anchor to the buoy using the tether.

Claims

CLAIMS1. An energy converter system, the system comprising: an anchor; a buoy; a plurality of tethers extending between the body and the anchor, the tethers being attached to the anchor at separate attachment points and configured to apply a mooring load in a primarily vertical direction; and a wind powered generator attached to the buoy.
2. An energy converter system according to claim 1, wherein the wind powered generator is an aerofoil-powered generator.
3. An energy converter system according to claim 1 or claim 2, wherein the wind powered generator is a horizontal-axis wind turbine (HAVVT) or a vertical-axis wind turbine (VAVVT).
4. An energy converter according to any preceding claim, further comprising a 15 wave powered generator;
5. An energy converter system according to claim 4, wherein the wave powered generator is an Oscillating Water Column (OWC) device.
6. An energy converter system according to claim 4 or claim 5, wherein the wave powered generator is a Wells Turbine.
7. An energy converter system according to any preceding claim, wherein the tethers between the buoy and anchor are tensionable using a winch or a strand jack.
8. An energy converter system according to claim 7, wherein the winch or strand jack is in the buoy.
9. An energy converter system according to claim 8, wherein the winch or strand jack is housed in a lower portion of the buoy to lower the centre of gravity of the buoy.
10. An energy converter system according to any preceding claim, wherein the buoy further comprises ballast, the ballast lowering the centre of gravity of the buoy.
11. An energy converter system according to claim 10, wherein the ballast is seawater.
12. An energy converter system according to claim 11, wherein the buoy comprises one or more tanks, the seawater pumpable into or out of the one or more tanks to control the centre of gravity of the buoy or control the position of the buoy in the water.
13. An energy converter system according to any preceding claim, wherein the buoy, anchor and tether are arranged, in use, to reduce the vertical, horizontal or roll motion of the buoy, thereby making the buoy more stable.
14. An energy converter system according to any preceding claim, wherein the anchor is a modular gravity base anchor.
15. An energy converter system according to claim 14, wherein the modular gravity base anchor has a skirt extending below a base of the anchor.
16. An energy converter system according to claim 14 or claim 15, wherein the modular gravity base anchor comprises a steel base for accommodating a number of reinforced concrete blocks.
17. An energy converter system according to claim 16, wherein the blocks are adapted to be stacked on top of each other.
18. A method of installing an energy converter system, the method comprising the steps of: attaching an anchor to a buoy using a plurality of tethers, the tethers being attached to the anchor at separate attachment points; attaching a wind powered generator to the buoy; at least partially submerging the buoy; locating the anchor on a seabed; and tensioning the tethers to apply a mooring load in a primarily vertical direction to control the position of the buoy relative to the anchor.
19. A method of installing an energy converter system according to claim 18, the method including the step of pumping or draining the seawater out of the buoy or one or more tanks in the buoy to reduce the mass of the buoy, thereby tensioning the 25 tether.
20. A method of installing an energy converter system according to claim 18 or claim 19, wherein a Remotely Operated Vehicle (ROV) is used in the step of attaching the anchor to the buoy using the tethers.
21. A method of installing an energy converter system according to any of claims 18 to 20, further comprising attaching a wave powered generator to the buoy.