NO347990B1 - Wave-power facility with horizontal movement - Google Patents

Description

WAVE-POWER FACILITY WITH HORIZONTAL MOVEMENT

Technical Field

[0001] The invention relates to a wave power facility. More particularly, the invention relates to a wave power facility arranged for harvesting energy from the horizontal movements of the waves.

Background Art

[0002] Wave movements in the sea and in large inland lakes constitute a potential source of energy. Although there have been a lot of different solutions for utilizing these renewable energy sources, the amount of energy produced in this way remains limited. It is problematic to achieve aggregates of this kind that are economically competitive, since the power output from these aggregates is typically low. Therefore, a large number of such aggregates are required to attain power of a significant, competitive level.

[0003] The challenge to achieve an economical competitive energy generating system based on these renewable energy sources is on one hand to provide efficient generator aggregates at low costs and on the other hand to provide an optimized system that can include a large number of such generator aggregates. The latter aspect is the crucial one for producing and supplying energy on a large commercial scale for the supply of the electric energy to an electric network.

[0004] Prior art publication WO2011096816 shows a platform with floating devices that moves vertically to generate power. The floating devices are coupled to a generator for power generation.

[0005] FR475834, CN203756429, ITTO20111060, EP2679802, W02009056854, CN108561265, WO2017086693 illustrate further examples of prior art of the wave power facilities.

[0006] Common for many known wave power facilities is the exploitation of the vertical movement of floating bodies. However, it has been recognized that exploiting the horizontal movements of the waves may be more efficient.

Summary of invention

[0007] According to a first aspect of the present invention, there is provided a wave power facility comprising an offshore structure and further comprising a plurality of generator units. The respective generator units comprise a power generator supported by the offshore structure at a distance above the sea surface, and a main line connected to the power generator and extending between the offshore structure and the seabed, as it is anchored to an anchoring device at the seabed. Furthermore, the respective generator units comprise a wave absorber in engagement with the main line and at the vertical level of the sea surface.

[0008] In some embodiments, the term "in engagement with the main line", will mean that the wave absorber is fixed to the main line or the main lines. In such embodiments, the wave absorber will not be able to move with respect to the main line along the extension of the main line. In other embodiments, the term will mean that the wave absorber is attached to the main line or main lines in a movable manner. In such embodiments, the wave absorber can move along the main line with respect to the main lines. Examples of these embodiments will be given further below.

[0009] In some embodiments, the wave absorber exhibits a mass density of more than 800 kg/m³. In other words, the wave absorber is not configured with significant buoyancy since it is not intended to follow the vertical movements of the waves.

[0010] By having high density, the wave absorber will not experience excessive forces from the waves in the vertical directions. Instead, the wave absorber will substantially move in the horizontal direction.

[0011] In some embodiments, the mass density of the wave absorber can be substantially 1000 kg/m³, i.e. a substantially neutral buoyancy. Moreover, in some embodiments it will be advantageous to have a wave absorber with a mass density above 1000 kg/m³, which enables or at least facilitates lowering the wave absorber into the sea and below the sea surface. In some embodiments, the mass density of the wave absorber can even be more than 1050 or 1100 kg/m<3>. This will ensure that the wave absorber will sink when lowered below the sea surface.

[0012] Moreover, in some embodiments, the wave absorber is compartment-less. With the term "compartment-less" is meant that the wave absorber does not comprise any closed compartments, such as air compartments. This distinguishes from prior solutions that employs buoyancy to provide a vertical movement of the wave absorber.

[0013] In some advantageous embodiments, the wave absorber comprises flat plates arranged in a straight star configuration.

[0014] With the term "straight star configuration" is meant that the wave absorber has a straight longitudinal portion with a constant cross section, such as a Y configuration or X configuration. Examples of a straight star configuration is shown in the detailed description below.

[0015] Such a configuration is well configured to adsorb horizontal forces from the waves, while exhibiting a low flow resistance in the vertical direction.

[0016] The mutual position of the upper part of the main line and its connection to the seabed, is such that a straight line between the connection points of the main line to the offshore structure and to the anchoring device, respectively, forms an angle to the vertical that is less than 30°.

[0017] Advantageously, the angle can even be less than 20°, 15°, or 10°, or even substantially zero. In the latter case, the main line would extend in a substantially vertical direction when in a straight configuration.

[0018] In some embodiments, the wave absorber is suspended with a winch line. Moreover, the wave absorber comprises a line guide that maintains a sliding connection between the wave absorber and the main line, such that the wave absorber may move along the extension of and with respect to the main line. The generator unit further comprises a winch configured to move the wave absorber up and down along the main line.

[0019] In some embodiments, typically where the mass density of the wave absorber is more than 1000 kg/m³, the winch can be used to lower the wave absorber down below the sea surface. This can typically take place in severe weather conditions with large waves and consequently large forces. In this manner, the wave absorber can be lowered down to an elevation where power from the waves can be harvested even during harsh weather conditions.

[0020] In some embodiments, the power generators of respective generator units may comprise a hydraulic cylinder moved by the main line. Moreover, the hydraulic cylinders of the respective generator units hydraulically connect, with a supply pipe and a return pipe, to a common hydraulic system that converts hydraulic power into electric power, as the hydraulic system comprises a hydraulic electric generator.

[0021] The respective generator units may comprise a generator cell comprising the said power generator. The generator cells can be arranged in two stacks of cell rows, wherein each cell row comprises at least five generator cells, and each stack of cell row comprises at least two rows of generator cells. Thus, for instance, if each cell row of generator cells comprises four generator cells, and each stack of cell row comprises two cell rows, the total number of generator cells is 2 x 2 x 4 = 16 generator cells.

[0022] It is noted that while some embodiments involve the use of a hydraulic system for converting mechanical power from the main line, one may also convert the mechanical power from the main line directly into electric power, such as by connecting the main line – directly or indirectly – to the moving part of an electric generator. In such embodiments, the power generator can be an electric generator.

[0023] According to another aspect of the invention, there is provided a method of producing electric energy with a wave power facility as discussed above. The method comprises the steps of

a) with the winch, lowering the wave absorber down to a position below the sea surface;

b) harvesting wave power by means of the power generator as the wave absorber provides pull in the main line.

Detailed description of the invention

[0024] While various features of the invention have been discussed in general terms above, a more detailed and non-limiting example of embodiment will be presented in the following with reference to the drawings, in which

Fig. 1 is a schematic side view of a wave power facility according to the invention, illustrating in particular its offshore structure standing on the seabed;

Fig. 2 depicts the same offshore structure as in Fig.1, however seen from another angle;

Fig. 3 is a schematic view of the structure shown in Fig.1 and Fig.2, seen from above;

Fig. 4 is a schematic side-view diagram of a generator unit, with a wave absorber reciprocating back and forth in the horizontal direction;

Fig. 5 is another schematic diagram of another embodiment of a generator unit;

Fig. 6 is a principle view of a power generator used for converting mechanical power;

Fig. 7 is a side view of a generator cell comprising a power generator, illustrating the interface between main lines and the power generator;

Fig. 8 is a top view of the generator cell shown in Fig.7;

Fig. 9 depicts the interface between several main lines with the generator cell with two different side views;

Fig. 10 is a schematic side view illustrating the connection of two main lines to respective power generators;

Fig. 11 is a detailed cross section view of a power generator;

Fig. 12 is a schematic diagram showing an embodiment of a power generator; and

Fig. 13 is a diagram illustrating the interface between two power generators and a hydraulic system for converting power into electric power.

[0025] Reference is made to Fig.1 and to Fig.2, which show a wave power facility 1 according to an embodiment of the invention in respective orthogonal directions. The wave power facility 1 has an offshore structure, here comprising a deck 2 and a foundation 4. The deck 2 is arranged above a sea surface S, resting on the foundation 4. The foundation 4 is preferably fixed to the seabed.

[0026] The wave power facility 1 may instead be a floater, such as in the form of a tension leg platform.

[0027] The deck 2 is supported by platform bars 5 extending between the seabed B and the deck 2, as well as platform wires 6.

[0028] On the deck 2 there is arranged a plurality of generator cells 3, wherein each generator cell 3 comprises a power generator 103 for transforming wave power.

[0029] In the shown embodiment, there are arranged six rows of generator cells 3. As appears from Fig.2, three rows are stacked on top of each other on the respective side of the deck 2.

[0030] The size of the generator cells 3 may be more than 30 m in the length, 11 m width, and 25 m heigh.

[0031] As can be seen in Fig.2, two main lines 13, 14 extend between a respective generator cell 3 and the seabed B.

[0032] The lower ends of the main lines 13, 14 are fixedly connected to the seabed B through one or more anchoring devices 8. The anchoring devices 8 can for instance comprise suction anchors or gravity-based anchors, such as concrete structures.

[0033] Indicated in Fig.2 is an angle α between a main line 13 and the vertical.

[0034] Fig. 3 is a schematic view of the wave power facility 1 seen from above, depicting how the main lines 13, 14 extend from the deck 2 and down to the anchoring devices 8 at the seabed.

[0035] Fig. 4 is a schematic side view of a generator unit 10, seen from the same angle as in Fig.2. The foundation 4 and the deck 5 supporting the generator cell 3 have been omitted, as Fig.4 is merely for illustrating the function of the generator unit 10.

[0036] The embodiment shown in Fig.4 is with just one of the main lines 13, 14, which were shown in Fig.2 and Fig.3. The generator unit 10 comprises a wave absorber 22, connected at the vertical level the waves, i.e. the level of the sea surface S by means of one main line 13. The generator unit 10 also comprises the main line 13. The main line 13 extends between the anchoring device 8 and the wave absorber 22, and between the wave absorber 22 and the generator cell 3. The main line 13 can be a wire, a rope, a chain, or other similar string.

[0037] The generator cell 3 comprises a power generator 103 that is connected to the main line 13. The power generator 103 comprises means for transforming a pull in the main line 13 into another form of power, such as electric power or hydraulic power.

[0038] Summarized, the generator unit 10 comprises the power generator 103, the main line 13, the wave absorber 22, and the anchoring device 8.

[0039] As the skilled reader will realize, when waves move the wave absorber 22 back and forth, substantially in the horizontal direction, the total length of the main line 13 between the generator cell 3 and the anchoring device 8 will change. This change of length is exploited for harvesting the wave energy with the power generator 103.

[0040] The main line 13 is tensioned with a (not shown) tensioning means, such that the main line 13 is pulled up (into the generator cell) when the main line 13 approaches a straight (short) configuration, while allowing pay out of main line 13 when a wave acts on the wave absorber 22. An example of such a tensioning means is a weight that by means of gravity provides a pull in the main line 13, or an elastic spring, such as a metal spiral spring.

[0041] In Fig.4, the angle α is again indicated. In the situation shown in Fig.4, the wave absorber 22 has been moved a distance in the horizontal direction. As a result, the main line 13 does not extend in the straight line between the power generator 103 (which is supported by the offshore structure) and the anchoring device 8.

Hence, to illustrate the angle α, a straight dashed line 25 is indicated between the power generator 103 and the anchoring device 8. The angle α thus is the angle between the straight line 25 that extends between the power generator 103 and the anchoring device 8, and the vertical. The angle α can typically be less than 30° or 20° or even less than 15° or 10°.

[0042] Fig. 5 depicts another embodiment of a generator unit 10 with a schematic front view. In this embodiment, two main lines 13, 14 are used. In addition to the main lines 13, 14, a winch line, here in the form of a winch wire 15, extends from the generator cell 3 and down to the wave absorber 22, to which the winch wire 15 is attached.

[0043] The wave absorber 22 comprises line guides 107 that interface with the main lines 13, 14. The line guides 107 maintains a connection between the wave absorber 22 and the main lines 13, 14, while allowing the wave absorber 22 to slide along the main lines 13, 14.

[0044] The wave absorber 22 is suspended with the winch wire 15 and is during normal use not moved vertically. However, the winch wire 15 connects to a winch 109 that enables the operator to pull the wave absorber 22 out of the water, such as for inspection or maintenance. Moreover, the operator may lift the wave absorber 22 out of the water, or deeper below the water surface if the weather (wave) conditions are too harsh.

[0045] During normal operation, the wave absorber 22 will be moved horizontally back and forth due to the forces from the waves. This will pull the main lines 13, 14 out from and back into a respective power generator 103. While the embodiment in Fig. 5 is shown with two power generators 103, one could also functionally connect the main lines 13, 14 to one common power generator 103.

[0046] Instead of having two main lines 13, 14, one could instead have only one, or more than two, such as four main lines.

[0047] Still referring to Fig.5, the wave absorber 22 exhibits a straight star configuration. Along a longitudinal portion of the wave absorber 22, it exhibits a constant cross section shaped as an X. The X-shape is formed with plane plates 22a that are attached together into the straight star configuration. As the skilled person will appreciate, instead of the X-shaped cross section, the wave absorber 22 could also have a Y-shaped cross section, or another cross section with more than four plane plates 22a extending out from the center, for instance five plates 22a.

[0048] While Fig.5 depicts an embodiment wherein the wave absorber 22 exhibits the said straight star configuration, other designs are possible. For instance, the wave absorber 22 may have a cylindrical configuration, or a spherical configuration (advantageously not entirely enclosing an inner compartment, but rather with apertures to allow inflow of water).

[0049] Fig. 6 is a more detailed view of the power generator 103, having a rotating generator sheave coupled to an electric generator.

[0050] Fig. 7 shows a generator cell 3 with a front view. This generator cell 3 is configured for use with the previously discussed main lines 13, 14, as shown in Fig. 2, Fig.3 and Fig.5.

[0051] The winch wire 15 extends from the (not shown) wave absorber 22 and up to the winch 109, here shown with a winch sheave.

[0052] Fig. 8 depicts the same generator cell 3 with a schematic top view. The main lines 13, 14 are guided into engagement with guide sheaves 111. From the respective guide sheaves 111, the main lines 13, 14 connect to a power generator 103, which in this embodiment is in the form of a linear generator. When the waves induce a pull in the main lines 13, 14 when acting on the wave absorber 22, the linear power generator 103 will be moved and will convert the pull into another form of power, such as electric power.

[0053] In the shown embodiment, the main lines 13, 14 are interconnected at the position of the linear power generator 103. Moreover, the main lines 13, 14 connect to the power generator 103 with a generator sheave 103a. This ensures that a nonbalanced pull in the respective main lines 13, 14 is accounted for.

[0054] Fig. 9 depicts a generator cell 3 with a side view, as well as a schematic diagram of the interface between main lines 13, 14 and the schematically depicted linear power generator 103 (shown on the left-hand side of Fig.9). In this image, there are also shown auxiliary guiding sheaves 115 that control the position of the main lines 13, 14.

[0055] In the illustration of Fig.9, the direction of the main lines 13, 14 are shown too close to the horizontal direction, and will thus be guided further such that they take a more vertical orientation towards the (not shown) wave absorber 22.

[0056] In this embodiment, four main lines 13, 14 are guided into engagement with the guide sheaves 111 and with the power generator 103.

[0057] Fig. 10 depicts, with a schematic side view, two generator units 10 having respective generator cells 3 arranged laterally opposite of each other. Their respective main lines 13 engage a respective guide sheave 71 and connect to a respective linear power generator 103.

[0058] The respective linear power generators 103 connect to a structure 3a of the cell 3, wherein the structure 3a is a fixed structure.

[0059] Fig. 11 depicts one linear power generator 103 with a more detailed view.

[0060] Fig. 12 depicts an embodiment of a power generator 103. In this embodiment, the power generator 103 comprises a hydraulic cylinder 201 with a piston (not shown). The hydraulic cylinder 201 is connected to a hydraulic inlet line 203 and a hydraulic outlet line 205. A check valve (not shown) may be arranged to ensure that the hydraulic fluid flows in one direction only. The hydraulic inlet line 203 and outlet line 205 will typically be part of a hydraulic loop that includes a hydraulic motor connected to an electric generator for conversion to electric power.

[0061] Furthermore, a spring 207 is connected to the generator sheave 103a. The spring 207 will allow the generator sheave 103a to reciprocate as the main lines 13, 14 moves it. Moreover, to the spring 207 there is connected a spring adjustment arrangement 209. The spring adjustment arrangement 209 is used to adjust the position of the spring 207. Typically, during periods of large waves, the spring adjustment arrangement 209 will pull the spring towards itself, to enable a longer reciprocating movement of the generator sheave 103a. During periods of smaller waves, the spring adjustment arrangement 209 will move the spring further away, to enable small reciprocating movements of the generator sheave 103a.

[0062] The power generator 103 shown in Fig.12 may in one embodiment be combined with the embodiment shown in Fig.5. Moreover, the power generator 103 shown in Fig.12 may be combined with the embodiment shown in Fig.9.

[0063] Fig. 13 shows an embodiment of a power generator 103 that interfaces with a hydraulic system 70. The power generator 103 transfers the movement of the main wire(s) 13, 14 into hydraulic power, while the hydraulic system 70 transfers the hydraulic power into electric power.

[0064] The power generator 103 comprises a hydraulic cylinder 72 attached between the main wires 13, 14 and the structure 3a.

[0065] To the power generator 103 the said hydraulic system 70 is connected. The hydraulic system 70 comprises a first accumulator bank 73, a second accumulator bank 75, a hydraulic electric generator 77 and a hydraulic tank 78. The hydraulic system 70 further has a pressure regulator and 74a and a pressure regulator valve 74b to control the flow of hydraulic fluid from the first accumulator bank 73 to the second accumulator bank 75.

[0066] The hydraulic system 70 also has a pressure control 76a and a pressure control valve 76b to control the flow of hydraulic fluid from the second accumulator bank 75. The second generator system G1 comprises pipes 81, 82, 83, 84, 85 for the flow of hydraulic fluid between the components 73, 75, 77, 78. In addition there are illustrated signal lines 87a, 87b, 87c, 87d between various components for the regulation the hydraulic flow.

[0067] The functioning of the hydraulic system 70 shown in Fig.13 is the following:

[0068] When there is a pull in the main wire 13, 14, the hydraulic cylinder 72 will act as a hydraulic reciprocating pump with a spring return, pumping hydraulic fluid under pressure to the first accumulator bank 73.

[0069] The pressure regulator valve 74b is arranged between the first and second accumulator banks 73, 75. The pressure regulator valve 74b is further controlled by the pressure regulator 74a that sets the limit pressure for opening the pressure regulator valve 74b. The pressure regulator 74a automatically adjusts the set point of the pressure regulator valve 74b based on a measured wave height.

[0070] The limit pressure for the pressure regulator valve 74b will increase with increasing wave heights. This means that the pressure regulator valve 74b may open even at small waves when there is less pumping of hydraulic fluid from the hydraulic cylinder 72 due to small movement of the main wires 13, 14.

[0071] The hydraulic fluid further flows into the second accumulator bank 75 when the pressure in the first accumulator bank 73 exceeds the pressure limit of the pressure regulator valve 74b.

[0072] Between the second accumulator bank 75 and the hydraulic electric generator 77, the pressure control valve 76b is arranged. The pressure control valve 76b is further controlled by the pressure control 76a. The pressure control 76a automatically adjusts the opening of the pressure regulator valve 76b.

[0073] The pressure regulator valve 76b will thus open at an upper pressure H-1 and close at a lower pressure L-1. The value of the upper pressure and lower pressure are not constant but shifts by the different wave heights. This makes it possible to operate the hydraulic electrical generator 77 efficient within a range of wave heights.

[0074] By setting a higher-pressure limit H-1 for the opening of the valve 76b than for closing of the valve 76b, it provides some pressure built up in the system for the power generating process. This provides a more efficient energy transition. The builtup also gains momentum for the forces in the system to provide a longer period of operation of the generator.

[0075] The hydraulic fluid flows further from the hydraulic electric generator 77 when the pressure in the second accumulator bank 75 is above the lower pressure L-1. The hydraulic electric generator 77 will only rotate to produce power when the pressure is between H-1 and L-1.

[0076] The flow of hydraulic fluid into the hydraulic electric generator 77 provides the transmission into power in the hydraulic electric generator 77.

[0077] It is to be noted that the pressure in the second accumulator bank 75 will always have a lower pressure than the first accumulator bank 73. This is due to the feeding of the hydraulic motor of the hydraulic electric generator 77.

[0078] In this manner, the first accumulator bank 73 will receive hydraulic liquid from the power generators 103 with varying pressure, depending on wave characteristics. The second accumulator bank 75 will, on the other hand, supply the hydraulic electric generator 77 with hydraulic pressure that is suited for running of the hydraulic electric generator 77.

[0079] From the hydraulic electrical generator 77, the hydraulic fluid is adapted to flow into a hydraulic tank 78. The hydraulic fluid may then be reused into the hydraulic cylinder 72 by supplying fluid through the return pipe 85 back into the hydraulic cylinder 72. The process may then be repeated.

[0080] In addition to the supply pipe 81 connecting the hydraulic cylinder(s) 72 and the first accumulator bank 73, there are indicated a plurality of further corresponding supply pipes 81 that extend from corresponding hydraulic cylinders 72 of additional (not shown) power generators 103. Correspondingly, there would be a plurality of return pipes 85 (not shown) that guide hydraulic fluid back to the additional, not shown power generators 103.

[0081] As shown in Fig.13, the power generator 103 comprises two hydraulic cylinders 72 that connect to respective main lines 13, 14. As the skilled person will appreciate, the hydraulic cylinders 72 could also be operated by one main line 13, such as shown in Fig.4.

[0082] The inlet and outlet lines of the hydraulic cylinder 72 are provided with check valves 89 to ensure one-way flow of the hydraulic fluid.

Claims (9)

Claims

1. A wave power facility (1) comprising an offshore structure (2, 4) and further comprising a plurality of generator units (10), wherein the respective generator units (10) comprise

- a power generator (103) supported by the offshore structure (2, 4) at a distance above the sea surface (S);

- a main line (13, 14) connected to the power generator (103) and extending between the offshore structure (2, 4) and the seabed (B), as it is anchored to an anchoring device (8) at the seabed;

- a wave absorber (22) in engagement with the main line (13, 14) and at the vertical level of the sea surface (S).

2. A wave power facility (1) according to claim 1, characterized in that the wave absorber (22) exhibits a mass density of more than 800 kg/m³.

3. A wave power facility (1) according to claim 1 or claim 2, characterized in that the wave absorber (22) is compartment-less.

4. A wave power facility (1) according to any one of the preceding claims, characterized in that the wave absorber (22) comprises flat plates (22a) arranged in a straight star configuration.

5. A wave power facility (1) according to any one of the preceding claims, characterized in that a straight line (25) between the connection points of the main line (13, 14) to the offshore structure (2, 4) and to the anchoring device (8), respectively, forms an angle (α) to the vertical that is less than 30°.

6. A wave power facility (1) according to any one of the preceding claims, characterized in that

- the wave absorber (22) is suspended with a winch line (15);

- the wave absorber (22) comprises a line guide (107) that maintains a sliding connection between the wave absorber (22) and the main line (13, 14), such that the wave absorber (22) may move along the extension of and with respect to the main line; and

- the generator unit (10) further comprises a winch (109) configured to move the wave absorber (22) up and down along the main line (13, 14).

7. A wave power facility (1) according to any one of the preceding claims, characterized in that the power generators (103) of respective generator units (10) comprise a hydraulic cylinder (72, 201) moved by the main line (13, 14) and that the hydraulic cylinders of the respective generator units (10) hydraulically connect, with a supply pipe (81) and a return pipe (85), to a common hydraulic system (70) that converts hydraulic power into electric power, as the hydraulic system comprises a hydraulic electric generator (77).

8. A wave power facility (1) according to any one of the preceding claims, characterized in that the respective generator units (10) comprise a generator cell (3) comprising the power generator (103), wherein the generator cells (3) are arranged in two stacks of cell rows, wherein each cell row comprises at least five generator cells (3), and each stack of cell row comprises at least two rows of generator cells (3).

9. A method of producing electric energy with a wave power facility according to claim 6, wherein the method comprises the following steps:

a) with the winch (109), lowering the wave absorber (22) down to a position below the sea surface;

b) harvesting wave power by means of the power generator (103) as the wave absorber (22) provides pull in the main line (13, 14).