GB2525966A

GB2525966A - A method of operating a wave power plant and wave energy converter

Info

Publication number: GB2525966A
Application number: GB1503854.0A
Authority: GB
Inventors: Benjamin Hagemann; Nik Scharmann; Alexander Poddey
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2014-03-07
Filing date: 2015-03-06
Publication date: 2015-11-11
Also published as: DE102014204248A1; GB201503854D0

Abstract

A wave energy plant comprises a rotor 1 with at least one lever arm carrying a coupling body 3 e.g. a blade or Flettner rotor which is driven by wave movement. Strength of the coupling between the vane or rotor 3 and water movement is varied by controlling the angle of the blade, or the speed of the Flettner rotor, using an actuator 5. Coupling strength (referred to as circulation strength) is controlled according to the phase angle between the angular position of the blade 3 and the flow angle of wave movement. This control allows more stable and efficient operation in non-uniform waves.

Description

Method for operating a wave energy plant and wave energy plant

Description

The invention relates to a method for operating a wave energy plant for converting energy from a wave movement and to such a wave energy plant.

Prior art

Wave energy plants (also called wave energy converters or wave power stations) convert the energy from sea waves into another form of energy, for example in order to produce electric current. Recent design approaches in this regard use rotating units (rotors) which convert the wave movement into a torgue. These can have one or more lever arms with coupling bodies fastened thereto. Hydrodynamic buoyant bodies (i.e. bodies which generate lift when there is a flow around them, such as, for example, lift profiles and/or Flettner rotors using the Magnus effect) can be used as coupling bodies, by means of which lift forces are generated from the inflowing wave and a torgue is generated by the arrangement of the coupling bodies on the lever arm, which torque can be converted into a rotational movement of the lever arm about a rotor rotational axis. A superimposed inflow formed of the orbital flow of the wave movement and the intrinsic rotation of the rotor results in lift forces on the coupling bodies, as a result of which a torque is applied to the rotor.

For example, from DE 10 2011 105 177 Al there is known a plant conoept in whioh the lift of a buoyant body around which there is a flow is converted into a rotational movement. The rotor with its coupling bodies is intended advantageously to orbit largely wave-synchronously, i.e. with an average rotational speed corresponding to the wave orbital movement or proportionally thereto. If, for example, if the rotational frequency of the rotor corresponds to the wave frequency, there result largely steady-state inflow conditions on the coupling bodies which lead to a largely continuous torque on the rotor shaft.

This can be fed directly into a generator. Excessive mechanical stresses and/or unevenness in the output power of the wave energy plant are thereby avoided.

In particular in the open sea, however, there exist very different wave states. These include, besides swells in which the waves occur very regularly, also wave states in which the wave characteristic changes continuously due to superimposition of different waves. In the context of this application, the first wave state is referred to as "monochromatic", the second wave state as "multichromatic".

Completely monochromatic wave states occur rarely in nature, and therefore the term monochromatic" also includes waves that have a certain, albeit low, multichromatic component.

Although the wave states generally do not change suddenly and in addition can be relatively well predicted, the rotational speed of a corresponding rotor often cannot be adapted quickly enough in practice. This is true in particular of multichromatic wave states. In DE 10 2012 012 096 Al, therefore, a synchronicity only in the time average per revolution is required. However, in real bodies of water, in particular the sea, this mode of operation does not deliver optimum results in all situations.

The invention therefore aims to improve the operation of generic wave energy plants in multichromatic wave states.

Disclosure of the invention

According to the invention, a method and a wave energy plant having the features of the independent claims are proposed. Advantageous configurations are the subject-matter of the subclaims and the following description.

Advantages of the invention The invention provides the possibility of operating a wave energy plant in particular with multichromatic waves with an energy yield as high as possible, that is to say efficiently. This is achieved by abandoning the synchronous operation and in the asynchronous operation influencing or modulating a circulation strength on at least one coupling body, which is carried by at least one lever arm of the rotor of the wave energy plant, in dependence on a phase angle between the angular position of the at least one lever arm and the flow angle of the wave movement.

In multichromatic waves (also called irregular waves) a sudden jump of the wave-induced orbital flow can occur.

This often happens at times when the flow almost disappears. In such cases, it is energetically extremely unfavourable for the rotor to track these jumps, i.e. in a synchronous operation of the rotor to remain with the wave movement. The flow velocity in such situations is imperceptibly small, so that there is in most cases no energy gain anyway due to hydrodynamic losses. Rather, owing to reaction forces, for example excessively high torque requirements on the drive train or the undesired radiation of waves occur. According to the invention, therefore, there is a departure from synchronous operation and the rotor is deliberately operated asynchronously with respect to the wave movement. In order to prevent or at least reduce energy losses or undesired forces, the circulation strength on the coupling body is therefore specifically preset. Consequently, the llndesired forces can be reduced.

Preferably, the circulation strength is changed by changing an adjustment parameter which influences a strength of a coupling of the coupling body with the fluid.

If the coupling bodies are formed as hydrodynarnic coupling bodies, the adjustment parameter is in particular a pitch angle or angle of incidence. Since the circulation strength depends inter alia on the inflow angle or angle of attack on a hydrodynamic coupling body, the circulation strength can be changed, for example, in a simple way by changing the pitch angle. The adjustment parameter may also include a change of the rotational speed. If the coupling bodies are Flettner rotors, i.e. cylinders with additional intrinsic rotation, the rotational speed and/or the rotational direction of the Flettner rotors can be adapted as adjustment parameters.

Since at certain phase angles, in particular at approx.

9Q0 no or hardly any energy can be extracted from the wave, but energy losses arise due, for example, to flow resistances, it is expedient to adapt the circulation strength of the circulation in dependence on the phase angle. A desired reduction can take place in particular by reducing the absolute value of the circulation strength, so that energy losses are minimised. Since the phase angle changes continuous'y, it therefore also passes through the same values again and again. A change of the circulation strength can therefore take place preferably by means of modulation with a trigonometric unctiori, e.g. a cosine function. A trigonometric function is particularly suitable, since with the aid thereof a change of sign of the phase angle, necessary for good energy extraction, is readily obtained. Depending on the conditions, it is also possible to deviate to a certain extent from the course of a trigonometric function.

Advantageously, the circulation strength is changed in a continuous manner, i.e. no abrupt transitions take place. A change of circulation is always accompanied by concomitant effects, which are in most cases undesired. In this case, for example, unsteady forces or wave radiation are thus produced. It is therefore expedient to change the circulation strength as little as possible. This can be done, for example, also by means of modulation with a trigonometric function.

In a preferred embodiment, a method according to the invention is employed in a wave energy plant with a rotor which comprises two coupling bodies which are offset in relation to the centre of rotation of the rotor by 1800+/_ 45°, preferably by 1800+/_200, particularly preferably by 1800+/_100 and most preferably by 1800. This is advantageous since undesired wave radiations of the two coupling bodies cancel each other out at least as far as possible. This can be explained by the wave theory, since waves which are phase-shifted by 1800 cancel each other out. In the case of a shift differing from 1800, at least a partial cancellation still takes place. This enables an efficient operation. Likewise, a higher even number of coupling bodies, which then are each offset from one another by a same angle, is possible, since each two opposite coupling bodies balance out with regard to undesired wave radiation.

In another preferred embodiment, a method according to the invention is employed in a wave energy plant with a rotor which comprises one or a higher odd number of coupling bodies which are offset from one another in relation to the centre of rotation of the rotor each by an angle which is the same or at least as far as possible the same. Mi efficiency disadvantage resulting from an odd number of coupling bodies (since with an even number respectively opposite coupling bodies were able to efficiently cancel cut undesired wave radiations) can be compensated for or even exceeded by a cost saving compared with a rotor having an additional blade and correspondingly even number of coupling bodies, since for example a lever arm (in the case of mounting of the coupling body on both sides correspondingly two lever arms) , a coupling body and associated adjustment actuator system and sensor system are not required as much.

A wave energy plant according to the invention is suitable for carrying out a method according to the invention, in particular a control device of & wave energy plant is configured, in particular in programming terms, to carry out a method according to the invention.

It is also advantageous to implement the invention in the form of software since this permits particularly low costs, in particular if a computing unit which is to be imp'emented is also used for other tasks and is therefore present in any case. Suitable data carriers for making available the computer program are, in particuiar, diskettes, hard disks, flash memories, FEPROMs, OD-ROMs, DVDs etc. It is also possible to download a program via computer networks (Internet, Intranet etc.).

Further advantages and configurations of the invention can be found in the description and the appended drawing.

Of course, the features which are mentioned above and which are to be explained below can be used not only in the respectively specified combination but also in other combinations or alone without departing from the scope of the present invention.

The invention is illustrated schematically in the drawing using exemplary embodiments and is described in detail below with reference to the drawing.

Description of the figures

Figure 1 shows a preferred embodiment of a wave energy plant according to the invention in a perspective view.

B

Figure 2 shows the wave energy plant according to Figure 1 in a side view and illustrates the pitch angle ap and the phase angle il between the rotor and the orbital flow.

Figure 3 shows schematically a further preferred embodiment of a wave energy plant according to the invention in a perspective view with an alternative rotor.

Figure 4 shows a resultant inflow angle cx-and the resultant forces at one of the coupling bodies from Figure 2 in an enlarged view.

Figures 5 to 9 show surface elevations due to radiation of waves at a water surface when using a method according to the invention in different configurations in a wave energy plant according to the invention with a rotor having two coupling bodies.

Figure 10 shows a surface elevation when using a method according to the invention in preferred configuration in a wave energy plant according to the invention with a rotor having one coupling body.

Figure 11 shows an output power of a rotor having a rotor unit when using a method according to the invention in a preferred configuration.

Figure 12 shows output powers of a rotor with two phase-shifted rotor units when using a method according to the invention in a preferred configuration.

Detailed description of the drawing

In the figures, identical or identically acting elements are specified with identical reference symbols. For the sake of clarity, the explanation will not be repeated.

The invention which is presented relates to the operation of rotating plants for acquiring energy from moving fluids, for example from the sea. The functional principle of such plants will be firstly explained below with reference to Figures 1 and 2.

Figure 1 shows a wave energy plant 1 with a rotor base 2, a housing 7 and four (two on each side) coupling bodies 3 which are respectively attached via lever arms 4 to the rotor base 2. The wave energy plant 1 is provided for operating below the water surface of a body of water where there is wave action, for example an ocean. In the example shown, the coupling bodies 3 are embodied in a profiled fashion, but can also be embodied as Flettner rotors, i.e. cylinders with additional intrinsic rotation. Mi adjustment device 5 with at least one degree of freedom is expediently available for each of the coupling bodies 3 in order to change the orientation (for example "pitch angle", i.e. the angle between the profile chord and the tangential speed) of the respective coupling body and therefore influence the interaction between the fluid and the coupling body. The degree of freedom of the adjustment devices is described here by adjustment parameters (pitch angle) . Alternatively, in the case of Flettner rotors as coupling bodies the rotational speed of the Flettner rotors can also be adapted. The adjustment devioes are preferably hydraulic (or electromotive or pneumatic) adjustment devices. A sensor system 6 for sensing the current adjustment is also preferably available. The components 2, 3, 4, 5, 6 are components of a rotor 11 which rotates about a rotor rotationa' axis x.

The housing 7 is a component of a frame 12. The rotor 11 is mounted so as to be rotatable relative to the frame 12. In the example shown, the frame 12 is connected in a rotationally fixed fashion to a stator of a directly driven generator for generating current, and the rotor 11 (here the rotor base 2) is connected in a rotationally fixed fashion to a rotor of this directly driven generator. It is also possible to provide a transmission or a hydrostatic drive train between the rotor base and the generator rotor.

A computing unit which is configured to carry out a method according to the invention is arranged inside the housing 7 and serves to control the operation of the wave energy plant 1. A provided means of attaching the wave energy plant 1 to the sea bed, which can also be done by means of a mooring system, in particular a monopile and more particularly by a jacket structure, for example, is not illustrated. In addition, it should further be noted that a form with respectively two lever arms per coupling body with a corresponding mounting on both sides may also be advantageous -Figure 2 shows a side view of the plant with lever arms rotated through 900 with respect to the position shown in Figure 1. The adjustment parameters can be seen as the pitch angle ap,i between the profile chord of the coupling bodies 3 and the tangent (illustrated with an arrow) on the orbit through the suspension point (centre of rotation) of the coupling bodies. The coupling bodies 3 are preferably suspended at their centre of pressure in order to reduce rotational moments which occur during operation and act on the coupling bodies, and therefore to reduce the requirements made of the support and/or of the adjustment devices.

The coupling bodies in Figure 2 and in the further figures are illustrated only by way of example in order to define the different machine parameters. In addition, curvature of the coupling bodies to the orbit can also be advantageous.

In Figure 3, a perspective view of a further preferred embodiment of a wave energy plant 1' according to the invention is illustrated schematically. The wave energy plant 1' according to Figure 3 differs from the wave energy plant 1 according to Figure 1 or 2 essentially by the rotor 11', which here has three lever arms 4 on one side. It can also be formed two-sided with respectively three lever arms per side. The lever arms 4 here are arranged offset from one another by respectively 1200 in relation to the rotational axis 9.

The wave energy plant 1 (also applies to 1') is surrounded by a flow vector field. In the described embodiments, it is assumed that the inflow comprises the orbital flow of sea waves whose direction changes continuously. In the illustrated case, the rotation of the orbital flow is oriented in the anti-clockwise direction, and the associated wave therefore propagates from right to left. In the monochromatic case, the inflow direction changes at the rotor rotational axis (x in Figure 1) here with the angular velocity Q = 2uf = const., where f represents the frequency of the monochromatic wave. In contrast, in multichromatic waves, 0 is subject to change over time, 0 = 1(t) since the frequency f is a function of time, f = 1(t) . The inflow results in forces at the coupling bodies. As a result, the angle ("rotor angle") of the rotor base 2 with respect to the horizontal changes with the rotational speed Wi = (? denotes the derivative of the time-dependent variable with respect to time) . Accordingly, W denotes the angle between the flow direction and the horizontal, which is referred to below as "flow angle".

A variable load torque M between the rotor base 2 and the housing 7 or frame 12 acts on the rotor 11. The load torque can act in a positive direction (in the opposite direction to the rotational speed i) but also in the negarive direction (that is to say in a driving fashion) . The load torque is caused, for example, by current generation in the generator.

An angle between the rotor orientation, illustrated by a lower dashed line which runs through the rotor rotational axis and the suspension point of a marked coupling body, and the direction of the orbital flow, which is illustrated by an upper dashed line which runs through one of the velocity arrows {right arrow over is referred to as phase angle A=W -ri, whose absolute value can be influenced by the setting of the drive torque and/or of the load torque.

In the context of the invention, the wave energy plant is operated asynchronously to the orbital movement, i.e. the phase angle =W - varies over time and Qw1, i.e. the rotational speed o of the lever arm 4 about the rotor rotational axis x, 9 does not correspond, in the time average, over one or more revolutions, to the orbital speed Q of the wave movement. Thus, the phase angle A changes continuously and passes through the entire angular range from 00 to 3600.

Figure 4 illustrates, taking one coupling body by way of example, the resulting inflow conditions and the forces occurring at the coupling bodies which give rise to a drive torque -The figure illustrates, on the coupling body (index i=1) the local inflows through the orbital flow (i) (w for wave) and through the intrinsic rotation (T,1) (T for tangent) , the inflow (,-) (R for result) resulting as a vector sum of these two inflows and the resulting inflow angles a between the resulting inflow R,1 and the profile chord S. Furthermore, the resulting lift forces and resistance forces Fres,i at the two coupling bodies are illustrated, which forces are dependent both on the absolute value of the inflow speed and on the inflow angle cx1 and therefore also on the pitch angle a,1 and, as is known, are oriented perpendicularly (FIfL,i) and respectively in parallel (Fres,i) with respect to the direction of The sum of a1 and ap, is given by In the case of steady-state multichromatic waves (waves with a plurality of different frequency components and amplitude components, but these components are constant) or mult±chromatic waves (the frequency components and amplitude components are variable over time) , an effectively resulting value, for example a mean value or a value of the main component, can be used as a local orbital flow ( ) -The local orbital flow can be measured or calculated.

For the case illustrated, the lift force F1-,-results in a rotor torque in the anti-clockwise direction, and the resistance force Fres,i results in a rotor torque which is smaller in absolute value and is in the opposite direction (that is to say in the clockwise direction) -The sum of the two rotor torques brings about a rotation of the rotor 11 whose speed can be set by influencing the drive torque and/or the load torque.

From the resultinq inflow Q and inflow angle a1, a variable referred to as circulation strength ir can be defined, which gives the circulation or flow at or around a coupling body i. Tn a simplified two-dimensional model concept, the circulation strength JPj is given as P1 = Ca (at) -V -Sr, with the lift coefficient Ca(aj), which depends, inter alia, on the inflow angle aj.

The circulation strength F1 makes it possible to characterise which energy can be extracted from the wave.

In the following description, specific phase angle values between the angular position of the lever arm and the flow angle of the wave movement (fj) are used by way of example.

In practice, these angles can also be taken into account only approximately, i.e. for example +/-45°, A+/-20°, The energy which can be extracted from the wave is, however, dependent on the phase angle A-. Thus, for example, with a phase angle of A-= 0° as shown approximately in Figure 4, the energy efficiency is almost optimal. With a phase angle of, for example, A1 = 90°, however, no or hardly any energy oan be extracted from the wave, since between two waves phase-shifted by 90° (wave radiated in and out at the coupling body) in principle no interaction is possible, as wave theory shows. Rather, for A = 900 energy has to be produced in order to overcome, for example, flow resistances at the coupling body, in order to maintain the rotation.

With a phase angle of A1 = 180°, the sign of the circulation strength Fj required for at least approximately optimal energy extraction is to be chosen, compared with A = 0°, to be opposite, P(A = 0°)= -F(A = 180°). With two coupling bodies 3 arranged uniformly over the circumference of the rotor 1, therefore, both coupling bodies 3 exchange their action, and an optimal energy efficiency is thus possible exactly as with A = 0°.

In order now to minimise or at least reduce the energy losses with an unfavourable phase angle, it is advantageous to continuously change the circulation strength Fj during the passage through the phase angle A-, i.e. during the operation of the wave energy plant. In particular, the circulation strength 1' with a phase angle of A = 90° = 270° should be zero, P(A = 90° = 270°) = 0.

In order to obtain the described behaviour of F1(A1), the circulation strength can be correspondingly modulated (in particular by presetting the inflow angle a) , for which e.g. a trigonometric function such as the cosine function is suitable. Accordingly, an effective circulation strength ",eff acting at the coupling bodies i according to = Frei005(Ai) can be chosen, where ref is an optimal circulation strength, e.g. with A = 0°.

The change of the circulation strength F at the coupling body 3 can be effected e.g. by changing the angle of incidence or pitch angle ap,. As a result, the inflow angle c and thus the circulation strength F also changes.

Undesired radiations of waves at the coupling bodies 3, which mean an energy loss, can thereby be systematically suppressed or at least reduced. Such radiations are in some cases visible at the surface of the water as surface elevations.

Furthermore, a change of the circulation strength, in particular a rapid or abrupt change, is always accompanied by concomitant effects, which are in most cases undesired.

These are, for example, unsteady forces at the rotor and further undesired wave radiation, which means wear of the wave energy plant and/or energy loss. This can be avoided by changing the circulation strength in a continuous manner. This can be achieved, for example, likewise by the modulation with a cosine function already mentioned above.

However, other functions which ensure a corresponding continuous change are also conceivable.

Figures 5 to 9 represent surface elevations due to radiation of waves during the operation of a wave energy plant according to the invention with a rotor having two coupling bodies and using a method according to the invention in different configurations, in particular in the form of different rotational speeds and corresponding changing of the circulation strength by means of modulation.

The location is plotted in the horizontal direction in m, the rotor being in each case at a position of 750 m. The surface elevation is plotted in each case in the vertical direction in m. The direction of propagation of the waves is from left to right. :is

In a simplified model concept, the interaction property of the rotor with an incident wave is dependent on how good a wave phase-shifted by 180° from the incident wave can be radiated from the machine position in the wave propagation direction. In order to be able to absorb, for example, a monochromatic wave, it must be possible to radiate a wave of the same frequency phase-shifted by 180° from the rotor (when operated without incident wave) . Undesired radiations are then shown in deviations of the downward wave and in upward components (in the figures to the left of the rotor) The ability to radiate (without incident waves) monochromatic waves (downwards from the machine in the wave propagation direction) is therefore a quality feature for assessing modes of operation.

Figure 5 shows an expeoted surface elevation caused by the rotor 1 at a period of the rotor of 8s and with a constant circulation strength. This serves as a reference example for the following illustrations in Figures 6 to 9.

Figure 6 shows a surface elevation in the case of asynchronous operation and a cosine-modulated circulation strength according to a preferred configuration of a method according to the invention. The period of the rotor here is 4s, i.e. the rotational freguency of the rotor corresponds to twice the frequency of the illustration in Figure 5. The frequency of the radiated wave, by contrast, corresponds to the frequency of Fiqure 5, i.e. to a period of 8s. This is explained by the modulation of the circulation strength(s) FL according to a method according to the invention. Waves having other frequencies, in particular those such as those of the rotation of the rotor which would not enable an effective interaction are no lonqer present or at least as far as possible suppressed.

It can further be seen that the amplitude of the surface elevation of the radiated wave is lower than in the reference example from Figure 5, which is caused by the reduced circulation strength in the time average. However, despite half the rotational speed, the frequency corresponds to the desired frequency (here period Bs) . This is important for an effective interaction. With a method according to the invention, efficient coupling to different multichromatic waves is therefore possible also in asynchronous operation (rotor period not equal to wave period) Figure 7 shows the example from Figure 6, but where an abrupt change takes place when changing the circulation strength, here by a modulation by means of a signum function of the cosine function, i.e. r:,eff = Fnetsign(cos(&j) . This abrupt change has a marked effect on the surface elevation, i.e. on the radiation of waves, which can be seen from the additional e'evation in the range from 400 m to 750 m. The wave shown in this range propagates from right to left, thus opposite the propagation direction of the sea wave (not shown) However, an effective interaction with waves opposite the propagation direction is not possible. Such abrupt changes should therefore be avoided for reasons of energy efficiency, as already mentioned. :15

Figures 8 and 9 show analogous examples to Figures 6 and 7, but with half the rotational frequency compared with the reference illustration in Figure 5, i.e. a period of 16 s.

Here it can again be seen that an abrupt change of the circulation strength shollld be avoided and that the modification of the circulation strength in the asynchronous operation is more efficient than an operation with a sudden change of the circulation strength, although the effect is not so pronounced as with a period of twice the duration.

As already mentioned, undesired wave radiations with suitably arranged coupling bodies (e.g. two opposite coupling bodies, possibly also with an odd number of coupling bodies) on the rotor cancel each other out at least as far as possible. For this purpose, Figure 10 shows, by way of example, a surface elevation with asynchronous operation of a rotor having only one coupling body and otherwise the same conditions as in Figure 6 (asynchronous operaticn means: the period of the rotor rotation, here 4 s, deviates from the period of the radiated principal wave) . Here, there can be clearly seen the additional elevations which result frcm there being no suitably arranged coupling bodies (e.g. an opposite coupling body) present, whereby the undesired wave radiations could cancel each other out.

Accordingly, a rotor should have an even number of coupling bodies, where each two coupling bodies are offset by 180° and respectively mutually cancel out undesired wave radiations. As already mentioned, other suitable positions and numbers of coupling bodies are also possible, so that undesired wave radiations cancel each other out. Undesired effects which would arise with a synchronous operation due to a disadvantageous phase angle in the additional coupling body pairs, are, however, not relevant with an asynchronous operation, in particular with an operation according to a method according to the invention, since the phase angle changes continuously, as this change is taken into account in the method according to the invention. A synchronous operation thus does not necessarily have to be maintained and nevertheless efficient coupling to the wave is possible.

Figure 11 shows a scaled output power of a rotor which is operated according to a method according to the invention, i.e. modulated circulation strength, with respect to the phase angle L\. Accordingly, the output power is maximal with a phase angle of, for example, =0° or £x=180°, but minimal with a phase angle of, for example, =90° and =270°, since there of course the circulation strength is reduced to a minimum. This output power shown applies both to a rotor having one coupling bcdy or two coupling bodies arranged offset by 180°, in each case also called a rotor unit, since the undesired wave radiation is not considered here.

Figure 12 shows output powers 20, 21 of two rotor units which each have two coupling bodies, with respect to the phase angle L. In this case, the two rotor units are phase-shifted by 90°. A simple addition of both output powers 20, 21 would result in the total output power 22. Since, however, the same energy cannot be extracted twice from a wave and owing to an increase in the number of rotor units possibly further losses due, for example, to flow resistances are added, in reality a lower output power, for instance such as shown by 23 or 24, is to be expected. At least for the first additional rotor units, however, the mean value of the output power is usually increased.

Moreover, the output power is smoothed owing to a greater number of rotor units.

If now overall an odd number of coupling bodies are arranged on the rotor, e.g. three coupling bodies, these are preferably arranged offset from one another by respectively an equal angle, thus e.g. 120°. This may in some cases result in disadvantages regarding the energy efficiency compared, for example, with four coupling bodies arranged offset accordingly by 900, since radiations may possibly no longer be optimally cancelled out, but a considerable cost saving is achieved by this omitting of one coupling body, the lever arm(s), the adjustment actuator system and a sensor system. Depending on other factors such as, for example, local conditions of the body of water or precise construction of the wave energy plant, the cost saving may compensate for or even exceed the disadvantages regarding the energy efficiency. Depending on the conditions, an economically optimal number of coupling bodies can thus be determined, which may in particular be odd.

Claims

Claims 1. Method for operating a wave energy plant (1) for converting energy from a wave movement of a fluid into another form of energy, wherein the wave energy plant (1) has at least one lever arm (4) rotatably mounted about a rotor rotational axis (x) and carrying a coupling body (3), and has an energy converter (2,7) coupled to the at least one rotatably mounted lever arm (4), wherein a circulation strength at the coupling body (3) is preset in dependence on a phase angle (fx) between an angular position () of the at least one lever arm (4) and a flow angle 01') of the wave movement.
2. Method according to Claim 1, wherein the rotational speed (o,) of the at least one lever arm (4) about the rotor rotational axis (x), in the time average over one or more revolutions, does not correspond to an orbital speed (Q) of the wave movement.
3. Method according to Claim 1 or 2, wherein the wave energy plant (1) is operated such that the phase angle () over time assumes all values from 0° to 360°.
4. Method according to one of the preceding claims, wherein the circulation strength is preset at a phase angle () of 90°+/-20°, in particular 90°+/-l0°, further in particular 90° and/or 270°+/-20°, in particular 270°+/-10°, further in particular 270° to zero.
5. Method according to one of the preceding claims, wherein the circulation strength is preset at a phase angle (A) of 0°+/-20°, in particular 0°+/-10°, further in particular 0° to the negative of the circulation strength at a phase angle (A) of 1800+/_200, in particular 180°+/ 10°, further in particular 1800.
6. Method according to one of the preceding claims, wherein the circulation strength is preset by predefining an adjustment parameter (a±,1, a±,2) which influences a strength of a coupling of the coupling body (3) with the fluid.
7. Method according to Claim 6, wherein the coupling body (3) is a hydrodynamic coupling body (3) and wherein a pitch angle (a9,1, a9,2) of the hydrodynamic coupling body (3) is preset as adjustment parameter.
8. Method according to one of the preceding claims, wherein the circulation strength is changed in a continuous manner.
9. Method according to one of the preceding claims, wherein the circulation strength is changed in accordance with a trigonometric function.
10. Method according to one of the preceding claims, wherein the wave energy plant (1) is operated in multichromatic waves.
11. Computing unit which is configured to carry out a method according to one of the preceding claims.
12. Wave energy plant (1) for converting energy from a wave movement of a fluid into another form of energy, having at least one lever arm (4) rotatably mounted about a rotor rotational axis (x, 9) and carrying a coupling body (3), an energy converter (2,7) coupled to the rotatably mounted lever arm (4) , and a computing unit according to Claim 11.
13. Wave energy pThnt (1) according to Claim 12, which has an even number of lever arms (4) , in particular two or four or more, or which has an odd nllmber of iever arms (4), in particular one or three or more.
14. Wave energy plant (1) according to Claim 13, wherein the lever arms are offset from one another in relation to the rotor rotational axis (x, 9) by in each case an angle 360°/(nur±er of lever arms)+/-20°, in particular 360°/(nurnber of lever arms)+/-1O°, further in particular 360 0/ (number of lever arms)