EP2705248A1

EP2705248A1 - Arrangement for energy recovery

Info

Publication number: EP2705248A1
Application number: EP12789168.7A
Authority: EP
Inventors: Markku Oikarainen
Original assignee: Raikamo Esko
Current assignee: Raikamo Esko
Priority date: 2011-05-05
Filing date: 2012-05-03
Publication date: 2014-03-12
Also published as: WO2012160244A8; FI123177B; WO2012160244A1; FI20115428A0; EP2705248A4

Abstract

An arrangement for recovering wave energy. The arrangement comprises: at least one hollow piece (1) which is provided with an outer casing (2) and an inner space (3) therein. The outer casing is engaged to be rotatable with respect to a body (8) of the hollow piece. The inner space (3) is provided with a sun-and-planet gear (4) and a first mechanical rectifier (5). An internal gear (7) of the sun-and-planet gear (4) is fastened with respect to the outer casing (2) so as to rotate therewith, and a planet gear (10) and a sun gear (6) of the sun-and-planet gear are pivotally mounted to the body (8) of the hollow piece and arranged to transmit reciprocating rotational motion between the outer casing (2) and the body (8) to said first mechanical rectifier (5) arranged to convert said reciprocating rotational motion into one-directional rotational motion of a rotating axle (14).

Description

ARRANGEMENT FOR ENERGY RECOVERY

BACKGROUND

[0001] The invention relates to an arrangement for recovering energy-

[0002] Numerous arrangements are known for recovering wave energy of water.

[0003] A problem with the known solutions is e.g. that they operate at a fairly low efficiency.

BRIEF DESCRIPTION

[0004] An object of the present invention is to provide a novel and improved arrangement for recovering wave energy.

[0005] An arrangement according to the invention is characterised in that the arrangement comprises: at least one hollow piece which is provided with an outer casing and an inner space therein, the outer casing being engaged to be rotatable with respect to a body of the hollow piece, the inner space being provided with a sun-and-planet gear and a first mechanical rectifier, an internal gear of the sun-and-planet gear being fastened with respect to the outer casing so as to rotate therewith and a planet gear and a sun gear of the sun-and-planet gear being pivotally mounted to the body of the hollow piece and arranged to transmit reciprocating rotational motion between the outer casing and the body to said first mechanical rectifier arranged to convert said reciprocating rotational motion into one-directional rotational motion of a rotating axle.

[0006] The invention is based on using the sun-and-planet gear arranged in the inner space of the hollow piece receiving energy of water for transmitting the motion of the casing of the hollow piece to a generator generating electricity.

[0007] According to an embodiment of the invention, an additional piece is engaged with the hollow piece to receive energy of water outside the hollow piece, the motion of the additional piece with respect to the body of the hollow piece being converted into rotational motion.

[0008] An advantage then is that the efficiency may be further increased. BRIEF DESCRIPTION OF THE FIGURES

[0009] The invention is now described in greater detail in connection with some embodiments and with reference to the accompanying drawings, in which:

Figures 1a and 1b are schematic cross-sectional top and end views of an embodiment of an arrangement,

Figures 2a, 2b are cross-sectional top and end views of a second embodiment of the arrangement,

Figure 3 is a perspective and partially sectional view of a third embodiment of the arrangement,

Figure 4 is a perspective and partially sectional view of a fourth embodiment of the arrangement,

Figure 5 is a perspective view of a fifth embodiment of the arrangement,

Figure 6 is a perspective and partially sectional view of a sixth embodiment of the arrangement,

Figure 7 is a perspective and partially sectional view of a seventh embodiment of the arrangement,

Figure 8 is a perspective view of an eighth embodiment of the arrangement,

Figures 9a, 9b show some alternative embodiments of details of the arrangement according to Figure 8, and

Figure 10 is a perspective view of a ninth embodiment of the arrangement.

[0010] For the sake of clarity, the figures show the embodiments in a simplified manner. In the figures, like reference numerals identify like elements.

DETAILED DESCRIPTION

[0011] Figure 1a is a schematic cross-sectional top view and Figure 1b a schematic cross-sectional end view of an embodiment of an arrangement.

[0012] The arrangement includes a hollow piece 1 provided with an outer casing 2 and an inner space 3 therein. The hollow piece 1 is placed in water, wherein the outer casing 2 moves due to the influence of motion of the water. The hollow formed by the inner space 3 may serve to float the hollow piece 1 on the surface of water, but this is not necessary. [0013] The outer casing 2 may rotate with respect to a body 8 of the hollow piece. The figures show no details, which are conventional per se, of the body 8. The body 8 is fastened to a support structure 11 located outside the hollow piece 1. The support structure 11 may be secured e.g. to dry land, bottom, vessel, bridge or the like. The outer casing 2 may thus rotate with respect to the support structure 11.

[0014] It is to be noted that in this description, the concept "outer casing" refers expressly to parts of an outer surface of the hollow structure 1 that are rotatably engaged with respect to the body 8.

[0015] The outer casing 2 shown in the figure has the shape of a circular cylinder surface. Of course, it may have another shape, e.g. that of a polygonal, such as a triangular, tetragonal or pentagonal, cylinder, or it may have a shape other than that of a cylinder. The cross section of the outer casing 2 may substantially differ from the rotationally symmetrical shape: it may be elliptical in shape, for instance.

[0016] The inner space 3 is provided with a sun-and-planet gear 4 and a first mechanical rectifier 5, as well as two second mechanical rectifiers 13a, 13b.

[0017] An internal gear 7 of the sun-and-planet gear 4 is fastened to the outer casing 2, to an inner surface thereof. The internal gear 7 thus rotates along with the outer casing 2. A planet gear 10 and a sun gear 6 of the sun- and-planet gear are pivotally mounted to the body 8 of the hollow piece. The sun-and-planet gear 4 shown in Figures 1a, 1b has four planet gears 10. However, it is obvious that the number may also be different.

[0018] The planet gears 10 and the sun gear 6 transmit rotational motion between the internal gear 7 - and, consequently, the outer casing 2 - and the body 8 to the first mechanical rectifier 5. The first rectifier 5 converts the reciprocal rotational motion into one-directional rotational motion to be conveyed to rotational motion of a rotating axle 14.

[0019] In the embodiment shown in Figures 1a to 1b, the inner space 3 has the shape of the outer casing 2, and the sun-and-planet gear 4 is arranged in the inner space 3 symmetrically with respect to the outer casing 2. This, however, is not necessary. For instance, the cross section of the outer casing 2 may have e.g. an elliptical shape while the cross section of the inner space 3 is circular. Further, the sun-and-planet gear 4 may be arranged asymmetrically with respect to the outer casing 2, for instance in the case of said elliptical outer casing 2, around a first focal point of the ellipsis. This means that a region surrounding a second focal point of the ellipsis is preferably provided with empty space. The difference in weight between the focal points caused by such placing tends to increase the rocking and swaying of the hollow piece in water moving in waves.

[0020] The rotating axle 14 is coaxial with the symmetry axis of the outer casing 1 and extends outside the hollow piece 1 to the support structure 11 , where it is arranged to rotate a generator 9 generating electricity.

[0021] The first rectifier 5 may be implemented in many ways known per se, for instance by a rectifier described in Fl Patent No. 1 2694, particularly in its Figures 2, 3, and 4 and the corresponding parts of the description, or by a rectifier disclosed in Finnish Utility Model Fl 8504.

[0022] The inner space 3 is provided with two second mechanical rectifiers 13a, 13b. These may have a structure similar to that of the above- described first rectifier 5.

[0023] With the second rectifier 13a, 13b, a floating additional piece 15a, 15b is engaged, respectively, arranged at a distance from the hollow piece 1 and receiving motion of water.

[0024] The motion of the additional piece 15a, 15b with respect to the hollow piece 1 is converted into reciprocal motion of a lever arm 16a, 16b and conveyed to an input axle 17a, 17b of the second rectifier. This reciprocal rotational motion is converted in the second rectifier 13a, 13b into one- directional rotational motion which, in this case, is conveyed to the first mechanical rectifier 5. The rotational motion provided by the second rectifier 13a, 13b may also be conveyed past the first mechanical rectifier 5 directly to the rotating axle 14, etc.

[0025] In the embodiment shown in Figure 1a, 1b, the input axle 17a, 17b is arranged to penetrate the sun-and-planet gear 4 in between its internal gear 7 and sun gear 6.

[0026] The input axle 17a, 17b is arranged to penetrate an end 22 of the hollow piece eccentrically with respect to the outer casing 2. The end 22 is thus attached to the body 8 of the hollow piece, making the outer casing 2 rotate with respect to the end 22. A sealed slide surface 23 allowing said rotary motion and preventing water from entering the inner space 3 is provided between the outer casing 2 and the end 22. [0027] Herein, two additional pieces 15a, 15b and a corresponding number of second mechanical rectifiers 13a, 13b are engaged with the hollow piece 1. However, no additional pieces 15a, 15b are necessary; further, their number may be higher than two.

[0028] Figure 2a is a cross-sectional top view and Figure 2b a cross-sectional end view of a second embodiment of the arrangement.

[0029] In the inner space 3 of the hollow piece, an electric generator 9 is arranged, rotated by the rotating axle 14. The rotating axle 14 is rotated by the first mechanical rectifier 5 to which the reciprocal motion of both the outer casing 2 and the additional pieces 5a, 15b is conveyed.

[0030] A difference from the previous embodiment is e.g. that the motion of the lever arms 16a, 6b is conveyed into the inner space 3 by means of a transmission axle 24a, 24b arranged coaxially with respect to the outer casing 2. Thus, the outer casing 2 moving with respect to the body 8 may also comprise an end 22 of the hollow piece.

[0031] The inner space 3 is provided with a first mechanical rectifier 5, as well as two second mechanical rectifiers 3a, 13b. The first mechanical rectifier 5 converts reciprocal rotational motion between the outer casing 2 and the body 8 of the hollow piece, transmitted via the sun-and-planet gear 4, into one-directional rotational motion to be conveyed to the electric generator 9.

[0032] The second mechanical rectifiers 3a, 13b are engaged with the additional pieces 15a, 15b mainly as explained in connection with Figures 1a, 1b. However, the solution disclosed herein is different in that the motion of the transmission axle 24a, 24b is first conveyed to an increase gear 18a, 18b which increases the rotation speed of power transmission. Thus, the typically slow motions of the additional pieces 15a, 5b can be converted into a relatively high rotation speed which is conveyed via the second mechanical rectifiers 13a, 13b to rotate the electric generator 9. It is to be noted that the rotating axle 14 may naturally be provided with a gear, e.g. an increase gear, in order to bring the rotation speed of the electric generator 9 to an optimal range.

[0033] The lever arms 16a, 16b shown in the figures have a determined length which is selected taking into account e.g. the wave conditions at a location. In a second embodiment, the length of the lever arms 16a, 16b may be adjusted. Such a lever arm 16a, 16b may be implemented e.g. as a telescopic structure, toggle joint solution or the like. The length is preferably adjustable remote-controllably by controlling an actuator adjusting the length. This enables the length of the lever arm to be adjusted to be optimal for the current wavelength, making the arrangement receive wave energy as efficiently as possible.

[0034] Figure 2b shows a mass piece 12 which is fastened to the body 8 of the hollow piece. The purpose of the mass piece 12 is to increase the inertia of the body 8 with respect to the outer casing 2, in other words to reduce the tendency of the body 8 to rotate along with the outer casing 2. In Figure 2a, the mass piece 12 is arranged at a distance from the hollow piece 1 , outside it. The mass piece 12 may also, completely or partly, be arranged inside the inner space 3. No mass piece 12 is always necessary, however: it is unnecessary e.g. if the body 8 is fastened to the support structure 11 which does not, at least substantially, rotate along with the outer casing 2.

[0035] The outer casing 2 of the hollow piece 1 is provided with side projections 21a, 21b which receive motion of waves and transmit it to the outer casing 2. In this embodiment, the side projection 21a, 21b is a float with a circular cross section, which, according to the figure, may be arranged at an end of an arm or, alternatively, fastened directly to the outer casing 2. It may also have another shape. The side projection 21a, 21b increases the motion of the outer casing 2. The side projection may also be arranged on one side of the hollow piece 1 only.

[0036] Figure 3 is a perspective and partially sectional view of a third embodiment of the arrangement,

[0037] The arrangement includes a pontoon 19 with which four hollow pieces 1 are engaged. The structure of the hollow piece 1 may be e.g. as shown in Figures 1a, 1b, only without any additional pieces 15a, 15b and related power transmission devices.

[0038] The pontoon 19 is a floating structure and provided with power transmission devices 20 arranged to receive the rotational motion of the rotating axle 14 of the hollow pieces 1. The rotational motion is transmitted to an electric generator 9 arranged in the pontoon 19, and electric energy generated by the electric generator is forwarded for use by arrangements known per se.

[0039] The pontoon 19 is elongated in its external shape and secured e.g. to the bottom of its water basin, such as a sea, lake or river, to the shore or a vessel so that it may turn according to a direction of water flow or wind. This enables the hollow pieces 1 to settle in an advantageous position in the flow or waves.

[0040] In the embodiment shown in the figure, the power transmission devices 20 comprise power transmission belts or chains engaging the rotating axles 14 with the electric generator 9. The power transmission devices 20 may naturally also be implemented otherwise; preferably, however, they comprise freewheel clutches 26a, 26b which lock up in the same direction and via which the motions from different rotating axles 14 are combined. In this manner, a rotating axle 14 possibly rotating at a lower rotation speed does not decelerate a faster rotating one.

[0041] One or more, not necessarily four, hollow pieces 1 may be engaged with the pontoon 19. Each hollow piece 1 , instead of the pontoon 9, may be provided with an electric generator 9. In such a case, the pontoon 19 mainly serves as a support structure for the hollow pieces 1 and as an element directing them according to the waves or flow of water.

[0042] The pontoon 19 is not necessarily self-floating. A non-self- floating pontoon 19 is placed in a suitable position with respect to water by securing it to a support structure.

[0043] The pontoon 19, e.g. an end thereof, may be provided with a transverse structure which forms an obstacle in flowing water, which, in turn, increases the height of waves and rocking. This is particularly advantageous particularly in an embodiment provided with an energy collector comprising an anchor wheel and a weight similar to that shown in Figure 4.

[0043] Figure 4 is a perspective and partially sectional view of a fourth embodiment of the arrangement.

[0044] The hollow piece 1 including the additional pieces 15a, 15b engaged therewith is engaged with the pontoon 19.

[0045] The casing of the hollow piece 1 is provided with two side projections 21a, 21b shaped as a fin or a wing.

[0046] The order of the components contained in the hollow piece 1 differs from those shown in Figures 1a and 2a in that the sun-and-planet gear 4 is arranged approximately in the middle of the length of the inner space.

[0047] The hollow pieces 1 are engaged with the pontoon 9 so that two rotating axles 14a, 14b are arranged oppositely and coaxially to rotate a power transmission member 27 receiving the same rotational motion. Between the first rotating axle 14a and the power transmission member 27 there is pro- vided a first freewheel clutch 26a while between the second rotating axle 14b and the power transmission member 27 there is provided a second freewheel clutch 26b. This solution is advantageous e.g. in that the same power transmission member 27 can be rotated by two rotating axles without the more slowly rotating axle decelerating the rotation of the power transmission member 27.

[0048] In this case, the power transmission member 27 is a chain wheel, but it may well be a member of another type as well.

[0049] It is to be noted that not only mutually similar hollow pieces 1 and additional pieces 15a, 15b possibly engaged therewith but also mutually different - for instance in dimensions or in shape or in lever arm length - hollow pieces and additional pieces may be engaged with the pontoon 19.

[0050] One or more anchor wheels 36 may be rotatably arranged in the pontoon 19. Such an anchor wheel is engaged with the power transmission member 27 via the freewheel clutch 26 and e.g. a power transmission chain or belt. The rim of the anchor wheel 36 is provided with a wire 37 or the like which is secured to a bottom or another corresponding immobile target by a securing member 38. The pontoon 19 is secured with the wire 37 by means of the securing member 38 to the immobile target. A weight 39 suspended from the anchor wheel 36, hanging between the surface of water and the bottom, is secured to an opposite end of the wire 37. The pontoon 19 moves up and down along with the waves, whereby the wire 37 rotates the anchor wheel 36 back and forth. Rotational motion in the other direction is transmitted via the freewheel clutch 26 to the power transmission member 27. This enables potential energy of waves to be recovered even more efficiently.

[0051] Figure 5 is a perspective view of a fifth embodiment of the arrangement. The arrangement includes an elongated pontoon 19 which is substantially narrower than its height and whose two sides are provided with a total of four hollow pieces 1 together with additional pieces 15a, 15b thereof. The pontoon 19 may be e.g. the body of a ship or another vessel in water. The arrangement includes at least one electric generator arranged either in the pontoon 19 or in the hollow piece 1.

[0052] The pontoon 19 may be provided with a weighted water tank and a pump necessary for filling and emptying such a tank, a channel system and valve arrangements. By filling up the weighted water tank, the entire arrangement can be submerged below the surface of the water, even all the way to the bottom. This enables the arrangement to be submerged so as to be protected from a heavy storm or the like.

[0053] Figure 6 is a perspective and partially sectional view of a sixth embodiment of the arrangement.

[0054] Three hollow pieces 1 are arranged in the pontoon 19 so as to form a symmetrical structure around a normal N of a plane of the surface of water. The structure of the hollow piece 1 may be as already described above. The outer casing 2 is provided with two kinds of side projections: cylindrical ones and ones resembling a fin or a wing, the latter ones being arranged at an angle with respect to the longitudinal direction of the hollow piece 1 , the sides thereof thus forming a spiral surface which receives water flow and/or wave motion.

[0055] The rotating axles 14, which rotate in one and the same rotating direction, are arranged to rotate the power transmission devices 20 of the pontoon which, in turn, rotate an electric generator 8 (not shown in the figure). The power transmission devices 20 may comprise e.g. a sun-and-planet gear whose gears are arranged in parallel to the plane of the surface of water.

[0056] A spherical float 28 is engaged with the pontoon 19 to bear the pontoon 19 on the surface of water or close thereto. The pontoon 19 and the float 28 are rotationally symmetrical in shape at the level of the surface of water, enabling their tendency to turn the arrangement along with the flows of water and/or wind to be minimized. The arrangement shown in Figure 6 is particularly advantageous in embodiments wherein the direction of the flow of water may change rapidly. In such an arrangement, the number of hollow pieces 1 may be four or even more.

[0057] The arrangement shown in Figure 6 is anchored to the bottom of a body of water by means of wires 37. It is, of course, also possible to secure the arrangement to another place and by using other devices.

[0058] Figure 7 is a perspective and partially sectional view of a seventh embodiment of the arrangement.

[0059] The cylindrical hollow piece 1 is arranged vertically and secured by its body 8 to the bottom of a water basin so that the body 8 allowed to rotate due to the influence of motions of water. Alternatively, the securement may be implemented to a fixed structure other than a bottom, or to a ship or another corresponding vessel, for instance. [0060] The outer casing 2 comprises two parts 2a, 2b which rotate with respect to one another and which are arranged to rotate around the normal of the plane of the surface of water, each one of which being arranged to rotate a sun-and-planet gear 4a, 4b of its own. The sun-and-planet gears 4a, 4b are arranged to rotate the first mechanical rectifier 5 and, further, the electric generator 9.

[0061] The number of rotating parts of the outer casing 2 is one at its lowest and more than two at its highest, for instance three or four. They are provided with side projections 21a, 21b for receiving energy of the motion of water.

[0062] Figure 8 is a perspective view of an eighth embodiment of the arrangement, and Figures 9a, 9b show some embodiments of details of the same arrangement.

[0063] In the arrangement shown in Figure 8, the cylindrical hollow piece 1 is arranged vertically. Its outer casing comprises two parts 2a, 2b which rotate with respect to one another and which are arranged to rotate around the normal of the plane of the surface of water, each of which being arranged to rotate a sun-and-planet gear of its own. Each rotating part 2a, 2b of the outer casing is provided with side projections 21a, 21b to receive energy of water.

[0064] The body 8 of the outer casing is provided with stabilization wings 29 whose purpose is to prevent the body 8 from rotating along with the rotating parts 2a, 2b of the outer casing. The surface area of the stabilization wings 29 is preferably substantially larger than the surface area of the side projections 2 a, 21b.

[0065] Two lever arms 16a, 16b are rotatably fastened to an upper part of the body 8. An end of the lever arm is provided with an additional piece 15a, 15b. The additional piece 15a, 15b floats on the surface of water, moving alternately up and down along with the waves. This motion is conveyed via the lever arm 15a, 15b to a push rod 30a, 30b arranged in the inner space 3 through a watertight lead-in.

[0066] Figure 9a shows a solution for converting the reciprocating and linear motion of the push rod 30a, 30b into reciprocating rotational motion. The push rod 30a has a spiral groove 31 wherein a pin 33 provided on the inner rim of a ring 32 is arranged. The ring 32 is allowed to rotate in a direction of its rim but not in a direction of the push rod. When the push rod 30a moves in a first direction, the groove 31 forces the pin 33 arranged therein to take up rotational motion, whereby the ring 32 rotates in its first direction. When the direction of motion of the push rod 30a changes, the direction of rotation of the ring 32 also changes. The reciprocating rotational motion of the ring 32 is converted in the mechanical rectifier into one-directional rotational motion.

[0067] Figure 9b shows a second solution for converting the reciprocating motion of the additional piece 15a, 15b arranged in the lever arm into reciprocating rotational motion. In the solution, the lever arm 16a is engaged with a gear rack 40 arranged to rotate a gear 41. This converts the reciprocating linear motion of the gear rack 40 into reciprocating rotational motion transmitted to the mechanical rectifier. In the disclosed embodiment, the gear 41 is placed inside a housing 42, but this is by no means necessary. The gear rack 40 and the gear 41 may be placed e.g. in the inner space 3 of the hollow piece, or outside the hollow piece.

[0068] Figure 10 is a perspective view of a ninth embodiment of the arrangement. Four power plant units 35 comprising a hollow piece 1 are arranged in a rectangular pattern and engaged with one another at least in their longitudinal directions by rigid support structures 11. The hollow piece 1 may be implemented e.g. according to the above-disclosed examples. A modular wave power plant 34 is thus provided, comprising a plurality of hollow pieces 1 , together with their optional additional pieces, for collecting energy of water. The modular wave power plant 34 may be considerably larger than what is shown in Figure 10: it may form a network-like structure containing tens or even hundreds of nodes, each being provided with a hollow piece 1 together with its optional additional pieces and connected by support structures 11.

[0069] The power plant units 35 of the wave power plant 34 may be either identical or mutually different. For instance, a hollow piece 1 of a power plant unit 35 located in edge parts of a large network-structured wave power plant 34 may be implemented in a manner different from one residing in a power plant unit 35 located in inner parts of the same wave power plant 34.

[0070] It will be apparent to a person skilled in the art that as technology advances, the basic idea of the invention may be implemented in many different ways. In some cases, features disclosed in this application may be used as such, irrespective of other features. On the other hand, when necessary, features disclosed in this application may be combined in order to provide various combinations. The invention and its embodiments are thus not restrict- ed to the above-described examples provided for the sake of illustration, but the invention may vary within the scope of the claims.

Reference numerals

I hollow piece

2, 2a, 2b outer casing

3 inner space

4 sun-and-planet gear

5 first mechanical rectifier

6 sun gear

7 internal gear

8 body of hollow piece

9 generator

10 planet gear

I I support structure

12 mass piece

13a, 3b second mechanical rectifier

14, 14a, 14b rotating axle

15a, 15b additional piece

16a, 16b lever arm

17a, 17b input axle of second rectifier

18a, 18b increase gear

19 pontoon

20 power transmission devices of pontoon 21a, 21b side projection

22 end of hollow piece

23 slide surface

4a, 24b transmission axle

5a, 25b increase gear

6, 26a, 26b freewheel clutch

7 power transmission member

8 float

9 stabilization wing

30a, 30b push rod

31 groove

32 ring

33 pin

34 wave power plant

5 power plant unit 36 anchor wheel

37 wire

38 securing member

39 weight

40 gear rack

41 gear

42 housing

Claims

1. An arrangement for recovering wave energy, characterized in that the arrangement comprises:

at least one hollow piece (1) which is provided with an outer casing (2) and an inner space (3) therein, the outer casing being engaged to be rotat- able with respect to a body (8) of the hollow piece, the inner space (3) being provided with

a sun-and-planet gear (4) and a first mechanical rectifier (5), an internal gear (7) of the sun-and-planet gear (4) being fastened with respect to the outer casing (2) so as to rotate therewith, and

a planet gear (10) and a sun gear (6) of the sun-and-planet gear being pivotally mounted to the body (8) of the hollow piece and arranged to transmit reciprocating rotational motion between the outer casing (2) and the body (8) to said first mechanical rectifier (5) arranged to convert said reciprocating rotational motion into one-directional rotational motion of a rotating axle (14).

2. An arrangement as claimed in claim 1, characterized in that the inner space (3) is provided with an electric generator (9) coupled via the rotating axle (14) to be rotated by the first mechanical rectifier (5).

3. An arrangement as claimed in claim 1 or 2, characterized in that the body (8) of the hollow piece is fastened to a support structure (11) which is located outside the hollow piece (1) and with respect to which the outer casing (2) is arranged rotatably.

4. An arrangement as claimed in claim 1 or 2, characterized in that the body (8) of the hollow piece comprises a mass piece (12) arranged to increase inertia of the body (8) with respect to the outer casing (2).

5. An arrangement as claimed in any one of the preceding claims, characterized in that the inner space (3) is provided with a second mechanical rectifier (13a, 13b) coupled to receive reciprocal motion from the motion of an additional piece (15a, 15b) arranged outside the hollow piece (1) and movably with respect thereto, and that the second mechanical rectifier ( 3a, 13b) is coupled to the rotating axle (14) and to transmit thereto the motion of the additional piece (15a, 15b) converted into one-directional rotational motion.

6. An arrangement as claimed in claim 5, characterized in that the second mechanical rectifier (13a, 13b) is coupled to feed one- directional rotational motion to the first mechanical rectifier (5).

7. An arrangement as claimed in any one of the preceding claims, characterized in that the outer casing (2) of the hollow piece comprises two parts (2a, 2b) rotating with respect to one another and engaged with the sun-and-planet gear (4).

8. An arrangement as claimed in any one of the preceding claims, characterized in that the hollow piece (1) is a piece substantially cylindrical in its external shape, preferably at least substantially spherical in cross section of its outer surface, whose centre axis is arranged parallel to a plane of the surface of water, and that the outer surface of the outer casing (2) is provided with a side projection (21a, 21b) resisting the motion of waves.

9. An arrangement as claimed in any one of the preceding claims, characterized in that one or more hollow pieces (1 ) are engaged with a pontoon (19) provided with power transmission devices (20) arranged to receive the rotational motion of the rotating axle (14) and transmit it to an electric generator (9) arranged in the pontoon (19).

10. An arrangement as claimed in claim 9, characterized in that the external shape of the pontoon (19) is at least substantially rotationally symmetrical with respect to a normal (N) of a plane of the surface of water, and that at least three hollow pieces (1) are arranged on sides of the pontoon (19) so as to form a symmetrical structure around the normal (N) of the plane of the surface of water.

11. An arrangement as claimed in claim 9 or 10, characterized in that two rotating axles (14) are in the pontoon (19) arranged oppositely and coaxially to rotate a power transmission member (27) receiving the same rotational motion such that a first freewheel clutch (26a) is provided between a first rotating axle (14a) and the power transmission member (27) while a second freewheel clutch (26b) is provided between a second rotating axle (14b) and the power transmission member (27).

12. An arrangement as claimed in any one of claims 1 to 7, c h a r- acterized in that the outer casing (2) of the hollow piece (1) and the sun gear of the sun-and-planet gear (4) are arranged to rotate around the normal (N) of the plane of the surface of water, and said outer casing (2) is provided with at least one side projection (21a, 21b) projecting therefrom.

13. An arrangement as claimed in any one of claims 9 to 12, characterized in that the pontoon (19) comprises an anchor wheel (36) rotatably arranged with respect thereto and coupled via the freewheel clutch (26) to the power transmission member (27), a rim of the anchor wheel (36) being provided with a wire (37) whose end is secured to an immobile target by a securing member (38), and an opposite end of the wire (37) being secured to a weight (39) arranged to suspend from the anchor wheel (36), between the surface of water and a bottom.