NO347801B1

NO347801B1 - Tidal power plant

Info

Publication number: NO347801B1
Application number: NO20230893A
Authority: NO
Inventors: Roy Magne Juvik
Original assignee: Roy Magne Juvik
Priority date: 2023-08-22
Filing date: 2023-08-22
Publication date: 2024-03-25
Also published as: NO20230893A1

Description

Tidal Power Plant

The present invention concerns a tidal power plant as indicated by the preamble of claim 1.

Background

Generally, little has been done to utilize the large energy potential encountered with tidal water flow. Tidal water flow is an extremely reliable energy source, since it is present near land and works 24/7, contrary to the case for wind energy or solar energy. The density of water, near 1000 times denser than water, has a potential of power generation based on much smaller moving volumes of water compared to the required volumes of air.

The challenge with tidal energy is to develop methods and devices that are able to collect the energy in a sufficiently cost-effective manner and to convert it to electrical energy. Naturally, costefficiency also depends upon the price of alternative energy sources and with increasing energy prices world-wide, focus on tidal energy is expected t attract new interest.

In Norway, one tidal power plant near Hammerfest, first established 2003, (http://www.nyttspor.no/Bakgrunn/StatkraftTidevannskraft.pdf), was tested for many years as the first full scale tidal power plant in the world. In spite of promising results, low cost of conventional hydroelectric power plants in the test period lead to a decline in the interest for tidal power plants and the one in Hammerfest stopped operation after a few years.

WO 05017349 A1 relates to an energy generator powered by tidal currents comprising a turbine in a turbine housing for rotation about an axis. The turbine is attached to a supporting column that is pivotally supported in a housing, allowing the orientation of the turbine to be adjusted.

WO 2017/088011 A1 concerns a hydroelectric installation in the form of an assembly of turbines arranged on a pivotal support, to thereby generate power from tidal water flows in opposite directions

WO 2019/103634 A2 teaches a cascading hydroelectric power plant of complex structure for harvesting power from rivers and tidal water flows.

GB 2489073 A (2012) describes a floating assembly for tidal power generation comprising a water wheel arranged in a tapered passage to turn a generator to thereby generate electric power. The application was withdrawn without having been granted,

GB 2463313 A (2010) teaches an arrangement for generating electric power from ocean or river currents, exhibiting a funnel shaped water inlet and one or more “rotors” arranged to be powered by said flow. The application was terminated without having been granted.

Objectives

It is an objective with the present invention to provide a tidal power plant which is cost-effective, inexpensive and allows easy maintenance and repair.

The present invention

The above indicated objectives is fulfilled by the power plant defined by claim 1, which constitutes the present invention.

Preferred embodiments are disclosed by the dependent claims.

The power plant according to the present invention may generally be seen as a two-part structure, comprising a first part in the form of a housing with a through opening in the direction in which tidal water is intended to flow during flow and ebb, i.e. an opening intended to be mainly horizontal when mounted for power production. The housing furthermore exhibits a vertical open passage or shaft from its top surface down to the through channel, said shaft being arranged to receive the second part of the structure, which is a turbine arranged in a cartridge that fits snugly into the shaft of the housing.

The through opening is tapered from a comparatively wide cross-section at its inlet/ outlet openings to a smaller cross-section at the mid-section which is where the cartridge with the turbine is to be localized for use.

The housing may furthermore comprise legs, preferably extendable legs, in order to arrange the housing at desired height under varying conditions. It is preferred to arrange the housing at a level where its upper part protrudes above the water surface, at least during ebb, to allow easy access to the cartridge for maintenance and/ or replacement.

The power plant according to the present invention is typically symmetrical around a vertical plane perpendicular to the axis of the through opening, thereby allowing power production in the same way during ebb as during flow, with reversal of the flow through the through opening in which the turbine is arranged.

The turbine exhibits dual propellers at both sides of a generator driven by said propellers, the propellers arranged proximal to the generator denoted the inside propellers and the two propellers arranged distal from the generator denoted the outside propellers. The outside propellers have blades that are oblique in the opposite direction compared to the inside propellers. Furthermore, the inside propellers are attached to a common rotational axis while the outside propellers are attached to a different rotational axis which is common for the outside propellers. This means that at any given time the inside propellers are rotating in the direction opposite of the rotation of the outside propellers, which means that the turbine is perfectly balanced with regard to rotational forces at all times.

The electric connections to/ from the turbine/ generator are typically arranged within the cartridge holding the turbine, and may have a detachable connection point at the top of the cartridge, naturally arranged in a water-proof manner.

In the following the invention is described in further detail in the form of non-limiting embodiments illustrated by the accompanying drawings.

Figure 1 is a perspectival view of a housing of a power plant according to an embodiment of the present invention.

Figure 2 is a schematic and simplified front view of a power plant according to an embodiment of the present invention.

Figure 3 is a schematic and simplified top sectional view of elements of a device according to the present invention.

Figure 4 is a schematic and simplified top sectional view of a device according to the present invention.

Figures 5A and 5B are front views of propellers suitable for use as elements of the present invention.

By schematic is understood that just the overall principles are illustrated and that size of any given component may be out of scale as compared to other components shown. By simplified is understood that only the parts relevant to the understanding of the principles of the invention are shown and that other parts that will normally be present in an operational device, may be omitted for simplification.

Figure 1 is a perspectival view of the housing 10 of a power plant according to the present invention. A circular inlet/outlet to a through opening 11 for water is shown in a lateral side while a similar opening at the other side is hidden from the view. Thus, there is an open passage between the inlet/outlet openings through which water will pass when the power plant is in use. The diameter of the open passage is reduced in a region of tapered walls 12 from a comparatively large diameter at the inlet to a smaller diameter at the centre of the housing, along an axis defined by the centre line of the open passage. The open passage may also be denoted a through opening.

At the top of the housing, a (vertical) shaft 13 with a rectangular cross-section is shown. The shaft, which has a width W, extends down to the open passage, and is arranged to receive a cartridge comprising the turbine of the power plant.

Figure 2 is a schematic and simplified front view of the housing 10. In this view a cartridge 20 supporting a turbine 30 has been inserted into the shaft 13 so that the turbine is centred in the through opening 11. The visible part of the turbine is a propeller 31o. The cartridge also supports a cylindric pipe 22 which has a diameter corresponding to the smallest diameter of the through opening, and is flush with the through opening in the inserted position. The cartridge 20, the structural part of which typically is constituted by an open frame 21 of a rigid material, will typically exhibit some means for its retrieval, such as a handle grip 21a or the like, accessible by a hook or the like of a crane (not shown).

The frame 21 as such is typically an open structure, i.e. a structure without walls, at least no walls at the lateral sides where water is supposed to enter and leave the turbine.

Figure 3 is a schematic and simplified top view of a turbine 30 arranged as part of a cartridge 20 which also includes the mentioned pipe 22. The structural part of the cartridge 20, holding all the elements in place, is a frame 21 consisting of bars mainly defining the shape of a dice, though typically without any walls.

An electric generator 32 constitutes the central part of the turbine while a double set of propellers 31i, 31o are arranged at both sides of the generator. The blades of the two 31i propellers are inclined in a common manner and attached to a common axis and will therefore rotate with mutually same direction and same speed at all times. Naturally, when the flow direction changes from ebb to flow, the direction of the rotation is also changed.

The blades of the two 31o propellers are inclined in a mutually common manner but different (opposite) from that of the 31i propellers. The two 31o propellers are attached to an axis different from the axis of the two 31i propellers and will at all times rotate in the direction opposite of the direction of the 31i propellers. Typically, the axis to which the 31i propellers are attached may have a comparatively large diameter and may have a central bore in which a smaller axis to which the two 31o propellers are attached, is arranged. The arrangement of dual blades with opposite rotation at both sides of the generator, ensures a well-balanced and smooth turbine operation.

Figure 3 also shows caps 33 at both lateral ends of the turbine, arranged with a smooth curvature to reduce turbulence in the water flow entering the turbine. The width W of the cartridge indicates that it is perfectly dimensioned to fit snugly into the shaft 13 in the housing 10.

The propeller axes are connected to the generator by means of gears or similar components in a manner well known I the art, not described in further detail here. Similarly, the electric output from the generator is transferred by means of cables (not shown) in a manner well known in the art. Since the turbine – including the generator – is arranged in a cartridge for swift replacement, the required cables are also arranged as part of the cables and leave the housing at the top of the shaft 13 when the cartridge is inserted in the shaft.

Figure 4 is a schematic and simplified top view of an embodiment of a power plant according to the present invention with the cartridge 20 – constituting a part of the power plant – inserted in the housing 10. The cartridge is similar to the one of Figure 3, just in smaller scale. As indicated by Figure 4, the walls in region 12 of the through passage are evenly or conically tapered, which is preferred but not mandatory feature. In the region 14 of the through passage, closer to the cartridge/ turbine, the tapering of the walls is gradually reduced in direction of the turbine, thereby making a flush transition to the pipe 22 in which the turbine is arranged.

The gradual narrowing (tapering) of the through passage from the inlet to the turbine, the cylindric pipe 22 around the turbine and the gradual broadening of the passage to the outlet, ensure a laminar flow of water past the turbine blades, which is significant in terms of the overall efficiency of the power plant. It is also of importance that the device is symmetrical in order to function equally well during ebb and flow.

Figures 5A and 5B are front views of propeller 31o and 31i respectively, illustrating oppositely curved blades that inevitably leads to rotation in opposite directions. As also indicated, the central bore of the 31o propeller is smaller than that of 31i propeller, illustrating that they are arranged to fit different axes.

Now turning to Fig.6. The power plant housing will typically be arranged at a site where the tidal currents are significant and at a vertical position in which the cartridge 20 is easily retrievable from the housing 10, i.e. with the top of the housing at or above the water surface 61. If required, the power plant may be positioned on legs 62 or other framework, typically adjustable in height, in order to obtain a desired position for its operation.

The housing of the power plant is typically casted from cement, a synthetic resin, or a combination thereof and is optionally provided by a surface protection in the form of a coating of synthetic or metallic material to reduce friction and to protect the surface from marine growth, wear and tear. Preferably, such coating is a high gloss coating to prevent algae and other marine species to adhere thereto. This is particularly useful for the tapered channel where presence of marine growth would lead to increased friction and reduced water flow.

While the housing of the power plant most typically is casted from cement or a synthetic resin, the present invention also holds open the possibility that the housing be made as a through opening in naturally occurring formations such as rocks being present partly above the surface in a fjord, strait or the like. Such through opening may be established by any convenient means, such as drilling, excavation, cautious blasting and combinations thereof. Also in this case, exposed surfaces through which water will flow may be covered by a coating to reduce friction and to protect the exposed surface.

Claims

1. A tidal power plant () comprising a turbine (30) comprising propellers (31i/ 31o) and a generator (32) connected thereto, mounted in a housing (10) with a through channel (11), the through channel (11) being tapered along its longitudinal axis from both ends towards the central area of the channel, where the turbine (30) is arranged, wherein the turbine (30) is mounted in a frame (21) that fits into a shaft (13) extending from a top surface of the housing (10) to a central part thereof, where the through channel (11) has its narrowest cross-section and that the frame (21) comprises or supports a pipe (22) delimiting the space around the turbine and that the pipe (22) has a cross-section similar to the narrowest cross-section of the through channel (11), the pipe and the through channel being flush with one another when the frame (21) is appropriately inserted in the shaft (13), characterized in that the turbine (30) exhibits two pairs of propellers (31i/ 31o), one pair at each lateral side of the generator (32) and that each propeller (31i) of each pair (31i/ 31o) is arranged to rotate oppositely of the other impeller (31o) of the same pair.

2. A tidal power plant as claimed in claim 1, wherein the pairs of propellers (31i/ 31o) and the generator (32) are combined as an integrated unit mounted in the frame (21).

3. A tidal power plant as claimed in claim 1 or 2, wherein the through channel (11) is arranged between oppositely lateral sides of the housing (10)

4. A tidal power plant as claimed in any one of the preceding claims, wherein the through channel (11) has a conical or curved tapered profile (12), wide at the inlet/ outlet and narrow at the shaft (13).

5. A tidal power plant as claimed in any one of the preceding claims, wherein the smallest crosssection of the through channel (11) is in the range of 8% to 35% of the largest cross-section of the channel (11).

6. A tidal power plant as claimed in any one of the preceding claims, wherein the inside propellers (31i) of both pairs of propellers are attached to a first common axis and that the outside propellers (31o) of both pairs of propellers are attached to a second common axis, the first and second axes being arranged concentrically with one another.

7. A tidal power plant as claimed in any one of the preceding claims, wherein the housing (10) is casted from cement, a synthetic resin, or a combination thereof.

8. A tidal power plant as claimed in any one of claims 1 to 7, wherein the housing (10) is formed in naturally occurring rock formations.

9. A tidal power plant as claimed in any one of the preceding claims, wherein the housing is at least partly covered by a coating of synthetic or metallic materials to protect the surface from marine growth, wear and tear.

10. A tidal power plant as claimed in claim 9, wherein the coating is a high-gloss coating.