GB2459352A

GB2459352A - Wave powered with fluid moving in chamber

Info

Publication number: GB2459352A
Application number: GB0905669A
Authority: GB
Inventors: Sean Lavelle
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-04-02
Filing date: 2009-04-02
Publication date: 2009-10-28
Anticipated expiration: 2029-04-02
Also published as: GB0905669D0; GB2459352B

Abstract

A wave power generating device 1 has a liquid filled chamber 2a-d, and is designed to pitch (rock) when exposed to waves. Relative movement of the fluid in the chamber causes movement of air in fore and aft chambers 3a, b, which drives generators 8. Extra buoyancy devices may be provided on each side of the device and may contain a mechanical generator using a rack and pinion or linear generator (figures 5, 6).

Description

Wave powered fluid filled electric generating device

Background information.

The invention relates to a wave powered fluid filled electric generating device for generating electric power from a wave-driven water body.

The development of a practical wave energy converter has been the focus of attention from a number of engineers and theoreticians for many years. Growing concern with global climate change has led to an increased sense of urgency in the quest for commercially viable renewable energy sources. With the ever increasing need to be environmentally conscious more attention is being paid to clean, renewable energy sources.

Wave Power Resource It has been estimated that the total wave power resource in all the oceans at any one time is about 1 TW (ITW=Terra Watt= 1 o kW) which corresponds directly to the present amount of electricity produced in the world. Due to Ireland's geographical location, on the downwind side of the Atlantic Ocean in the region of prevailing south-westerly winds, her coastline is exposed to one of the most vigorous wave climates in the world. The overall resource around the west and south coasts of Treland is about 25 GW (1GW -1 Gita Watt -106 kW) mean The Offshore Resource is Greater than inshore.

Wave energy is lost by friction with the sea bottom as the sea becomes shallow (water depths of half a wavelength or less). This is most pronounced where wavelengths tend to be long, as off the NW coast of Europe. On or close to the shore the availability of this already attenuated resource is greatly diminished by the lack of physically suitable sites and restrictions imposed by planning controls.

Categories of Wave Energy Converters.

Wave Energy Converters (WEC5) may be classified in different ways according to their operating principle and the ways in which they react with waves. Tn terms of practical application, only a very few types of device are presently, or in the recent past have been, in use or under test.

Point absorbers are usually axi-symmetric about a vertical axis, and by definition their dimensions are small with respect to the wavelength of the predominant wave. The devices usually operate in a vertical mode, often referred to as heave'. Typically, a surface-piercing float rises and falls with the passing waves and reacts against the seabed or a taut mooring. As such they are capable of absorbing energy arising from changes in the surface level rather than from forward motion of breaking seas. The theoretical limit for the energy that can be absorbed by a single isolated, heaving, axi-symmetrical point absorber has been shown to depend on the wavelength of the incident waves rather than the cross sectional area of the device, i.e. from the wavelength divided by it. Thus the wavelength is a critically important criterion, resulting in the attraction of locating the point absorber devices well outside the region of breaking waves, and where they will be open to long wavelength ocean swell or heave'.

Point absorbers may react against the seabed (therefore necessarily sited in relatively shallow water, usually near-shore), or be floating and react against the inherent inertia of one of its components.

Small-scale practical point absorbers such as fog horns and navigation buoys, both of which may incorporate OWCs, have been in use for many years. Typically these have a power of a few hundred watts.

Self-Reacting Heaving Buoy Point Absorbers.

There have been several attempts to develop wave energy converters based on the self-reacting heaving buoy principle. One such example is a heaving buoy which reacts against an inertial plate suspended below. This concept has been described and analysed by Berggren, L. and Johansson, M., Hydrodynamic coefficients of a wave energy device consisting of a buoy and a submerged plate. Applied Ocean Research, 0141-1187/92/05.00 and by Falnes, J., Wave-energy conversion through relative motion between two single-mode oscillating bodies (OMAE, Lisbon, Portugal, Jul.

5-9, 1998).

A second variation of the heaving buoy principle is described in an international patent application, WO 97/4 1349. In this, a single heaving buoy reacts against a column of water trapped in a cylinder suspended vertically below and open at either end, by means of a wide piston moving reciprocally within the cylinder. The column of water moved by the piston acts as an inertial mass; this arrangement is known as an accelerator tube. Similar technology is known and described in U.S. Pat. No. 4,773,221.

However these inventions have limitation and could not compete economically with existing energy sources or generator's susceptibility to damage due to extreme weather conditions.

A significant fraction of the present generation of WEC devices incorporates an Oscillating Water Column (OWC).

OWC devices are typically those where the wave is confined in a vertical tube or a larger chamber and, as it surges back and forth, drives air through a power conversion device typically an air-turbine. Megawatt-scale OWC devices are now at an advanced stage of development. One such device, built in a rocky gully on the western shore of Pico in the Azores, is a reinforced concrete chamber partly open at one side below the waterline to the action of the waves. A similar but slightly smaller device, the LIMPET, has been installed on the cliff face of Islay in Scotland. These two installations would seem to be the best-developed and perfected WEC systems of this size currently available. It is, however, unlikely that any one such installation will have an installed capacity greater than two megawatts and the number of suitable sites has to be extremely limited.

Wave energy converters in the sea, in a lake or other such expanse of water are disclosed in European Patent Specification No. 0,950,8 12 of Masuda et al, U.S. Patent Specification No. 4,741,157 of Nishikawa, U.S. Patent Specification No. 4,858,434 of Masuda assigned to Nishikawa and in international patent application, WO/2008!047337. All such wave energy converters disclosed in these four prior art specifications comprise of a housing which extends between a forward and an aft end, and is moored so that the forward end faces into oncoming waves with the air chamber in the front or in the rear of the housing. The mooring of the housing is arranged so that the housing oscillates by pitching in a forward/aft direction in response to passing waves. A turbine located in the air accommodating duct is driven by air passing through the air accommodating duct in response to the rising and falling water level in the air chamber for driving an electrical generator, which in turn produces electricity from the oscillating motion of the housing. A buoyancy material is located aft or forward of the air chamber over the water accommodating duct in the wave energy converters, with any one of the wave energy converters moored by a suitable mooring system with the forward end of the housing facing into the oncoming waves, the passing waves cause the housing to oscillate with a pitching movement in a forward/aft direction which in turn causes water to flow into and out of the air chamber on each oscillating cycle of the housing through the water accommodating duct. As the water flows into and out of the air chamber the water level in the air chamber rises and falls. This results in air being sequentially urged outwardly and inwardly through the air accommodating duct. Depending on the type of turbine used, the turbine is rotated in the same direction irrespective of the direction of flow of air through the air accommodating duct, or alternatively, may only rotate in one direction in response to air either being urged outwardly or inwardly through the air accommodating duct.

While such wave energy converters do act to convert wave energy to mechanical rotational energy, they are limited in so far as with the air chamber in the front of the housing facing on coming waves its is very unstable but provide high yields, with the air chamber in the rear of the housing facing on coming waves its is more stable but provide lower yields. All prior art are using an opening in front or rear of the device to perform the air pressure in the air chamber, this can lead to cavitations and air pockets within the water chamber the present invention where the fluid is contained and remains in the chamber allow for a greater performance as their will be no air pockets and reduced cavitations, this in turn improve the efficiency on both air chambers.

Another limitation is the loss of use of the flotation of the buoyancy section of all prior art. There is a need for a Wave energy converter that will to address these limitations.

The present invention is directed towards providing a wave energy converter that will have the following characteristics Stable in all weather conditions Convert wave motion to electrically energy with high yields, economically.

Be low cost to build and reproduce.

Very few moving parts.

Be structurally hydrodynamic but still remove maximum amount of energy.

Easily transportable.

High yields from variety wave types and conditions.

To store energy from large waves in a cluster.

Be environmentally friendly in construction and running.

Have good resistance to corrosion.

Not be adversely effect by tidal and current changes.

Easily adopted for new technologies in turbine design.

Easily maintained with easy of access in situ.

This invention relates to a device which is designed to extract useable amounts of energy from both the rise and fall of a wave on a body of fluid.

The invention incorporate a chamber for driving an electrical generator which is fitted to the front and rear of a housing which rises and falls with the action of the waves, The invention may also have an horizontal travelling point absorber, which can work independently (fig 1) or together (Fig 2).

The invention comprises (Fig 1) of a housing (1) which may take a number of shapes to provide buoyancy and will be structurally hydrodynamic but still remove maximum amount of energy from the waves, incorporating in to this housing can be at least one fluid filled chamber (2) this said chamber can be partitioned both along (2a) and across (2b) the axis of the housing and can be adjusted, but still allowing fluid to travel between the front and rear of the fluid filled container.

This which allows this invention to harness the energy contained in the wave motion over a wide range of wave heights including those measuring only a few centimetres in height. With this capability considered the present invention demonstrates its operational versatility. The material used in construction can be varied but will be adapted to get the best corrosion resistance survivability combination.

The said fluid chamber will have openings in top front (2c) and back (2d) leading to air chambers (3a) and (3b) and may also have opening in the bottom (4) leading to outside. The said air chambers may also have a water level controller (3c) and (3d). The opening may be needed to offset pressure off the water controllers.

In another embodiment the Wave energy converter can be towed to and from its working site with less fluid in the chambers to make it easier to be towed due to the reduced drag and the level adjusted on site.

Tn one embodiment a front section (5) will be position around the front air chamber to improve sea keeping ability.

A further embodiment is to have front fins (6) to improve the lift and an extended keel (7) to reduce roll and prevent rotation of housing. Variation of the fins and keel may be used but their will remain the same to improve front lift and reduce roll. An keel may be used along the complete length of the housing In another embodiment of the invention, bidirectional turbines (8) or turbines with valves may be fitted on both front and back air chambers to generate power but other means may use to extract power from these chambers.

The buoyancy around the housing Fig 4 (24) will be used to create neutral buoyancy to the level equal to the top of the fluid filled container this may be adjust forward or aft to improve performance but will still maintain a positive overall buoyancy of the complete housing. The buoyancy substance can be varied but will produce the same desired effect to create buoyany to the device The side containers (Fig 2), (9) and (10) which provide extra buoyancy can be attached to the housing (1) to aid to the existing buoyancy can contain a buoyancy substance which can be varied but will produce the same desired effect to create buoyany to the device The side containers (Fig 2), (9) and (10) can also be used to generate electric or can be used independently to generate electricty, will have air as the buoyancy substance in this case.

Tn one embodiment of the invention the side containers generate electricity by means of a mechanical generating device moving along the length of the side containers as they moves up and down with the waves.

The mechanical generating device moving along the length of the side containers can be constructed in Varity of ways, but general the mechanical generating device (Fig 5) will turn on a toothed gear (11) moving along a rack (12). The gear is attached to a ratchet (13) and flywheel (14) and transfers rotary motion to a generator (18) using gears (16) and (17).

In another embodiment of the invention as the wave device is in a negative incline a further gear (15) transfer's rotary motion to the above same generator again making use of the upward and downward stroke of this device.

Tn another embodiment the flywheel (14) is used to make the rotation constant while the wave machine pitches.

In another embodiment the ratchet allows the generator to continue traversing in the same direction, even if the toothed gears are going in opposite directions.

In another embodiment of the invention the side containers generate electricity by means of a induction generator and a permanent magnetic assembly (Fig 6) by means of a permanent magnet (21) which is geared (22a) and (22b) up and running on a same tooted track (21) as the a coil (23) but in a opposite direction.

Tn another embodiment (Fig 3) a front anchoring point, (1 c) is aided by a float (25) placed in front of the housing to aid its buoyancy while the device is negatively inclined and in a wave through, extra anchoring point may be added to the device rear of the device as well as tie off points on the side of the housing.

Damping rams enclosed either end of the side containers or inserted in the mechanical generating device can also be added to slow down the speed of the mechanical generating device and can also used to generate electricity.

The energy extracted from the motion of the wave may be utilized for such purposes as the generation of electricity, desalination of salt water, the production of chemicals or the supply of fresh water.

The invention is not limited to the embodiments described, but may varied in construction and detail within the scope of the claims.