ZA201004376B - Wave energy converter - Google Patents

Description

e_ 2010/7 04376

WAVE ENERGY CONVERTER

FIELD OF THE INVENTION

This invention relates generally to wave energy converter devices for converting wave motion into electricity.

BACKGROUND TO THE INVENTION

Wave energy is a potential source of renewable energy and various wave energy conversion devices have been proposed that aim to extract useful energy from wave motion in a body of liquid, such as the sea.

One such wave energy conversion device makes use of an oscillating water column which typically comprises a partially submerged vertical tube or chamber in which incident waves surge back and forth. The rising and falling of the water column alternately compresses and decompresses the air column in the vertical tube or chamber, driving air through a turbine from which electricity is generated.

One of the disadvantages of oscillating water column-based systems is that they require comparatively expensive turbine arrangements capable of operating and generating electricity from the reversing bi-directional airflow pumped by the oscillating water column through the turbine arrangement.

Furthermore, this bi-directional airflow frequently results in energy losses due to large scale vortex shedding from surfaces where there is a rapid change in flow direction, thereby decreasing energy efficiencies.

Another wave energy conversion device, known as an overtopping device, makes use of uni-directional water flow and consists of a wall that collects water from rising waves into a reservoir positioned above water-level. The

P1949ZA00 (Wave Energy Converter)

£.2010/ 04376 water so collected then passes, under force of gravity, through an opening in the reservoir, and in so doing drives a turbine from which electricity is : generated. However, such devices that are located at or near the water surface experience large wave impact loads in extreme sea states and weather conditions and are therefore prone to wear and damage.

OBJECT OF THE INVENTION

It is an object of this invention to provide a wave energy converter which will at least partially alleviate some of the abovementioned problems.

SUMMARY OF THE INVENTION

In accordance with the invention there is provided a wave energy converter comprising a buoyant member which provides an inlet through a passage to a reservoir which depends therefrom, with a turbine operable by water flowing through the passage, and the reservoir having an outlet in flow communication with a substantially stationary variable volume chamber through a uni-directional valve and the variable volume chamber having an outlet through a further uni-directional valve, and wherein movement of the buoyant member in response to wave height causes variation in chamber volume such that the chamber acts as a pump to drain water from the reservoir.

A further feature of the invention provides for the inlet to the reservoir to include means for controlling the rate of water flowing into the reservoir.

Still further features of the invention provide for the wave energy converter to have a plurality of variable volume chambers; for the or each variable volume chamber to be an elongate tube having a flexible wall compressible along its length bellows-fashion; alternately for the variable volume chamber to be a cylinder having a piston running therein.

P1949ZA00 (Wave Energy Converter)

« 2010/ 04376

BRIEF DESCRIPTION OF THE DRAWINGS

One embodiment of the invention will be described, by way of example only, with reference to the drawings in which:

Figure 1 is a sectional diagrammatic elevation of a wave energy converter in an extended condition; and

Figure 2 is a sectional diagrammatic elevation of a wave energy converter in Figure 1 in a compressed condition; and

Figure 3 is a diagrammatic top plan view of a wave energy converter in Figure 1.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

A wave energy converter (1) for use in converting wave energy in a body of water (2), such as the sea, into electrical energy is shown in Figures 1 to 3.

The wave energy converter (1), includes a hollow buoyant member (4) having a plurality of inlets (6) at water level for the regulated inflow of sea water (2) into the buoyant member (4) and through a passage (7) into a cylindrical reservoir (8) depending therefrom and in gravity flow communication therewith. A turbine (10) is located within the passage (7) intermediate the buoyant member (4) and the reservoir (8), and a generator (12) is connected to thereto.

The reservoir (8) has an outlet (14.1) at its lower end (8.1) which is connected through a uni-directional valve to the inlet (14.2) of a chamber (16) at its upper end (16.1). The chamber (16) has an outlet (20) which feeds into the surrounding water (2) through a further uni-directional valve.

The variable volume chamber (16) is of a generally cylindrical shape having a central portion with a bellows type flexible wall (17) which permits expansion

P1949ZA00 (Wave Energy Converter)

_2010/ 04376 and contraction of the chamber along its length so that the internal volume of the chamber (16) is variable. The operatively lower end thereof is fixed to a submerged surface such as that of an oil rig or platform (18). 5 The buoyant member (4) is held in a generally upright position by means of steel guide rods (22) which are of an appropriate length such that expansion of the variable volume chamber (16), as shown in Figure 1, is not restricted.

As shown in Figure 3, elastic cables (24) are also secured to the buoyant member (4) from the underside of an oil rig platform (26) to anchor the wave energy converter (1) against buffeting by currents.

In use, the wave energy converter (1) is submerged in a body of water (2) having passing waves or swells and to an appropriate depth such that the buoyant member (4) floats on the surface of the body of water (2). Water (2) flows through the inlets (6) into the reservoir (8) under the force of gravity.

The water passes through the turbine (10) depending from the buoyant member (4) causing it fo operate and in turn operate the generator (12) which produces electrical energy for further relay or storage (not shown). In this embodiment, the electricity from the turbine (10) is 3 phase 6000-7000 volt, which is stepped up to 33 KV and relayed to land by way of submerged cables (not shown).

As shown in Figure 1, as the crest of a wave (2.1) passes, the buoyant member (4) and reservoir (8) are lifted relative to the variable volume chamber (16). This causes the chamber (16) to expand along its length and so draw water from the reservoir into it.

As shown in Figure 2, as the trough of the wave (2.2) passes, the buoyant member (4) now falls back towards the chamber (16). This causes the chamber (16) to compress and expel the water contained therein through the outlet (20) and into the surrounding water (2). Hereafter the cycle is

P1949ZA00 (Wave Energy Converter)

2.20107 04376 repeated with each passing wave. The chamber (16) thus acts as a pump operated by wave action to draw water from the reservoir (8).

The inlets (6) regulate the flow of water into the reservoir (8) such that it is filled to capacity within the average time between crests of consecutive waves to pass the buoyant member (4). In this way, a continual flow of water is passed through the turbine and drained from the chamber (16) at a regulated rate so that the turbine is operated at a constant rate.

Control of the rate of water (2) inflow may also be effected to regulate the buoyancy of the buoyant member (4) in response to weather conditions, water movement and wave period length.

The invention has the advantage that the flow of water is uni-directional such that the oscillating wave motion is converted to uni-directional motion which permits relatively inexpensive turbines to be used in combination with the wave energy converter of the invention. Furthermore, the submersion of the wave energy converter minimises wave impact loads in extreme sea states and weather conditions as compared to currently used exposed overtopping devices so that the wave energy converter of the invention is comparatively less prone to wear and damage.

It will be apparent, however, that many other embodiments of a wave energy converter exist which fall within scope of the invention. For example, a plurality of variable volume chambers (16) may be used which each draw water from the reservoir (8). The variable volume chamber (16) may also be in the form of a cylinder having a piston running therein, or any other suitable mechanical equivalent, such that the pumping action effect is similar to that of the chamber (16). The reservoir (8) may also require a vacuum breaker or breather pipe which extends from the reservoir (8) to the surface of the body of water (2) and permits air to enter or exit the reservoir (8) and prevents a vacuum being formed in the reservoir (8) when water is drawn out of it. Also,

P1949ZA00 (Wave Energy Converter)

£20107 04376 the buoyant member need not float on the surface but could be made to float at any suitable distance below the surface if required. Any suitable means could be used to monitor and control the wave energy convertor.

P1949ZA00 (Wave Energy Converter)

Claims (6)

mie .2010/ 04376 oL_ CLAIMS:

1. A wave energy converter comprising a buoyant member which provides an inlet through a passage to a reservoir which depends therefrom, with a turbine operable by water flowing through the passage, and the reservoir having an outlet in flow communication with a substantially stationary variable volume chamber through a uni- directional valve and the variable volume chamber having an outlet through a further uni-directional valve, and wherein movement of the buoyant member in response fo wave height causes variation in chamber volume such that the chamber acts as a pump to drain water from the reservoir.

2. A wave energy converter as claimed in claim 1 in which the inlet to the reservoir includes means for controlling the rate of water flowing into the reservoir.

3. A wave energy converter as claimed in claim 1 or claim 2 in which a plurality of variable volume chambers are in flow communication with the reservoir.

4. A wave energy converter as claimed in claim 3 in which each variable volume chamber is an elongate tube having a flexible wall compressible along its length bellows-fashion.

5. A wave energy converter as claimed in any one of claims 1 to 3 wherein the or each variable volume chamber includes a cylinder having a piston running therein.

6. A wave energy converter substantially as herein described and as illustrated with reference to Figures 1 to 3. P1949ZA00 (Wave Energy Converter)

-20107 043768

Dated this 18th day of June 2010 yr VON SHEIDELS Intellectual Property Attorneys for the applicant

P1949ZA00 (Wave Energy Converter)