WO2012095669A1

WO2012095669A1 - Wave energy converter

Info

Publication number: WO2012095669A1
Application number: PCT/GB2012/050061
Authority: WO
Inventors: Norman West Bellamy; Neil Michael Bellamy; Robert Ian Smith
Original assignee: Norman West Bellamy; Neil Michael Bellamy; Robert Ian Smith
Priority date: 2011-01-12
Filing date: 2012-01-12
Publication date: 2012-07-19
Also published as: GB201100446D0

Abstract

A wave energy converter (100) for extracting energy from waves in a body of liquid. The wave energy converter (100) comprises an endless spine (102) supporting a plurality of pneumatic absorbers (106) spaced about the spine (102). Each of the pneumatic absorbers (106) includes an oscillator (108) that is displaceable cyclically on contact with an incident wave to pump a fluid contained within the pneumatic absorber (106) and thereby extract energy from the wave in the form of pneumatic energy. The pneumatic absorbers (106) define at least one group of pneumatic absorbers (106). The pneumatic absorbers (106) in the or each group are connected in series by means of non-return valves (112) so as to direct fluid along a uni-directional flow pathway (A) through the group of pneumatic absorbers (106) and thereby aggregate and rectify pneumatic energy extracted via the group of pneumatic absorbers (106).

Description

WAVE ENERGY CONVERTER

The invention relates to apparatus for extracting energy from waves in a body of liquid. The movement of air caused when wind blows over an extensive stretch of water, such as an ocean, sea, lake, river or canal, generates waves on the surface of the water as the moving air displaces the water and thereby transmits energy to the water.

The energy stored in ocean and sea waves is considerable, the power of waves off the Atlantic coast of the UK typically measuring 70kW per metre in deep water and dissipating to 20kW per metre at the shoreline. Storm conditions generate waves having megawatts of power per metre that are destructive in nature, particularly in shoreline surf zones. Since wind derives from solar energy, sea waves are considered a renewable energy source and the effects of climate change and the depletion of fossil fuels means that it is becoming increasingly desirable to harness the energy stored in sea waves.

The nature of sea waves however presents enormous engineering challenges, and there have been numerous attempts to devise an economical solution to harvest the power available from these waves.

A problem is that sea waves are generally random in height, period and direction. On a wave to wave basis, instantaneous power levels vary by the square of the wave height. Consequently the wave power profile varies from zero to random peaks every half wave cycle. This rapid variability of power level provides a challenge, particularly in terms of power conversion in a single unit.

One solution to handle this extreme dynamic power range is to aggregate energy from multiple phased units prior to conversion of the energy to mechanical energy. Another solution involves smoothing the fluctuations in power through the use of some form of energy storage. The storage capacity required is relatively modest bearing in mind that over a period of time the characteristics of sea waves remain constant, thereby defining a steady sea state.

The designs of wave energy converters typically fall into six groups: point absorbers, attenuators, terminators, overtopping reservoirs and submerged seabed devices. Onboard power conversion to electricity is usually mechanical, hydraulic or pneumatic in nature and, if large scale energy at acceptable cost is required, then offshore floating terminators with pneumatic power conversion are generally considered to offer the most flexible of solutions. This is because terminator devices may be deployed freely in groups in the open sea where the density of wave energy is high and it is possible to maximize capture length.

Long terminator structures use their wave bridging ability as a stable frame of reference for wave absorbing mechanisms. Prior art structures known as spines, which are aligned in use along wave fronts, have proven practical for many types of wave energy converters including that disclosed in UK patent no. 2 075 127. These devices effectively terminate waves by absorbing their energy through the use of pneumatic or mechanical means.

However straight rigid spines must resist wave induced structural forces. This limits the practical length of individual spine devices and means that long spines, required for stability and high power output, are expensive to build. In addition, the movement of straight spines resulting from wave forces substantially reduces the efficiency of such wave energy converters. More stable platforms that can be produced at a lower cost therefore provide an economic advantage.

A more stable wave energy structure than the straight spine is a circular spine such as that disclosed in UK patent no. 2 161 864, which includes a plurality of individual wave absorbing sections connected end to end to form a ring.

The circular spine has been found to provide an effective frame of reference that maximizes energy capture efficiency and minimizes structural mass with respect to device size. In particular, the use of a torus structure means that the device behaves as both a terminator and an attenuator and extracts energy across the wave front and progressively as the wave passes through the device.

The stability of the ring structure also minimizes the surge, pitch and sway motion of the individual wave absorbing sections and removes any restriction on the location of the centre of gravity or buoyancy of the individual sections. UK patent no. 2 161 864 discloses a circular spine device that is described as a simple device and uses the displacement of air to extract energy from sea waves. Typically twelve air chambers having outer faces formed from flexible rubber membranes are placed around a floating ring structure. Differential wave action moves the membrane air bag in and out forcing air to be exchanged between chambers. Self rectifying air turbines placed in the manifolds between the air chambers extract power from the air flow and drive electrical generators. The rigid torus structure, typically 60m diameter or more, acts as a stable reference body and, in use, is moored a few kilometers offshore. Typically a 25MW scheme deployed off the west coast of Scotland would feature 10 floating units and produce over 50GWh per year of electricity.

When the device is in its inactive, closed-down mode the membrane air bags lie protected in their chambers and the freeboard of the structure reduces to a minimum, allowing storm waves to overtop and thereby avoid severe, slamming wave forces. This close-down mode also permits access to the device for maintenance purposes during calm conditions. To activate the device the closed circuit air system is pressurized to inflate the air bags to a mean displacement to allow the air bags to interchange air through the air turbines to deliver power in response to interacting phased random waves. The structure is designed to receive wave energy from all directions and at different phases of the wave motion. The output of each of the twelve turbo-generators is aggregated to provide the total electrical output from the apparatus. This aggregation of different phased outputs provides some smoothing of the total power output. Features such as omni-directional phased energy capture, high efficiency wave absorbers and a structurally efficient stable spine contribute towards high productivity and low energy cost.

Circular spine structures may be built economically with diameters of 60m to 80m, and thereby take advantage of the half wavelength resonance of swell waves. Structures of this size can therefore interact with large amounts of wave energy and, when sited off the west coast of the British Isles, produce annual average powers of 1 MW per device. Wave farms connected to the electrical grid onshore can therefore produce significant amounts of renewable energy and contribute to reducing dependence on fossil fuels.

The circular spine structure may be constructed from steel, concrete or any other suitable material. Steel structures based on ship design and built in shipyards are economic, quick to build and light weight. A typical steel ring spine structure may weigh around 1000 tonnes but requires up to 4000 tonnes of water ballast to achieve floating operational depth levels, which uses up to 80% of the structural space. Consequently while the inherent stability of the floating ring structure gives the freedom to design the internal space of the individual wave absorbing sections without the normal restrictions on centre of gravity and buoyancy, the space required to accommodate the water ballast renders it difficult to optimize the structural dimensions and utilize the space in the individual wave absorbing sections more effectively in order to improve performance of the wave energy converter.

In addition, while the use of self-rectifying turbines is attractive in that they are simple and produce uni-directional shaft power from reversing air flow without the use of rectifying valves, the efficiency band of current turbine designs is very narrow in comparison with the instantaneous air power input produced by wave action. At low power the turbine efficiency is low due to losses and at high power the turbine tends to stall with a rapid fall off in efficiency. While various design modifications have been tried, including variable pitch turbine blades, after 30 years of development overall turbine efficiency in real sea waves has remained low. Sea trials have also shown that the leading air bags absorb most of the wave energy with the rear bags contributing only a few percent of the total. This unbalanced distribution of input power from air bag absorbers around the circular structure can vary by a factor of ten in average sea states. Furthermore, the under-utilised air bags reduce the effective capacity of the device.

According to an aspect of the invention there is provided a wave energy converter for extracting energy from waves in a body of liquid, the wave energy converter comprising an endless spine supporting a plurality of pneumatic absorbers spaced about the spine, each of the pneumatic absorbers including an oscillator that is displaceable cyclically on contact with an incident wave to pump a fluid contained within the pneumatic absorber and thereby extract energy from the wave in the form of pneumatic energy, characterised in that the pneumatic absorbers define at least one group of pneumatic absorbers and the pneumatic absorbers in the or each group are connected in series by means of nonreturn valves so as to direct fluid along a uni-directional flow pathway through the group of pneumatic absorbers and thereby aggregate and rectify pneumatic energy extracted via the group of pneumatic absorbers. The use of non-return valves, otherwise known as check valves, allows all pneumatic energy absorbed in each pneumatic absorber to be aggregated at an early stage before conversion to a more useable form of energy. It leads to the creation of a simple rectifying system having a minimum number of moving parts, the only moving parts comprising the oscillators of the pneumatic absorbers, the valve assemblies and any turbo-generator equipment that might be harnessed to the wave energy converter in order to convert the pneumatic energy into electrical power.

The aggregation of phased power considerably reduces any fluctuation in power delivered to mechanical, electrical and grid equipment and provides an improved match to the high efficiency characteristic of certain types of turbine, such as Francis, Kaplan or Impulse. The equipment rating problem is also eased in that the wave energy converter can accommodate variations in mean air pressure, if required, by varying adjustable guide vanes. Variations in air flow can also be accommodated by varying numbers of turbo-generator units operating in parallel.

The term "spine" is commonly used in the field of wave energy converters to refer to the main support structure of such devices. It is no intended to be limited to the use of an elongate support structure but is intended also to encompass circular, oval or other shaped support structures. The term "endless spine" is intended to refer to a continuous structure, such as a circular or oval support for example, having no ends.

Spacing the pneumatic absorbers about the spine is advantageous in that it allows the wave energy converter to extract and absorb energy from waves incident from any direction.

The fluid contained in each pneumatic absorber is preferably air. It is envisaged however that in other embodiments of the invention the pneumatic absorbers may contain another gas, such as a noble gas, or a liquid, such as water.

The spine preferably includes a plurality of spine sections connected end to end to define a circular, oval or otherwise continuous structure, each spine section housing at least one pneumatic absorber. The use of such a spine structure means that, in use, the pneumatic absorbers are able to absorb and extract energy across a wave front and progressively as the wave passes the spine. It also leads to a particularly stable wave energy converter in use. The sea keeping of each section, and the total ring structure, requires structural integrity and sufficient buoyancy to maintain floatation and damage stability. The device is too wide to capsize in any sea condition and will only be in danger of sinking when two or more sections are compromised. Normal floating structures that include the functional arrangements outlined above might otherwise require expensive stabilizing structures to account for issues relating to centre of gravity and buoyancy in order to avoid being subject to capsize.

Each pneumatic absorber preferably includes an oscillator in the form of a flexible membrane mounted on a frame to define a fluid chamber. The use of a flexible membrane leads to the creation of an oscillator that is readily movable in a cyclic motion on contact with an incident wave and minimises the amount of energy that might otherwise be absorbed by the wave in order to cause movement of the oscillator. The pneumatic absorbers may define a single group of pneumatic absorbers. In one such embodiment the pneumatic absorbers may be connected in series by means of non-return valves so as to direct fluid along a uni-directional flow pathway through the pneumatic absorbers from a low pressure terminal absorber towards a high pressure terminal pneumatic absorber, the low and high pressure terminal pneumatic absorbers being interconnected via a pneumatic energy converter to convert the aggregated and rectified pneumatic energy extracted via the pneumatic absorbers.

In other embodiments the pneumatic absorbers may define two or more distinct groups of pneumatic energy converters.

In embodiments where the pneumatic absorbers define first and second groups of pneumatic absorbers, the pneumatic absorbers of each of the first and second groups of pneumatic absorbers may be connected in series by means of non-return valves so as to direct fluid along respective uni-directional flow pathways through the pneumatic absorbers, the uni-directional flow pathway through each of the first and second groups of pneumatic absorbers flowing from a low pressure terminal pneumatic absorber to a high pressure terminal pneumatic absorber, the low and high pressure terminal pneumatic absorbers of each of the first second groups of pneumatic absorbers being interconnected via a pneumatic energy converter to convert the aggregated and rectified pneumatic energy extracted via the respective group of pneumatic absorbers. In one such embodiment the first and second groups of pneumatic absorbers may be spaced about the spine so that the low pressure terminal pneumatic absorbers of the first and second groups of pneumatic absorbers are located adjacent each other at a low pressure point and the high pressure terminal pneumatic absorbers of the first and second groups of pneumatic absorbers are located adjacent each other at a high pressure point. In such an embodiment, the uni-directional flow pathways through the first and second groups of pneumatic absorbers flow in opposite directions relative to the spine from the low pressure point towards the high pressure point. In such an embodiment, where the low and high pressure terminal pneumatic absorber of each group of pneumatic absorbers are not located next to each other so as to allow the flow of fluid from the high pressure terminal pneumatic absorber into the low pressure terminal pneumatic absorber for re-circulation, after conversion of the aggregated and rectified pneumatic energy, the pneumatic energy converter connected between the low and high pressure terminal pneumatic absorbers of each of the first and second groups may be located in a low pressure duct interconnecting the respective low and high pressure terminal pneumatic absorbers.

The provision of the low pressure duct to allow re-circulation of fluid along the uni- directional flow pathway through the group of pneumatic absorbers facilitates the creation of a closed system.

In another such embodiment the pneumatic absorbers of the first and second groups of pneumatic absorbers may be spaced about the spine so that the low pressure terminal pneumatic absorbers of the first and second groups of pneumatic absorbers are located adjacent each other and alternate pneumatic absorbers spaced about the spine between the low pressure terminal pneumatic absorbers belong to the first and second groups of pneumatic absorbers respectively so that the high pressure terminal pneumatic absorber of each of the first and second groups of pneumatic absorbers are located adjacent the low pressure terminal pneumatic absorber of the other group of pneumatic absorbers. In such an embodiment the uni-directional flow pathways through the first and second groups of pneumatic absorbers flow in opposite directions about the spine through alternate pneumatic absorbers. Preferably, in each of the embodiments referred to above, each of the pneumatic absorbers contains air and the or each pneumatic energy converter includes an air turbine coupled to an electrical generator to produce electrical power for transmission to land.

In embodiments where the pneumatic absorbers contain air, or another gas, the wave energy converter may include one or more ballast compartments to selectively receive ballast in the form of water or another liquid so as to alter the distribution of buoyancy about the wave energy converter and thereby selectively alter, in use, the freeboard of the wave energy converter in a body of liquid so as to alter the positions of each of the pneumatic absorbers relative to the surface of the body of liquid.

The ability to alter the buoyancy distribution of the wave energy converter, and thus freeboard of the wave energy converter in use, allows the efficiency of operation of the pneumatic absorbers to be maintained at the required pressures. Altering the ballast within the ballast compartments allows the wave energy converter to be moored, in use, so that the pneumatic absorbers facing incident waves, otherwise referred to as the front of the wave energy converter, are raised relative to the surface of the body of liquid and the pneumatic absorbers on the opposite side of the spine, otherwise referred to as the rear of the wave energy converter, are lowered relative to the surface of the body of liquid.

This means that if the wave energy converter is moored so as to locate any air turbine at the rear of the wave energy converter, relative to the direction of travel of incident waves, the operational pressure of air contained within the pneumatic absorbers at the rear of the wave energy converter is increased. This in turn means that air is pumped progressively through the pneumatic absorbers of the or each group with increasing pressure to any air turbine at the rear of the wave energy converter.

This arrangement has the added advantage of providing a means of energy storage when energetic groups of waves pump extra air to the rear of the wave energy converter and tips the spine structure to further lower the rear of the wave energy converter relative to the surface of the body of liquid - otherwise referred to as reducing the freeboard of the wave energy converter. When the energetic waves have passed the freeboard of the wave energy converter returns to normal and the high pressure stored air is forced through the turbine. So as to reduce any fluctuation in air pressure and power, the wave energy converter preferably further includes at least two air storage reservoirs under differential pressure from an internal water head, the air storage reservoirs being connected at or towards the bottom to allow water passage between them and connected at or towards the top respectively to a high pressure inlet of the or a respective air turbine and a low pressure outlet of the or a respective air turbine.

The air pressure applied to the tanks will adjust the water to match the air pressure difference between the high pressure inlet and low pressure outlet of the or a respective air turbine. This means that if the differential air pressure between the high pressure inlet and the low pressure outlet increases, due to increased wave activity, air will be pumped into the high pressure tank and cause water to flow out of the high pressure tank and into the low pressure tank. Alternatively, if the differential pressure decreases due to a decrease in wave activity, then water will be pumped in the opposite direction and cause air to flow into the high pressure inlet and out of the low pressure outlet, effectively feeding stored energy into the system. The provision of air storage reservoirs under differential pressure from an internal water head, connected respectively to a high pressure inlet of the or a respective air turbine and a low pressure outlet of the or a respective air turbine, is an effective means of balancing a differential pressure between the high pressure inlet and the low pressure outlet and acts to smooth fluctuations in the rate of air-flow through the or each group of pneumatic absorbers.

This arrangement therefore can be used in embodiments of the invention to make effective and efficient use of ballast water, and the space it occupies, to store compressed air for the purpose of reducing fluctuations in air pressure and power. In such embodiments the potential storage capacity of the ballast water is sufficient to smooth power delivered to the grid to acceptable standards and output power variations will generally be according to sea state and not individual wave motion.

Preferred embodiments of the invention will now be described, by way of non-limiting examples, with reference to the accompanying drawings in which: Figure 1 is a plan view of the circular clam wave energy converter disclosed in UK patent no. 2 161 864;

Figure 2 is a sectional elevational side view of the wave energy converter shown in Figure 1 ;

Figure 3 is a perspective elevational view of the wave energy converter shown in

Figure 1 ;

Figure 4 is a schematic plan view of a wave energy converter according to a first embodiment of the invention;

Figure 5 shows a cross-sectional view along line l-l of a spine section of the wave energy converter shown in Figure 4;

Figure 6 shows a cross-sectional view along line ll-ll of adjacent spine sections of the wave energy converter shown in Figure 4;

Figures 7a - 7d are cross-sectional views along the line Ill-Ill of the wave energy converter shown in Figure 4 to illustrate the operation of the wave energy converter when it is subjected to four different phases of an incident wave;

Figures 8a - 8e are cross-sectional views along the line Ill-Ill of the wave energy converter shown in Figure 4 to illustrate the effect of ballast on the freeboard and operation of the wave energy converter;

Figure 9 is a cross-sectional view of a spine section of a wave energy converter according to a second embodiment of the invention;

Figure 10 is a schematic plan view of a wave energy converter according to a third embodiment of the invention; and

Figure 11 is a schematic plan view of a wave energy converter according to a fourth embodiment of the invention.

Figure 1 shows a ring spine forming part of an apparatus for extracting and converting the energy of waves in a body of liquid, typically the sea or ocean. The ring spine includes a number of sections 10 connected end to end. While the sections 10 are connected essentially to define a circular spine, it is not necessary for the spine to be circular. It must however be endless or otherwise continuous.

The apparatus may be designed for floating on a surface of a body of water, or it may be designed for anchorage, for example, on the sea bed. In all cases however it must come under the influence of waves in order to functional. The typical mean level of water 11 relative to the apparatus, in use, is shown in Figure 2.

Each of the sections 10 forms a pneumatic absorber and includes an outer surface formed from a flexible membrane bag 12 having a typical S-shaped profile 13. The bag 12 forms a drive member or oscillator for extracting energy from incident waves.

The bag 12 contains air or another fluid under pressure and, by virtue of the action of an incident wave, is subjected in use cyclically to compressive forces whereby it cats as a pump. In each cycle, when the incident wave subsides, the bag 12 is free to expand and draw in air or fluid.

The expansion and contraction of the bag 12 of each section 10 is utilise for energy conservation in that displacement of fluid by the expansion and contraction is used to drive a prime mover in the form of a turbo-generator.

A rectangular buoyant spine section 10 is shown in Figure 3, which forms part of the ring spine shown in Figure 1.

The front face of the section 10 is depressed to form a cavity 16 between the end buttresses 17 to create an inclined frame 18 designed to support the edges 19 of the flexible membrane bag 12. The edges of the flexible membrane bag 12 are bonded and held to the edge faces of the buttresses 17 and the top and bottom edges 21 ,19 of the spine so that an airtight cavity 16 is formed between the flexible membrane bag 12, the buttresses 17 and the spine.

The geometric shape and stretch characteristics of the flexible membrane bag 12 allows it to form an S-shaped vertical profile 13 when under operating pressure and immersed in water. Each cavity 16 is pneumatically connected via a short duct 22 to a ring main duct 23 that runs around the spine in order to form a closed circuit pressurized air system.

Power is extracted from the air flow by a self-rectifying turbine coupled to an electrical generator and located in either the short duct 22 connected between the cavity 16 and the ring main duct 23, so as to create a parallel air system arrangement, or in the ring main duct 23 connecting to the neighbouring section 10, so as to create a series air system. In each case the electrical power outputs from the turbo-generator of each section 10 are aggregated, or otherwise collected, to provide the total output of the apparatus. A wave energy converter 100 according to an embodiment of the invention is illustrated in Figures 4 to 6. The wave energy converter 100 includes a plurality of spine sections 104 connected end to end to form a circular spine 102. In other embodiments it is envisaged that the spine sections 104 may be connected to define an endless spine of another shape, such as a triangular, square or rectangular spine. Each spine section 104 houses a pneumatic absorber 106 (Figure 5) including an oscillator in the form of a flexible membrane 108 mounted on a frame 1 14 to define a fluid chamber 116 in fluid communication with a valve chamber 120 housing a non-return valve 112. The flexible membrane 114 is displaceable cyclically on contact with an incident wave 110 to pump air contained within the fluid chamber 1 16 of the pneumatic absorber 106 and thereby extract energy from the wave 110 in the form of pneumatic energy. It is envisaged that in other embodiments a different fluid may be contained within the fluid chamber 116 of the pneumatic oscillator 106. The fluid may for example be another gas, such as a noble gas, or a liquid, such as water. In the embodiment shown in Figure 4, the pneumatic absorbers 106 define a single group of pneumatic absorbers connected in series by means of the non-return valves 112 so as direct air along a uni-directional flow pathway (denoted in Figure 4 by arrows A) through the group of pneumatic absorbers 106 and thereby aggregate and rectify pneumatic energy extracted via the group of pneumatic absorbers 106.

The uni-directional flow pathway A flows from a low pressure terminal pneumatic absorber 106a towards a high pressure terminal pneumatic absorber 106b. The low and high pressure terminal pneumatic absorbers 106a,106b are interconnected by means of a pair of air turbines 122 coupled to an electrical generator (not shown), a high power inlet 124 of the air turbines 122 being connected to the high pressure terminal pneumatic absorber 106b and a low pressure output 126 of the air turbines 122 being connected to the low pressure terminal pneumatic absorber 106a. These connections created a closed pneumatic system so as to allow the re-circulation of air along the uni-directional flow path A through the pneumatic absorbers 106 once it has passed through the air turbines 122. Each of the spine sections 104 includes a ballast compartment 136 to selectively receive ballast 138 in the form of water or another liquid.

The wave energy converter 100 is designed as a floating body with a single point mooring system 128 attached from a position on the spine 102 located opposite the air turbines 122 so as to define a front or bow 130 of the wave energy converter 100. In use the single point mooring system 128, in the form of a lazy-S soft mooring system, is attached to a leading buoy so as to position the bow 130 of the wave energy converter 100 to face incident waves travelling in the direction of arrow B.

A restraining mooring 132 at the rear or stern 134 of the wave energy converter 100, opposite the bow 130 and aligned with the air turbines 122, ensures the wave energy converter 100 is maintained in a given area and provides reserve anchorage. The converter generally faces the wave front and automatically aligns itself in the direction of arrow B in energetic sea states.

The wave energy converter 100 is ballasted by water in the ballast compartments 136 of the spine sections 104 to float with a minimum freeboard to give it a safe reserve buoyancy. In this closed down state, the wave energy converter 100 is inactive and the flexible membranes 108 of the pneumatic absorbers 106 are in pressure contact with the frames 1 14 of the respective spine sections 104.

The wave energy converter 100 is activated by pumping air into the closed pneumatic system so that the flexible membranes 108 inflate to their mid point of operation so that incident waves can compress or de-compress the flexible membranes 108.

On compression of a flexible membrane of a first pneumatic absorber 106' (Figure 6), air is pumped from the fluid chamber 116' into the valve chamber 120' and via the nonreturn valve 112' into the valve chamber 120" of the next pneumatic absorber 106" providing the air pressure in the valve chamber 120' is higher than the air pressure in the valve chamber 120" of the next pneumatic absorber 106". In the event the air pressure in valve chamber 120" of the next pneumatic absorber 106", the non-return valve 112' of the first pneumatic absorber 106' will close and thereby prevent the flow of air in the reverse direction from the valve chamber 120" of the next pneumatic absorber 106" into the valve chamber 120' of the first pneumatic absorber 106'. Wave induced oscillation of the flexible membranes 108 of the pneumatic absorbers 106 thereby generates airflow through the pneumatic absorbers 106 along the uni-directional flow pathway A, around the spine 102 and ensures air cannot flow in the reverse direction. In operation at least one of the non-return valves 112 will be closed due to reverse pressure and this valve closure sequence will progress, at the wave velocity, along the valve chambers 120 in the direction of the uni-directional air.

As air is pumped from one pneumatic absorber 106' (Figure 6) to the next pneumatic absorber 106" along the uni-directional flow pathway, aggregation and rectification of the pneumatic energy leads to an increase in the air pressure in each subsequent pneumatic absorber 106 along the uni-directional flow pathway as each pneumatic absorber 106" is fed lower pressure air from the previous pneumatic absorber 106' via return valve 112' and feeds higher pressure to the next pneumatic absorber 106"' via return valve 112". Air is therefore pumped from the low pressure terminal pneumatic absorber 106a towards the high pressure terminal pneumatic absorber 106b where the air accumulates and drives air into the high pressure inlet 124 of the air turbines 122 to extract and convert pneumatic energy into electrical energy via the electrical generator for transmission to land. Once the air has passed through the air turbines 122 it is directed via the low pressure outlet 126 of the air turbines 122 into the low pressure terminal pneumatic absorber 106a for re-circulation along the uni-directional flow pathway A as a result of incident waves pumping air via the flexible membranes 108 of the pneumatic absorbers 106. In effect therefore the flexible membranes 108 absorb the power from incident waves and deliver it as pneumatic power to drive the air turbines 122. Sea waves normally come in groups of individual waves varying in power, height and period. The pneumatic power conversion system of the wave energy converter 100 will automatically smooth the varying power from these waves. This is because the pressurised flexible membranes 108 provide an air storage action before driving the air turbines 122. Energetic waves will tend to inflate the flexible membranes 108 towards the stern 134 of the wave energy converter 100 and hence recover that stored energy. This storage action can be further reinforced by connecting air accumulators to the high pressure inlet 124 and low pressure outlet 126 of the air turbines 122.

Figures 7a - 7d show cross-sectional side elevations of the wave energy converter 100 shown in Figures 4 to 6 and illustrate the effects of energetic waves incident on the wave energy converter 100. When incident waves are relatively small, the wave energy converter 100 is very stable in the sea with relatively little movement of the spine 102. When the waves become more energetic however the motion of the spine 102 becomes more significant and influences the behaviour of the power conversion system of the wave energy converter 100.

Preferably the size and number of the spine sections 104 are chosen so that the resultant diameter of the circular spine 102 is half the wave length of the average wave at the deployment site. This allows the wave energy converter 100 to take advantage of the half wave tuning effect on the pitch motion of the circular spine 102.

When incident waves excite this half wave resonance effect, the motion of the spine 102 increases with a combined motion of pitch, heave and surge in the direction of travel of the wave. Pitching is the dominant effect in this case and is the only motion considered for the sake of simplicity.

Figure 7a shows the crest of an incident wave C passing over the bow 130 of the wave energy converter 100. The buoyancy of the submerged bow 130 applies a clockwise torque to the circular spine 102 that causes a clockwise pitch motion. The phasing of the pitch motion is a quarter wavelength behind the wave making the slope of the spine 102 horizontal, as shown in Figure 7a. The flexible membranes 108 of the pneumatic absorbers 106 located towards the bow 130 will inflate and the flexible membranes 108 of the pneumatic absorbers 106 located towards the stern 134 will inflate.

As the crest of the incident wave C passes over the centre of the wave energy converter 100, as shown in Figure 7b, the buoyancy torque applied to the spine 102 changes from a clockwise torque to an anti-clockwise torque that causes the clockwise pitch to reverse. The phasing of the pitch motion is a quarter wavelength behind the wave making the spine 102 high at the bow 130, as shown in Figure 7b. The flexible membranes 108 of the pneumatic absorbers 106 located towards the bow 130 will therefore be fully deflated and the flexible membranes 108 of the pneumatic absorbers 106 located towards the stern 134 will be fully inflated.

As the crest of the incident wave C passes over the stern 134 of the wave energy converter 100, as shown in Figure 7c, the buoyancy of the submerged stem 134 applies an anti-clockwise torque to the spine 102 that causes an anti-clockwise pitch motion. As above, the phasing of the pitch motion is a quarter wavelength behind the wave making the slope of the spine 102 horizontal, as shown in Figure 7c. The flexible membranes 108 of the pneumatic absorbers 106 located towards the bow 130 will be inflating and the flexible membranes 108 of the pneumatic absorbers 106 located towards the stern 134 deflating. As the trough of the incident wave C passes over the centre of the wave energy converter 100, as shown in Figure 7d, the buoyancy torque applied to the spine 102 changes from an anti-clockwise torque to a clockwise torque that causes the anticlockwise pitch to reverse. The phasing of the pitch motion is again a quarter wavelength behind the wave making the spine 102 high at the stern 134, as shown in Figure 7d. The flexible membranes 108 of the pneumatic absorbers 106 located towards the bow 130 will be fully inflated and the flexible membranes 108 of the pneumatic absorbers 106 located towards the stern 134 will be fully deflated.

The action thus maximises the energy that the pneumatic absorbers 106 are able to extract from the incident waves in the form of pneumatic energy, the provision of the nonreturn valves 112 between the pneumatic absorbers 106 ensuring that air is pumped along the uni-directional flow pathway A so as to aggregate and rectify the resultant pneumatic energy directed towards the high pressure terminal pneumatic absorber 106b. The operation of the wave energy converter 100 may also be adjusted by altering the ballast 138 contained in the ballast compartments 136 of the spine sections 104. The ballast 138 generally effects the freeboard and thus operation of the wave energy converter 100 as a result of the positions of the flexible membranes 108 of the pneumatic absorbers 106 relative to the surface of a body of liquid. The addition of ballast 138 towards the stern 134 however increases the air pressure in the fluid chambers 116 of the pneumatic absorbers 106 located towards the stem 134 and hence increases the air power available to drive the air turbines 122.

Figures 8a - 8e show cross-sectional side elevations of the wave energy converter 100 shown in Figures 4 to 6 and illustrate the effects of altering the ballast 138.

Figure 8a shows the wave energy converter 100 floating on a calm sea in its close down mode. The wave energy converter 100 is ballasted by means of water contained in the ballast compartments 136 of each spine section 104 so as to float with enough reserve buoyancy and freeboard D for safe sea-keeping. In this closed down state, the wave energy converter 100 is inactive and the flexible membranes 108 of the pneumatic absorbers 106 are deflated and in pressure contact with the frames 114 of the respective spine sections 104.

The converter is activated by pumping air into the closed pneumatic system to inflate the flexible membranes 108 to their mid point of operation, as shown in Figure 8b. This substantially increases the buoyancy of the wave energy converter 100 and increases the operating freeboard D accordingly. Incident waves can now compress, or de- compress, the flexible membranes 108 and pump air around the uni-directional flow pathway A towards the high pressure terminal pneumatic absorber 106b and the air turbines 122.

Moving ballast 138 from spine sections 104 located towards the bow 130 to spine sections 104 located towards the stem 134 results in a reduced freeboard D at the 134 and, as a result, an increased freeboard D at the bow 130, as shown in Figure 8c.

With this arrangement of ballast 138, the flexible membranes 108 of the pneumatic absorbers 106 located towards the stern 134 are under a higher pressure from sea water and hence compress to minimum inflation. The flexible membranes 108 of the pneumatic absorbers 106 located towards the bow 130 in contrast are de-compressed to maximum inflation.

This means that incident waves can now compress, or de-compress, the flexible membranes 108 of the pneumatic absorbers 106 and drive air around the uni-directional flow pathway A towards the high pressure terminal pneumatic absorber 106b and the air turbines 122. However, in this configuration the flexible membranes 108 of the pneumatic absorbers 106 located towards the stern 134 must work at a much higher air pressure than those located towards the bow 130.

Figure 8d illustrates the effect of waves on the pitch motion of the spine 102 when air has been pumped towards the high pressure terminal pneumatic absorber 106b at the stern 134 so as to inflate the flexible membrane 108 of the high pressure terminal pneumatic absorber 106b to a higher pressure.

This wave action on the wave energy converter 100 has the effect of moving buoyancy towards the stern 134, thereby levelling the mean slope of the spine 102. However, the wave action still causes the wave energy converter 100 to pitch about this mean slope and cause varying pressure changes in the air system.

In Figure 8d, the crest of the incident wave D is at a peak 140 at the bow 130 of the wave energy converter 100 and hence applies a clockwise torque causing the spine 102 to pitch clockwise. The damping effect of the air turbine controls the air flow in the system and then can be used to maximise energy output by maintaining the buoyancy distribution to give an optimum mean slope. Wave action is again illustrated in Figure 8e, the wave action causing the spine 102 to pitch about its mean slope but with the cost of the incident wave at a peak 140 at the stern 134 of the wave energy converter 100. In this case the crest of the wave applies an anti-clockwise torque causing the spine 102 to pitch anti-clockwise. Again the damping effect of the air turbines 122 maximises the energy output of the wave energy converter 100.

In another embodiment of the invention, the ballast compartment 136 of each spine section 104 may be adapted to include a vertical divider 142 and thereby split the ballast compartment 136 into a high pressure tank 144 and a low pressure tank 144, as shown in Figure 9.

The high and low pressure tanks 142,144 are connected by a bottom aperture 146 to enable free movement of water between the two tanks 142,144. The high pressure tank 142 may then be connected to the high pressure inlet 124 of the air turbines 122 via a high pressure duct (now shown) and the low pressure tank 144 may be connected to the low pressure outlet 126 of the air turbines 122 via a low pressure duct (now shown). In use, the water levels 148,150 in the high and low pressure tanks 142,144 adjust to the differential air pressure in the system and the resultant internal water head will act to smooth pressure variations in the system.

In the event the differential air pressure between the high pressure inlet 124 and the low pressure outlet 126 increases, due to increased wave activity, air will be pumped into the high pressure tank 142 and cause water to flow out of the high pressure tank 142 and into the low pressure tank 144. Alternatively, if the differential pressure decreases due to a decrease in wave activity, then water will be pumped in the opposite direction and cause air to flow into the high pressure inlet 124 and out of the low pressure outlet 126, effectively feeding stored energy into the system.

The effective capacity of this air storage system is proportional to the surface area of the high and low pressure tanks 142,144. This only applies over the range of operational differential pressures, which in practice is much less than the depth of the tanks illustrated in Figure 9. It is envisaged that the amount of ballast 138 in the spine sections 104 will be relatively large, which means that there would potentially be a relatively large smoothing capacity available if required.

A wave energy converter 100' according to a third embodiment of the invention is shown in Figure 10. The wave energy converter 100' shown in Figure 10 is constructed in a very similar manner to the wave energy converter 100 shown, and described with reference to, Figures 4 to 6. The same reference numerals will therefore be used to identify common components and features. In a same manner to the wave energy converter 100 shown in Figure 4, the wave energy converter 100' shown in Figure 10 includes a plurality of spine sections 104 connected end to end to form a circular spine 102. The structure of each spine section 104 is identical to that shown in Figure 5 and further detailed description is not therefore required.

The wave energy converter 100' shown in Figure 10 however differs from the wave energy converter shown in Figure 4 in that the pneumatic absorbers 106 define first and second groups of pneumatic absorbers. In this regard a first group of pneumatic absorbers 106' extend in a first, clockwise direction about the spine 102 from a low pressure point 152 at the bow 130 of the wave energy converter 100 to a high pressure point 154 at the stern 134. A second group of pneumatic absorbers 106" extend in the opposite, anti-clockwise direction about the spine 102 from the low pressure point 152 to the high pressure point 154. The low pressure terminal pneumatic absorbers 106a', 106a" of the first and second groups of pneumatic absorbers are located adjacent each other relative to the spine 102 at the bow 130. The high pressure terminal pneumatic absorbers 106b', 106b" of the first and second groups of pneumatic absorbers are located adjacent each other relative to the spine 102 at the stern 134.

The first group of pneumatic absorbers 106' are connected in series by means of non- return valves 112' so as to direct, in use, air along a uni-directional flow pathway A' extending from the respective low pressure terminal pneumatic absorber 106a' to the respective high pressure terminal pneumatic absorber 106b' and thereby aggregate and rectify pneumatic energy extracted via the first group of pneumatic absorbers 106'. Similarly the second group of pneumatic absorbers 106" are connected in series by means of non-return valves 112" so as to direct, in use, air along a uni-directional flow pathway A" extending from the respective low pressure terminal pneumatic absorber 106a" to the respective high pressure terminal pneumatic absorber 106b" and thereby aggregate and rectify pneumatic energy extracted via the second group of pneumatic absorbers 106".

The structure of each of the pneumatic absorbers 106 is identical to that shown in Figure 5 and so a detailed description of the structure An air turbines 122' coupled to an electrical generator (not shown) is connected between the low and high pressure terminal pneumatic absorbers 106a',106b' of the first group and, similarly, an air turbine 122" coupled to the electrical generator (not shown) is connected between the low and high pressure terminal pneumatic absorbers 106a".106b" of the second group.

Each of the air turbines 122,122" is connected to a respective one of the high pressure terminal pneumatic absorbers 106b', 106b" via a high pressure inlet 124 of the air turbine 122', 122". Each of the air turbines 122,122" is also connected to a respective one of the low pressure terminal pneumatic absorbers 106a', 106a" via a low pressure outlet 126 of the air turbine 122', 122". For simplicity, only a single high pressure inlet 124 and a single low pressure outlet 126 is shown in Figure 10. It will be appreciated however that the air flow will be directed accordingly between the first and second groups of pneumatic absorbers 106', 106" and the respective air turbines 122', 122". Unlike the wave energy converter 100 shown in Figure 1 , the low and high pressure terminal pneumatic absorbers 106a', 106b';106a",106b" of the first and second groups are not located adjacent each other. Consequently the wave energy converter 100 shown in Figure 10 includes a low pressure duct 156',156" interconnecting the low and high pressure terminal pneumatic absorbers 106a', 106b';106a", 106b", the air turbines 122', 122" each being located in a respective one of the low pressure ducts 156', 156". In use, the wave energy converter 100' operates in the same manner as the wave energy converter 100 shown in Figure 4. Consequently a detailed description is not provided. It will however be appreciated that on contact with incident waves, compression and de-compression of the flexible membranes 108 of the pneumatic absorbers 106', 106" will cause air to be pumped along the two uni-directional flow pathways A,A" towards the respective high pressure terminal pneumatic absorbers 106b',106b".

The wave energy converter 100' will also respond to the four different phases of an incident wave in the same manner as the wave energy converter 100, which is illustrated in Figures 7a - 7d. Similarly the wave energy converter 100' will also respond to the effect of ballast in the same manner as the wave energy converter 100, which is illustrated in Figures 8a - 8e.

In order to provide a smoothing effect, the ballast compartment 136 of each spine section 104 of the wave energy converter 100' may be adapted to define high and low pressure tanks 142,144 in the same manner as that shown in Figure 9.

A wave energy converter 100' according to a fourth embodiment of the invention is shown in Figure 11. The wave energy converter 100' shown in Figure 11 is again constructed in a very similar manner to the wave energy converter 100 shown, and described with reference to, Figures 4 to 6. The same reference numerals will therefore be used to identify common components and features.

In a same manner to the wave energy converter 100 shown in Figure 4, the wave energy converter 100" shown in Figure 11 includes a plurality of spine sections 104 connected end to end to form a circular spine 102. The structure of each spine section 104 is identical to that shown in Figure 5 and further detailed description is not therefore required. The wave energy converter 100' shown in Figure 1 1 again however differs from the wave energy converter shown in Figure 4 in that the pneumatic absorbers 106 define first and second groups of pneumatic absorbers. In this regard the pneumatic absorbers of the first and second groups are spaced about the spine 102 so that the low pressure terminal pneumatic absorbers 106a', 106a" of the first and second groups are located adjacent each other at the stern 134. Alternate pneumatic absorbers spaced about the spine 102 between the low pressure terminal pneumatic absorbers 106a', 106a" belong to the first and second groups of pneumatic absorbers respectively so that the high pressure terminal pneumatic absorbers 106b', 106b" of each of the first and second groups are located adjacent the low pressure terminal pneumatic absorber 106a', 106a" of the other group.

As with the wave converter 100' shown in Figure 10, the first group of pneumatic absorbers 106' are connected in series by means of non-return valves 112' so as to direct, in use, air along a uni-directional flow pathway A' extending from the respective low pressure terminal pneumatic absorber 106a' to the respective high pressure terminal pneumatic absorber 106b' and thereby aggregate and rectify pneumatic energy extracted via the first group of pneumatic absorbers 106'.

Similarly the second group of pneumatic absorbers 106" are connected in series by means of non-return valves 112" so as to direct, in use, air along a uni-directional flow pathway A" extending from the respective low pressure terminal pneumatic absorber 106a" to the respective high pressure terminal pneumatic absorber 106b" and thereby aggregate and rectify pneumatic energy extracted via the second group of pneumatic absorbers 106". Referring to Figure 11 , it can be seen that the uni-directional flow pathway A' extending through the first group of pneumatic absorbers 106' extends in an anti-clockwise direction about the spine 102. The uni-directional flow pathway A" extends through the second group of pneumatic absorbers 106" in a clockwise direction about the spine 102. The structure of each of the pneumatic absorbers 106 is identical to that shown in Figure 5 and so a detailed description of the structure

An air turbines 122' coupled to an electrical generator (not shown) is connected between the low and high pressure terminal pneumatic absorbers 106a',106b' of the first group and, similarly, an air turbine 122" coupled to the electrical generator (not shown) is connected between the low and high pressure terminal pneumatic absorbers 106a".106b" of the second group. Each of the air turbines 122,122" is connected to a respective one of the high pressure terminal pneumatic absorbers 106b', 106b" via a high pressure inlet 124', 124" of the air turbine 122', 122". Each of the air turbines 122,122" is also connected to a respective one of the low pressure terminal pneumatic absorbers 106a',106a" via a low pressure outlet 126', 126" of the air turbine 122', 122".

In use, the wave energy converter 100' operates in the same manner as the wave energy converter 100 shown in Figure 4. Consequently a detailed description is not provided. It will however be appreciated that on contact with incident waves, compression and de-compression of the flexible membranes 108 of the pneumatic absorbers 106', 106" will cause air to be pumped along the two uni-directional flow pathways A,A" towards the respective high pressure terminal pneumatic absorbers 106b',106b".

Claims

1. A wave energy converter for extracting energy from waves in a body of liquid, the wave energy converter comprising an endless spine supporting a plurality of pneumatic absorbers spaced about the spine, each of the pneumatic absorbers including an oscillator that is displaceable cyclically on contact with an incident wave to pump a fluid contained within the pneumatic absorber and thereby extract energy from the wave in the form of pneumatic energy, characterised in that the pneumatic absorbers define at least one group of pneumatic absorbers and the pneumatic absorbers in the or each group are connected in series by means of non-return valves so as to direct fluid along a uni-directional flow pathway through the group of pneumatic absorbers and thereby aggregate and rectify pneumatic energy extracted via the group of pneumatic absorbers.

2. A wave energy converter according to Claim 1 wherein the spine includes a plurality of spine sections connected end to end to define a circular, oval or otherwise continuous structure, each spine section housing at least one pneumatic absorber.

3. A wave energy converter according to Claim 1 or Claim 2 wherein each pneumatic absorber includes an oscillator in the form of a flexible membrane mounted on a frame to define a fluid chamber.

4. A wave energy converter according to any one of the preceding claims wherein the pneumatic absorbers define a single group of pneumatic absorbers, the pneumatic absorbers being connected in series by means of non-return valves so as to direct fluid along a uni-directional flow pathway through the pneumatic absorbers from a low pressure terminal pneumatic absorber towards a high pressure terminal pneumatic absorber, the low and high pressure terminal pneumatic absorbers being interconnected via a pneumatic energy converter to convert the aggregated and rectified pneumatic energy extracted via the pneumatic absorbers.

5. A wave energy converter according to any one of Claims 1 to 3 wherein the pneumatic absorbers define first and second groups of pneumatic absorbers, the pneumatic absorbers of each of the first and second groups of pneumatic absorbers being connected in series by means of non-return valves so as to direct fluid along respective uni-directional flow pathways through the pneumatic absorbers, the unidirectional flow pathway through each of the first and second groups of pneumatic absorbers flowing from a low pressure terminal pneumatic absorber to a high pressure terminal pneumatic absorber, the low and high pressure terminal pneumatic absorbers of each of the first and second groups of pneumatic absorbers being interconnected via a pneumatic energy converter to convert the aggregated and rectified pneumatic energy extracted via the respective group of pneumatic absorbers.

6. A wave energy converter according to Claim 5 wherein the pneumatic absorbers of the first and second groups of pneumatic absorbers are spaced about the spine so that the low pressure terminal pneumatic absorbers of the first and second groups of pneumatic absorbers are located adjacent each other at a low pressure point and the high pressure terminal pneumatic absorbers of the first and second groups of pneumatic absorbers are located adjacent each other at a high pressure point, the unidirectional flow pathways through the first and second groups of pneumatic absorbers flowing in opposite directions relative to the spine from the low pressure point towards the high pressure point.

7. A wave energy converter according to Claim 6 wherein the pneumatic energy converter connected between the low and high pressure terminal pneumatic absorbers of each of the first and second groups is located in a low pressure duct interconnecting the respective low and high pressure terminal pneumatic absorbers.

8. A wave energy converter according to Claim 5 wherein the pneumatic absorbers of the first and second groups of pneumatic absorbers are spaced about the spine so that the low pressure terminal pneumatic absorbers of the first and second groups of pneumatic absorbers are located adjacent each other and alternate pneumatic absorbers spaced about the spine between the low pressure terminal pneumatic absorbers belong to the first and second groups of pneumatic absorbers respectively so that the high pressure terminal pneumatic absorbers of each of the first and second groups of pneumatic absorbers are located adjacent the low pressure terminal pneumatic absorber of the other group of pneumatic absorbers, the uni-directional flow pathways through the first and second groups of pneumatic absorbers flowing in opposite directions about the spine through alternate pneumatic absorbers.

9. A wave energy converter according to any one of Claims 4 to 8 wherein each pneumatic absorber contains air and the or each pneumatic energy converter includes an air turbine coupled to an electrical generator to produce electrical power for transmission to land.

10. A wave energy converter according to any one of the preceding claims wherein each of the pneumatic absorbers contains air, or another gas, the wave energy converter further includes one of more ballast compartments to selectively receive ballast in the form of water, or another liquid, so as to selectively alter the distribution of buoyancy about the wave energy converter and thereby selectively alter, in use, the freeboard of the wave energy converter in a body of liquid so as to alter the position of each of the pneumatic absorbers relative to the surface of the body of liquid.

11. A wave energy converter according to Claims 9 and 10 wherein the or each ballast compartment is formed to define at least two air storage reservoirs under differential pressure from an internal water head, the air storage reservoirs being connected respectively to a high pressure inlet into the or a respective air turbine and a low pressure outlet of the or a respective air turbine.

12. A wave energy converter for extracting energy from waves in a body of liquid comprising an endless spine, said spine including a plurality of pneumatic absorbers in contact with incident waves to pump air contained within the pneumatic absorber and thereby extract energy from the wave in the form of pneumatic energy, characterised in that the pneumatic energy of each pneumatic absorber is series rectified and aggregated before conversion to a more useable form of energy.

13. A wave energy converter according to Claim 12 wherein the pneumatic absorber comprises flexible membrane bag elements located and spaced about the periphery of the spine and located behind each membrane is an air cavity through which air is pumped, along each side of the spine in the direction of wave propagation, to a higher pressure through non-return valves fitted between each absorber.

14. A wave energy converter according to Claim 12 or Claim 13 wherein the high pressure air pumped to the rear of the spine for power generation is returned as low pressure air to the front of the spine through a low pressure return duct, along each side of the spine against the direction of the wave propagation, and hence defining two unidirectional air-flow pathways around the spine.

15. A wave energy converter according to Claim 12 or Claim 13 wherein the series rectifier action smoothes the pneumatic power by accumulating air power at pressure in the membrane air bags located at the rear of the spine.

16. A wave energy converter according to any one of Claims 12 to 15 where the ring structure is ballasted to reduce the waterline freeboard at the rear, hence increasing the operating pressure within those flexible membrane absorbers and thereby increasing the air power captured.

17. A wave energy converter according to any one of Claims 12 to 16 wherein the spine further includes at least two air storage reservoirs under differential pressure from an internal water head the air storage reservoirs being connected to the high and low pressure ducts.

18. A wave energy converter according to any one of Claims 12 to 17 wherein the spine defines a substantially circular ring.

19. A wave energy converter according to any one of Claims 12 to 18 wherein the spine includes a plurality of ring sections connected end to end.

20. A wave energy converter according to any one of Claims 12 to 19 wherein each of the two high pressure ducts direct air pumped through the pneumatic absorbers to at least one air turbine that is coupled to an electrical generator to produce electrical power for transmission to land.