WO2012123700A2

WO2012123700A2 - Electrical energy generating system

Info

Publication number: WO2012123700A2
Application number: PCT/GB2012/000241
Authority: WO
Inventors: Alan Rogers; John Rutt
Original assignee: CLEAN ENERGY Ltd
Current assignee: CLEAN ENERGY Ltd
Priority date: 2011-03-14
Filing date: 2012-03-14
Publication date: 2012-09-20
Anticipated expiration: 2013-09-14
Also published as: WO2012123700A3; GB201104273D0; GB201321192D0; GB2505591A

Abstract

An electrical energy generation system including a compressor adapted to compress and/or pump a fluid, a fluid-powered electrical generator and a pipe network arranged therebetween, wherein the pipe network is adapted to transport and store the compressed fluid.

Description

Electrical Energy Generating System

The present invention relates to an energy collection, transmission and storage system and to the use of this energy to generate electricity. In particular, the invention re)ates to a system which does not result in the release of any "greenhouse gases" or other pollutants into the atmosphere.

Current fossil fuel power stations generate electrical energy through the burning of fossil fuels such as coal, gas and oil. However, they present a number of distinct problems: the combustion process generates as a by-product significant amounts of greenhouse gases mainly carbon dioxide (C0₂), and other atmospheric pollutants, which are released into the atmosphere; and the electricity generated is not transmitted without loss. This means that the overall efficiency of the electrical energy generation process is reduced, there are increased costs for those involved in the electrical generation and transmission business, and that therefore the quantity of greenhouse gas produced per unit of electricity is, in fact, higher than typically stated. A further inefficiency inherent in fossil fuel power stations is the loss of utilisable heat to the atmosphere, representing, as it does, further wasted energy.

Current renewable energy systems generate electrical energy without the emission of greenhouse gases, but they suffer from a number of problems that have prevented widespread uptake of their technologies. More specifically, they are not designed to make the most efficient use of the relevant driver e.g. wind. For example, as a result of the sporadic nature of the driver (e.g. the wind) the continuity and specification of the energy produced cannot always be sufficiently regulated to match the electrical grid requirements. In addition, they also tend to suffer from storage problems, from transmission losses, and the systems are often expensive to build and commission, often requiring substantial government subsidies to initiate.

According to a first aspect of the invention, there is provided an electrical energy generation system including a renewable energy capture device located off-shore; a compressor operably connected to the energy capture device and adapted to compress and/or pump a working fluid, a fluid-powered electrical generator and a pipe network arranged between the compressor and the generator, wherein the pipe network includes a primary pressurised fluid storage portion, the primary pressurised fluid storage portion being located under water and comprising a plurality of flow pipes arranged in parallel, wherein each flow pipe of the pressurised fluid storage portion includes an inlet at one end thereof and an exit at the opposite end. The use of a working fluid (i.e. a liquid or a gas) as an energy storage medium between the compressor and electrical energy generator addresses many of the problems associated with known electrical energy generating systems in which the generator is powered directly from the power source (e.g. oil, coal, natural gas, wind, wave, solar, etc.).

In the context of the current invention, the term "compressor" refers to any apparatus which generates a high pressure fluid from a lower pressure fluid, including generating a liquid from a gas. Thus, where the working fluid is a substantially incompressible liquid, the compressor acts to pressurise the liquid, rather than to actually compress it.

By locating the renewable energy capture device (or multiple renewable energy capture devices) off-shore, a number of advantages are obtained. Firstly, the capture devices do not interfere with land-based activities or require the purchase of costly land. Secondly, the primary pressurised fluid storage portion of the pipe network is located underwater. This provides for the quick and easy removal of the heat generated within the working fluid as a result of being compressed or pressurised.

The provision of a pressurised fluid storage portion in the form of a plurality of flow pipes arranged in parallel also allows for the system to continue to operate in the event of a problem or fault with one of the flow pipes forming the pressurised fluid storage portion. The damaged or faulty pipe may be isolated, but the pressurised fluid stored in the remaining pipes may still be utilised to ensure a continuous flow of pressurised fluid to the generator.

Having the pressurised fluid storage portion underwater also provides a safety feature, as if there is a fault with one of the pipes, the energy of the rapidly vented working fluid is substantially absorbed by the body of water surrounding the relevant pipe.

The advantages of this deployment are obvious, especially for a country like the United Kingdom where networks of pipes in the sea or major waterways around and within the country makes for an efficient method of delivering electrical energy to the areas of greatest demand, many of which are located at or near to the coast or other major waterway. This would have the beneficial consequence of relieving the already overtaxed electrical grid by moving power conversion units closer to the demand points. The method of delivering power to the fluid network is simple and much less demanding than that of the electricity grid.

By providing a network of flow pipes arranged in parallel to store the pressurised working fluid, the need for one or more costly storage tanks may be avoided or reduced. Such storage tanks often contain complicated arrangements of pistons and such like to maintain a substantially constant pressure within the tank and are often reinforced or encased in concrete or other materials to provide the desired strength.

Nevertheless, the network, however large, may not be able to store off peak energy effectively to sustain supply over the peak periods of demand, so one or more secondary energy storage units may be included as part of the invention. Such secondary energy storage units may include compressed fluid storage tanks for example. This is much like water being pumped into high reservoirs on the land at off-peak times and discharged through water driven generators when the demands peak beyond the capabilities of the available power generators. The same can occur with these secondary energy storage units (i.e. "potential energy batteries"), they never lose the energy stored in them, so they can be 'charged' and then not used until the electricity network is no longer able to match supply, whereupon this extra energy is instantly available. Also, secondary energy storage units can be deployed as a buffer and also as a safety feature: if the network was damaged or failed in some way, these energy stores would soften the impact and might in some cases even be able to bridge the repair and recovery period.

Thus, the skilled person will appreciate that where a very large volume of the working fluid needs to be stored, the invention may include a secondary pressurised fluid storage component, which may be located on-shore or off-shore.

In an embodiment of the invention in which the working fluid is pressurised water, the system includes one or more secondary storage components. Suitably, the or each secondary storage component includes a gas against which the water is pumped. For example, the or each secondary storage component includes an air pocket located above the water such that the water is pumped against the air, which in turn is compressed by the water to provide a "head" of water pressure. The secondary storage components are suitably also located within the body of water. This provides a safety feature in the sense that any failure in the secondary storage component will result in water and compressed gas being rapidly released into the surrounding water, which will absorb most of the energy of the release, thereby preventing or reducing the "explosive" impact of the failure.

The secondary storage component(s) suitably include a float valve adapted to sense the level of water present in the component. If the water is removed from the secondary storage component faster than it is added, the float valve will sense a drop in the water level. If the level drops to below a threshold level, a water outlet valve may be closed to prevent the component being emptied and pressurised air entering the pipe network.

In a furt her embodiment, a compressed gas replacement apparatus is provided. The compressed gas replacement apparatus is adapted to replace gas within the secondary storage component(s) which may reduce via dissolution into the pressurised water. The skilled person will appreciate that carbon dioxide and oxygen present in air is able to dissolve in pressurised water. This may reduce the volume of gas located within the secondary storage component(s) over time, which may be replaced via the compressed gas replacement apparatus.

The compressed gas replacement apparatus may include a compressor and/or a container which contains a compressed gas, such as for example, air or nitrogen at or above the pressure of the air within the secondary storage component(s).

Where the working fluid is air or water, the system may include a flow pipe network, but no return pipe network, as the working fluid may be released or vented after having had the stored energy converted to electrical energy by the generator. However, in embodiments in which the working fluid is to be maintained within the system via a closed network, the pipe network includes both flow and return pipes. In such embodiments, the return pipes suitably also run under the relevant body of water, such that the body of water can provide heat energy to the cooled working fluid returning from the generator.

In embodiments which include a flow network of pipes which are adapted to transport the compressed fluid from the compressor to the generator, and a return network of pipes adapted to transport the fluid from the generator to the compressor, the fluid within the flow pipe(s) may be in one phase (e.g. a liquid) and the fluid within the return pipe(s) may be in the same or a different phase (e.g. a gas).

An embodiment of the current invention utilises air as the fluid because of its prevalence. Being perceivable as broadly equivalent to a natural spring, air absorbs more potential energy as you add more pressure to the system. Air may be drawn from the environment and compressed by the compressor. It may be vented back into the atmosphere after use with no net negative effect on the environment.

Alternatively, the spent air may be stored and sold as a by-product. In this way, the system may include an air capture station which captures the still compressed air and stores it in suitable containers.

As an alternative to air as the energy transmission fluid, carbon dioxide may be used. The carbon dioxide may be sourced from traditional electricity producing power stations which burn fossil fuels and generate significant amounts of carbon dioxide. The captured carbon dioxide used as a gas in the present invention is therefore prevented from being released into the atmosphere.

Thus, according to an embodiment of the invention, the carbon dioxide is recovered from a man- made source of carbon dioxide. Furthermore, the system may include a gas-release station adapted to release carbon dioxide from a carbon capture medium. This embodiment allows for carbon dioxide which has been captured from a man-made source of carbon dioxide to be used as the gas in the invention.

It can be seen that this embodiment of the current invention allows carbon dioxide to be used for power generation - not just once but continuously. It can be seen that utilising carbon dioxide from fossil fuel power stations reduces the amounts being emitted, removes the need for geological sequestration, and, by producing electrical energy, results in a higher efficiency rate for the power station. Also, as the amount of power being generated from renewable energy sources increases this leads to a reduction in the amount of coal that needs to be combusted and atmospheric C02 released.

For the purposes of the current invention, the storage and generating system described may utilise carbon dioxide that has been taken from fossil fuel power stations. This could have been obtained by scrubbing e.g. by the compression of the exhaust gasses and using the heat from that to preheat the air to feed combustion leading to better efficiency for the plant, then refracting the liquefied portion of the gasses into C0₂, S0₂, N0₂, N₂0, etc.. However it will also be obvious to the skilled person that carbon dioxide can equally well be obtained from other sources e.g. air fractionating, as a by product of industrial processes e.g. brewing, etc.

The compressor, pipe network and generator typically form a closed system from which the carbon dioxide does not escape into the atmosphere.

Pressure applied to cooled carbon dioxide will result in it becoming liquid at about 56 atmospheres and below 20°C; therefore conversion from liquid to gaseous and back to liquid in a closed loop pressurised system would mean the gas can be thought of much like a closed steam circuit. This would mean utilising the heat transfer method, where the gas is heated and passed through an engine (turbine etc.) to generate power, then back to the liquid state. This process enables the generation of electricity using lower temperature heat sources not currently considered suitable.

Liquid carbon dioxide is very energetic and expansive: 220g of liquid C0₂ will give 112 litres of the gas at atmospheric pressure. Thus, liquid C0₂ expanded to a gas returns a volume hundreds of times larger, so this amount of expansion conveys the real potential of the gas for power storage.

The atmosphere has a pressure at sea level of 101.325 kPa, but if the pressure on the return side of the generator or pump were to be reduced by using a vacuum pump, then the expansion of the carbon dioxide through the generator/pump would be even greater, attaining even higher efficiencies.

A further advantage of using carbon dioxide as the gas in the system is that it has low friction.

This means that frictional losses through the pipe network are reduced compared with some other gases.

In a further embodiment, the system may comprise a mixed gas network in which carbon dioxide is compressed and stored in a C0₂ storage area of the system. Once a desired store of carbon dioxide is achieved, the system may switch to the use of compressed air as the working fluid. In such an embodiment, the stored carbon dioxide may be fed into the system at times of high demand or in the event of insufficient compressed air being available. Thus, the stored carbon dioxide would act as an emergency "back-up" system in the event that the compressed air system was unable to cope or failed.

As a further alternative, water, for example sea water may be used as the fluid of the invention. As with air, this has the advantage that it can be vented back into a suitable body of water after use with no net negative effects on the environment. Such an arrangement would avoid the need for a return pipe network and associated components.

The skilled person will appreciate that fluid dynamics plays a large role in the behaviour of the working fluid within the pipe network. As a result of this, pressure waves, resonances and oscillations can form within the working fluid, all of which are undesirable. In particular, as mentioned above, compressed air can act as a spring and this includes some of the less desirable aspects of springs, such as resonance, etc. In order to minimise or reduce these undesirable fluid dynamic phenomena, the pipe network may include one or more pressure control elements or damping elements. Where the working fluid is a pressurised gas, the or each pressure control elements may include one or more stub pipes or nodes. Each stub pipe or node may include a control valve. A stub pipe is a closed pipe extending from a flow pipe which can act as a baffle or a loop of pipe which smoothes the flow of the fluid via the natural impedance of the pipe loop to the fluid flow. Baffle plates and other known modifiers of fluid dynamic behaviours may also be incorporated into the pipe network.

Additionally or alternatively, the system may include one or more surge valves adapted to control the flow of the fluid within the pipe network.

Where the working fluid is a pressurised liquid, the pressure may be generated by pumping the liquid against a trapped gas which acts as a spring. As such, the flow dynamic issues discussed above, such as the issue of resonance may apply equally to embodiments in which the working fluid is a liquid.

In embodiments in which the working fluid is a pressurised aqueous liquid, the one or more membranes may be included within portions of the pipe network to modify and/or control the pressure within the pipe network. An advantage of using seawater as the fluid is that if the pressure of the sea water is at about 1 000psi or more, then reverse osmosis can occur. It may also be possible to achieve reverse osmosis at lower pressures, for example around 700psi, when using specific known membranes.

The skilled person will appreciate that even lower pressures may be used to achieve reverse osmosis, although the efficiency is likely to be less at lower pressures. Thus, if pipes are used that include a concentric inner liner of a semi-permeable (osmotic) membrane (e.g. polyamide thin film composites, cellulose acetate or cellulose triacetate), the system is able to generate potable water as a by product, as well as using the concentrated sea water to drive the generator. Accordingly, an embodiment of the invention provides a pipe forming part of the pipe network, wherein the pipe includes an osmotic (semi permeable) membrane located concentrically within a portion of the pipe. In such an embodiment, the pipe may define an inner core which is adapted to transport desalinated water; and an annular shaped outer channel which is adapted to transport increasingly concentrated sea water (i.e. water having an increasing concentration of salt) to the generator. Of course, other configurations of the membrane within the pipe and the different channels which are defined to carry the concentrated and desalinated water may be provided. The desalinated water may be transported to a water storage container for later use or it may be fed into a mains water network, optionally after further treatment.

The skilled person will appreciate that for systems using pressurised water as the transmission fluid, conventional hydro-electric generators may be used. Advantageously, seawater is denser than freshwater and therefore has a higher power content per litre than freshwater, which is typically used in hydro-electric power stations. Accordingly, the power generation for a given pressure of water would be greater than the equivalent pressure of freshwater, despite using the same generating equipment. Moreover, the concentrated sea water resulting from the above- described osmosis process has an even greater density.

Hydro-electric generators (e.g. Francis turbines) are well known to those skilled in the art and need not be discussed in detail herein.

In an embodiment of the invention, the compressor is driven by a renewable energy source selected from kinetic energy derived from wind, waves or tides.

For example, the compressor may be driven by kinetic energy derived from the wind. Many energy capture sources are now located at sea in the shape of wind turbines. These acquire energy from this variable source and endeavour to produce electricity in a constant form over a wide wind performance curve which is very variable. The result is a minimum wind speed where no useful power can be delivered to the grid, and a maximum wind speed where the equipment cannot respond to or tolerate the gusts however useful the extracted energy might be.

Additionally or alternatively, the or each compressor may be driven by kinetic energy from other renewable energy sources, such as wave energy, tidal energy, etc.

A fluid based collection solution would be far in advance of the electricity grid methods used today and offers a greater efficiency from each wind generator deployed, by widening the performance spectrum alone. In such an embodiment, the wind would be used to drive one or more compressors to compress and or pressurise the working fluid. In this way, the wind can be used to power the compressor over a much wider range of wind speeds, as it is not being used directly to power a generator and the pressurised working fluid smoothes out the peaks and troughs in the wind strength.

In a further embodiment of the invention, the compressor could be built close to the sites or within the wind generators themselves. In this scenario wind speeds within the pre-set operating parameters would be used to power a generator directly, and wind speeds that did not correlate with Grid specification would still be used, but instead to drive the compressor system, extending the operational capabilities of the wind turbines beyond their present limits.

One issue associated with compressing and/or pressurising a working fluid is that the pressure and quantity of the working fluid directly affects the torque applied to the drive shaft of the compressor itself. The resistance of a fully driven compressor may "stall" a low torque primary input shaft.

In order to address this issue, the invention may further include one or more intermediate compressors located between the renewable energy capture device and the primary input shaft of the primary compressor(s), wherein the or each intermediate compressor may convert a low torque output from the renewable energy capture device to a higher torque input to the primary input shaft. By the term "primary input shaft", it is meant a shaft which is powered by a renewable energy capture device and which is used to drive the or each compressor.

To address this issue, a plurality of compressors may be connectable to the wind turbine or other renewable energy collection apparatus. For example, the compressors may each include a clutch and the system may include a controller which controls the number of compressors connected to the energy capture apparatus. The number of compressors which are actively coupled to the primary input shaft may be determined by the speed and/or torque being provided by the shaft. Accordingly, the speed of the primary input shaft may control the number of individual compressors dynamically connected to it at any point in time. The system may suitably be able to register the available torque and speed from the primary input shaft and apply a stepped response.

Such a process is flexible in its application, the speed of the primary input shaft may be monitored as it increases and decreases, and the compressor clutches are either engaged or disengaged in response to this feedback mechanism.

Thus, it may be the torque range the wind turbine can produce, whatever the blade size, which determines the number of compressors connected to the primary input shaft. If a turbine is being used in calm weather, it is still possible to utilise the limited power from the wind, it simply means that a lower volume of fluid will be compressed. By contrast, at high wind speeds a single low volume compressor would be unable to utilise the torque and speed generated by the primary input shaft. It follows from this that by having two or more compressors adapted to be driven by the primary input shaft, a controller could detect the torque and speed of the shaft and then gate into service the optimum number of compressors.

As the speed of the input shaft can vary over a single revolution by more than 12%, the present invention may use a CvT design that provides a substantially constant torque output from the variable input torque. Thus, the apparatus of the present invention may include a continuously variable transmission which is adapted to provide a substantially constant output torque from a variable input torque.

There are many different designs of wind generators, but they all have in common the gearbox and alternator. An efficient method of putting the present invention into practice is to remove the alternator, or the alternator and gearbox, and replace them with the above described fluid compressor assembly. As the wind gets stronger, a larger number of compressors are placed on line; as the wind velocity reduces, compressors may be taken off line, thus matching the available torque with the number of compressors operably connected to the primary input shaft. This extracts the maximum available energy from the wind in the form of compressed fluid delivered to the system at the correct total pressure.

As mentioned above, the compressed fluid system can be driven by a number of different renewable power sources, and be able to volumetrically meter the input to the network opening it up to many sources. In one embodiment of the innovation, this could be from a tidal and/or wave energy capture aspect.

As with wind driven compressors, it would be possible to run one or more compressors from an existing wave or tidal power conversion apparatus in an intermediate stage, utilising the "out of specification" power, prior to full conversion of the apparatus. Alternatively or additionally, a generating system of the following system design could be used.

Wave and tidal power is a sinusoidal waveform. If bladders, filled with a transmission fluid, are sunk to the bottom of an ocean, sea, river or estuary, for example, then the weight of the water will modulate the pressure of the transmission fluid in the bladders; they would "breathe" like lungs. The more bladders there are, then the more modulation. As the tides ebb and flow the pressure on the bladders change proportionally, and large waves also have a modulating effect on these bladders.

The bladders expanding and contracting results in a pumping motion, and they are ventilated via separate input and output valved hoses. The compressed fluid forced out of the bladder is used to drive a primary input shaft.

Extraction of power from the moving fluid columns is a very good application for a low mass piston assembly, where the smallest pressure differentials are translated to significant forces, high enough to act on a pump or turn a shaft. The system may include a controller such that as the volume of available fluid decreases, the number of pistons being driven decreases.

The deeper the bladders are located, the better they work, and if sat on the sea bed held down e.g. by rocks, would be largely maintenance free. Eventually they could form part of e.g. an ocean, sea, river or estuary bed, hidden in the silt, but they would still flex in the same fashion.

The design offers cheapness of construction, lack of maintenance, and lack of disruption to shipping.

If one tidal stroke of pumping takes half a day at a time, it may deliver thousands of cubic feet of gas every time and is very regular and reliable (tides can be calculated years in advance).

Conversely a wave could supply hundreds of strokes an hour, individually small i n energy but with many units together rivalling a wind generator. The physics of tidal and wave power are well known, and so need no further description.

It will by now be apparent to the reader that any renewable source which currently generates electricity could be modified such as to pump a transmission fluid around a fluid grid forming a part of the invention, with the energy then stored (either as compressed air, compressed carbon dioxide, compressed water or another compressed fluid) close to point of eventual energy use.

A further example of a renewable energy source which may be used is solar power. This could be by the use of photovoltaic technology, for example applied to wind generator blades as an additional method for such sites to maximise the capture of available energy. The electricity could then be used in the same manner as the example of "out of band" power, discussed hereinabove.

Alternatively, individual or group mounted panels may be used to harness energy from the sun which is then used to power the compressor or to heat the compressed fluid prior to it being used to drive the generator.

Given the nature of this aspect, it is not felt necessary to describe in any further detail how this aspect would feed in to the rest of the system.

Turning now to the pipe network aspect, the system of the invention includes a primary pressurised fluid storage portion of a pipe network which includes a plurality of pipes arranged in parallel.

A benefit of using a plurality of pipes is that they are able to act as a reservoir for the compressed gas in the form of a distributed container between the compressor and the generator. A furt her embodiment provides for more than one generator in the system. The more generators there are, the more pipes, giving the system a naturally extended built in storage capability, and allowing damage limitation against a 'holed' pipe. The pipes may be thought of as coaxial signal pathways and may be used as such to allow monitoring of the network. Pressure management is a useful technique and may be used to provide respective generators with a pre-determined working pressure. A pipe network including a sets of pipes which can be "opened" and "closed", e.g. via appropriate valves, can be controlled and/or configured to control and/or stabilise the pressure profile of the network or a part thereof. This may be matched to the requirements of specific generators connected to the network. Thus, each of the flow pipes forming part of the primary pressurised fluid storage port ion may include a valve which is capable of isolating the relevant pipe.

Such an arrangement would be useful in a start-up mode, as all of the pipes may initially be isolated to allow the pressure within the system to build up. As the pressure increases, the individual pipes may be sequentially opened to the system to store therein the pressurised fluid.

This would allow the pressure in the system to be brought up to the desired minimum operating pressure more quickly.

Where the pipes transferring (flow) and optionally returning (return) the compressed fluid form part of a network, they may include conductive element, providing a means of detecting over a long distance any damage however slight that has occurred to the pipework in any part icular circuit, with an automated diagnosis and location-reporting system.

Additionally or alternatively, if a pipe ruptures, it would result in loss of pressure which may be detected. The system may also include one or more "self sealing" element(s). The pipe network may include at one or more points therein a sealing element adapted to seal a pipe in the event that the fluid flow exceed a predetermined value. For example, the pipe network may include a maximum flow constrictor. In one embodiment, the flow restrictor may comprise a ball located within a branch of the pipe network and an associated receiving seat within one of the main pipes. The ball is released and urged into sealing engagement with the seat once the flow exceeds a certain rate, thus permanently cutting off the flow through that specific pipe until the ball is reset. In a further example a calibrated spring and ball assembly is provided that achieves exactly the same function but self-resets when the differential pressure falls to within operational limits. In a yet further embodiment one or more flow control valves may close down the flow when the pipes reach critically low pressures. In these embodiments, damaged pipes may limit electrical energy generation, but would not be catastrophic, as the pipe network provides many flow routes from the compressor(s) to the generator(s).

The pipes may be any suitable diameter. However, pipes conventionally laid underwater via a boat tend to be in the 50mm to 125mm (2 to 5 inch) range. Suitably, the pipe has a diameter of about 76mm (3 inch) such that the pipes may conveniently be located in the desired position via a boat.

The skilled person will appreciate that compressing a gas generates heat according to Boyles law. By locating the primary pressurised fluid storage portion within a body of water, the water is able to act as a heat exchanger to cool the working fluid within the pipe network. This may be the sea, a lake or a waterway such as a river, for example.

The skilled person will also appreciate that when a compressed fluid (i.e. a compressed or liquefied gas) is expanded, the resultant lower pressure gas is cooled (this, after all, is the method by which refrigerators work). A second heat exchanger may be included as part of the pipe network to provide heat energy to the cooled, expanded fluid.

The first and second heat exchangers may be the same. For example, the compressor and the generator may both be located near to or within a body of water and that body of water may operate as both the first and second heat exchangers. Thus it may both cool the compressed fluid and warm the expanded fluid.

As mentioned above, in embodiments where the transmission fluid is water, the system may include one or more secondary storage tanks. The or each secondary storage tank may include a gas pocket (e.g. an air pocket) located above the stored water. The gas acts as a spring and maintains the pressure in the water. The skilled person will appreciate that the use of a gas pocket in this way is beneficial, It means that the pressure in the container can be "tuned" to a specific head of pressure corresponding to an equivalent height. The or each secondary storage tank may also be located within a body of water. This helps to reduce the pressure acting on the walls of the tank and also would act to contain any failure in the tank, as the compressed gas and water would simply be vented into the body of water. This also regulates the temperature within the tank.

The or each secondary storage tank may include a level sensor to measure the volume of water present in the tank. In such embodiments, an outlet valve may be closed when the water level reaches a pre-determined mi nimum value.

In an embodiment of the invention the system includes a first compressor connected to a first pipe network; and a second compressor connected to a second pipe network, wherein the second pipe network includes an energy transfer apparatus operable connected to the first pipe network such that the energy stored by the working fluid within the second pipe network can be transferred to the working fluid within the first pipe network; and wherein the first pipe network is connected to the electrical generator.

In such an embodiment, it would be possible to construct a "mains pressure" system off-shore which provides a pressurised working fluid (i.e. a first working fluid) to power an electrical generator. A plurality of individual renewable energy capture devices could generate their own respective pressurised working fluids and the energy stored in these could be transferred to the "mains" system connected to the electrical generator.

This would allow a number of separate renewable energy capture devices to be combined, regardless of whether the separate capture devices were the same or were different. Thus, a first energy capture devices may be adapted to capture wind energy and a second energy capture device may be adapted to capture wave energy.

It would also allow the energy to be transferred from a second (or further) working fluid to a first or "mains" working fluid, where the first and second working fluids may be the same or different.

Thus, for example, the first working fluid may be pressurised sea water and the second working fluid may be compressed air or compressed carbon dioxide.

Moreover, the "mains" working fluid may be located within an enclosed pipe network and recycled through the system, but the working fluid in the second (or further) pipe networks may be released to a local environment after the energy stored therein has been transferred or otherwise utilised.

The energy transfer apparatus includes any apparatus known for transferring energy from one fluid to a second fluid. One example of such a device is a turbo charger used in vehicles which transfers energy from one working fluid (exhaust gases) to a second fluid (inlet air charge for the engine). The skilled person will appreciate that the principle behind the turbo charger may be adapted for use in the present invention such that a compressor on one side of an energy transfer apparatus may be driven by energy stored within a working fluid on an opposite side of the apparatus, such that energy is transferred from one working fluid to the other.

Additionally or alternatively, the mains working fluid may be compressed or pressurised by one or more secondary working fluids, wherein the or each secondary working fluid operates a transfer compressor which transfers the or some of the energy stored within the secondary working fluid to the mains working fluid. The or each transfer compressor may include a piston arrangement or a screw arrangement or be based on a turbo charger as discussed above.

The generator(s) are suitably located on-shore and may include a turbine, reciprocating engine or a rotary engine as a primary alternator driver, dependent upon the amount of power demanded from the supply, with an associated alternator. Such compressed fluid driven primary alternator drivers are known to the skilled person.

The compressed fluid, for example, a gas such as air or carbon dioxide, would only be used when the load demanded it. A further embodiment provides a plurality of primary alternator driver units driving a common alternator input shaft, and a controller to control which of the primary alternator driver units are operably connected to the alternator input shaft. Thus, most of them may be idle or not operably connected when the demand is low. This provides a system which has a better response to the demand curve - meaning (ess energy used, and also a smaller generating station delivering better power density than the large ones that exist currently.

Most of the alternator drivers work on the principle of a high pressure on one side and a low pressure on the other. This pressure differential can be increased by applying a partial vacuum on the return side of the or each primary alternator driver. The dual pipe flow and return typically both have an energy potential, one provides a substantial positive high pressure and the other furnishes negative pressures, at least lower than atmospheric and usually much lower. All primary alternator drivers, be they reciprocating or turbine, rely upon the differential pressure across them, and it is here that the energy conversion process of the present invention is particularly effective.

Where the working fluid is air, a fuel may be added to the compressed air upstream of the generator. The fuel/air mixture may then be ignited to provide additional energy to the generator. For example, the fuel may be derived from a renewable energy source, such as methane derived from biomass processing or from land fill sites.

An alternative primary alternator driver may be used with the present invention. Steam engines are well known. The principle behind such primary drivers can be adapted to provide a "steam engine" adapted to be powered by a compressed fluid. Such an arrangement is referred to herein as an "air motor" and can be considered as a primary alternator driver for the generator of the present invention when coupled to a suitable alternator.

Thus, the design is based upon the idea of a steam engine, except that in this instance it is adapted to be powered by compressed fluid, such as compressed air or carbon dioxide for example, rather than steam. The problems with standard steam engine designs were in the complex mechanics required to drive the sleeves; in this modified design, the required manipulating parts are already there and are the very essence of the machine's operation.

Sleeve valve motors are very efficient in that the exhaust port s can be as large as required to release the compressed gasses from the cylinders. There may be a small degree of 'latching' of the sleeve at the open end of its travel. For example, a latch may be formed as an impression on the 'crank' end of the sleeve with an arrangement such as a small spring and a ball-bearing as a latching release set into the cylinder/s. The sleeve flange may be held against the ports by the pressure of the driving fluid (e.g. C0₂ or air) increasing the positivity of the exhaust seal and ensuring that the piston seal resistance does not drag the sleeve back with it on the power stroke, at the end of this stroke the fluid pressure is depleted and the other cylinders on the crank are still well into their power strokes, this gives this piston (at the end of its travel) enough power to draw back the sleeve releasing the exhaust fluid through the port s. The piston now reverses its direction sliding back up the 'open' sleeve until it reaches the 'valve' end where it contacts the flange of the sleeve and resets the exhaust port s to their closed position starting the next power cycle, where the valve is opened to drive it back. The opening of the valve may be achieved electronically by a suitable component well known to those skilled in the art.

Electronically operating the valves makes it possible to control at any instance the amount of gasses used in the driving of the motor, and consequently the amount of speed and torque delivered to the load. This result s in being able to extract the maximum amount of energy from the driving gasses, and removes the usual 'tick over' losses by the use of both careful firmware and mechanical design.

The motor is a significant design innovation, and may represent a major advance in low manufacturing cost efficient engine design. Such a motor can be scaled up to a very large unit, and where electronic control is not needed a simple cam operated valve design makes it autonomous of external control.

In an embodiment of the invention, two cylinders opposite each other share the same sleeve action. This overcomes the possible requirement for latching the sleeves, relaxing design constraints and offering a complimentary function between the two power strokes. If another pair of pistons is then placed at 90 degrees to the other two, here the sleeve actuation will always be at the centre of the power stroke of each active cylinder set, making the action smoother and easier to run at very low speeds. Thus, a further embodiment provides a four cylinder motor where the four pistons are arranged substantially perpendicularly to their neighbours. A benefit of a four cylinder motor is that the engine will self -start with little effort, very important if the motor needs to be stopped to conserve energy, and to be started very quickly.

The motor may be further extended. For example another four-stroke unit may be provided at 45 degrees to the first; or three stages which would then be displaced at 30 degrees and so on. The addition of stages allows incremental power handling with additional performance and smoother running by adding the stages displaced by a divisional angle to the whole.

The size and shape of the piston and cylinders are a function of fluid pressure, design speed and flow of fluid through the motor. Stainless steel spun tubing may be used as a cylinder material, simply cut into lengths and fitted with caps each end, with a steel shaft passing through one end connected inside to the piston. The shaft itself may be sealed against the cap with another seal set. Each cap may be fitted with two ports and the shaft would drive a linear slide which in turn drives the crank via an articulated push rod. The cylinder size itself is scalable. The controlling part of the system may be post use, which means the back pressure may operate a one way valve, for example.

The skilled person will appreciate that much work has gone into providing existing wind and wave energy capture devices which are able to generate electricity directly and provide the generated electricity to a national grid. Such capture devices typically have pre-defined operating parameters, within which they generate electrical energy directly and outside of which, they become dormant. The system of the present invention may be incorporated into a conventional renewable energy capture device, whereby when the operating parameters are within a predefined range, then the capture device operates to generate electrical energy directly and when the operating parameters are outside of the pre-defined range, then rather than entering a dormant mode, the capture device is instead used to power the compressor of the present invention. Thus, a second aspect of the invention may provide a renewable energy capture device which has a first operating mode in which it powers directly an electrical energy generator, and a second operating mode in which it powers a generation system according to the first aspect of the invention.

The skilled person will appreciate that the features described and defined in connection with the aspect of the invention and the embodiments thereof may be combined in any combination, regardless of whether the specific combination is expressly mentioned herein. Thus, all such combinations are considered to be made available to the skilled person. In part icular, the system may include one or more compressors driven by one or more sources of renewable power. It may also include one or more generators, which may be the same or different.

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

Figure 1 is a schematic representation of a first embodiment of the invention; and Figure 2 is a schematic representation of a second embodiment of the invention. For the avoidance of doubt, the skilled person will appreciate that in this specification, the terms "up", "down", "front", "rear", "upper", "lower", "width", etc. refer to the orientation of the components as found in the example when installed for normal use as shown in the Figures.

Figure 1 shows an electrical energy generating system 2 according to the invention. The system 2 includes a conventional wind turbine 4 which is driven by three blades 6. The wind turbine 4 is located offshore. The conventional generator component of the wind turbine is replaced with a compressor 8.

The compressor 8 compresses carbon dioxide into a liquid phase, which is fed into a 76.2mm (3 inch) flow pipe 10. The flow pipe 10 extends downwards into the sea surrounding the wind turbine 4. The flow pipe 10 is in fluid connection with a plurality of parallel 76.2 mm (3 inch) flow pipes 12 which together form a primary pressurised fluid storage port ion of the pipe network comprising parallel pipes containing the liquified carbon dioxide.

The pressurised fluid storage portion of flow pipes 12 store the liquified carbon dioxide until it is required, at which point it is fed into a single pipe 14 which carries the carbon dioxide to a generating station 16 located on-shore and housing a compressed gas-driven generator 18.

The generator 18 is driven by the carbon dioxide and generates electrical energy, which is carried by cable 20 to the electrical grid 22.

The carbon dioxide is expanded and returned to a gaseous phase as it passes through the generator 18 and the expanded, lower pressure gas is exhausted via a return pipe 24. The return pipe 24 carried the carbon dioxide gas back to the compressor 8, where it is re-cycled.

The skilled person will appreciate that the sea water surrounding the wind turbine initially cools the liquefied carbon dioxide following its compression and then warms the expanded spent carbon dioxide as it is returned to the compressor.

It will also be appreciated that the system is a closed system which releases no pollutants into the environment.

Turning now to Figure 2, there is provided a second embodiment of the invention. In this embodiment, the system uses compressed air as the working fluid. The air enters the system and is compressed by a compressor 102 to around lOOOpsi. The compressor is driven by a renewable energy capture device (not shown). As the skilled person will appreciate, the energy capture device may itself be driven by wind energy or by wave energy or any other known renewable energy.

The compressed air is fed into a mains inlet pipe 104 via a valve 106. The mains inlet pipe 104 transports the compressed air to a primary storage pipe network 108. In this embodiment, the primary storage pipe network includes four storage pipes arranged in parallel. More specifically, it includes a first storage pipe 110 which includes flow control valves 112, 114 located at each end thereof; a second storage pipe 116 which includes flow control valves 118, 1120 located at each end thereof; a third storage pipe 122 which includes flow control valves 124, 126 located at each end thereof; and a fourth storage pipe 128 which includes flow control valves 130, 132 located at each end thereof. The skilled person will appreciate that the storage pipes 110, 116, 122, 128 can be as long as desired in order to provide the appropriate storage volume. The pipes 110, 116, 122, 128 are suitably conventional 3 inch diameter pipes used to contain high pressure gases.

A secondary storage component 140 is provided as part of the network to provide additional storage for the compressed air. The secondary storage component 140 is connected to the control valve 118. However, the skilled person will appreciate that it may be connected to any of the flow control valves shown in Figure 2.

The control valves 114, 120, 126, 132 all connect to a common outlet pipe 142 which connects the storage network 108 to a valve 144. The valve 144 connects the common outlet pipe 142 to a tertiary storage component 146 and to a generator 148 which is powered by the compressed air to generate electrical energy which can be fed into a mains electrical grid.

The generator 148 includes an exhaust pipe 150 which vents the air downstream of the generator (i.e. low energy air) back into the atmosphere.

In use, the compressed air is delivered to the first storage pipe, while the second, third and fourth storage pipes 116, 122, 128 remain closed (i.e. control valves 118, 124, 130 prevent compressed air entering the relevant pipes). When there is sufficient pressure within the first pipe 110, it may be transmitted to common outlet pipe 142 if required by the generator 148. When the storage pipe 110 contains compressed air at the desired pressure, the inlet valve 112 may be closed and the inlet valve 118 to the second storage pipe 116 is opened. Assuming that the generator 148 does not call for compressed air, the inlet and outlet valves 112, 114 of the first storage pipe 110 will remain closed and the second storage pipe 116 will fill with compressed air until the desired pressure within the second storage pipe 116 is achieved. At this point the inlet valve 118 will close and the inlet valve 124 to the third storage pipe 122 will open and so on until all of the storage pipes 110, 116, 122, 128 contain compressed air at the desired pressure. When al) of the storage pipes 110, 116, 122, 128 contain compressed air, the inlet valve 118 will connect the mains inlet pipe 104 to the secondary storage component 140.

When the generator requires a flow of compressed gas to generate electrical energy, one of the outlet valves 114, 120, 126, 132 will open to connect the common outlet pipe to a source of compressed air. When the relevant outlet valve 114, 120, 126, 132 is open, the corresponding inlet valve 112, 118, 124, 130 will also open to maintain the pressure within the relevant storage pipe 110, 116, 122, 128.

If there is significant demand from the generator 148 or in embodiments in which there are multiple generators 148 connected to the network 108, then more than one of the outlet valves 114, 120, 126, 132 may open.

If the demand from the generator 148 is low, and the primary storage network 108 and the secondary storage component 140 both contain compressed air at the desired pressure, then the tertiary storage component 146 may be filled with compressed air via the common outlet pipe 142 and the valve 144.

When the compressed air has passed through the generator and its stored energy has been released or partially released, then it is vented to the atmosphere via the exhaust pipe 150.

The skilled person will appreciate that if any part of the compressed air storage apparatus 108, 140, 146 fails or is ruptured, then it can be isolated via the relevant valves and the system will still be able to supply compressed air to the electrical generator 148.

The second example has been described above in relation to a compressed air working fluid. However, the skilled person will appreciate that a corresponding system could be used in relation to a pressurised seawater working fluid. In such an embodiment, the secondary storage component 140 would include an air pocket that would maintain the pressure of the seawater within the desired range.

In an example of the invention which uses pressurised seawater as the working fluid, the pressure of the working fluid is about lOOOpsi and one or more of the pipes 110, 116, 122, 128 includes an osmotic membrane to effect reverse osmosis of the seawater, thus providing desalinated water and seawater with a concentrated salt content. In this example, the concentrated seawater is used to power the generator and the concentrated seawater is returned to the sea via the exhaust pipe 150. The desalinated water is transported to a treatment plant for further treatment (addition of mineral salts and other additives at the desired levels) before being introduced into the mains water network.

Claims

1. An electrical energy generation system including a renewable energy capture device located off-shore; a compressor operably connected to the energy capture device and adapted to compress and/or pump a working fluid, a fluid-powered electrical generator and a pipe network arranged between the compressor and the generator, wherein the pipe network includes a primary pressurised fluid storage port ion, the primary pressurised fluid storage portion being located within a body of water and comprising a plurality of flow pipes arranged in parallel, wherein each flow pipe of the pressurised fluid storage port ion includes an inlet at one end thereof and an exit at the opposite end.

2. An electrical energy generation system according to Claim 1, wherein the compressor is adapted to compress and/or pump air drawn from the environment.

3. An electrical energy generation system according to Claim 1, wherein the compressor is adapted to compress and/or pump seawater.

4. An electrical energy generation system according to Claim 1, wherein the compressor is adapted to compress and/or pump carbon dioxide.

5. An electrical energy generation system according to any preceding claim, wherein the renewable energy capture device captures wind energy or wave energy.

6. An electrical energy generation system according to any preceding claim, wherein each of the flow pipes forming the primary pressurised fluid storage portion includes a valve which is capable of isolating the relevant pipe.

7. An electrical energy generation system according to any preceding claim, wherein the system further includes one or more secondary pressurised fluid storage components.

8. An electrical energy generation system according to Claim 7, wherein the or each secondary storage components is located within the body of water.

9. An electrical energy generation system according to any preceding claim, wherein the pipe network includes one or more pressure control elements adapted to minimise or reduce pressure waves forming within the pipe network.

10. An electrical energy generation system according to Claim 9, wherein the pipe network is adapted to store and transport pressurised gas and the or each pressure control element includes one or more stub pipes.

11. An electrical energy generation system according to Claim 9, wherein the pipe network is adapted to store and transport pressurised sea water and the or each pressure control element includes an osmotic membrane.

12. An electrical energy generation system according to Claim 11, wherein the or each

osmotic membrane is located concentrically within a portion of the pipe network.

13. An electrical energy generation system according to Claim 12, wherein the system

includes a generator pipe network adapted to transport concentrated sea water to the electrical generator; and a desalinated pipe network adapted to transport the desalinated water to a water storage container.

14. An electrical energy generation system according to any preceding claim, wherein the system includes a first compressor connected to a first pipe network; and a second compressor connected to a second pipe network, wherein the second pipe network includes an energy transfer apparatus operable connected to the first pipe network such that the energy stored by the working fluid within the second pipe network can be transferred to the working fluid within the first pipe network; and wherein the first pipe network is connected to the electrical generator.

15. An electrical energy generation system according to Claim 14, wherein the first compressor is driven by a respective first renewable energy capture device and the second compressor is driven by a respective second renewable energy capture device.

16. An electrical energy generation system according to Claim 14 or Claim 15, wherein the working fluid in the first pipe network is a compressed gas or a pressurised liquid and the working fluid in the second pipe network may be the same as the working fluid in the first pipe network or it may be different.

17. An electrical energy generation system according to any preceding claim, wherein the electrical generator is located on-shore.

18. An electrical energy generation system according to any preceding claim, wherein the working fluid is compressed air and the system includes a fuel inlet located upstream of the generator and an ignition apparatus located between the fuel inlet and the generator.

19. An electrical energy generation system according to any preceding claim, wherein the system includes a plurality of compressors and a controller adapted to control the number of compressors which are actively connected to the renewable energy source.