AU2006272373A1 - Power generation system - Google Patents

Description

WO 2007/009192 PCT/AU2006/001034 -1 POWER GENERATION SYSTEM The present invention relates to a hydro electric power generating system. 5 There have been proposals to produce electrical power using so-called pumped hydro systems. In accordance with these prior proposals, water is pumped from a lower reservoir to an upper reservoir in an off-peak or low demand period using electrical power at a low price. At periods of peak power demand when the price of electricity has risen to a significantly higher level, the water is released from the upper reservoir back into the lower 10 reservoir via a turbine system which generates electricity at that peak price and feeds it direct to the power grid. Power is thereby generated on the basis of the difference between the sale of electrical power at peak periods and the cost of pumping the water from the lower reservoir back into the upper reservoir during the off-peak period. However, the infrastructure costs of such systems are substantial as it is necessary to build upper and 15 lower reservoirs of substantial capacity and which will usually require a dam wall or similar to define a boundary of the upper reservoir. The construction of the two reservoirs themselves will usually also involve adverse environmental impact. Moreover a system of this type can, in practice, only be installed in areas having the appropriate topography suitable for the construction of the upper and lower reservoirs and accordingly, its 20 applicability is rather limited. The present invention provides a pumped hydro system of a form which avoids the need to construct land-based upper and lower reservoirs. 25 According to one aspect of the invention, there is provided a system for generating electricity comprising at least one water-containing vessel adapted to be immersed into a body of water with the lower end of the vessel spaced above the water bed, an inlet at a lower end of the vessel, valve means for selectively enabling and preventing flow of water into the vessel via the inlet under the effect of hydrostatic pressure, a pump for at least 30 partially emptying the vessel of water, a turbine within the vessel and driven by water flowing into the vessel via the inlet when the valve means is open, and a generator driven WO 2007/009192 PCT/AU2006/001034 -2 by the turbine. In a preferred embodiment, there is provided a system for generating electricity comprising at least one tube adapted to be immersed into a body of water, with its axis extending 5 substantially vertically, a water inlet at a lower end of the tube, a pumped chamber within the tube above the inlet, valve means for selectively enabling and preventing flow of water into the chamber via the inlet under the effect of hydrostatic pressure, a pump for emptying the chamber of water when the valve means is closed whereby when the valve means is next opened water is able to enter the tube via the inlet under the effect of hydrostatic 10 pressure to pass into the chamber, a turbine within the tube and driven by the water flowing through the inlet and into the pumped chamber, and a generator driven by the turbine. Effectively, emptying of the pumped chamber by operation of the pump creates a pressure 15 differential between the chamber and the body of water in which the tube is immersed whereby potential energy is stored within the system and which is released to cause the turbine to be driven when the valve means is next opened. Although, of course, the net energy output from the generator will be less than the energy input required to drive the pump, by operating the system to generate electricity during periods of premium pricing 20 and driving the pump during periods of minimum pricing, commercially effective power generation can be achieved. As an alternative to, or in addition to, operating the pump using low price electricity, it can use energy input from solar and/or wind power and/or other available energy source such as tidal or wave whereby that energy is also "stored" within the system. 25 In a typical installation, the tube will have a diameter of several metres and a length of at least several tens of metres. Advantageously the generation system will be formed from an array of several such power 30 generation tubes operated in sequence during the generation phase. All of the tubes of the array may be associated with a common pump which operates to empty their pumped WO 2007/009192 PCT/AU2006/001034 -3 chambers either simultaneously or in sequence. The system will typically be installed in sea water at an offshore location or within an existing lake or dam of sufficient depth. The array of tubes can be mounted to a fixed or 5 floating platform structure similar to that used for offshore oil/gas rigs, with the tubes being suspended from that structure. Existing rigs or de-commissioned rigs could be converted for this purpose. In other preferred embodiments, instead of tubes, the pumped vessels may be stable, 10 floating vessels, for example of conical, spherical, spheroidal, ellipsoidal, or cylindrical shape, the vessels being tethered relative to the water bed. An embodiment of the invention will now be further described by way of example only with reference to the accompanying drawings in which: 15 Figure 1 is a schematic section showing a single power generating tube of a pumped hydro system in accordance with one embodiment of the invention; Figure 2 is a plan view showing, schematically, how a group of such tubes may be arrayed to provide a system of significant generating capacity; Figure 3 is a schematic section showing a power generating vessel in the form of a 20 floating cone; and Figure 4 is a schematic section of a power generating vessel in the form of a floating sphere. The pumped hydro system in accordance with the one embodiment of the invention 25 consists of at least one, and preferably an array of, large diameter power generator tubes 2 immersed to a substantial depth in a body of water such as sea water or a deep fresh water lake or an existing dam. By way of illustrative, but non-limiting, example the diameter of the or each tube 2 can be of the order of 3 metres and the depth of immersion about 60 metres. At its lower end at the maximum depth of immersion, the tube includes a water 30 inlet 4 controlled by one or more valves 6 and downstream of that, in a lower part of the tube, one or more turbines 8 coupled directly or indirectly to a generator having an output WO 2007/009192 PCT/AU2006/001034 -4 which feeds power to the grid. The upper end of the tube 2 is open and above water level or, alternatively, may be closed but vented to atmosphere; in either case the configuration is such that water will not fill the 5 tube 2 from its upper end. The tube 2 is suspended at its upper end from a structure 10 such as a platform mounted above the surface of the water and anchored in position relative to the water bed by legs or pylons 12. The suspension for the tube 2 from the structure 10 is a substantially rigid suspension, and for stability, the tube may also be tethered to the water bed. The generator and other equipment may be mounted on the 10 structure 10. Alternatively, the generator may be in the same compartment as the turbine or may be formed as an integral unit with the turbine. A pump 14 serves to pump water out of the tube 2. Although Figure 1 shows the pump 14 positioned at the upper end of the tube 2, that is a schematic depiction only and it can be 15 mounted at any suitable position within the tube 2. Alternatively the pump 14 can be mounted at a convenient position outside of the tube 2, on the structure 10, for example. A substantial part of the interior of the tube 2 extending from its upper end downwards constitutes a pumped chamber 16 from which the water is withdrawn when the pump 14 is operated with the valve(s) 6 closed. 20 The basic cycle of operation is as follows. With the valve(s) 6 closed, the pumped chamber 16 of the tube is emptied of water by operation of the pump 14 powered by off peak, low price, electricity and/or by other energy sources such as wind and/or solar or other available energy sources such as wave or tidal. At periods of peak electricity price, 25 the valve(s) 6 is opened whereby the hydrostatic pressure causes water to flow through the inlet 4 and into the pumped chamber 16 to progressively fill the pumped chamber. The incoming water drives the turbine(s) 8 thereby driving the generator which generates peak price electricity which is directed into the grid. Figure 1 shows the inlet 4 purely schematically and in practice it will be profiled with a venturi profile or other suitable 30 profile to provide optimum flow conditions into the chamber for efficient drive of the turbine(s) 8. When the pumped chamber 16 is filled with water, the valve(s) 6 is closed WO 2007/009192 PCT/AU2006/001034 -5 and the cycle is repeated when low cost energy (or other energy such as wind and/or solar or other available energy sources such as wave or tidal) is next available to operate the pump 14. 5 Although from the standpoint of obtaining maximum output, the pumped chamber 16 should extend over as much of the length of the tube 2 as is practically possible, having regard to considerations of its stability and buoyancy it may be desirable for the lower part of the tube always to be filled with water. Modelling will determine the optimum relationship of the pumped chamber 16 to the overall length of the tube, taking into 10 account the overall design and construction of the tube, and the particular site situation in which the system itself will be installed. If, however, the tube is fixed, weighted and/or restrained to the water bed at its lower end, in many situations it should be possible for the pumped chamber 16 to extend over substantially the entirety of the length of the tube 2 thereby maximising its potential storage capacity. 15 The valve(s) 6 are controlled to vary the flow rate into the tube in accordance with the instantaneous output required into the grid. For example for a tube of approximately 3m in diameter and 60m in length (a relatively small tube size within the likely range of sizes envisaged for this usage), at maximum water inflow, up to 10 mW may be generated over 20 a short period of time, with reduced output being generated over longer periods of time when the valve(s) 6 is controlled to provide reduced input flow. Although in principle, the system could operate with just a single tube, in practice due to the basic set up costs, and associated infrastructure, the system will have one or more 25 arrays each consisting of several such tubes operated to generate substantial output for much longer periods of time. Figure 2 illustrates by way of example several tubes 2 of the system in a generally circular array carried by a suitable structure such as a platform 10, although arrays other than circular may also be used. The tubes are suspended from the platform 10, as described in relation to Figure 1. The respective tubes within the array 30 may be operated and emptied in a programmed sequence to provide a smooth power output across the array and also to maintain an appropriate balance of buoyancy conditions across WO 2007/009192 PCT/AU2006/001034 -6 the array. To reduce capital costs a single pump 14 carried by the platform 10 may service the entire array of tubes, although to ensure continuing operation of the system in the event of failure of that pump it may be desirable also to incorporate a reserve or back-up pump. 5 In one form of the system, the pump(s) 14 may be operated only by off-peak electricity drawn from the grid. Alternatively the system can include at least one wind turbine and/or solar panels or other available energy sources such as wave or tidal which produce electricity either to supplement or replace the off-peak electricity input when suitable conditions exist and also possibly to operate the pump(s) to permit further cycling of the 10 system during peak tariff periods. Certain of these energy sources (a wind turbine, for example) can be mounted on the platform 10. Another available energy source for this purpose could be sea floor natural gas which can either be gas which is unwanted for supply to an onshore gas facility or high pressure gas being fed to an onshore gas facility, in which case the pump could be directly driven by that high pressure gas. 15 The system may also be associated with a high capacity energy storage module 22 carried by the platform 10 or other structure and consisting of high thermal capacity graphite blocks electrically heated to high temperature using off-peak electricity, supplemented by solar power and wind power if provided. Steam generated by heat stored within the 20 module 22 can drive a turbine directly coupled to the pump. A suitable energy storage module of this type is available as the "Lloyd Energy System" (www.lloyvdenergy.com). With an energy storage system of this type, energy stored during off-peak can be used to drive the pump for continuous operation during peak periods. However due to considerations of efficiency effecting the energy conversion in a storage system of this 25 type it is likely to be of benefit only in situations where a high pricing differential exists between peak and off-peak electricity tariffs and accordingly it will not be viable in all cases. As previously mentioned, the array of tubes 2 forming the system is mounted to a structure 30 such as a platform 10 so as to be suspended from the platform. The platform itself could be free floating, floating and tethered to the sea floor, or fixed to the sea floor.

WO 2007/009192 PCT/AU2006/001034 -7 Structurally, it could be similar to that of offshore oil/gas rigs, and existing or de commissioned rigs could be converted to suit this usage. They will also provide convenient access such as via a helipad for maintenance purposes. 5 It will be appreciated from the foregoing that each tube provides an immersed vessel which is at least partially emptied by pumping using lower cost power and generates power as the vessel is refilled at periods of higher tariff under the effect of hydrostatic pressure. The invention is not restricted to the use of vessels in the form of tubes. Figure 3 shows a vessel 30 of conical form with an inlet 4 at its lower end, one or more valves 6 for 10 controlling flow through the inlet, one or more turbines 8 downstream of the inlet being driven by the incoming flow and a pump 14 for emptying the vessel. A vessel of this shape will have substantial stability as a floating structure and although it will still be tethered to the water bed, the tethering principally serves to maintain the vessel in position rather than to maintain the stability of the vessel. The conical vessel 30 is designed to float 15 and in view of its stability it may be possible to completely empty the vessel during the pump out phase of the cycle thereby maximising its capacity. However, even if it is necessary to maintain some water always present in the vessel for stability reasons, owing to its conical shape water remaining in the lower part of the vessel will not significantly reduce the overall infill capacity of the vessel. Moreover, during water inflow, again due 20 to its conical shape a larger differential in pressure head between the water within the vessel during inflow and the surface level of the surrounding body of water will be maintained for a longer period of time in comparison with an equivalent tubular vessel, and as the vessel fills it will progressively lower within the body of water owing to its decreased buoyancy thereby increasing the head differential somewhat. 25 A typical generating system may comprise one or more arrays of several such vessels, as described with reference to the first embodiment. Vessels of a shape other than conical could be used to achieve a similar effect. For example, a vessel of V-shaped cross-section similar to that of a cone but elongated horizontally to form a shape resembling that of the 30 hull of a ship could alternatively be used.

WO 2007/009192 PCT/AU2006/001034 -8 Figure 4 shows a vessel 40 of generally spherical or spherical form to achieve a similar effect and that could likewise be elongated horizontally in the manner of a cylinder, for example. In another variant, the vessel could be of an ellipsoidal shape. 5 A generating system consisting of an array (or arrays) of several tubes or other vessels as just described avoids the substantial infrastructure costs associated with a pumped hydro system using upper and lower land-based reservoirs. It also has the significant advantage of substantial versatility in location, as depth contours of the likely required depth (in excess of 60 metres) are found within a few kilometres of most coastlines. The technology 10 for underwater high voltage power transmission is itself very well established. It is envisaged that a typical generation facility would involve the use of many arrays of generating vessels as described, arranged offshore or in large dams or lakes. 15 In most circumstances, the commercial viability of the system, as with all pumped hydro systems, is principally determined by the cost differential between the peak electricity tariff and the off-peak tariff. While pricing structures in some countries would permit viable operation, this does not apply everywhere. However it is possible that in some situations, operation of the system principally by wind power and/or solar power or other 20 energy sources might minimise, or even negate the reliance on peak/off-peak pricing differentials and may lead to viability in a greater number of situations. More particularly, operation may be feasible on a relatively continuous basis. For example, a wind turbine may have a direct drive to the pump(s) as may an energy source operated by wave or tidal power; a similar situation could exist when the pump(s) is directly driven by sea floor 25 natural gas. Relatively continuous operation is feasible even when an alternative energy source generates electrical power to drive the pump(s). Throughout this specification and claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" or "comprising", will 30 be understood to imply the inclusion of a stated integer or group of integers or steps but not the exclusion of any other integer or group of integers.

Claims (17)

1. A system for generating electricity comprising at least one water-containing vessel adapted to be immersed into a body of water with the lower end of the vessel spaced above 5 the water bed, an inlet at a lower end of the vessel, valve means for selectively enabling and preventing flow of water into the vessel via the inlet under the effect of hydrostatic pressure, a pump for at least partially emptying the vessel of water, a turbine within the vessel and driven by water flowing into the vessel via the inlet when the valve means is open, and a generator driven by the turbine. 10

2. A system according to claim 1 having an array of such vessels, wherein the valve means of the respective vessels are operated to actuate the respective vessels for power generation in a predetermined sequence. 15

3. A system according to claim 2, wherein the pump is associated with some or all of the vessels of the array to pump water from those vessels.

4. A system according to any one of claims 1 to 3, wherein the or each generator is connected to an electricity grid for operation during periods of premium pricing and the or 20 each pump is connected to the same grid for operation during periods of minimum pricing.

5. A system according to any one of the preceding claims, wherein the or each vessel is in the form of a tube installed with its axis substantially vertical. 25

6. A system according to claim 5, wherein the tube is open at its upper end which is above the surface of the water.

7. A system according to claim 5 or claim 6, wherein the or each tube is carried by structure above the surface of the water so as to be suspended from the structure. 30 WO 2007/009192 PCT/AU2006/001034 -10

8. A system according to any one of claims 1 to 4, wherein the or each vessel floats within the body of water and is tethered relative to the water bed.

9. A system according to claim 8, wherein the vessel increases in cross-sectional size 5 from its lower end towards its upper end.

10. A vessel according to claim 9, wherein the vessel is of generally conical shape with its base uppermost. 10

11. A system according to claim 8, wherein the vessel is of an approximately V-shaped cross-section.

12. A system according to claim 8, wherein the vessel is of spherical, spheroidal, or ellipsoidal shape. 15

13. A system according to claim 8, wherein the vessel is of generally cylindrical shape orientated with its axis substantially horizontal.

14. A system according to any one of claims 8 to 11, wherein the upper end of the 20 vessel is above the surface of the water.

15. A system for generating electricity comprising an array of tubes carried by a common structure and immersed into a body of water with the axis of each tube extending substantially vertical, each tube having: 25 a water inlet at its lower end; a pumped chamber above the inlet; valve means for selectively enabling and preventing flow of water into the chamber via the inlet under the effect of hydrostatic pressure; and a turbine driven by water flowing through the inlet and into the chamber to thereby 30 drive a generator, said system further comprising pump means operable to pump water WO 2007/009192 PCT/AU2006/001034 -11 from the chambers of the tubes so as to empty the chambers when the valve means are closed.

16. A system for generating electricity comprising an array of floating vessels 5 immersed into a body of water, each vessel having: a water inlet at its lower end; a pumped chamber above the inlet; valve means for selectively enabling and preventing flow of water into the chamber via the inlet under the effect of hydrostatic pressure; and 10 a turbine driven by water flowing through the inlet and into the chamber to thereby drive a generator, said system further comprising pump means operable to pump water from the chambers of the vessels so as to empty the chambers when the valve means are closed. 15

17. A method of generating electricity for supply to a grid using a system according to claim 15 or claim 16, wherein the pump means is operated to empty the chambers during periods of low tariff and generation is effected at periods of high tariff, and generation takes place by opening the valve means in a predetermined sequence across the array.