WO2024168025A2 - High mass-flow, low-pressure turbine - Google Patents

Abstract

A turbine assembly that can be used in apparatus for generating electricity and apparatus and methods of generating electricity are provided. The turbine assembly is configured to be operated by a flow of a fluid having a high mass flow rate and relatively low head pressure. The turbine assembly includes at least one turbine that can be installed within a fluid flow path. The turbine assembly can be operably connected to a generator for generating electricity.

Description

HIGH MASS-FLOW, LOW-PRESSURE TURBINE

RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63/483,823, filed on February 8, 2023, which is incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

[0002] Embodiments of the present invention are directed toward a turbine assembly, apparatus for generating electricity, and methods of generating electricity. The turbine assembly is configured to be operated by a high-mass flow of a low-pressure fluid. To this end, the turbine assembly comprises at least one annular’ turbine, and preferably at least two concentric annular turbines, that can be installed within a fluid flow path. The turbine assembly can be operably connected to a generator for generating electricity.

Description of the Prior Art

[0003] The natural movement of surface fluids, particularly water, such as in ocean waves and rivers, represents a significant, but underutilized source of energy. Conventionally, harnessing river energy involved the construction of dams behind which a reservoir would be formed to create a significant head pressure required to spin a hydropower turbine and generator assembly. Construction of such dams can have significant capital cost as well as environmental impact.

[0004] A number of devices have been proposed in order to capture the energy contained in ocean waves and convert it into electrical power. One such class of devices are wave profile devices. Wave profile devices float on or near to the ocean surface and move in response to the shape of the incident wave in a substantially vertical motion. The pitching and heaving of the waves cause a relative motion between an absorber and a reaction point to produce an oscillating system that powers a hydraulic pump, which in turn rotates a generator. A major shortcoming of these types of devices is the ability to scale them sufficiently to produce energy in sufficient quantity to be useful to a city or municipality. Typically, these types of devices are used only to power small devices such as navigational buoys.

[0005] Another class of devices used to harness wave energy is the oscillating column wave energy device. These devices are normally positioned onto or near rocks or cliffs which are next to a deep sea bottom. They comprise a partially submerged hollow chamber that is fixed directly at the shoreline. As a wave enters the device, an air column is compressed. As the wave recedes, the air column is decompressed. This oscillating column of air is directed through a wind turbine which produces electricity. Scalability is also a concern with these types of devices. Moreover, finding suitable locations to install such devices can also prove challenging, not to mention the potential environmental and aesthetic impacts these devices might have in being situated on a shoreline.

[0006] A third class of devices is capture wave energy devices. These devices comprise structure configured to capture water within a floating reservoir, typically by providing a ramp upon which the wave can ride up and spill over into the reservoir. Once captured, the water is then directed out of the reservoir through a turbine. However, these types of devices are designed to operate in connection with waves having a minimum amplitude so that the water does in fact spill over into the reservoir. If such minimum amplitude is not met, the device will not generate power. Thus, these types of devices can be as unpredictable in providing power as conventional wind turbines. Moreover, there is a lack of workable low-head turbine technology to generate power on a scale comparable to conventional municipal or regional power generation facilities.

[0007] Accordingly, a need exists in the art for a device that can harness wave energy that is not encumbered by the difficulties with existing technologies as noted above. In particular, there is a need for a device that can be positioned away from land, that is scalable to provide power on par with conventional land-based power plants for providing power to a municipality, and that can provide power even in sea conditions where wave amplitude can vary considerably.

SUMMARY OF THE INVENTION

[0008] According to one embodiment of the present invention there is provided a turbine assembly comprising at least two concentric, annular turbines located within a turbine housing, and at least one drive shaft operably coupled to the at least two annular turbines. The turbine housing comprises conduit structure configured to simultaneously flow a fluid across and rotate the annular turbines.

[0009] According to another embodiment there is provided a turbine assembly that comprises a plurality of concentric, annular turbines located within a turbine housing, which includes conduit structure configured to flow a fluid across and rotate the annular turbines. The plurality of annular turbines are configured for rotation at different angular velocities when the fluid is flowed thereacross. Also, the turbine assembly comprises at least first and second independently rotatable arm assemblies that are connected, respectively, to at least first and second annular turbines of the plurality of annular turbines. The first and second arm assemblies are connected to respective first and second drive shafts.

[0010] According to still another embodiment there is provided a turbine assembly that comprises at least a first annular turbine located within a turbine housing. The turbine housing comprises conduit structure configured to direct a fluid through at least a first upflow passage within which the at least first annular turbine is installed. The upflow passage is configured to direct the fluid upward across the at least first annular turbine thereby causing the turbine to rotate. The conduit structure further comprises at least a first downflow passage configured to receive the fluid after having passed through the at least first annular turbines. The downflow passage is configured to direct the fluid toward a fluid outlet. The assembly further comprises at least one arm assembly connected to the at least first annular turbine and that interconnects the at least first annular turbine with a first drive shaft. [0011] According to a further embodiment there is provided apparatus for generating electricity comprising a turbine assembly according to any embodiment described herein and a generator operably connected thereto.

[0012] According to another embodiment there is provided a method of generating electricity. The method comprises flowing water into a first tank of a body located in a body of water. Water is caused to flow from the first tank through a conduit structure and into a second tank, the second tank being located at a lower elevation within the buoyant body than the first tank. As the flow of water traverses the conduit structure, the water is passed across at least first and second concentric annular turbines thereby causing the at least first and second annular turbines to rotate. The at least first and second annular turbines are operably connected to a generator. Electricity is generated using the generator upon rotation of the at least first and second annular turbines.

[0013] According to yet a further embodiment there is provided a method of generating electricity. A turbine assembly according to any embodiment described herein is provided within a body located in a body of water. Water is flowed into the conduit structure and caused to flow upwardly through one or more upflow passages and across the at least one annular turbine causing the at elast one annular turbine to rotate. The turbine assembly is operably connected to a generator, and electricity is generated by the generator which in turn generates upon rotation of the at least one annular turbine.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a perspective view of power generating apparatus according to one embodiment of the present invention positioned in a body of water;

[0015] Fig. 2 is an exploded view of the apparatus of Fig. 1;

[0016] Fig. 3 is an exploded view of a turbine assembly according to one embodiment of the present invention;

[0017] Fig. 4 is a sectioned view of the apparatus of Fig. 1;

[0018] Fig. 5 is an alternate sectioned view of the apparatus of Fig. 1 and depicting the flow path of fluid through the apparatus; and

[0019] Fig. 6 is a close up view of a gearbox assembly used to merge energy from a plurality of drive shafts into a single output shaft. [0020] While the drawings do not necessarily provide exact dimensions or tolerances for the illustrated components or structures, the drawings are to scale with respect to the relationships between the components of the structures illustrated in the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0021] A wave power generation system is described in International Patent Application No. PCT/US2022/39372, filed August 4, 2022, which claims the benefit of U.S. Provisional Patent Application No. 63/229,629, filed August 5, 2021, the disclosure of both of which are incorporated by reference herein in their entireties. The described wave power generation system includes tank structure and water flowing between those tanks to rotate a turbine. Embodiments of the present invention can also make use of a similar tank structure and water flowing therebetween to rotate a turbine assembly as described in further detail below.

[0022] According to one or more embodiments, a turbine assembly is provided that comprises at least one, and preferably at least two, annular turbines located within a turbine housing. In the case of the turbine assembly being provided with a plurality of turbines, the annular turbines are preferably concentric in that they rotate about a common central axis. Also, as shown in the Figures, the at least two annular turbines are preferably located within the turbine housing at the same or a substantially similar elevation. Thus, the at least two annular turbines can be configured to rotate about the common central axis within the same or substantially the same plane. Alternatively, it is within the scope of the present invention for the at least two annular turbines to be positioned at different elevations within the turbine housing or in “stacked” planes.

[0023] Because the turbines are annular and concentric, the diameters of each turbine will generally decrease from the outer most to inner most turbine. Accordingly, the mass flow rate of the fluid flowing across each turbine also correspondingly decreases. Thus, in one or more embodiments, the annular turbines may be configured with different turbine blade configurations in order to account for this difference in mass flow rate thereacross.

[0024] In some embodiments, it may be desirable to closely match the angular velocity and/or rotational speed of adjacent turbines so that they can be coupled to a common rotatable arm assembly for transferring the turbine’s torque to a common driveshaft. However, it certain embodiments, it is undesirable for multiple turbines to be connected to a common drive shaft via a common arm assembly. Due to the differences in angular velocity between turbines of different diameters, it is desirable to decouple the turbines so that a smaller turbine does not become a pump (sucking fluid in through the turbine blades), rather than harnessing the energy being provided by the fluid moving across the turbine blades.

[0025] In one or more embodiments, the one or more annular turbines are capable of being rotated by the fluid flowing thereacross under very low head pressures. In particular embodiments, especially in the context of the fluid being a liquid, such as water, the head pressure of fluid being supplied to the inlet side of the turbine is less than 36 inches of H2O gauge, less than 24 inches of H2O gauge, or less than 12 inches of H2O gauge. In other embodiments, the total head pressure supplied to the inlet side of the turbine is from 6 to 36 inches of H2O gauge, from 12 to 30 inches of H2O gauge, or from 18 to 24 inches of H2O gauge.

[0026] In one or more embodiments, the annular turbines can be configured to have a relatively low pressure drop thereacross, In particular’ embodiments, the pressure drop across the annular turbines is less than 12 inches of H2O gauge, less than 10 inches of H2O gauge, or less than 8 inches of H2O gauge. Alternatively, the pressure drop across the annular turbines is from 2 to 12 inches of H2O gauge, from 4 to 10 inches of H2O gauge, or from 6 to 8 inches of H2O gauge.

[0027] In embodiments in which the fluid being flowed across the turbine is a gas, the gas can be supplied to the turbine assembly at a pressure of less than 100 psia, less than 80 psia, or less than 60 psia. Alternatively, the gas pressure at the turbine inlet is from 25 to 100 psia, from 35 to 90 psia, or from 45 to 80 psia.

[0028] Fluid is supplied to the turbine assembly via conduit structure provided within the turbine housing. The conduit structure generally comprises passages that deliver the fluid to and cany the fluid away from each of the annular turbines. In particular embodiments, the fluid is delivered to the annular turbines by way of respective upflow passages that are configured to direct the flow of fluid in an upward direction, approaching the turbine inlet from below the turbine. The fluid is carried away from each of the annular turbines by respective downflow passages that are configured to direct the flow of fluid in a downward direction, with the fluid entering the downflow passage from the turbine outlet that is above the turbine. It is preferable for the conduit structure to be configured to ensure that the fluid fully covers the turbine blades as it flows across the turbine.

[0029] Turbine assemblies as described herein can be used in apparatus that is operable to generate electricity by coupling the turbine assembly with a generator. Generally, the turbine assembly and generator are operably connected via a drive shaft assembly whose configuration is determined by a number of factors, including the number of annular turbines present, whether the annular turbines are coupled together or operate independently from each other, and whether more than one drive shaft is required. In certain embodiments, a single drive shaft may be coupled to the generator. In other embodiments, more than one drive shaft is present as at least two of the turbines are operated independently at different rotational speeds and/or angular velocities. The at least two drive shafts are preferably arranged to be concentric, i.e., configured to rotate about a common longitudinal axis. The plurality of drive shafts can then be connected to the generator via a torque-combining gearbox that converts the multiple inputs into a single output shaft that can be operably connected to the generator.

[0030] Turning now to Fig. 1, power generation apparatus 10 is depicted positioned in a body of water 12, such as an ocean, lake, or river. Apparatus 10 comprises a body 14, which is preferably buoyant and may resemble the hull of a barge or other marine vessel. Body 14 is configured to contain at least first and second tanks 16, 18 (see, Fig. 2), and a turbine assembly 20. Body 14 can be formed from any material that is adaptable for the purposes described herein. For example, body 14 can comprise concrete (e.g., reinforced concrete), metal plate, fiberglass, or the like. In one or more embodiments, it is preferable for the apparatus 10 to remain stationary, or at the very least within a confined area. Thus, apparatus 10 may be tethered to the sea floor, anchored to a riverbed, bank, or shoreline, or be equipped with location stabilizing equipment, such as directional propellers and other control surfaces (not shown).

[0031] Apparatus 10 may comprise a plurality of inlets 17 configured to intake an external fluid and direct it into first tank 16, and a plurality of outlets 19 configured to direct the fluid from the second tank to the outside of the apparatus. In one or more embodiments, the inlets 17 and outlets 19 may comprise simple openings or one-way flow or check valves that operate to permit, for example, flow of the fluid into first tank 16 and prevent or at least retard flow of fluid in the opposite direction. Any type of suitable one-way flow valve may be used, including, for example, a ball-check valve, a Tesla valve, a duckbill valve, a flapper valve, a diaphragm valve, a lift-check valve, and a reed valve. The inlets 17 may be configured to admit water into first tank 16 resulting from a wave crest or from a directional flow of water, such as a river or aqueduct. Likewise, the outlets 19 may be configured to discharge water resulting from a wave trough or the natural current of a river. In particular embodiments suited for use in rivers, the inlets may be positioned on an upstream facing side of the appar atus 10 be configured to capture water flowing with the natural current present in the river. The inlets and outlets may be located at any elevation within the apparatus, provided that they are below the surface level of the river. In one embodiment, the inlet may be located at the same or a lower elevation within the apparatus than the outlet. Likewise, the outlets may be positioned on a downstream facing side of the apparatus 10 to release water in the general direction of the river’s current.

[0032] In one or more embodiments, first tank 16 is located immediately above and in covering relationship to at least a portion of the second tank. In fact, tanks 16, 18 may be separated by a common wall structure, if desired. In certain embodiments, the volume of the lower tank 18 is less than the volume of the first tank 16, although this need not always be the case.

[0033] As can be seen in Figs. 3-5, turbine assembly 20 comprises a plurality of concentric turbines 22, 24, 26, 28, 30 that are installed within a turbine housing 31. Turbine housing 31 further comprises conduit structure 32 that defines a fluid flow path between first tank 16 and second tank 18. Conduit structure 32 need not be configured as conventional piping, but may be configured as duct work for directing a flow of fluid between the two tanks. At least one fluid collector 34 is configured to receive fluid from first tank 18 and direct the fluid into a manifold section 36 where the fluid can be distributed to a plurality of upflow passages 38, 40, 42, 44, 46. Upflow passages 38, 40, 42, 44, 46 can have an annular configuration and be arranged concentrically. Like the concentric turbines 22, 24, 26, 28, 30, the upflow passages 38, 40, 42, 44, 46 can have a decreasing diameter from the outermost structure to the innermost structure. Conduit structure 32 further comprises a plurality of downflow passages 48, 50, 52, 54, 56, 58 that are configured to receive fluid that has flown across turbines 22, 24, 26, 28, 30 and direct the fluid into the second tank 18. A majority of the downflow passages 48, 50, 52, 54, 56 have an annular configuration with diameters that decrease from outermost to innermost. In certain embodiments, the central or innermost downflow passage 58 is cylindrical. Also in certain embodiments, there may be a greater number of downflow passages than upflow passages.

[0034] Each of turbines 22, 24, 26, 28, 30 comprises a plurality of blades 60a-e, respectively. In one or more embodiments, blades 60a-e are independently configured, that is, have a distinctive shape for a specific turbine in order to best address the fluid flow characteristics across each turbine. In certain embodiments, the blade pitch may also vary from turbine to turbine. For example, as illustrated in the Figures, turbine 22 has a shorter blade pitch than turbines 24 and 26. Blade density (the number of blades per unit length) may also vary from turbine to turbine with turbine 22 having a greater blade density than turbines 24 and 26.

[0035] Each of turbines 22, 24, 26, 28, 30 are supported by a plurality of radial support members 62a-c. In certain embodiments, one radial support member 62 a can be provided for each individual turbine 22, or multiple turbines 24, 26 can be connected to the same support arm 62b. As illustrated in the Figures, the turbine assembly 20 may comprise a combination of individually supported turbines and turbines that are linked together via a common support member. By decoupling the turbines, turbine assembly 20 is configured to permit rotation of turbines at different angular velocities and/or rotational speeds.

[0036] Each support member 62a-c is connected to a rotatable drive shaft 64a-c, respectively. In certain embodiments, drive shafts 64a-c arc concentrically or telescopically positioned relative to each other. Thus, the shaft 64a that is connected to the support member 62a that supports the outermost turbine 22 is has a larger diameter and inside of which the other drive shafts 64b-c are received. The drive shafts 64a-c are configured to be rotated at different angular velocities and/or rotational speeds. However, in certain embodiments, it may be desirable to combine the energy and torque from these differently rotating shafts into a single output shaft that can be connected to a single electrical generator. Alternatively, one or more of the drive shafts 64a-c could be coupled to individual electrical generators that generate electricity independently from each other.

[0037] If transfer of the energy and torque from multiple drive shafts 64a-c to a common output shaft is desired, turbine assembly 20 can comprise a torque-combining gearbox assembly 66. As can be seen in Fig. 6, gearbox assembly 66 comprises a plurality of drive shaft gears 68a-c that are operably connected to respective drive shafts 64a-c. The drive shaft gears 68a-c are connected to a plurality of respective output gears 70a- c, such as through intermeshed gear teeth. However, alternate arrangements are within the scope of the present invention. The output gears 70a-c are connected to a common output shaft 72 that may then be operably connected to an electrical generator 74.

[0038] The turbine assembly 20 is supported primarily by a mounting support 76 that is secured to buoyant body 14. Attached to mounting support 76 are other necessary structural components desired to be included within the turbine assembly such as a drive shaft bearing 78 and a cover 80.

[0039] Turning to Fig. 5, operation of apparatus 10 is illustrated. A fluid, preferably water, can be taken in through inlets 17 and directed into first tank 16. As described previously, the intake of fluid can be the result of the capture of water from a wave crest, or by the current of a river or other flow of water. Fluid is collected within tank 16 to create a water level within the tank that develops a head pressure that provides the necessary force for transference of the water from tank 16 into second tank 18.

[0040] In one or more embodiments, the turbine assembly 20 is configured to operate, that is, to cause the turbines contained therein to rotate when fluid is flowed thereacross, at a total head pressure of less than 48, less than 36, or less than 24 inches of HzO, and/or at least 10, at least 12, or at least 15 inches of H2O. In one or more embodiments, the turbine assembly 20 is configured to operate such that the pressure drop across one or more of the turbines is less than 12, less than 8, or less than 6 inches of H2O and/or at least 1, at least 3, or at least 5 inches of H2O. [0041] It is also noted that turbine assembly 20 may be utilized in connection with apparatus specially configured to process a flow of a gas, such as a flue gas from a powerplant or other industrial process. In such case, the flow of gas may not necessarily be contained between tanks 16 and 18. Rather, turbine assembly 20 may be located within a duct or channel through which the flow of gas is contained. In one or more embodiments, turbine assembly 20 is configured to accept a low-pressure supply of gas having a pressure of less than 100 psia, less than 90 psia, less than 80 psia, or less than 70 psia, and/or at least 20 psia, at least 25 psia, or at least 30 psia.

[0042] In one or more embodiments, tank 16 is configured to direct a flow of fluid into conduit structure 32. Preferably, there is no mechanical valve or controller to control the flow rate of the fluid into conduit structure 32; however, using some type of flow control system is within the scope of the present invention. The fluid initially enters fluid collector 34 where it is directly downwardly into manifold section 36. The fluid within fluid collector 34 flows below the elevation of turbines 22, 24, 26, 28, 30 and into manifold section 36. In manifold section 36, the flow of fluid is divided and directed upwardly through upflow passages 38, 40, 42, 44, 46 towards the respective turbines located within those passages. The fluid flows upwardly through the respective turbines thereby causing them to rotate, which in turn rotates the various drive shafts 64a-c and output shaft 72.

[0043] In the context of a river application, fluid flowing as a result of the river’ s current can be taken directly into the conduit structure 32, and in particular manifold section 36, without first having to be fed into a tank. The fluid combing into the manifold section is then directed upwardly into upflow passages 38, 40, 42, 44, 46 without first having to be directed downwardly into a fluid collector 34.

[0044] Once the fluid has flowed across the respective turbines, the fluid is then directed into one or more of downflow passes 48, 50, 52, 54, 56, 58 where it flows in a direction that is opposite the direction of fluid flow through upflow passages 38, 40, 42, 44, 46. The fluid then is directed into second tank 18 and is ultimately discharged through the tank outlets.

[0045] As mentioned above, the turbines 22, 24, 26, 28, 30 are configured such that they do not require a large head pressure acting directly on the turbine blades. Rather, the energy required to cause the turbines to rotate is provided by the mass flow rate of fluid through conduit structure 32. In one or more embodiments, the water flowing through conduit structure 32 has a linear velocity of at least 1 m/s, at least 2 m/s, or at least 4 m/s. However, it is important to note that apparatus 10 is fully scalable to meet the characteristics of the fluid in which it operates. For example, if the environment into which apparatus 10 is to be placed into service is expected to produce a lower head pressure or lower linear flow rate of fluid, the turbine sizes can be increased so that the mass flow of fluid across the turbines will be greater.

[00461 Because the turbines are not all directly connected to a common drive shaft, the rotational characteristics of each turbine can remain independent to ensure optimal turbine performance and peak power generation. For instance, the outermost turbine 22 may rotate with a different angular velocity and rotational speed than any of turbines 24. 26, 28, 30. Alternatively, some turbines can be coupled together so that they share certain rotational characteristics. As can be seen in Fig. 3, turbines 24, 26 and turbines 28, 30 are lined by respective support members 62b and 62c. Accordingly, these turbine pairs transmit mechanical energy to the same drive shaft 64b, 64c, respectively.

[0047] Since the present invention permits the decoupling of the various turbines, drive shafts 64a-c will have different rotational characteristics. The energies delivered by each drive shaft 64a-c are preferably merged via gear box assembly 66 to turn output shaft 72 which then drives generator 74 to produce electricity.

Claims

I claim :

1. A turbine assembly comprising: at least two concentric, annular turbines located within a turbine housing, the turbine housing comprising conduit structure configured to simultaneously flow a fluid across and rotate the annular turbines; and at least one drive shaft operably coupled to the at least two annular turbines.

2. The turbine assembly of claim 1, further comprising at least one arm assembly connected to at least one of the annular turbines and interconnecting the at least one of the annular turbines with the drive shaft, the drive shaft being configured for operable connection to a generator.

3. The turbine assembly of claim 1, wherein the at least two annular turbines each having a different turbine blade configuration.

4. The turbine assembly of claim 1, wherein the turbine housing comprises conduit structure configured to direct the fluid toward and away from the at least two annular turbines.

5. The turbine assembly of claim 4, wherein the conduit structure comprises at least two upflow passages configured to direct the fluid upwardly through the at least two annular turbines respectively, and at least two downflow passages configured to direct the fluid downwardly after passage through the at least two annular turbines respectively.

6. The turbine assembly of claim 1, wherein the turbine assembly is configured to flow the fluid across and rotate the at least two annular turbines under a total head pressure of less than 36 inches of H2O.

7. The turbine assembly of claim 1, wherein the turbine assembly is configured such that the pressure drop across the at least two annular turbines required to rotate the at least two annular turbines is less than 12 inches of H2O.

8. The turbine assembly of claim 1, wherein the at least two annular turbines are configured to rotate with different angular- velocities when the fluid is flowed thereacross.

9. The turbine assembly of claim 8, wherein the turbine assembly further comprises at least two arm assemblies connected to the at least two annular turbines respectively, the at least two arm assemblies being connected to at least two concentric drive shafts respectively.

10. The turbine assembly of claim 9, wherein the at least two concentric drive shafts are operably connected a torque-combining gearbox having a single output shaft configured to be operably connected to a generator.

11. The turbine assembly of claim 1 , wherein the fluid is water.

12. The turbine assembly of claim 1, wherein the fluid is a gas.

13. The turbine assembly of claim 12, wherein the gas supplied to the turbine assembly has a pressure of less than 100 psia.

14. A turbine assembly comprising: a plurality of concentric, annular turbines located within a turbine housing, the turbine housing comprising conduit structure configured to flow a fluid across and rotate the annular turbines, the plurality of annular turbines being configured for rotation at different angular velocities when the fluid is flowed thereacross; and at least first and second independently rotatable arm assemblies being connected, respectively, to at least first and second annular turbines of the plurality of annular turbines, the first and second arm assemblies being connected to respective first and second drive shafts.

15. The turbine assembly of claim 14, wherein the first and second drive shafts are concentric.

16. The turbine assembly of claim 14, wherein the first and second drive shafts are connected to a torque-combining gearbox having a single output shaft configured to be operably connected to a generator.

17. The turbine assembly of claim 14, wherein the first and second annular turbines are configured to rotate with different angular velocities when the fluid is flowed thereacross.

18. The turbine assembly of claim 17, wherein the first and second drive shafts are driven at different rotational speeds.

19. The turbine assembly of claim 14, wherein the conduit structure comprises at least two upflow passages configured to direct the fluid upwardly through the at least two annular turbines respectively, and at least two downflow passages configured to direct the fluid downwardly after passage through the at least two annular turbines respectively.

20. The turbine assembly of claim 14, wherein the turbine assembly is configured to flow the fluid across and rotate the plurality of annular turbines under a total head pressure of less than 36 inches of H2O.

21. The turbine assembly of claim 1, wherein the turbine assembly is configured such that the pressure drop across the plurality of annular turbines required to rotate the plurality of annular turbines is less than 12 inches of H2O.

22. The turbine assembly of claim 14, wherein the fluid is water.

23. The turbine assembly of claim 14, wherein the fluid is a gas.

24. The turbine assembly of claim 23, wherein the gas supplied to the turbine assembly has a pressure of less than 100 psia.

25. A turbine assembly comprising: at least a first annular turbine located within a turbine housing, the turbine housing comprising conduit structure configured to direct a fluid through at least a first upflow passage within which the at least first annular' turbine is installed, the upflow passage being configured to direct the fluid upward across the at least first annular turbine thereby causing the turbine to rotate, the conduit structure further comprising at least a first downflow passage configured to receive the fluid after having passed through the at least first annular' turbine, the downflow passage being configured to direct the fluid toward a fluid outlet; and at least a first arm assembly connected to the at least first annular turbine and interconnecting the at least first annular turbine with a first drive shaft.

26. The turbine assembly of claim 25, wherein the turbine assembly further comprises: at least a second annular turbine that is concentric with the first annular turbine; at least a second upflow passage that is configured to direct the fluid upard across the second annular turbine; and at least a second downflow passage that is configured to receive at least a portion of the fluid that has passed through the second annular turbine, and direct that portion of the fluid towaid the fluid outlet.

27. The turbine assembly of claim 26, wherein the at least first and second annular turbines are configured for rotation at different angular velocities when the fluid is flowed thereacross.

28. The turbine assembly of claim 26, wherein the first drive shaft is configured for operable connection to a generator.

29. The turbine assembly of claim 26, wherein the turbine assembly further comprises a third annular turbine that is concentric with the first and second annular turbines and a second arm assembly that is connected to the third annular turbine.

30. The turbine assembly of claim 29, wherein the second arm assembly is operably connected with a second drive shaft that is concentric with the first drive shaft.

31. The turbine assembly of claim 30, wherein the first and second drive shafts arc connected to a torque-combining gearbox having a single output shaft configured to be operably connected to a generator.

32. The turbine assembly of claim 26, wherein the at least first and second annular turbines each have a different turbine blade configuration.

33. The turbine assembly of claim 25, wherein the turbine assembly is configured to flow the fluid across and rotate the at least first annular turbine under a total head pressure of less than 36 inches of H2O.

34. The turbine assembly of claim 25, wherein the turbine assembly is configured such that the pressure drop across the at least first annular turbine required to rotate the at least first annular turbine is less than 12 inches of H2O.

35. The turbine assembly of claim 25, wherein the fluid is water.

36. The turbine assembly of claim 25, wherein the fluid is a gas.

37. The turbine assembly of claim 35, wherein the gas supplied to the turbine assembly has a pressure of less than 100 psia.

38. Apparatus for generating electricity comprising the turbine assembly according to any of claims 1-37 and a generator operably connected thereto.

39. The apparatus of claim 38, wherein the apparatus further comprises: a body comprising first and second tanks, the first tank being located at a higher elevation within the buoyant body than the second tank; a plurality of water inlets formed in the body and interconnecting the body’s exterior with the interior of the first tank and permitting flow of water into the first tank from the exterior of the buoyant body; a plurality of water outlets formed in the body and interconnecting the body’s exterior with the interior of the second tank and permitting flow from the interior of the second tank to the exterior of the body.

40. The apparatus of claim 39, wherein the conduit structure interconnects the first and second tanks and is configured to direct a flow of water from the first tank and into the second tank.

41. The apparatus of claim 40, wherein a generator operably connected with the at least first and second annular turbines and configured to generate electrical power upon rotation of the at least first and second annular turbines.

42. A method of generating electricity comprising: flowing a fluid across a plurality of concentric annular turbines and causing the plurality of annular turbines to rotate, the annular turbines being operably connected to a generator; and generating electricity using the generator upon rotation of the plurality of annular turbines.

43. The method of claim 42, wherein the fluid is caused to flow through conduit structure comprising a plurality of upflow passages and a plurality of downflow passages.

44. The method of claim 43, wherein the plurality of annular turbines are located within respective upflow passages of the conduit structure.

45. The method of claim 44, wherein the fluid is caused to flow upward through the plurality of upflow passages and across the plurality of annular turbines thereby rotating the plurality of annular turbines.

46. The method of claim 45, wherein after flowing across the plurality of annular turbines the fluid is caused to flow downward through the plurality of downflow passages.

47. The method of claim 42, wherein at least one of the plurality of annular turbines is connected to a first arm assembly that operably connects the at least one annular turbine with the generator, and wherein at least one other of the plurality of annular turbines is connected to a second arm assembly that operably connects the at least one other annular turbine with the generator.

48. The method of claim 47, wherein the first arm assembly is connected to the generator via a first drive shaft, and wherein the second arm assembly is connected to the generator via a second drive shaft that is concentric with the first drive shaft.

49. The method of claim 48, wherein the at least one annular turbine that is connected to the first arm assembly rotates with an angular velocity that is different from the at least one other annular turbine that is connected to the second arm assembly.

50. The method of claim 49, wherein the first and second drive shafts are connected to a torque-combining gearbox having a single output shaft connected to the generator.

51. The method of claim 42, wherein the fluid flows across the plurality of annular turbines under a total head pressure of less than 36 inches of H2O.

52. The method of claim 42, the pressure drop across the plurality of annular turbines is less than 12 inches of H2O.

53. The method of claim 42, wherein the fluid is water.

54. The method of claim 42, wherein the fluid is a gas.

55. The method of claim 54, wherein the gas supplied to the plurality of turbines has a pressure of less than 100 psia,

56. A method of generating electricity comprising: flowing water into a first tank of a body located in a body of water; causing the water to flow from the first tank through a conduit structure and into a second tank, the second tank being located at a lower elevation within the body than the first tank; as the flow of water traverses the conduit structure, passing the water across at least a first annular turbine and causing the at least first annular turbine to rotate, the at least first annular turbine being operably connected to a generator; and generating electricity using the generator upon rotation of the at least first annular turbine.

57. A method of generating electricity comprising: providing the turbine assembly according to any of claims 1-37 within a body located in a body of water; flowing water into the conduit structure causing the water to flow upwardly through one or more upflow passages and across the at least one annular turbine and causing the at least one annular turbine to rotate, the turbine assembly being operably connected to a generator; and generating electricity using the generator upon rotation of the at least one annular turbine.