Improved wave energy generator

Abstract

A energy generator assembly for installation in an aquatic environment, the generator assembly comprising: a hollow and elongate impeller extending between two ends, the impeller comprising a cylindrical impeller body with an outer surface and an inner surface defining an internal volume comprising a radially central hollow region to allow fluid to flow between the two ends wherein the inner surface comprises a plurality of fluid flow directing vanes extending axially along the length of the inner surface, said vanes projecting radially towards said central hollow region wherein the vanes are arranged to induce rotation of the impeller during flow of fluid between the two ends of the hollow impeller.

Description

IMPROVED WAVE ENERGY GENERATOR TECHNICAL FIELD

[0001] The present invention relates to an improved wave energy generator for generating electricity from flow of water. More specifically the BACKGROUND

[0002] Any references to methods, apparatus or documents of the prior art are not to be taken as constituting any evidence or admission that they formed, or form part of the common general knowledge.

[0003] The demand for energy from renewable energy sources is increasing as the earth’s fossil fuels are depleted. Furthermore, it is desirable to generate electricity from clean energy sources that do not contribute to global warming.

[0004] One common renewable energy source is hydro-electric power which is generated by harnessing the potential head of a fluid, such as water. A typical hydro electric power generation system requires a water source, such as a river to be dammed at a high location to create a head of water with stored potential energy. A pipeline runs from the dam to a lower location. A turbine generator is installed at the end of pipeline so that water discharged from the high location flows through the turbine. The water drives the turbine which in turn drives an electrical generator which generates electricity. The problem with a dam-type hydro-electric generation arrangement is that the flooding caused by the dam has a negative impact on thelocal environment. The flooding destroys the natural landscape and displaces people living in the vicinity.

[0005] In view of the above, it would be desirable to provide an energy generation system that can utilize a smaller body of water in which water flows at relatively lower velocities. It would also be desirable to provide a small scale energy generation system that is suitable for utilizing gravity fed municipal water distribution pipelines for energy generation. SUMMARY OF INVENTION

[0006] In an aspect, the invention provides an energy generator assembly for installation in an aquatic environment, the generator assembly comprising: a hollow and elongate impeller extending between two ends, the impeller comprising a cylindrical impeller body with an outer surface and an inner surface defining an internal volume comprising a radially central hollow region to allow fluid to flow between the two ends wherein the inner surface comprises a plurality of fluid flow directing vanes extending axially along the length of the inner surface, said vanes projecting radially towards said central hollow region wherein the vanes are arranged to induce rotation of the impeller during flow of fluid between the two ends of the hollow impeller wherein diameter of the central hollow region is at least 1 / 3rd the diameter of the impeller.

[0007] In an embodiment, the plurality of flow directing vanes are integrally formed with the body of the impeller.

[0008] In an embodiment, one or more of said flow directing vanes extend helically relative to the central region of the cylindrical impeller body.

[0009] In an embodment, each flow directing vane comprises respective edge portions extending axially along the length of the impeller body, the respective edge portions defining said central hollow region of the impeller body.

[0010] In an embodiment, a pair of adjacently located vanes define a corresponding spiral flow path for allowing flow of fluid between the ends.

[0011] In an embodiment, respective pairs of adjacently located vanes form radially arranged spiral flow paths within the hollow impeller body wherein flow of fluid through the radially arranged flow paths induces rotation of the hollow impeller body during flow of fluid between the two ends of the hollow impeller.

[0012] In an embodiment, the energy generator further comprises one or more radial bearing assemblies to surround and support one or more sections of the elongate impeller body.

[0013] In an embodiment the radial bearing assembly is located to surround and support one of the ends of the impeller body and a second of said radial bearing assembly is located to surround and support the other of the ends of the impeller body.

[0014] In an embodiment, the outer surface of the impeller body comprises a plurality of magnetic elements arranged across the outer surface such that rotation of the impeller body effected by flow of fluid through the hollow impeller body results in movement of the magnetic elements.

[0015] Preferably, the outer surface comprises a plurality of recessed cavities configured to receive and fixedly engage a respective magnetic element.

[0016] In an embodiment, the energy generator further comprises a stator assembly comprising an elongate and hollow stator body comprising a stator passage extending therethrough, the stator passage being dimensioned to accommodate the impeller body therein wherein stator body comprises stator windings being located such that rotation of the impeller body and the magnetic elements thereon relative to the stator body results in generation of current in the stator windings of the stator assembly.

[0017] In a first embodiment, the stator assembly comprises a plurality of stator slots (Ns) and wherein the magnetic elements on the outer surface provide a plurality of rotor poles (NM) such that when outer diameter of the rotor is greater than 1000mm and when inner diameter of the stator is greater than 1000mm, with axial length of the rotor and stator being greater than 3000mm, ratio of Ns / NM is greater than 4 and preferably greater than 5.

[0018] In an alternative embodiment, the stator assembly comprises a plurality of stator slots (Ns) and wherein the magnetic elements on the outer surface provide a plurality of rotor poles (NM) such that when outer diameter of the rotor is less than 500mm and when inner diameter of the stator is greater than 500mm, with axial length of the rotor and stator being less than 500mm, ratio of Ns / NM is less than 2.

[0019] In an embodiment, the stator body extends between first and second ends such at the first and / or second end further comprises a recessed channel for accommodating the bearing assembly.

[0020] In an embodiment, the energy generator further comprises a housing sub- assembly that at least partially houses the stator assembly and the impeller body received within the passage of the stator body.

[0021] In an embodiment, the housing subassembly comprises: a. an inlet housing portion comprising an inlet for receiving a flow water, the inlet housing portion for conveying the received water to one of said ends of the hollow impeller body; and b. an outlet housing portion comprising an outlet for expelling water from the housing, the outlet housing being fluidly coupled with the other of said ends of the hollow impeller body to receive water from said other end of the impeller body and convey the received water to the outlet thereby effecting expulsion of the water from the housing.

[0022] In an embodiment, the inlet housing portion comprises a divergent configuration to allow the received flow of water to diverge towards said one of the ends of the hollow impeller body.

[0023] In an embodiment, the outlet housing portion comprises a convergent configuration to allow the water flowing from said other end of the impeller body to converge towards the outlet.

[0024] In an embodiment, the housing sub-assembly further comprises an intermediate housing portion adapted to be located in between the inlet housing portion and the outlet housing portion wherein the intermediate housing portion comprises an internal volume to substantially accommodate the stator assembly andthe impeller body received within the passage of the stator body of the stator assembly. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Preferred features, embodiments and variations of the invention may be discerned from the following Detailed Description which provides sufficient information for those skilled in the art to perform the invention. The Detailed Description is not to be regarded as limiting the scope of the preceding Summary of the Invention in any way. The Detailed Description will make reference to a number of drawings as follows: Figure 1 is a top perspective view of an energy generation system 1000 in accordance with a preferred embodiment. Figure 2 is a sectional view of the energy generation system 1000. Figure 3 is a top perspective view of an impeller assembly 100 that forms part of the energy generation system 1000. Figure 4 is a top perspective view of a stator assembly 200 that forms part of the energy generation system 1000. Figures 5 and 6 illustrates perspective views of the impeller assembly 100. Figures 7 and 8 illustrates perspective views of the stator assembly 200. Figures 9 and 10 illustrate end perspective views of an energy generation assembly 2000 that utilizes the energy generation system 1000. Figures 11 and 12 illustrate sectional views of the energy generation assembly 2000.Figure 13 illustrates a top perspective view of an energy generation assembly 3000 that utilizes the energy generation system 1000. Figure 14 illustrates a side view of the energy generation assembly 3000, Figures 15 and 16 illustrate end views of the energy generation assembly 3000. Figure 17 is a sectional view of the energy generation assembly 3000. Figures 18 to 24 illustrate a small scale stator 200A and rotor 100A combination in accordance with a first alternative embodiment. Figures 25 to 31 illustrate a large scale stator 200B and rotor 100B combination in accordance with a second alternative embodiment. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0026] Figures 1 to 8 illustrate an energy generation system 1000 comprising a hollow and elongate impeller assembly 100 that is rotatably mounted within a stator assembly 200. As will be evident from the foregoing sections, the working principle of the energy generation system involves the flow of water through the hollow impeller assembly which effects rotation of the impeller body 110 which in turn results in current being generated in the stator assembly 120.

[0027] The impeller assembly 100 comprises a hollow and elongate cylindrical impeller body 110 extending between two ends 112 and 114. The impeller body 110 comprises an outer surface 116 and inner surface 118 that defines an internal volume that allows flow of water or any other fluid between the two ends 112 and 114. The internal volume comprises a radially central hollow and continuous region111 that extends between the two ends 112 and 114 to allow fluid to flow between the two ends. The inner surface 118 of the impeller body comprises a plurality of fluid flow directing vanes 113 extending axially along the length of the inner surface 118. Each of these vanes 113 projects radially towards the central and hollow region 111. , said vanes projecting radially towards said central hollow region wherein the vanes are arranged to induce rotation of the impeller during flow of fluid between the two ends of the hollow impeller.

[0028] The flow directing vanes 113 extend helically relative to the central hollow region 111 of the cylindrical impeller body 110. These helical vanes 113 comprise a helical edge that extends between the ends 112 and 114 to define the central hollow region 111 of the impeller body 110. Each pair of adjacently located helical vanes 113 forms a spiral flow path defined along the inner surface 118 of the impeller body 110. Respective pairs of adjacently located vanes 113 form radially arranged spiral flow paths within the hollow impeller body 110. During use, flow of fluid through the radially arranged flow paths induces rotation of the hollow impeller body 110 during flow of fluid between the two ends (112 and 114) of the hollow impeller body 110. Each of he ends 112 and 114 of the impeller body is supported by respective bearing assemblies 300 that enables rotation of the cylindrical and hollow impeller body 110 as fluid flows through the spiral flow paths of the impeller body 110 that induces the rotation of the impeller body 110. The flow rate or velocity of the fluid flowing into the impeller body 110 determines the rotational velocity of the impeller body 110 during use. Each of the bearing assembly 300 is generally annular and is configured to surround and support the two ends 112 and 114 of the hollow and cylindrical impeller body 110.

[0029] The outer surface 116 of the impeller body 110 comprises a plurality of magnetic elements (not shown) that are embedded within small and recessed cavities that extend across the entire outer surface of the impeller body 110. During use, the flow of fluid though the spiral flow paths and the central region 110 effects rotation of the impeller body 110. As the impeller body 110 undergoes rotation, the magnetic elements on the outer surface 116 also undergo rotation which in turn results in constantly changing magnetic flux. The role of the magnetic elements will become evident in the foregoing sections.

[0030] The hollow impeller 100 is located within a stator assembly 200 so that the changing magnetic flux, during rotation of the hollow impeller body 110, results in generation of electricity in stator coils that form part of the stator assembly 200. The stator assembly 200 comprises an elongate and hollow stator body 210 comprising a stator passage 211 extending through the stator body 210. The stator passage 211 is dimensioned to accommodate the impeller body 110. As mentioned earlier, the stator body 210 includes stator windings (now shown) that are located along the length of the cylindrical stator body 210 such that rotation of the magnetic elements on the outer surface the impeller body 110 relative to the stator body 210 results in generation of current in the stator windings of the stator assembly. Each of the two ends 212 and 214 of the stator body 210 comprises a respective recessed channel for accommodating and generally supporting each of the bearing assemblies 300 that enables rotation of the impeller body 110 as the fluid flows through the hollow impeller body 110.

[0031] The energy generation system 1000 may be utilized in a number of ways for using flow of low velocity water for generating electricity. Figures 9 to 12 illustrate afirst optional embodiment of an energy generation assembly 2000 that utilizes the energy generation system 1000 described in the previous sections. The energy generation assembly 2000 is particularly well suited for utilizing low velocity water. A housing assembly 400 comprises an inlet housing portion 410 comprising an inlet 402 for receiving a flow water. The inlet housing portion 410 comprises a convergent configuration to receive a flow of low velocity via the inlet opening 402. The convergent configuration increases the velocity of the water (due to the venturi effect) as the water is conveyed through the convergent configuration of the inlet housing portion 410 before the water with increased velocity enters the first end 112 of the impeller body 110 which in-turn effects rotation of the impeller body 110 to generate electricity. The housing assembly 400 also comprises an outlet housing 420 for expelling water from the outlet housing portion 420. The outlet housing portion 420 is fluidly coupled with the second end 114 of the hollow impeller body 110 to receive water from the second end 114 of the impeller body 110 and convey the received water to the outlet 414 thereby effecting expulsion of the water from the housing. The energy generation system 1000 is housed within an intermediate housing portion 415 located in between the inlet housing portion 410 and the outlet housing portion 420.

[0032] Figures 13 to 17 illustrate a second optional embodiment of an energy generation assembly 3000 that utilizes the energy generation system 1000 described in the previous sections. The energy generation assembly 3000 is particularly well suited for being utilized with pipelines (such as municipal pipelines) where water flows under gravity at low velocities. A housing assembly 500 comprises an inlet housing portion 510 comprising an inlet 502 with fluid couplings for receiving a flowwater from a pipeline coupled with the inlet 502. The inlet housing portion 510 comprises an inlet passage with a slightly divergent configuration to receive a flow of low velocity via the inlet opening 502. The water is conveyed through the inlet housing portion 510 before the water enters the first end 112 of the impeller body 110 which in-turn effects rotation of the impeller body 110 to generate electricity. The housing assembly 400 also comprises an outlet housing 520 for expelling water from the outlet housing portion 520. The outlet housing portion 520 is fluidly coupled with the second end 114 of the hollow impeller body 110 to receive water from the second end 114 of the impeller body 110 and convey the received water to the outlet 514 thereby effecting expulsion of the water from the housing into a pipeline via fluid couplings associated with the outlet 514.

[0033] During the development of the energy generator system described herein, the inventor has surprisingly realized that the size and scale of the device namely the rotor can play an important role in designing the stator assembly 200. The following passages refer to two alternative embodiments 200A and 200B of the stator assembly 200.

[0034] Referring to Figure 18 to 23, a first alternative embodiment of a stator assembly 200A is shown. The stator assembly 200A is a small scale stator that is particularly suitable for use in conjunction with a small scale rotor 100A.

[0035] The stator 200A shown in the Figures has an outer diameter of 225mm and an inner diameter of 171.4mm. The rotor 100A has an outer diameter of 164.4mm and an inner diameter of 149.4mm. The airgap length is 3.5mm and the axial length for the rotor 100A and the stator 200A is 455mm. The stator 200A in combinationwith the rotor 100A is particularly suitable for use with water pipelines that are around 100mm in diameter.

[0036] The optimization of a small permanent magnet generator was analysed using both 2D and 3D simulations, highlighting key differences in performance. The 2D simulation results indicate a peak cogging torque of 5.1 Nm, which is less than 1% of the rated torque of 666 Nm. The no-load voltage peaks are 530.1 V at 200 rpm, 1590.2 V at 600 rpm, and 3180.3 V at 1200 rpm, showing a linear increase with speed. Under full load conditions, the generator delivers a torque of 666 Nm, with voltage peaks of 1189.3 V at 200 rpm, 3595 V at 600 rpm, and 7189.9 V at 1200 rpm.

[0037] In contrast, the 3D simulation results show a reduced peak cogging torque of 3.8 Nm. The full load torque is slightly lower at 626 Nm, with full load voltage peaks of 960 V at 200 rpm, 2950 V at 600 rpm, and 5610 V at 1200 rpm. The summary table shows that the 2D simulation estimates power outputs of 13.9 kW at 200 rpm, 41.9 kW at 600 rpm, and 83.7 kW at 1200 rpm. Meanwhile, the 3D simulation predicts slightly lower power outputs of 13.1 kW, 39.3 kW, and 78.6 kW at the same respective speeds. The generator design exhibits linearity with axial length. The optimal selection of the dimensions will not change for different axial lengths. When the axial length of the generator is modified, several changes occur. Increasing the axial length typically enhances the power output and torque production, as the machine's active material volume increases, allowing it to handle more magnetic flux and generate higher electromagnetic forces.The three-phase stator 200A can benefit from simplifying the winding layout by having a slot number divisible by 6. Therefore, slot numbers 18, 24,30, 36, 48 etc., are potential stator number of slot (or teeth). Considering the dimensions, and enabling teeth to be above 5mm minimum width, the tooth number need to be below 36 as thinner teeth resulting in manufacturing challenges. Therefore 36-teeth was selected as an appropriate value for this design.TABLE 1 The highlighted row has a high value of least common multiple resulting in low cogging torque.

[0038] 26 rotor poles was selected as this design achieved less than 1% of cogging torque. A higher number of rotor pole values such as 34 or 38 will likely produce lower cogging torque, however, will increase the fundamental frequency.

[0039] The design of a 36-slot, 26-pole permanent magnet generator shows a peak cogging torque of 5.1 Nm. The no-load peak voltages are at 520.5 V, 1561.4 V, and 3123 V for 200, 600, and 1200 rpm, respectively, demonstrating a linear increase with speed. Under full load, the torque is 203.5 Nm, with voltage peaks at 556.8 V, 1688.7 V, and 3377.8 V for the same speeds.TABLE 2

[0040] In summary, it was observed that the stator design for smaller stators that have less than 500mm and more preferably less than 200m as outer diameter and an axial length of less than 500mm should have a stator to pole ratio (Ns / NM) of less than 2. Ns denotes the number stator slots and NM denotes the number of poles for optimal operation.

[0041] Figures 24 to 31 illustrate a large-scale stator assembly 200B in combination with a large scale rotor 100B. The stator 200B shown in the Figures has an outer diameter of 3000mm and an inner diameter of 2285mm. The rotor 100B has an outer diameter of 2225mm and an inner diameter of 1000mm. The airgap length is 30mmand the axial length for the rotor 100B and the stator 200B is 6200mm. The stator 200B in combination with the rotor 100B is particularly suitable for large scale operations as will be evident from some of the preliminary simulation studies that have been carried out.

[0042] The results of 2D and 3D simulations for generator design highlight differences in performance metrics. The cogging torque peak in 3D simulation (13.5 kNm) is much higher compared to 2D (5.4 kNm), indicating 3D effects and more accurate modelling of magnetic forces. The full load torque is nearly identical, with 4550 kNm for 2D and 4500 kNm for 3D, suggesting minimal dimensional impact on torque output. The no-load per-phase peak voltage at various speeds (200, 600, 1200 rpm) shows slight discrepancies between 2D and 3D, with 3D simulations consistently lower by about 0.1 to 0.6 kV. Similarly, full-load perphase peak voltages also show slight reductions in 3D simulations. Power output at different speeds follows the same trend, with 3D simulations showing slightly lower values, reflecting more accurate losses and 3D effects.

[0043] In order to achieve a simplified winding configuration, the number of slots per pole per phase is kept as an integer resulting in an integer lot machine. As a result, the 180 slot / 30 pole machine is selected as a suitable candidate for the large-scale machine. The selected 180-slot, 30-pole machine has a winding with a coil throw of 5, The slot per pole per phase (SPP) is 2, meaning each pole pair spans 6 slots. With a coil throw of 5, each coil spans 5 slots, so if the starting end of a coil is in slot n, the finishing end will be in slot n+5. The winding layout ensure a 120° electrical phase separation between phases, repeating every 6 slots to maintain the three- phase symmetry and minimize harmonics.

[0044] The summary table shows that the 2D simulation estimates power outputs of 95.3 MW at 200 rpm, 285.9 MW at 600 rpm, and 571.8 MW at 1200 rpm. Meanwhile, the 3D simulation predicts slightly lower power outputs of 94.2 MW, 282.7 MW, and 565.5 kW at the same respective speeds. The generator design exhibits linearity with axial length. The optimal selection of the dimensions will not change for different axial lengths. When the axial length of the generator is modified, several changes occur. Increasing the axial length typically enhances the power output and torque production, as the machine's active material volume increases, allowing it to handle more magnetic flux and generate higher electromagnetic forces.TABLE 3

[0045] The selection of the slot / pole combination for the large machine is mainly influenced by the simplicity of the winding configuration. Due to the large size and high torque production, the cogging torque is comparatively low, i.e., is a low percentage of the rated torque compared with the small-scale machine. Therefore, seeking the least common multiple between the slot / pole numbers appeared to beirrelevant. Further having a low pole count results in difficulty to use rectangular shaped magnet pieces. As a result, the rotor pole number in the neighborhood of 24 o 36 appeared to be suitable. In order to achieve a simplified winding configuration, the number of slots per pole per phase is kept as an integer resulting in an integer lot machine. As a result, the 180 slot / 30 pole machine is selected as a suitable candidate for the large-scale machine.

[0046] The selected 180-slot, 30-pole machine has a winding with a coil throw of 5, The slot per pole per phase (SPP) is 2, meaning each pole pair spans 6 slots. With a coil throw of 5, each coil spans 5 slots, so if the starting end of a coil is in slot n, the finishing end will be in slot n+5. The winding layout ensure a 120° electrical phase separation between phases, repeating every 6 slots to maintain the three-phase symmetry and minimize harmonics.

[0047] In summary, it was observed that the stator design for larger stators that have more than 1000mm and more preferably more than 1500mm as outer diameter and an axial length of less than 3000mm should have a stator to pole ratio (Ns / NM) of greater than 4. Ns denotes the number stator slots and NM denotes the number of poles for optimal operation.

[0048] In compliance with the statute, the invention has been described in language more or less specific to structural or methodical features. The term “comprises” and its variations, such as “comprising” and “comprised of” is used throughout in an inclusive sense and not to the exclusion of any additional features.

[0049] It is to be understood that the invention is not limited to specific features shown or described since the means herein described comprises preferred forms of putting the invention into effect.

[0050] The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted by those skilled in the art.

Claims

CLAIMS 1. An energy generator assembly for installation in an aquatic environment, the generator assembly comprising: a hollow and elongate impeller extending between two ends, the impeller comprising a cylindrical impeller body with an outer surface and an inner surface defining an internal volume comprising a radially central hollow region to allow fluid to flow between the two ends wherein the inner surface comprises a plurality of fluid flow directing vanes extending axially along the length of the inner surface, said vanes projecting radially towards said central hollow region wherein the vanes are arranged to induce rotation of the impeller during flow of fluid between the two ends of the hollow impeller wherein diameter of the central hollow region is at least 1 / 3rdof the diameter of the impeller; one or more radial bearing assemblies to surround and support one or more sections of the elongate impeller body wherein a first of said radial bearing assembly is located to surround and support one of the ends of the impeller body and a second of said radial bearing assembly is located to surround and support the other of the ends of the impeller body; wherein the plurality of flow directing vanes are integrally formed with the body of the impeller; and wherein the entire outer surface of the impeller body comprises a plurality of magnetic elements arranged across the outer surface extending between the ends of the impeller body such that rotation of the impeller body effected by flow of fluid through the hollow impeller body results in movement of the magnetic elements wherein the outer surface comprises aplurality of recessed cavities configured to receive and fixedly engage a respective magnetic element; a stator assembly comprising an elongate and hollow stator body comprising a stator passage extending therethrough, the stator passage being dimensioned to accommodate the impeller body therein wherein stator body comprises stator windings being located such that rotation of the impeller body and the magnetic elements thereon relative to the stator body results in generation of current in the stator windings of the stator assembly wherein the stator body extends between first and second ends such at the first and / or second end further comprises a recessed channel for accommodating the bearing assembly.

2. An energy generator in accordance with claim 1 wherein one or more of said flow directing vanes extend helically relative to the central region of the cylindrical impeller body.

3. An energy generator in accordance with claim 1 or claim 2 wherein each flow directing vane comprises respective edge portions extending axially along the length of the impeller body, the respective edge portions defining said central hollow region of the impeller body.

4. An energy generator in accordance with claim 3 wherein a pair of adjacently located vanes define a corresponding spiral flow path for allowing flow of fluid between the ends.

5. An energy generator in accordance with claim 4 wherein respective pairs of adjacently located vanes form radially arranged spiral flow paths within thehollow impeller body wherein flow of fluid through the radially arranged flow paths induces rotation of the hollow impeller body during flow of fluid between the two ends of the hollow impeller.

6. An energy generator in accordance with any one of the preceding claims wherein the stator assembly comprises a plurality of stator slots (Ns) and wherein the magnetic elements on the outer surface provide a plurality of rotor poles (NM) such that when outer diameter of the rotor is greater than 1000mm and when inner diameter of the stator is greater than 1000mm, with axial length of the rotor and stator being greater than 3000mm, ratio of Ns / NM is greater than 4 and preferably greater than 5.

7. An energy generator in accordance with any one of the preceding claims wherein the stator assembly comprises a plurality of stator slots (Ns) and wherein the magnetic elements on the outer surface provide a plurality of rotor poles (NM) such that when outer diameter of the rotor is less than 500mm and when inner diameter of the stator is greater than 500mm, with axial length of the rotor and stator being less than 500mm, ratio of Ns / NM is less than 2.

8. An energy generator in accordance with any one of the preceding claims further comprising a housing sub-assembly that at least partially houses the stator assembly and the impeller body received within the passage of the stator body.

9. An energy generator in accordance with claim 8 wherein the housing subassembly comprises:a. an inlet housing portion comprising an inlet for receiving a flow water, the inlet housing portion for conveying the received water to one of said ends of the hollow impeller body; and b. an outlet housing portion comprising an outlet for expelling water from the housing, the outlet housing being fluidly coupled with the other of said ends of the hollow impeller body to receive water from said other end of the impeller body and convey the received water to the outlet thereby effecting expulsion of the water from the housing.

10. An energy generator in accordance with claim 9 wherein the inlet housing portion comprises a convergent configuration to allow the received flow of water to converge towards said one of the ends of the hollow impeller body.

11. An energy generator in accordance with claim 9 or claim 10 wherein the outlet housing portion comprises a divergent configuration to allow the water flowing from said other end of the impeller body to diverge towards the outlet.

12. A energy generator in accordance with any one of claims 9 to 11 wherein the housing sub-assembly further comprises an intermediate housing portion adapted to be located in between the inlet housing portion and the outlet housing portion wherein the intermediate housing portion comprises an internal volume to substantially accommodate the stator assembly and the impeller body received within the passage of the stator body of the stator assembly.

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