GB2544347A

GB2544347A - Low cost underwater turbine

Info

Publication number: GB2544347A
Application number: GB1520158.5A
Authority: GB
Inventors: Smith Rodney; Smith Jonathan
Original assignee: Individual
Current assignee: Individual
Priority date: 2015-11-14
Filing date: 2015-11-14
Publication date: 2017-05-17
Also published as: GB201520158D0

Abstract

An underwater turbine 1 for generating electrical power from water with an augmenter 2, 4, consisting of two nozzles interconnected by a cylinder duct 3, a rotor hub 10 having a plurality of twisted blades 11 attached by the tip to a magnet support ring 46 that rotates about a stationary coil support ring 47 with coils 49, surrounded by a two part ducting 43. A power cable 22 connects the apparatus to an onshore power distribution system. There are support vanes 12 between the outer ducting cylinder and the two part ducting around the generator. Bearings 45 allow bi-directional rotation of the rotatable hub, the hub shaft, the plurality of blades and the magnet support ring. The open faces of the augmenter cones are fitted with releasable mesh cones 13, 41 that minimise foreign object ingestion into the rotating blades. The apparatus floats on the water surface using pontoons 31, 32 secured using anchors 36, anchors cables 35 and anchor cable tensioners 38, 39, 40. There are actuators 15, 16, 17 to lift the turbine above the water surface. The apparatus is preferably for river and estuary deployment and is driven by river and tidal currents.

Description

Low cost underwater turbine

For centuries people have sought to harness the kinetic energy of tides and currents of the earth's rivers, estuaries and oceans. With the increasing realisation that man's combustion of fossil fuels to generate electricity is having a negative effect on the earth's climate, an increasing array of renewable electricity production technologies and systems are being developed globally ranging from solar power farms, wind turbines, hydroelectric dams and underwater turbines.

Harnessing energy from natural resources such as solar, wind and wave energy entails numerous technological and financial obstacles, and this is certainly the case with tidal power production systems. In order to generate electrical power from tidal energy it may be necessary to install large and multi-million pound underwater turbines in some of the earth's harshest marine environments, such as off rugged coasts that experience severe weather throughout the year. Such harsh environmental conditions mean that tidal power generation systems need to be well maintained after they have been built and installed, which collectively means that tidal power generation systems have not been as widely deployed to-date as solar power farms or onshore or off-shore wind turbines, as tidal power systems have higher manufacturing and installation costs than other forms of renewable energy systems.

Many dozens of companies globally are investing and producing a diverse array of tidal power systems including Kawasaki, Rolls Royce and Voith that are using their great engineering design and manufacturing capabilities to overcome the engineering challenges presented by tidal power generation. Siemens, one of the world's largest engineering companies, is a major developer and investor of the SeaGen project, the world’s first commercial tidal current energy generator, off the coast of Northern Ireland.

An underwater turbine is a device that generates electricity from moving water currents or ocean tides. Strong water currents and oceanic tides are a great source of kinetic energy and an underwater turbine exploits the kinetic energy from water using turbine blades that rotate with an attached turbine generator that can generate electricity. An underwater turbine closely resembles a wind turbine but instead of passing air molecules, water spins the blades of the turbine. Underwater turbines can be strategically located in areas with consistently strong currents which will provide sufficient water flow needed for electrical power generation.

The world’s first tidal power facility opened in 1966 on the estuary of the River Ranee in Brittany, France. The 24-turbine facility took almost 3 years to construct and it was not until about 1986 that the plant managed to pay for its own construction costs from the electricity it produced in the intervening 20 years. It has been estimated that the Ranee facility generates enough electricity to supply the needs of about 280,000 people.

The Ranee plant is an estuary-based power production facility that depends on the natural ebb and flow of tides to generate power, which amounts to about 10 hours a day. In contrast, offshore underwater turbines have a constant source of energy generated by oceanic currents and therefore have the potential to collectively produce far greater amounts of electricity than estuary-based underwater turbines.

An important advantage of underwater turbines is that water is about 830 times more dense than air, which means that an underwater turbine can reach the necessary rotating speeds for electrical power generation from slowly moving water. A wind turbine by comparison needs much higher wind speeds to operate efficiently than the water current speed needed to operate an underwater turbine.

Tides occur because the earth and the moon are attracted to each other through the pull of gravity. The gravitational pull of the moon causes the ocean to bulge out towards the moon, which is on average 242,600 miles from earth, pulling it to its highest level, or high tide. The earth is also pulled toward the moon, but with less strength. This pulls the earth away from the water on the far side of the earth, so high tide occurs on both sides of the planet at the same time, and because the earth rotates, we experience two tides per day in a pattern so reliable that it can be predicted months and even years in advance. This relationship between the earth and the moon makes tidal energy a predictable energy source, whereas other forms of renewable energy, such as wind and solar energy, are dependent on random weather patterns, which explains why more and more companies and investment are being made into a diverse array of tidal energy production systems.

Tidal energy is the energy obtained from the rise and fall of tides. As the tides rise and fall, a massive amount of water moves toward and then away from shore. Turbines placed in the path of this moving water spin as the water passes by and these spinning turbines are connected to generators that create electricity. One way tidal energy is captured is with the use of underwater tidal turbines. Tidal turbines look like and work like underwater windmills. They utilize turbines with short but strong blades that spin as the tides move and then transmit their energy to an electricity generator. It is a clean energy source because, unlike the burning of fossil fuels, it does not release greenhouse gases or other pollutants into the air or contribute to the production of acid rain. It is also a relatively cheap energy source, after the initial investment is paid ofF, the cost of generating electricity is very low. These turbines also require no land space, only underwater space for construction and they create less noise and visual pollution than onshore or offshore wind turbines, for example.

With greater stress being placed on the planet’s finite supply of fossil fuels - and increasing demand for businesses to develop sustainable supply chains - tidal power will likely play a growing role in the quest for a clean and renewable energy source. Tidal energy also has a high energy density, meaning that the tides store a larger amount of energy than most other forms of renewable energy, such as the wind. A major advantage of harnessing tidal currents for the generation of electricity is the predictability and reliability of the energy source. From an engineering and manufacturing perspective, tidal current turbines are fairly straightforward to design as they are built on the same principles as wind turbines. Due to the reliability and predictability of tidal currents, extreme force loadings are typically no more than 100% of normal operating loads. Their impacts on marine life is minimal as the rotational speed of the turbine blades are very slow compared to wind turbines and foreign object prevention meshes can be fitted which prevent ingestion fish without impacting on the efficiency of the underwater turbine.

As 71% of the Earth’s surface is covered by water, there is considerable scope to generate electricity from underwater turbines. Efficiency of tidal power generation is higher than coal, solar or wind energy generation, its efficiency is around 60%. The life of tidal energy power plant can be many tens of years so that the ratio of electricity generated versus manufacturing, installation and maintenance costs can be high.

Existing underwater turbine designs can be categorized into five main groups based on their actuation principles: vertical axis turbines, horizontal axis turbines, venturi turbines, reciprocating turbines and other models.

Vertical axis turbines have a rotation axis perpendicular to the water flow direction and can be categorised into upright and lying types. The advantages of vertical axis turbines include: a lower cut-in speed, a simple blade geometry that confers into a lower manufacturing cost, is less likely to induce cavitation and a yaw drive is not required. The rectangular shaped swept area of vertical axis turbine blades makes them suitable for application in shallow, long and narrow water streams. Examples of vertical axis turbines include GCK Technology Inc, USA Gorlov turbine, described in patent W02005061173 (A1) and Tidal Energy Pty Ltd, Australia DHV turbine, described in patent AU2003213510 (A1).

Horizontal axis turbines have a rotation axis that is parallel to the water flow direction and the turbine blades converts the water currents kinetic energy into electricity via rotating blades and gear sets. The advantages of horizontal axis turbines includes: the manufacturing costs for the lower solidity blades are lower than for a vertical axis turbine, higher energy conversion efficiency compared to a vertical axis turbine because the rotation plane is perpendicular to the water current flow direction, due to a more even axis thrust, and horizontal axis turbine blades and rotation axes are less likely to undergo fatigue damage. Examples of horizontal axis turbines include Sea Generation Ltd, UK, as described in patent US2006125242 (A1) and Hammerfest Strom, Norway, as described in patent W02004022968 (A1).

The low cost bi-directional scalable underwater turbine that we are describing here can be classified in the third category of underwater turbines, venturi turbines.

Venturi turbines can be categorized as a group of turbines fitted with a venturishaped shroud that prevents the invasion of foreign objects into the machine, rectifies the water current so making it flow through the turbine more uniformly and takes advantage of the pressure differential induced by the accelerated water to introduce a secondary flow that enhances the kinetic energy of the water flow. Examples of venturi turbines include the Clean Current Power Systems Corp,

Canada clean current tidal turbine, as described in patent CA2460479(A1) and UEK Corp, Canada, as described in patent WO0227151 (A1). A reciprocating turbine converts the kinetic energy of the water current into electrical energy by using an oscillating hydrofoil. The oscillating hydrofoil moves up and down to create changing lift and drag forces and a connecting rod interconnects the oscillating hydrofoil and a hydraulic pump. The hydraulic pump pressurises the working fluid which drives an electrical generator. Examples of reciprocating turbines include the Pulse Generation Ltd, UK pulse generator turbine, as described in patent W02005108781 (A1) and the BioPower Systems Pty Ltd, Australia BioStream reciprocating turbine, as described in patent US2010140933 (A1).

There are many other designs of underwater electricity generating turbines that are none of the four previously described main categories of turbines. Some examples of these other types of turbines include the HydroCoil Power Inc, USA HydroCoil turbine that features a cylinder with a screw-like turbine blade with varying pitch along its length. Water flows in from the wider pitch end and along the turbine blades and out from the narrower pitch end, as described in patent US6357997 (B1).

Another example is the Vortex Induced Vibrations Aquatic Clean Energy VORTEX turbine designed and patented by Vortex Hydro Energy Inc, USA, that utilises horizontally orientated cylinders held between two vertical plates, wherein the lateral vibration of approximately 1 Hz, induced by vortex flows in the wake of the cylinders, is used as the driving force to generate electricity.

We have previously described the manufacturing, economic and environmental benefits of underwater turbines, but as with all man-made technologies and integrated systems, nothing is perfect and the existing designs of underwater turbine that we categorised into 5 groups earlier all have their own disadvantages which we will describe in more detail here.

Disadvantages of the Blue Energy Ocean vertical axis turbine is that its anchoring system needs to be redesigned to withstand earthquake forces, and the area of the parte floating above the water level needs to be reduced to mitigate damage caused by adverse weather conditions like typhoons.

Disadvantages of Kobold vertical axis turbines are that the above water platform is likely to be influenced by typhoons and its horizontal wing surfaces could be vulnerable to cavitation damage.

Disadvantages of the Gorlov vertical axis turbine are that it is expensive to manufacture its complicated geometry helical turbine blades. It has been said that the selection of an appropriate blade material and resultant lower manufacturing costs are the key to the economic viability of Gorlov turbines for commercial electrical power generation.

Disadvantages of the DHV vertical axis turbine are its high manufacturing costs that needs to be lowered and the issue of sea creature invasion on the non-moving parts of the DHV vertical axis turbine still needs to be solved.

Disadvantages of the Atlantisstrom vertical axis turbine include its low efficiency at low water currrent speeds and its horizontal wing surfaces are likely to induce cavitation, which is expected to shorten its service life and increase maintenance costs.

Disadvantages of the WWTurbine vertical axis turbine include its non applicability of being used in deep waters and the area of the parts floating above the water surface level are large, making them vulnerable to damage in harsh weather conditions.

Disadvantages of the Neptune Proteus vertical turbine include the level of reliability of its computer-controlled shutter sub-system, its potentially negative influence on marine creatures and parts of the Neptune Proteus floating above the water level may make it vulnerable to typhoon weather conditions. A disadvantage of the Osprey vertical axis turbine is the vulnerability of its floating platforms to adverse weather conditions. A disadvantage of the HydroVolts vertical axis turbine includes its reduced electrical generating capability due to ingested marine debris and creatures. A disadvantage of the Tideng vertical axis turbine is that the addition of a computer control system increases its long term operational risks unless it can perform with high reliability over extended periods of time. A disadvantage of the Neo-Aerodynamic vertical axis turbine is the reliability and vulnerability to damage of its complicated blade structures which may be expensive to manufacture and expensive to maintain.

Disadvantages of the SeaGen horizontal axis turbine include the systems inability to achieve optimal performance in a low-speed water flow because it requires a relatively high cut-in speed. It has also been suggested that redesigning the anchoring system and changing the SeaGen to a whole underwater system is required.

Disadvantages of the Hammerfest horizontal axis turbine include the reliability of its control system in deep sea water that needs to be ascertained and it has been suggested that its anchoring system needs to be redesigned.

Disadvantages of the Tocardo horizontal axis turbine include expanding the application to a large power plant may require a lot of machinery and a redesign of its anchoring system, which will cumulatively increase its manufacturing cost and may make maintenance more difficult and expensive.

Disadvantages of the Neptune horizontal axis turbine include the necessity of improving the systems anchoring system and the platforms above water levels subsystems vulnerability to harsh weather conditions. A disadvantage of the Morild horizontal axis turbine is that its floatable body subsystem is likely to be affected by adverse weather conditions like typhoons. A disadvantage of the GEM-ocean's kite horizontal axis turbine is that its system structure is relatively expensive to manufacture compared to other horizontal axis turbines. A disadvantage of the Scot Renewables Tidal Turbine horizontal axis turbine is that its cut-in speed is quite high, meaning that it is not suitable for low water current sites. A disadvantage of the Clean Current Tidal venturi turbine is that it uses aerofoil cross-section blades and venturi ducts, that collectively increases its manufacturing costs. A disadvantage of the Hydro-gen venturi turbine is that its semi-floating structure may be vulnerable to adverse weather conditions like typhoons. A disadvantage of the Underwater electric kite venturi turbine is that it uses a variable pitch blade system that increases its manufacturing costs. A disadvantage of the Hydrokinetic venturi turbine is that its turbine rotors are suspended beneath a floating platform that may be vulnerable to adverse weather conditions like typhoons.

Disadvantages of the Spectral Marine Energy Convertor venturi turbine include its main pipe that may get clogged by silt over time which would lower its efficiency and its installation costs may be relatively high compared with other venturi turbine designs.

Disadvantages of the Pulse Generator reciprocating turbine are its anchoring system as well as its electromechanical sub-systems may need to be redesigned to prevent seismic damage or damage from adverse weather conditions. A disadvantage of the Tidalsails is that the system is unable to react to any changes in flow direction, so as the flow direction changes slightly the efficiency of the Tidalsails will decrease. A disadvantage of the HydroCoil system is that its variable pitch blade geometry would be relatively expensive to manufacture compared to other fixed pitch turbine blade designs.

Underwater turbines in general can be hazardous to fish or other mammals that use river, estuary and ocean currents for migration, feeding, or breeding. The high construction and maintenance costs associated with undertaking large scale underwater turbine projects in challenging physical environments are also a potential deterrent to the widespread deployment of tidal power systems. Questions also remain on the long-term impact of underwater turbines and barrages on ecosystems, as well as on recreation and tourism in a particular location.

For tidal current turbines to be a viable means of generating electricity, a predictable current of at least 2 m/s (3.9 knots) is required which may restrict the deployment of many types of underwater turbine. A disadvantage of tidal barrages is their environmental impact and their large capital costs. The biggest environmental impact is due to the fact that a dam is essentially being placed across the entire mouth of a bay which will undoubtedly impact marine life, tidal flow, and sediment transport. While there are few tidal barrages available in order to do a detailed analysis of their environmental impact, the impact of the La Ranee tidal barrage is well documented. The entire estuary was completely closed off from the ocean for 2-3 years during construction and there was a long recovery period before a new equilibrium was achieved. Other negative consequences of constructing the La Ranee tidal barrage was a reduction of inertial area, slower currents, reduced salinity ranges, and changes in the characteristics of the bottom water, which all greatly affected the marine life.

Tidal power plants have relatively high upfront costs needed for construction, and therefore lack cost-competitiveness on the global energy market. Another disadvantage of underwater turbines in general is that they are usually located in remote locations which means that the electricity transmission cable installation and transmissions costs can be difficult and expensive.

To overcome the problems described previously for existing types of underwater electricity generating turbines, it would be beneficial to provide a new concept in underwater electricity generating turbine which we will describe here called a low cost underwater turbine.

The low cost underwater turbine is designed to have low manufacturing costs, as the underwater turbine blades, ducting and augmenter are all made from low cost steel flat plate that is twisted to form blades and curved and folded to produce the ducting and augmenters. By comparison, existing underwater turbines use aerofoil cross-section blades, ducting and augmenters which are much more expensive to manufacture.

The low cost underwater turbine is also designed to have lower installation costs compared to existing designs of underwater turbines, as it does not require expensive foundations in river, estuary or sea beds. Instead low cost anchors and anchor cables are used to securely locate the low cost underwater turbine in place.

The low cost underwater turbine also features lower cost to manufacture torpedoshaped buoyant pontoons which are designed to minimise hydrodynamic and aerodynamic drag, so making the above water level structures of the low cost underwater turbine inherently resilient to adverse weather conditions.

The low cost underwater turbine is designed to have lower maintenance life-time costs compared to existing designs of underwater turbines, as it employs buoyant pontoons and an elevatable underwater turbine unit that can be lowered and raised for easier, quicker, cheaper in-situ maintenance purposes.

Our low cost underwater turbine will now be described in more detail with reference to Figures 1-4.

Figure 1 - Isometric projection of the low cost underwater turbine.

Figure 2 - Front view of the low cost underwater turbine from Figure 1.

Figure 3 - Side view of the low cost underwater turbine from Figure 1.

Figure 4 - Cross-sectional side view of the low cost underwater turbine generator and augmenters from Figure 1.

An isometric view of the low cost underwater turbine 1 is shown in Figure 1 and a front view of the low cost underwater turbine 1 is shown in Figure 2.

The low cost underwater turbine 1 has an outer augmenter 2, 3,4 that has a cone 2 connected to a central cylinder 3 and then another cone 4. The cone 2, central cylinder 3 and cone 4 are all manufactured from steel plate rolled and welded into shape, eliminating the need for much more expensive aerofoil cross-section augmenters used on other underwater turbines. The central cylinder 3 supports the inner two-part turbine duct 5, 43 using support vanes 12A, 12B, 12C, and there is a clearance gap 6 between the central cylinder 3 and the inner two-part turbine duct 5. Three support vanes 7A, 7B, 7C are equi-distantly positioned 120 degrees apart from each other and interconnect the half of the two part turbine duct 5 to the central support bearing 8. A turbine support shaft 9 is supported by the central support bearing 8 and the turbine support shaft 9 supports and passes through the centre of the turbine hub 10. Turbine blades 11A, 11B, 11C, 11D, 11E, 11F are attached to the turbine hub 10. Unlike other underwater turbines, the turbine blades 11A, 11B, 11C, 11D, 11E, 11F do not have expensive to manufacture aerofoil cross-sections and are instead manufactured from flat metal plates which are twisted about their inner and outer edges. To prevent foreign object ingestion into the open circular entrance of the cone 2, a conical mesh 13 is secured to the lip of the cone 2 with a releasable attachment ring 14.

To allow the underwater turbine 1 to be maintained as easily as possible, the cone 2, central cylinder 3, cone 4, two part turbine duct 5,43 support vanes 7A, 7B, 7C, central support bearing 8, turbine support shaft 9, turbine hub 10, turbine blades 11A, 11B, 11C, 11D, 11E, 11F, support vanes 12A, 12B, 12C, conical mesh 13 and releasable attachment ring 14, can all be raised above the water level 33 and below the water level 33 towards the river/estuary/sea bed 34 using actuators 15,15A, 16, 17, by actuating the actuators 15,15A, 16,17 that interconnect the cones 2,4 with the vertical support rails. The actuators 15,15A, 16,17 may be wheeled bogies that can be powered by electric motors, hydraulic cylinders or cable winches. Electrical power generated by the underwater turbine is fed through an armoured power cable 22. Load bearing support arms 23,24, interconnect the tops of the pontoons 31, 32 and ensure that the pontoons are rigidly separated from one another, essential to allow the low cost underwater turbine to survive adverse weather conditions that it will be subjected to throughout its expected life-time of over 20 years.

The low cost underwater turbine 1 uses two semi-submersible buoyant pontoons 31, 32 to ensure that the underwater turbine 1 floats in the water 33 it is located in, whether that be a river, estuary or sea. Locked attachment fittings 27, 28, 29, 30, are used to interconnect the four vertical support rails 18,19,20, 21 to the two buoyant pontoons 31, 32. To ensure that the underwater turbine 1 remains in place in a river, estuary or the sea, four anchors 36A, 36B, 36C, 36D are connected via four anchor cables 35A, 35B, 35C, 35D to the two semi-submersible buoyant pontoons 31, 32.

The four anchors 36A, 36B, 36C, 36D will embed themselves in the river, estuary or sea bed 34, and also minimise the installation costs of this low cost underwater turbine 1 compared to other underwater turbines that often require expensive to construct and install foundations that are embedded in the river, estuary or sea-bed 34. The four anchors 36A, 36B, 36C, 36D also reduce the environmental impact of installing the low cost underwater turbine 1 shown in Figure 1 and allow the low cost underwater turbine 1 to be installed as rapidly and cheaply as possible in its desired location.

The low cost underwater turbine 1 will be aligned to the tidal flow and currents 37 of the water 33 that it is located in, and as the low cost underwater turbine 1 is bidirectional in design, it will be able to generate electricity as the predictable tide comes in and goes out. In order to maintain the position of the underwater turbine 1 in the river, estuary or sea it is located in as the water 33 level rises and falls daily, it may be desirable to maintain the tension in the four anchor cables 35A, 35B, 35C, 35D using anchor cable tensioner units 38, 39,40,40A, located within the floating pontoons 31, 32, as shown in Figure 2. The anchor cable tensioner units 38, 39,40, 40A, could consist of winding reels that are spring loaded to ensure that the tension in the four anchor cables 35A, 35B, 35C, 35D are maintained over time.

Figure 3 and Figure 4 show side views with hidden details of the low cost underwater turbine 1 shown in Figurel and in Figure 2.

The low cost underwater turbine 1 has an outer augmenter 2, 3, 4 that has a cone 2 connected to a central cylinder 3 which is also connected to another cone 4. The cone 2, central cylinder 3 and cone 4 are all manufactured from plate steel and rolled and welded into shape, eliminating the need for much more expensive aerofoil cross-section augmenters that are used on other underwater turbine designs. The central cylinder 3 supports the inner two part turbine duct 5,43 using support vanes 12A, 12B, 12C and there is a clearance gap 6 between the central cylinder 3 and the inner two part turbine duct 5,43. Three support vanes 7A, 7B, 7C are equi-distantly positioned 120 degrees apart from each other and interconnect the turbine duct 5 to the central support bearing 8. An additional three support vanes 44A, 44B, 44C are equi-distantly positioned 120 degrees apart from each other and interconnect the turbine duct 43 to the central support bearing 45. A turbine support shaft 9 is supported by the two central support bearings 8, 45 and the turbine support shaft 9 supports and passes through the centre of the turbine hub 10. Turbine blades 11A, 11B, 11C, 11D, 11E, 11F are attached to the turbine hub 10. Unlike other underwater turbines, the turbine blades 11 A, 11B, 11C, 11D, 11E, 11F are not expensive to manufacture aerofoil cross-sections, and are instead manufactured from flat metal plates which are twisted about their inner and outer edges. As the low cost underwater turbine 1 is designed to be bi-directional and operate when the tidal flow of water 37 is going in and out, to prevent foreign object ingestion into the open circular entrance of the cones 2,4, conical meshes 13,41 are secured to the lip of the cone 2 with a releasable attachment ring 14. To prevent foreign object ingestion into the open circular entrance of the cone 4 a second conical mesh 41 is secured to the lip of the cone 4 with a second releasable attachment ring 42.

To allow the low cost underwater turbine 1 to be maintained as easily as possible, the cone 2, central cylinder 3, cone 4, two part turbine duct 5,43, support vanes 7A, 7B, 7C, 44A, 44B, 44C, central support bearings 8,45, turbine support shaft 9, turbine hub 10, turbine blades 11A, 11B, 11C, 11D, 11E, 11F, support vanes 12A, 12B, 12C, conical meshes 13,41 and the two releasable attachment rings 14,42 can all be raised above the water level 33 and below the water level 33 towards the river, estuary or sea bed 34 by actuating the actuators 15,15A, 16,17 that interconnect the cones 2,4 with the vertical support rails 18,19,20,21. The actuators 15,15A, 16,17 may be wheeled bogies that can be powered by electric motors, hydraulic motors or cable winches. Electrical power generated by the low cost underwater turbine is fed through an armoured power cable 22. Load bearing support arms 23, 24 interconnect the tops of the floating pontoons 31, 32 and ensure that the floating pontoons are rigidly separated from one another.

The low cost underwater turbine 1 uses floating pontoons 31, 32 to ensure that the low cost underwater turbine 1 floats in the water 33 it is located in, whether that be a river, estuary or sea. Fixed attachment fittings 27,28, 29, 30 are used to interconnect the four vertical support rails 18,19, 20,21 to the floating pontoons 31, 32. To ensure that the low cost underwater turbine 1 remains in place in a river, estuary or the sea, four anchors 36A, 36B, 36C, 36D are connected via four anchor cables 35A, 35B, 35C, 35D to the floating pontoons 31, 32. The four anchors 36A, 36B, 36C, 36D will embed themselves in the river, estuary or sea bed 34, and also help to minimise the installation costs of this low cost underwater turbine 1 compared to other underwater turbine designs that require expensive to construct and install foundations that are embedded in the river, estuary or sea-bed 34. The four anchors 36A, 36B, 36C, 36D also reduce the environmental impact of installing the low cost underwater turbine 1 and allow the low cost underwater turbine 1 to be installed as rapidly and cheaply as possible in its desired location.

The low cost underwater turbine 1 will be aligned to the tidal flow and currents 37 of the water 33 that it is located in and as the low cost underwater turbine 1 is bidirectional in design it will be able to generate electricity as the predictable tide comes in and goes out. In order to maintain the position of the low cost underwater turbine 1 in the river, estuary or sea it is located in as the water 33 level rises and falls daily, it may be desirable to maintain the tension in the four anchor cables 35A, 35B, 35C, 35D using anchor cable tensioner units 38, 39,40,40A located within the floating pontoons 31, 32. The anchor cable tensioner units 38, 39,40, 40A could consist of winding reels that are spring loaded to ensure that the tension in the four anchor cables 35A, 35B, 35C, 35D are maintained over time.

Figure 4 shows a more detailed side cross-sectional view of the low cost underwater turbine 1.

The low cost underwater turbine 1 has an outer augmenter 2, 3,4 that has a cone 2 connected to a central cylinder 3 and another cone 4. The cone 2, central cylinder 3 and cone 4 are all manufactured from plate metal and rolled and welded into shape, eliminating the need for much more expensive aerofoil cross-section augmenters used on other underwater turbine designs. The central cylinder 3 supports the inner two part turbine duct 5, 43 using support vanes 12A, 12B, 12C, and there is a clearance gap 6 between the central cylinder 3 and the inner two part turbine duct 5, 43. Three support vanes 7A, 7B, 7C are equi-distantly positioned 120 degrees apart from each other and interconnect the turbine duct 5 to the central support bearing 8. Another set of three support vanes 44A, 44B, 44C are equi-distantly positioned 120 degrees apart from each other and interconnect the turbine duct 43 to the central support bearing 45. A turbine support shaft 9 is supported by the two central support bearings 8,45 and the turbine support shaft 9 supports and passes through the centre of the turbine hub 10. Retaining collars 48A, 48B ensure that the turbine support shaft 9 securely rotates with the turbine hub 10. The roots of the turbine blades 11 A, 11B, 11C, 11D, 11E, 11F are securely interconnected with the turbine hub 10 using streamlined blocks 52A, 52B, 52C, 52D, 52E, 52F. The tips of the turbine blades 11 A, 11B, 11C, 11D, 11E, 11F are securely interconnected with the magnet support ring 46 using streamlined blocks 53A, 53B, 53C, 53D, 53E, 53F.

The magnet support ring 46 encircles the turbine blades 11 A, 11B, 11C, 11D, 11E, 11F and the magnet support ring 46 sits within the central recess 54 of the inner two part turbine duct 5,43, as shown in Figure 4. The magnet support ring 46 has a C-shaped cross-section that has north pole magnets 50A, 50B, 50C, 50D, 50E, 50F, 50G, 50H, 50I, 50J, 50K, 50L, 50M, 50N, 500, 50P, 50Q, 50R embedded in its inner face closest to the tips of the turbine blades 11 A, 11B, 11C, 11D, 11E, 11F. The magnet support ring 46 has a C-shaped cross-section that has south pole magnets 51 A, 51B, 51C, 51D, 51E, 51F, 51G, 51H, 511, 51J, 51K, 51L, 51M, 51N, 510, 51P, 51Q, 51R embedded in its outer face closest to the central recess 54 of the inner two part turbine duct 5,43, as shown in Figure 4.

Located between the north pole magnets 50A, 50B, 50C, 50D, 50E, 50F, 50G, 50H, 50I, 50J, 50K, 50L, 50M, 50N, 500, 50P, 50Q, 50R and the south pole magnets 51 A, 51B, 51C, 51D, 51E, 51F, 51G, 51H, 511, 51J, 51K, 51L, 51M, 51N, 510, 51P, 51Q, 51R are coils 49A, 49B, 49C, 49D, 49E, 49F, 49G, 49H, 491,49J, 49K, 49L, 49M, 49N, 490, 49P, 49Q, 49R, 49S, 49T, 49U, 49V, 49W, 49X, 49Y, 49Z that are embedded in the coil support ring 47. The coil support ring 47 remains stationary and is securely fixed in the central recess 54 of the inner two part turbine duct 5,43. When the water flow 37 impinges on the turbine blades 11 A, 11B, 11C, 11D, 11E, 11F the turbine blades 11 A, 11B, 11C, 11D, 11E, 11F and the magnet support ring 46 are rotated about the stationary coils 49A, 49B, 49C, 49D, 49E, 49F, 49G, 49H, 491,49J, 49K, 49L, 49M, 49N, 490,49P, 49Q, 49R, 49S, 49T, 49U, 49V, 49W, 49X, 49Y, 49Z that are embedded in the coil support ring 47. This results in magnetic induction and the generated electrical current flows from the stationary coils 49A, 49B, 49C, 49D, 49E, 49F, 49G, 49H, 491,49J, 49K, 49L, 49M, 49N, 490, 49P, 49Q, 49R, 49S, 49T, 49U, 49V, 49W, 49X, 49Y, 49Z and into the power cable 22 which feeds the electricity generated by the underwater turbine 1 back to shore.

Unlike other underwater turbines, the turbine blades 11 A, 11B, 11C, 11D, 11E, 11F do not have expensive to manufacture aerofoil cross-sections and are instead manufactured from flat metal plates which are twisted about their inner and outer edges. As the low cost underwater turbine 1 is designed to be bi-directional and operate when the tidal flow of water 37 is going in and out, to prevent foreign object ingestion into the open circular entrance of the cone 2 a conical mesh 13 is secured to the lip of the cone 2 with a releasable attachment ring 14. To prevent foreign object ingestion into the open circular entrance of the cone 4 a conical mesh 41 is secured to the lip of the cone 4 with a releasable attachment ring 42.

As an example, the low cost underwater turbine 1 has an outer augmenter 2, 3,4 that has cones 2, 4 that varies from an outer diameter of 6.6 metres to an inner diameter of 5.5 metres and is manufactured from rolled mild steel plate 12mm thick. The cones 2, 4 are connected to a central cylinder 3 that is 5.5 metres in outer diameter, 2 metres wide and is 12mm thick. The cone 2, central cylinder 3 and cone 4 are all manufactured from plate metal and rolled and welded into shape, eliminating the need for much more expensive aerofoil cross-section augmenters used on other underwater turbine designs described previously. The central cylinder 3 supports the inner two part turbine duct 5, 43 that has an outer diameter of 4 metres using support vanes 12A, 12B, 12C, that are each 0.75 metres long and there is a clearance gap 6 between the central cylinder 3 and the inner two part turbine duct 5,43 of 0.75 metres. Three support vanes 7A, 7B, 7C approximately 1.8 metres long are equi-distantly positioned 120 degrees apart from each other and interconnect the turbine duct 5 to the central support bearing 8. Another set of three support vanes 44A, 44B, 44C approximately 1.8 metres long are equi-distantly positioned 120 degrees apart from each other and interconnect the turbine duct 43 to the central support bearing 45. A turbine support shaft 9,2 metres long and 0.1 metres in diameter is supported by two central support bearings 8,45 and the turbine support shaft 9 supports and passes through the centre of the turbine hub 10 that is approximately 1.5 metres long and 0.6 metres diameter. Retaining collars 48A, 48B ensure that the turbine support shaft 9 securely rotates with the turbine hub 10. The roots of the turbine blades 11 A, 11B, 11C, 11D, 11E, 11F are securely interconnected with the turbine hub 10 using streamlined blocks 52A, 52B, 52C, 52D, 52E, 52F. The tips of the turbine blades 11 A, 11B, 11C, 11D, 11E, 11F are securely interconnected with the magnet support ring 46 that has an outer diameter of 3.4 metres and is 0.5 metres wide, using streamlined blocks 53A, 53B, 53C, 53D, 53E, 53F. The magnet support ring 46 encircles the turbine blades 11 A, 11B, 11C, 11D, 11E, 11F that are each approximately 1.2 metres long and 0.4 metres wide, and the magnet support ring 46 sits within the central recess 54 of the inner two-part turbine duct 5,43, as shown in Figure 4, that is approximately 1.8 metres wide and has an outer diameter of 4 metres. The magnet support ring 46 has a C-shaped cross-section that has north pole magnets 50A, 50B, 50C, 50D, 50E, 50F, 50G, 50H, 50I, 50J, 50K, 50L, 50M, 50N, 500, 50P, 50Q, 50R embedded in its inner face closest to the tips of the turbine blades 11 A, 11B, 11C, 11D, 11E, 11F. The magnet support ring 46 has a C-shaped cross-section that has south pole magnets 51 A, 51B, 51C, 51D, 51E, 51F, 51G, 51H, 511, 51J, 51K, 51L, 51M, 51N, 510, 51P, 51Q, 51R embedded in its outer face closest to the central recess 54 of the inner two-part turbine duct 5,43, as shown in Figure 4.

Located between the north pole magnets 50A, 50B, 50C, 50D, 50E, 50F, 50G, 50H, 50I, 50J, 50K, 50L, 50M, 50N, 500, 50P, 50Q, 50R and the south pole magnets 51 A, 51B, 51C, 51D, 51E, 51F, 51G, 51H, 511, 51J, 51K, 51L, 51M, 51N, 510, 51P, 51Q, 51R are coils 49A, 49B, 49C, 49D, 49E, 49F, 49G, 49H, 491,49J, 49K, 49L, 49M, 49N, 490,49P, 49Q, 49R, 49S, 49T, 49U, 49V, 49W, 49X, 49Y, 49Z that are embedded in the coil support ring 47, that has an outer diameter of 3.6 metres and is 0.5 metres wide. The coil support ring 47 remains stationary and is securely fixed in the central recess 54 of the inner two-part turbine duct 5, 43. When the water flow 37 impinges on the turbine blades 11 A, 11B, 11C, 11D, 11E, 11F the turbine blades 11 A, 11B, 11C, 11D, 11E, 11F and the magnet support ring 46 are rotated about the stationary coils 49A, 49B, 49C, 49D, 49E, 49F, 49G, 49H, 491,49J, 49K, 49L, 49M, 49N, 490,49P, 49Q, 49R, 49S, 49T, 49U, 49V, 49W, 49X, 49Y, 49Z that are embedded in the coil support ring 47. This results in magnetic induction and the resultant current flows from the stationary coils 49A, 49B, 49C, 49D, 49E, 49F, 49G, 49H, 49I, 49J, 49K, 49L, 49M, 49N, 490, 49P, 49Q, 49R, 49S, 49T, 49U, 49V, 49W, 49X, 49Y, 49Z and into the power cable 22 which feeds the electricity generated by the low cost underwater turbine 1 back to shore.

For this example we have used 18 north pole and 18 south pole magnets and 26 interconnected stationary coils, but other ratios of north and south poles rotating about a different number of stationary coils is possible dependent on the size and electrical generating capacity of the low cost underwater turbine 1 required for a particular application. It is estimated that this low cost underwater turbine 1 design in an average water flow of 3.5 knots will generate 125kW of electricity at 415 Volts and it is estimated that it will be half the cost of existing underwater turbine designs to manufacture, install and maintain, thereby increasing the economic viability of this low cost underwater turbine 1 design to diverse locations globally.

Claims

1. A low cost underwater turbine generator for generating electrical power from water flow, comprising: (a) floating pontoons with anchor cable tensioner units mounted within; (b) anchors attached to anchor cables and attached to floating pontoons; (c) a plurality of actuators to lift and lower the underwater turbine above and underwater for ease of maintainability; (d) ducting made from flat plate that is formed into a cylindrical shape; (e) augmenters made from flat plate that are formed into a nozzle shape; (f) a plurality of blades made from flat plate twisted along their length; (g) the roots of the plurality of blades are securely attached to a rotatable hub; (h) the tips of the plurality of blades are securely attached to a magnet support ring that has a plurality of north pole magnets and south pole magnets inset in the magnet support ring; (i) the magnet support ring rotates about a stationary coil support ring that has a plurality of coils inset in it that are interconnected with one another and are attached to a power cable that goes to an onshore power distribution system; (j) a two-part ducting securely holds the coil support ring about the rotating magnet support ring and the rotating plurality of blades; (k) support vanes keep the ducting and the two-part ducting separated; (l) support vanes support bearings that allows bi-directional rotation of the rotatable hub, the hub shaft, the plurality of blades and the magnet support ring.

2. The apparatus according to Claim 1 wherein said plurality of blades are symmetric twisted parallel cross-section blades.

3. The apparatus according to Claim 1 wherein the ducting is a parallel-sided cross-section cylinder.

4. The apparatus according to Claim 1 wherein the augmenters are parallelsided cross-section cones set at 15 degrees to the water flow direction.

5. The apparatus according to Claim 1 wherein the blades, ducting and augmenter are made from plates of metal or composite material.

6. The apparatus according to Claim 1 wherein a releasable mesh is fitted to the open faces of the augmenters to minimise foreign object ingestion into the apparatus.

7. The apparatus according to Claim 1 that has lower manufacturing costs than other underwater turbines as flat plates of material are used, none of the components have aerofoil cross-sections.

8. The apparatus of Claim 1 that has lower installation costs than other underwater turbines as low cost anchors and anchor cables are used to anchor the apparatus to a river, estuary or sea bed.

9. The apparatus of Claim 1 that has lower maintenance costs than other underwater turbines as the apparatus can be raised above the water level to allow easier access and maintenance.

10. The apparatus of Claim 1 that has floating pontoons that are relatively cheap to manufacture and also robust enough to withstand adverse weather conditions.