Patent Application
20150014996
The invention pertains to underwater energy plants utilizing water movement due to e.g. waves, tide or stream. The invention also relates parts of such a plant, namely an underwater wing for capturing energy of water movement, apparatus to convert the mechanical energy to electrical energy, and a connector for transfer-ring the electrical energy.
A prior art solution for providing a wave energy plant is disclosed in document WO2004/097212. The wave energy plant has two or more production units and the water mass of the water basin is adapted to actuate production units or their parts submersed at the bottom of the water basin. The production units are used for transforming the kinetic energy of the water mass into other form of energy like electric energy, mechanical energy or pressure of an intermediate agent.
Certain problems are related to the prior art wave energy plants. Any profile in flow causes forces due to increased pressure on the flow side and decreased pressure (suction) on the other side. The suction is more important, causing typically up to ⅔ of the pressure forces. Underwater flaps as presented in WO 2004/097212 A1 utilize stagnation pressure against a plate-like body. It develops overpressure to the front/flow side of the plate but the more important suction on the opposite side does not develop effectively because there is no increased flow velocity along the opposite surface. In addition, the flow around the side edges (see 4 of the enclosed
When energy of water movement is captured to moving surfaces like planes or wings, or floating volumes like buoys, there is a problem of very slow speed with high forces. Therefore straight drive generators would be extremely large machinery due to magnetic saturation and increase of speed is needed. This is usually provided with separate hydraulics. Current hydraulic transmission systems in bottom or intermediate water have long pipework lines with flexible hoses and several connectors and valves. This causes following problems:
The flow resistance heats up the hydraulic fluid which needs to be cooled in separate coolers or cooling lines which in turn add more flow resistance to the system.
Increased flow resistance cuts the system's ability to react to and capture transient energy peaks. Dimensioning according to these peaks would make system oversized for average use and with average duty dimensioning pressure has to be released with pressure limiting valves thus loosing provided energy.
Long lines make efficient use of hydraulic accumulators difficult.
All components and lines also add space requirements and size, thus increasing costs.
Generator systems regularly stopping and restarting with waves cause harmful peaks to mains network lowering the usability of entire plants.
The underwater electric connections are done with technology known from dry environment and they are therefore impractical in underwater environment. They are also impossible to connect/disconnect while generators are running. Making high power connections in wet environment by divers, remotely operated underwater vehicles or other remote equipment is also too risky because of possible electric leaks and shortages. Therefore replacing non-functional units is very costly and requires shutdown of entire plant.
As a consequence, the systems are very difficult to maintain on site as would be preferred.
The object of the invention is to provide new solutions for providing an energy plant and parts of an energy plant for utilizing water movement, with which the problems of the prior art energy plants can be avoided or reduced.
According to one aspect of the invention the object is achieved with an underwater wing of an energy plant for capturing energy from water movements into reciprocating motion of the wing, which is characterised in that the wing has a non-planar profile. The wing profile has preferably such a form that high lift with low friction is achieved.
According to another aspect of the invention the object is achieved with a converter for converting mechanical energy into electrical energy in an energy plant utilizing water movement, which converter is characterised in that the converter is a hinge-type converter comprising a cover and a shaft within the cover, which shaft and cover can rotate in relation to each other, the converter further comprising:
According to further aspect of the invention the object is achieved with a connector for transmission of electrical energy in underwater environment, which connector is characterised in that the connector comprises means for transferring electrical energy using magnetic induction between two halves of the connector, wherein the connector has a ferromagnetic core, which is split into two parts, one in each of the connector halves, which are at least partially closed in watertight housings.
According to further aspect of the invention the object is achieved with an energy plant utilizing water movements caused by water waves, tide or currents for providing electrical energy, comprising at least one energy production unit, the energy production unit comprising an underwater wing for capturing mechanical energy from water movements into reciprocating motion of the wing, and an energy converter for converting the mechanical energy into electrical energy when the underwater wing applies a rotational force to the converter, which energy plant is characterised in that the production unit comprises at least one of:
Some preferable embodiments of the invention are described in dependent claims.
According to one embodiment of the invention the profile form of the underwater wing is symmetric or asymmetric. According to a further embodiment the asymmetric wing profile has two leading edges mirrored as this structure is preferably used in wave energy plants where the flow has reciprocating direction. A symmetric wing profile is preferably used in tide or river streams where the flow direction is constant for a long time and the reciprocal movement of the wing is achieved by adjusting the angle of attack by turning the wings around their support axis, for example.
The wing preferably has a form where water flow causes forces according to reaction principle, as known from e.g. reaction turbines. Such a wing has a profile in which a flowing water causes reaction forces that are larger than action forces, which are known from e.g. impulse turbines. More particularly, wing profiles of the plant preferably have such forms and are in such positions that the force component caused by the water flow on the wing profile is smaller in the direction of the of the water flow than the force component in the direction which is orthogonal to the direction of the water flow. In other words, lift force caused by the water flow is higher than force caused by stagnating pressure. The form and position of the wing is preferably optimized so that the lift force provides maximum energy from the water flow with minimum drag. In another embodiment of the invention the surface angle of attack of the wing is adjustable by turning it around support axis.
The wing is preferably arranged to provide reciprocating movement in a direction which is closer to a plane which is orthogonal to the water flow than to the direction of the water flow. Accordingly, the rotating axis of the wing has a direction which is closer to the direction of the water flow than to a plane which is orthogonal to the water flow. Most preferably, the wing moves in a plane which is orthogonal to the water flow direction and the axis of rotation has the direction of the water flow.
In one embodiment of the invention the converter has either the cover or shaft rotationally fixed and the other part rotating. In another embodiment the converter has a connection for an underwater wing for using water movement to cause rotating force to the hinge-type converter. In a further embodiment the converter has means for turning a wing to a preferred position.
According to one embodiment the converter has hydraulic transmission comprising a high pressure accumulator without pipework built into the shaft to enable receiving high energy peaks and to regulate power production. According to another embodiment the converter a hydraulic transmission comprising low pressure accumulator keeping positive pressure in the system.
In one embodiment the converter has mechanical transmission, which comprises one or more epicyclic gear stages. In a further embodiment the converter is autonomous and has a bilge pump, a sealing flushing pump and/or a hydraulic fluid return pump. In another embodiment the converter is tethered and has external hydraulic fluid recirculation with filtering and leak removal.
In one embodiment of the invention the converter is remote controlled.
According to one embodiment the housings of inductive connector halves are be fixed together in coupling the connector. In a further embodiment the connector is rated for higher frequency than mains frequency.
In one embodiment of the invention the energy plant comprises several adjacent production units, which have underwater wings with asymmetric profiles, wherein the profiles are installed right handed or left handed in relation to the water flow direction, and the underwater wings of two successive production units are opposite handed.
In a further embodiment the converters of the production units are attached to a non-rotating foundation giving support to the stationary part of converter at the bottom, submerged or above the water surface.
In one embodiment of the invention actuator surface angle of attack is adjustable by turning it around support axis. In a further embodiment the wing profiles are in such a position that the wing profile forces are caused by pressure differences caused by flow velocity differences on different sides of the profile. The flow velocity is preferably higher at the back side of the wing than at the front side of the wing, seen from the direction of coming water flow.
In one embodiment of the invention the actuator is turned around its support axis between two positions, a first position is used for the movement of the actuator to a first direction and the second position is used for the movement of the actuator to a second, opposite direction, whereby energy of a stream flowing in constant direction can be utilized. This way the inventive solution can be used in tide and river streams, for example.
In the following the invention is described with help of the enclosed drawings, in which:
The wing according to the inventive embodiment includes more efficient actuator surfaces. It is a profile turned approximately along the flow 1 caused by e.g. waves 2, tide or river, to generate forces with both the overpressure and suction on different sizes of the profile. The angle of attack is preferably adjustable, see 6 in
As generally known, majority of pressure induced forces develop at the leading half of any profile. Therefore, one embodiment of the profile according to the invention has two mirrored leading edges.
The wing profile can be symmetric, sides being mirror images of each other as in profile 7. Opposite ends can have different shapes according to flow conditions in each direction. This solution is preferred for constant or long term flow from same direction when oscillating movement is caused by adjusting the angle of attack between two positions: a first position is used for providing movement of the wing in a first direction, and a second position is used for providing movement of the wing in a second, opposite direction. This way it is possible to use the inventive solution in tide and river stream generators, for example.
The wing profile can also be asymmetric, having different shapes on left and right side as in profile 5. Opposite ends can have different shapes according to flow conditions in each direction. This solution is preferred for naturally oscillating flow like waves. A wing may also be comprised of a set of ribs instead of one uniform part.
Angle of attack can also be adjustable to maximize the rotating moment on the hinge, optimizing energy capture in different flow speeds and flow direction variations. In case of using asymmetric profiles, it is beneficial to use downstream of flow 8,
On both profiles, it should be noted that the angle of attack and profile can vary along the wing due to flow speed differences along it. The angle of attack of the wings is preferably higher near to the converter, due to the smaller speed of water flow, than at the distant end from the converter. This can be arranged in the permanent form of the wings, or dynamical control. The dynamic adjustment of the angle of attack can thus be done either by rotating the entire profile or parts of it.
On areas where average flow (constant or reciprocating) has near constant direction, the units can be mounted stationary. On areas where direction of flow can change remarkably like waves coming in due to different weather conditions in spring and autumn storms, the units can be mounted on lockable carousel foundations. Their orientation is then adjustable according to the main expected flow direction.
If average flow direction is not known, it can be measured either with external sensors and direction data being fed into the units or with local pressure or flow sensors on the wing or hinge foundation. This measurement is not essential, the units can sense average flow by searching for angle of attack which causes the wing to remain in vertical position.
In reciprocating flow, e.g. waves, the wing can be adjusted to constant angle of attack. It is however beneficial to do minor adjustments to the angle of attack during rotation, to maximize the hinge turning moment. This can be done either according to prescribed angular data or by searching for maximum moment with small temporary variations in angle of attack. The turning moment is measured from shear deformation with strain gauges on the stationary part of the hinge and/or pressure sensor on the hydraulic fluid.
In almost stationary flow, angle of attack is adjusted to both sides of neutral angle causing the wing to stand in vertical position. In this case, the angle of attack has to be changed at the end of each movement to reverse the rotation. Small adjustments to angle of attack during rotation is beneficial and will be done as in resiprocating case.
In hydraulic hinge-type converter, the shaft 22,
Low pressure volume can be arranged into the shaft 27 or around it, depending on the arrangement. Being in the shaft, the hydraulic fluid is fed to the expanding chambers 34 directly through valves 28. Low pressure volume includes also a gas bladder 29 to compensate for volume changes keeping positive pressure against surrounding water. It should be noted, that either the shaft or the cover can be the stationary member, and the other one being the rotating one.
In rotating cover arrangement, a hydraulic motor or turbine 30 running an electric generator rotor 31 can be either inside of the shaft next to the high pressure volume, or between the shaft and cover as shown. In stationary cover arrangement, the generator is preferably located between the shaft and cover, although other location, such as inside the shaft, is possible. Generator stator 32 is attached to the fixed part of hinge.
The shaft, the cover, the transmission and the generator are preferably arranged coaxial in the converter in order to facilitate the integration of the assembly.
A possible additional use for the hinge is in producing pressurized hydraulic fluid to external generation unit with local accumulators filtering the power peaks thus regulating flow. Pressure accumulators are pressurized with a fluid which boils in the functional pressure and temperature, thus keeping accumulator pressure constant. One such fluid is carbon dioxide.
Hydraulic fluid is pressurized in variable volume chambers between the shaft and cover 26,
Bilge pumping and sealing rinsing is arranged with channel, pumps and piping as in
Electricity generated with the generator is converted to DC, then chopped to suitable voltage and frequency for further transfer with inverter. External connections (electrical power line, remote sensing and controls) are attached to stationary parts of hinges.
An Inverter unit of the converter senses network frequency and phase, synchronizing output accordingly.
The apparatus can also be inverted to run the generator as a motor generating hydraulic power. With this function the flow capturing surfaces can be turned remotely down to bottom when needed, instead of letting them idle.
It must be noted that above only some embodiments of the solution according to the invention have been described. The principle of the invention can naturally be modified within the scope of protection determined by the patent claims, e.g. in details of implementation and areas of use.
It is also to be noted that the underwater wing, the hinge-type converter apparatus and the induction connector can also be applied separately and independently in different types of wave power plants.
It should further be noted that the energy plant according to the invention preferably utilizes water movements caused waves, but it may alternatively or additionally utilize water movements caused by tide, river stream etc.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20125048 | Jan 2012 | FI | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FI2013/050046 | 1/16/2013 | WO | 00 |
