Field of application

The present invention relates to the field of the offshore wind energy production; particularly the invention relates to a floating platform for a wind turbine.

Prior art

Offshore wind turbines can benefit from a more constant and undisturbed flow of air compared to on-land wind turbines. For this reason, the offshore market is experiencing a significant growth and is expected to move faster in the near future.

However, the offshore installation requires a suitable platform and the current technique of platforms for wind turbines is not fully satisfactory. The conventional platforms for wind turbines are designed on the basis of the experience gained with platforms for the oil and gas industry. Nevertheless, the requirements of oil and gas industry are much different from those of the wind energy industry. The adaptation to wind energy application of a platform originally designed for oil/gas application results in a in massive and expensive structure increasing the capital cost and the operational cost of offshore wind farms.

In most cases, the platform of wind turbines is made of concrete and/or steel. Both materials however have disadvantages. Concrete is heavy, which complicates the transportation and deployment of the platform or parts thereof. Steel may suffer from corrosion in seawater; special steels resistant to corrosion in seawater are available but are generally expensive.

The turbine is typically mounted on a tower. The connection between the tower and the platform is another crucial feature; the prior art typically uses metal parts, such as metal flanges, with the problems outlined above of corrosion, unless very expensive materials are used. Furthermore, the conventional platforms are generally fixed platforms which are unable to rotate in order to point the turbine in the direction of the wind. This disadvantage can be obviated by installing a wind turbine with a rotating head, which however increases the cost and complication of the turbine.

EP 2 668 090 describes a floating platform which may be used for a wind turbine. It has the drawback, however, of an asymmetric position of the wind turbine with respect to the structure. A floating platform for a wind turbine is also described in US 10,598,155.

Summary of the invention

The purpose of the invention is to overcome the above disadvantages and limitations of the prior art. Particularly, the invention addresses the need to provide a floating platform for an off-shore wind turbine having a lighter structure than the current platforms, a seamless assembly, a competitive manufacturing cost, a low maintenance required. A further aim of the invention is a platform easily orientable so that the wind turbine can point to the direction of the wind to maximize the output.

The above problem is solved with a platform according to the claims.

The platform comprises a vertically arranged support and a toroidal body arranged horizontally and coaxially around said support, so that a vertical axis of the support passes through the centre of the toroidal body. The support has an upper portion with a connection seat for the tower of a wind turbine and a lower portion which extends below the toroidal body. The platform further comprises a plurality of connection arms which extends radially to connect the support to the toroidal body; at least one of the support, the toroidal body and the connection arms is made of a reinforced composite material.

The invention has, among others, the following advantages: the use of composites provides a seamless assembly of the various subparts, increasing the aesthetic appeal of the structure and reducing weak points induced by a riveted or bolted assembly. Composite materials are much lighter than steel/concrete, offering comparative advantages for the dragging from the shore to the site of installation; furthermore the installation is possible with smaller lifting equipment.

Composite materials have better environmental footprint compared to steel and concrete; particularly in maritime installation they do not corrode and do not release heavy metals and toxic chemicals to the sea. The composite structure needs much less maintenance compared to the steel/concrete counterparts.

The use of a composite (light weight) wind turbine tower can affect positively the system dynamic behaviour since the entire structure will be more flexible that the stiff metallic structures.

The axis-symmetric shape of the inventive platform with a central main cylinder surrounded by a toroidal body provides a stable buoyancy, a symmetric distribution of loads, an easy rotation of the whole structure to follow the wind. Furthermore the platform can be easily moored e.g. with a mooring line or a mooring chain connected to one of the radial arms.

The central position of the wind turbine tower is also advantageous in terms of stability and even distribution of loads. Still another interesting feature of the invention is that the tower of the wind turbine is practically an extension of the central main cylinder of the platform, which is surrounded by the toroidal element.

An aspect of the invention is also a wind turbine structure including the above described inventive platform and a turbine tower connected to the central support of the platform. In a preferred embodiment the tower and the central support are made of composite materials, and the tower is received in a seat of the central support and operatively connected, such as adhesively bonded, to said seat with no metal connection parts between the tower and the support. A further object of the invention is a system for generating electric power and green hydrogen according to the claims.

The term green hydrogen is used hereinbelow to indicate hydrogen which is produced from renewable energy sources e.g. wind.

The present invention provides a unique system that combines wind-powered hydrolysis and green hydrogen production to cover energy needs of grids or isolated areas. Particularly, the invention provides a composite platform with integrated hydrogen storage for renewable energy on demand.

The system is configured to float on a waterbody and comprises a wind turbine; a generator coupled to the wind turbine for transforming the mechanical power output by the wind turbine into electric power; an electrolyzer configured to produce green hydrogen from water using electrical power from said generator.

The system is particularly advantageous because it combines green hydrogen production and electric power generation in a single unit exploiting a renewable energy source such as wind so that no carbon dioxide is emitted into the atmosphere. The system of the invention can be connected to a local electrical grid and be used to supply electric power to isolated areas acting as an energy island.

Detailed description of the invention

The connection arms may include first connection arms which extend horizontally between the support and the toroidal body, and second connection arms which extend diagonally between the support and the toroidal body, each of said second connection arms being connected to the lower portion of the support at a connection point below the toroidal body.

Preferably the number of the first connection arms is equal to the number of the second connection arms. For example, in a preferred embodiment the number of the first connection arms is three and the number of second connection arms is three. Any of the vertically arranged support, the toroidal body and one or more of the connection arms may have a hollow structure. The tower of the wind turbine typically has a hollow structure. The outer diameter of the horizontal ring structure could be as large as 60-70 m, while the diameter of the individual toroidal body and other tubes (legs and stabilizers) can rise to 6-7 m, with wall thicknesses of a few tens of centimeters.

Another aspect of the invention is the use of a natural fibre-reinforced composite material (bio-composite).

Preferably, said bio-composite materials include hybrid glass and/or flax fabrics combined with fully recyclable thermoplastic acrylic-based composite systems obtained by using state of the art liquid thermoplastic resins and/or bio-based resin solutions and low toxicity resin solutions. A related advantage is reduction of CO2 footprint.

One or more of the vertically arranged support, the toroidal body, the connection arms and the tower of the turbine may be made of such composite material. Use of bio-composites can facilitate the use of adhesively bonded connections with the advantage of avoiding steel connections and related drawbacks such as corrosion.

A preferred feature of the invention is the use of a hybrid composite material including natural fiber and glass fiber embedded in bio-based polymer resins and low toxicity resin solutions. A related advantage is inexpensive mass production and the potential for using natural fiber composites in a hybrid configuration with glass fiber composites for better durability. Particularly preferably the composite material is a sandwich including a layer of flax fibre pultruded elements with a protective coating layer of a glass fibre. The outer layer protects the flax fibers from environmental attacks.

In a preferred embodiment the support, the toroidal body and the connection arms are all made of one or more composite material(s). It should be noted however that the inventive floating platform may also be used in combination with a conventional steel tower of a wind turbine.

Typically the vertically arranged support is cylindrical or substantially cylindrical.

The platform is preferably designed so that the buoyancy line of the platform in seawater intersects the toroidal body.

The torus is an important part of the structure. The torus can be manufactured, preferably, with the same technique described above of pultruded flax fibers internally and filament winding glass fibers externally in a sandwich configuration. Furthermore the torus may be made in segments to facilitate the transportation. On shore manufacturing close to the installation location is also possible due to the simple manufacturing methods. The torus can therefore be assembled on shore and connected to other parts of the platform such as the legs, the main cylinder and stabilizers before it is placed in the sea.

The weight of the inventive floating platform is ca. 50% less than a conventional steel platform. For example the weight of the platform is estimated less than 1500 tons compared to ca. 3000 tons of a steel platform for a 10-15 MW turbine.

The torus diameter is ca. 65 m for a 10 MW wind turbine, which is smaller than a conventional steel platform for a wind turbine of the same power.

A further aspect of the invention is that the turbine tower is connected centrally to the floating platform. Accordingly, the platform is balanced offering better stability and the entire system can rotate around a central vertical axis to follow the wind. The floating platform is substantially symmetrical around a vertical axis allowing easy repositioning to follow the wind.

The vertical cylinder of the structure, which can be termed the main cylinder, the torus and the connection arms are preferably hollow structures so that the floating platform can be regarded as a large vessel. The lower part of the main cylinder may be used for accommodation of a ballast.

A further innovation concerns the connection of the tower to the platform. In the prior art, this is usually done with a metallic flange that connects the two structural components with metallic bolts, involving the above-mentioned drawbacks of possible corrosion. In an interesting embodiment of the invention, the tower extends down to the main cylinder of the platform; the tower and the main cylinder are operatively connected, using at least one adhesive, together internally to avoid having metallic elements, thereby avoiding corrosion. Similarly, a metal-free joint can be provided between the connection arms and the main torus and/or between the connection arms and the main cylinder.

For example in a preferred embodiment the tower has a first connection part and the main cylinder has a second connection part adapted to match with said first connection part, and said first connection part and second connection part are coupled to each other and adhesively connected without metallic elements.

The hollow structure of one or more of the structural components, for example of the toroidal element and the tower, offer space for accommodation. This can be profitable for lodging maintenance workers as well as other applications of the platform. For example the platform may be equipped with hydrogen and electric energy storage stations that can be used for recharging electric vessels.

One advantageous aspect of the design of the platform of the invention foresees the use of the vast empty space, which in some embodiments may extend up to 10’000 m ³ , inside the main cylinder and/or the toroidal body and/or at least some of the arms for fluid storage, such as pressurized hydrogen storage.

Hydrogen may be stored as a liquid or a gas. The term fluid is used indifferently to indicate a liquid or a gas. Storage of hydrogen as a gas is preferred to allow storage at a relatively low pressure.

One aspect of the invention relates to the use of the platform as herein disclosed for fluid storage, such as for hydrogen storage. In addition, batteries, fuel cells and electrolysers can be housed in this space. According to a related aspect of the invention, the main cylinder and/or the toroidal body and/or at least some of the arms are configured as storage tanks for fluid storage, particularly for pressurized hydrogen storage. Advantageously, the composite materials substantially composing the structures of the platform are particularly suitable to this task, in particular as structural materials for low-pressure fluid (e.g. hydrogen) storage tanks.

Additionally or alternatively, the platform and the turbine wind structure of the invention can be adapted and configured to operate as an energy island integrating one or more of electrolysis for green hydrogen production, fluid storage and a fuel cell with wind energy. Thanks to its modular design, the ease of transportation (due to modularity and light weight) and its versatility, the platform can be utilized for providing green electricity generation in isolated/remote locations, or may operate as a green hydrogen production hub/buffer for connected systems to the hydrogen distribution network.

Interestingly, in times of excess electricity production from wind, instead of curtailing electricity as is commonly done, it is possible to use this excess electricity to produce hydrogen through electrolysis. Accordingly, in one aspect, the wind turbine structure of the invention is adapted and configured so that the wind turbine is operatively coupled with an electrolyser, so that at least part of the energy produced by the wind turbine is used by an electrolyser for water electrolysis. Most preferably, the electrolyser is located in/on the platform of the invention. Still another aspect of the invention, therefore, relates to the use of the wind turbine of the wind turbine structure for production of hydrogen by electrolysis, the wind turbine being in operative relationship to a water electrolyser. Combination of the various embodiments related to the wind turbine structure and the platform of the invention are of course envisageable.

A further aspect of the invention concerns the mooring lines of the platform. In a preferred embodiment, a mooring line includes an anchor cable which forms a loop around one arm of the platform. Preferably, the anchor cable is made of a composite material. Said mooring line, thanks to the easy coupling with the structure of the platform, offers significant advantages in terms of cost.

Another aspect of the invention is a system for generating electric power and green hydrogen comprising the above described floating platform and further comprising: a wind turbine; a generator coupled to the wind turbine and configured for transforming the mechanical power of the turbine into electrical power; an electrolyzer configured to produce green hydrogen from water using electrical power from the generator.

The wind turbine may have a tower rotationally coupled the connection seat of said floating platform.

Preferably said system comprises a hydrogen storage chamber configured for collecting hydrogen gas at a selected storage pressure. Hydrogen may be stored at a storage pressure which may be the same as, or greater than, the production pressure of said electrolyzer. The green hydrogen produced by the electrolyzer may be raised to storage pressure by a suitable compressor.

Said hydrogen storage chamber may be arranged within one of the connection arms of the platform and/or within said vertically arranged support and/or within said toroidal body of the platform. According to various embodiments, more than one hydrogen storage chamber may be provided in the above components of the platform.

The platform is configured to float on a waterbody, such as a lake or sea, particularly for offshore applications. The water for the production of green hydrogen can be taken from said waterbody. The system may include a water collection chamber and comprise a pumping apparatus configured for transferring water from the waterbody to said water collection chamber. The system of the present invention can be configured as a standalone unit so that all the electric energy produced from the generator is used for the synthesis of green hydrogen.

The system of the invention can also be connected to an electrical grid, when available. When the system is connected to a grid, a part of the power generated by the turbine can be used for the synthesis and storage of hydrogen and a remaining part can be transferred to the grid. In other words, the energy produced by the turbine can be either stored as hydrogen gas (via the conversion into electrical energy and subsequent electrolysis of water) or transferred to a grid. The amount of power stored as hydrogen gas Vs. the power transferred to the grid can be varied according to circumstances such as instant demand, capacity of the turbine to produce power, amount of hydrogen currently stored, or other parameters.

For example energy can be used to produce and store hydrogen when the output of the wind turbine is greater than an instant demand. On the contrary when the demand exceeds the output of the turbine, electric energy can be produced from the stored hydrogen for example via a fuel cell.

According to a particularly interesting application the system further comprises a control system configured to adjust the amount of electrical power which is supplied to the electrical grid and the amount of water transferred to the water electrolyzer.

The system may include a fuel cell for conversion of hydrogen into electrical energy. Accordingly, hydrogen may be used as a means for storing the energy produced by the wind turbine. This can advantageously compensate the short-term fluctuation of the wind power and stabilize the output of the system.

The system of the present invention can be used for the production of renewable energy on demand. The invention provides a wind-powered production of green hydrogen which can be conveniently stored and used for production of renewable energy on demand. Hydrogen is stored preferably as a gas. The apparatus of the invention can be configured for transferring the energy to a grid or storing energy as hydrogen according to the circumstances, for example according to the demand of energy and the instant output of the wind turbine. The apparatus can be particularly attractive for isolated areas serving as an energy island.

In some embodiments the system may include batteries as an additional means for storing electric energy.

Fig. 1 is a sketch of a wind turbine assembly including a floating platform according to an embodiment of the invention.

Fig. 2 is a detail of Fig. 1 showing the floating platform.

Fig. 3 illustrates an exploded view of pre-assembled components of a floating platform according to an embodiment of the invention.

Fig. 4 illustrates a preferred embodiment of a connection between the platform and the mooring lines.

Fig. 5 illustrates a detail of a cable attached to the platform

Fig. 6 illustrates a schematic of a system for generation of power and hydrogen in accordance with an embodiment.

Fig. 1 illustrates a wind turbine assembly including a floating platform 1 and a wind turbine 2 mounted on a tower 3.

The floating platform 1 includes a vertically arranged support in the form of a main cylinder 10 and a toroidal body represented by a main torus 11. The torus 11 is coaxial to the main cylinder 10 and has a connection seat 12 for connection with the tower 3. The main cylinder 10 has also a lower part 13 extending below the torus 11 with a lower end connection 14 for a ballast. In use, the buoyancy line is normally at the torus 11 and the lower part 13 of the torus is below the water level.

The platform 1 further comprises a plurality of connection elements which extends radially between the main support 10 and the torus 11. In the example, said connection elements include radial arms 14 and inclined arms 15.

Preferably the radial arms 14 and the inclined arms 15 are part of a V-shaped preassembled structure 16 as shown in Fig. 3. More particularly, Fig. 3 illustrates an embodiment wherein the tower 3, the main torus 11 , the main cylinder 10 and the radial arms 16 are pre-assembled elements.

A suitable mooring line may be attached to the main torus and/or to one of the arms when appropriate. The platform may also include barge-like elements to compensate tipping.

In accordance with the preferred embodiment, the main cylinder 10 and/or the torus 11 and/or at least some of the arms 14, 15 are hollow structures.

Particularly preferably, said elements are made of a composite material such as a sandwich structure including a layer of flax fibre pultruded elements with a protective coating layer of a glass fibre.

Figs. 4 and 5 disclose a mooring line 20 of the floating platform 1 . The mooring line 20 includes an anchor cable 21 and a loop 22 around one arm of the platform 1 or around the torus 11 .

Fig. 6 illustrated a system 100 for the generation of hydrogen and electric power, which may be hosted in the platform 1 as above described.

Said system 100 comprises a wind turbine 23 to transform wind power 38 into a mechanical power output 24, a generator 25 coupled to the wind turbine 23 to convert the mechanical power output 24 into electrical power 26, an electrolyzer 27 connected to the generator 25 and configured to produce hydrogen 28 from a water feed 37 using at least a portion of the electrical power output 26 of said generator 25.

The system further includes a water treatment unit 36 configured to produce the water feed 37 by purifying a water stream 29 taken from a suitable source. The water stream 29 can be for instance seawater and the water treatment unit 36 can be a desalinization unit configured to produce a water feed which is free or substantially free of sodium chloride.

The system 100 further includes a hydrogen storage unit 30 which is in communication with the electrolyzer 27, a fuel cell 32 which is in communication with the hydrogen storage unit 30, a batteries system 35 which is connected to an output of the generator 25 and to an input of the electrolyzer 27. Said hydrogen storage unit 30 may include one or more hydrogen storage chambers.

The hydrogen 28 produced by the electrolyzer 27 can be supplied to the hydrogen storage unit 30. A compressor can be also provided prior to the hydrogen storage unit 30 to store hydrogen as a compressed gas.

A hydrogen stream 31 from the storage unit 30 can be supplied to the fuel cell 32 to produce electrical power 33.

The system is connected to an electrical power grid 34 so that said grid 34 can receive electrical power 26 from the generator and/or from the fuel cell 32 and provide power to one or more utilities 39.

In operation, the electrical power 26 can be supplied to one or more of the grid 34, the batteries system 35 and the electrolyzer 27.

A control system which is not represented in the figure is used to determine the amount of power that is supplied to each of the above-mentioned units according to the circumstances such as for instant the demand of electric power of the utilities, the capacity of the wind turbine to produce power, and the amount of hydrogen currently stored.

The control system can also decide to supply the entire electrical power available to just one or some of the above-mentioned units e.g. to the electrolyzer or to the electrolyzer 27 and to the batteries system 35.

A hydrogen stream 40 from the electrolyzer and a hydrogen stream 41 withdrawn from H2 storage unit 30 can also be exported outside the plant. In some embodiments a hydrogen stream exported from the plant can be sent to local users via a distribution grid as illustrated in Fig. 6. Accordingly, a user connected to said grid may receive a hydrogen stream for local conversion into electricity with a fuel cell or for a different use. This option may be of particular interest in remote island applications.

The production of electric power 33 by the fuel cell 32 is particularly advantageous to provide electric power even when the wind power 38 is not available. Electrical power 42 can also be supplied from the batteries system 35 to the electrolyzer 27 when needed.