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Offshore wind turbines. Maintenance, repair, replacement. Recent Patents

One of most important problems of wind energy is the relatively low capacity factor, which in real practice of wind turbines rarely exceeds 30%. As a result, huge material-intensive and expensive structures of wind turbines sit idle for a considerable time without generating electricity, reducing the investment attractiveness of the industry, hindering a decrease in selling prices for electricity and limiting the competitiveness of this industry. Ensuring the maximum capacity factor of wind turbines is hampered by objective factors in the form of local natural resources, first of all, the magnitude and range of wind speed, its stability and tendency to powerful gusts. These are undoubtedly important but inevitable costs of generating electricity from wind turbines. The leading trends in the development of wind energy are the increase in the size of wind turbines and the rapid construction of wind farms in offshore zones, which allows maximum capacity factor to be achieved.

However, the maintenance of wind farms with such large structures, especially in marine areas, is a difficult technical task. Also, there is a large group of subjective factors that impede the extraction of the maximum possible capacity factor. These include, for example: ineffective equipment condition monitoring, especially remote monitoring; poor-quality maintenance; untimely delivery of component parts; suboptimal organization of transportation or repair work; lack of high-performance tools for maintenance, which leads to unexpected shutdowns of wind turbines. Solving these problems can provide additional reserves for the use of power and represents the most promising way to improve the efficiency of the wind power industry in general.

This review considers a selection of the latest inventions related to the maintenance, repair and replacement of offshore wind turbines. Among the technological operations related to offshore wind turbines, the most interesting are mounting & maintenance of blades, offshore transportation, inspection, working platforms, and robotics. The largest number of patents in recent years have been granted on topics related to mounting & maintenance of blades and inspection. The topic related to robotics also demonstrated progressive dynamics. More than a half of patents and patent applications have been granted or filed with the top three patent offices – EPO, USPTO (the United States), and CNIPA (China).

Patent leaders in this area are Vestas Wind Systems A/S and MHI Vestas Offshore Wind A/S (Denmark); Wobben Properties GmbH Siemens AG, Siemens Gamesa Renewable Energy A/S, and Senvion Deutschland GmbH (Germany); General Electric and Principle Power Inc (the United States); Mitsubishi Heavy Industries, Ltd. and Hitachi, Ltd. (Japan). Beijing Goldwind Science & Creation Windpower Equipment Co Ltd should be noted among the representatives of China.
In the vast majority of cases, the technical solutions proposed by the inventors in the patent documents were aimed at solving the problems of High OPEX / operational maintenance, repair, and replacement.

Mounting & maintenance of blades

Different methods of mounting a wind turbine blade proposed in this group of inventions include variants of craneless installation. Such technical solutions to a substantial degree allow costs related to transportation and installation of cranes to be reduced, and time for mounting/dismounting of blades to be minimized. In the selection of documents under review such technical solutions are disclosed, for instance, in the following documents:

• Core document* US9500090B2: WO2012065613A1, EP2640965A1, EP2640965B1, CN103403344A, CN103403344B, US20140010658A1;
• Core document EP1592882B1: PL213119B1, NZ541052A, KR20050096131A, CA2512168A1, BR318003B1, AU2003276272B2, AR42945A1, AU2003276272A1, BR318003A, CA2512168C, CN1742157A, CN100445551C, DE10303555A1, DE10303555B4, JP2006513356A, JP4204556B2, PL376528A1, US20060228220A1, US20090058096A1, US7785073B2, WO2004067954A1, EP1592882A1;
• Core document US8651462B2: AU2009236783A1, AU2009236783B2, CA2721676A1, CA2721676C, EP2279345A2, EP2279345B1, NL1035301C1, US20110042632A1, WO2009128708A2.

*Core document is a base document for which a complete description of the invention is available in generally-accessible patent databases.

Method for craneless wind turbine blade handling via a turbine hub / US9500090B2/ Vestas Wind Systems A/S, Hvid Nielsen Kennet / Publ. date: 22.11.2016. The invention discloses a method aimed to avoid using separate cranes or lifting mechanisms in blade dismounting process. The description and claims of the patent specify the list of technological operations, the order these operations should be performed in. The key operations are: “…releasing the blade, moving the blade to an intermediate blade position using the bolt-like extensions, attaching a lifting yoke to a number of fastening bolts in the intermediate blade position, and lowering the blade to a desired position using the lifting yoke”.

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Method for mounting a rotor blade of a wind energy installation without using a crane / US7785073B2 / WOBBEN ALOYS / WOBBEN ALOYS / Publ. date: 31.08.2010.
The patent proposes a technical solution aimed to avoid the costs-related disadvantages of using stationary cranes in blade mounting operations. The description and claims of the invention define the set of technological operations needed to achieve the stated object, and sequence of their implementation. The following key procedures should be outlined: “…extending at least one cable between a part in a hub region of the wind power installation and a bottom region of the wind power installation; coupling the rotor blade to a horizontal elongate member extending between a first winch movable along the cable and a second winch; positioning the rotor blade in a receiving device; moving the rotor blade carried by the elongated member along the cable upwardly upon mounting or downwardly upon dismantling”.

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Offshore transport

The present group of inventions includes technical solutions related to the use of specialized vessels for transportation, repair and maintenance of wind turbines in offshore areas. Sea transportation of large wind turbine structures has many distinctive aspects, while transport vessels must feature increased reliability and carry a set of specialized tools onboard to perform mounting operations. The devices and methods of their employment proposed in the inventions in most cases are aimed to reduce the costs of transportation and mounting of wind turbines. In the group of patent documents under review such solutions can be found, for instance, in the following documents:

• Core document EP2436593A1: EP2436593B1, JP5639557B2, KR101412094B1;
• Core document US8753050B2: TWI481543B, JP5373965B2, EP2416986B1, CN102548797B, CN102548797B, AU2010233708B2, CA2756158C;
• Core document US8770126B2: CA2733700C, GB2462602B, US8770126B2, KR101478397B1, JP5468072B2, EP2318701B1, CN102171446B, BRPI0917983B1;
• Core document KR20190128432A: KR102092198B1.

Examples of specific technical solutions are provided here:

Method For Installing An Offshore Wind Turbine And A Barge System / P: CA2710058C / Vestas Wind Sys As / Publ. date: 19.04.2016. The patent proposes technical solutions defining the order of installing an offshore wind turbine and a barge system, and the configuration of a barge system. In particular, the invention proposes: “…transporting barge system to the site of said offshore foundation, moving said wind turbine from said transit position to an installation position on said barge system, positioning said part of the wind turbine in relation to said foundation, and lowering the barge system in relation to the water level so that said part of the wind turbine engages with said prepared offshore foundation…”.                                                                                                                                            
Image from US20100316450A1

System for transporting and installing wind turbines on the seafloor / US9988128B2 / Ocean Shift, S.L. / Publ. date: 05.06.2018. The claims disclose the list and configuration of equipment in a system for transporting and installing wind turbines on the seafloor. The system is “…made up of a structure that has adjustable flotation capacity and is made up of two floating hulls and a series of columns onto which they are mounted with the capacity to move over the same, an upper peripheral frame and a lower peripheral frame, on which means are mounted for fastening and manipulating the wind turbines and piles and ferrules for anchoring said wind turbines to the seafloor”.

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A method for performing maintenance on a wind turbine part / US20200256320A1 / MHI Vestas Offshore Wind AS / Publ. date: 13.08.2020. The invention represents a method that allows the losses in power production of offshore wind turbine due to maintenance process be minimized. The description and claims of the patent define the list of technological procedures necessary to achieve the object, and the order these procedures should be implemented in. The following key procedures should be mentioned, for example: “…transporting an access system to a site of the offshore wind turbine, transferring the access system to a transition platform at a lower part of the offshore wind turbine, while operating the offshore wind turbine in accordance with a normal operating mode, stopping normal operation of the offshore wind turbine, performing maintenance on an outer surface of at least one wind turbine part of the offshore wind turbine, using the access system, and restarting normal operation”.
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Some methods of wind turbine component inspection can be carried out without damaging the surface of the component. This is advantageous as it can cut costs related to subsequent repair, and possibly make the process less time-consuming. In the group of documents under review such solutions can be found, for example, in the following patents and applications:

• Core document US20130235897A1: US9562870B2, JP6001540B2, FR2965353A1, FR2965353B1, WO2012041848A1, EP2622316A1, CN103154697A, CN103154697B, BR112013007550A2, JP2013542360A;
• Core document US20200025176A1: CN110735768A, GB2576976A, GB2576976B;
• Core document US20200057002A1: EP3622175A1, WO2018208320A1.

Cable-suspended Non-destructive Inspection Units For Rapid Large-area Scanning / US20200025176A1 / Boeing Co / Publ. date: 23.01.2020. The patent application discloses a device and method aimed to avoid difficult and time-consuming manual inspection of wind turbine. The claims of the patent application define the list and configuration of the system’s units, and the list and sequence of technological  operations. The key operations are: “…attaching the flexible track to the airfoil-shaped body so that the flexible track lies in a generally horizontal plane; coupling a first wheeled vehicle to the flexible track in a manner so that the first wheeled vehicle is movable along the flexible track; suspending a first scan head from the first wheeled vehicle using first and second cables; adhering the first scan head to a first non-horizontal surface of the airfoil-shaped body so that the first scan head is free to float across the first non-horizontal surface; unwinding the first and second cables until the first scan head is suspended at a first elevation”.
Image from US20200025176A1

Apparatus And Method For Non-destructive In Situ Testing Of Windmill Blades Using Penetrating Dye / US20200057002A1 / Pro Drones Usa Llc / Publ. date: 20.02.2020. The invention describes a method aimed to make the process less time consuming, costly, and less dangerous. The claims of the patent application disclose the set of technological operations procedures and the order these operations should be implemented in. The following key operations should be mentioned: “…providing at least one remotely controlled drone aircraft; applying a water soluble penetrant from said  remotely controlled drone aircraft to a test surface area of said wind turbine blade; waiting for said water soluble penetrant to substantially dry; applying a dry powder developer from said remotely controlled drone aircraft to said test surface area; waiting for said dry powder developer to substantially set; illuminating said test surface area with an ultraviolet light source from said remotely controlled drone aircraft; and photographing said test surface area from said remotely controlled drone aircraft to effect an inspection for visible latent defects”.

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Working platforms

One of the major objects in developing working platforms used in wind turbine maintenance is ensuring the maximum possible level of personnel safety. The group of inventions aimed to solve this problem is relatively extensive and includes a wide variety of technical devices and methods. In the group of patent documents under consideration such solutions can be found, for instance, in the following documents:

• Core document EP2906817A1: WO2014108216A1, US20150354233A1, CN104884789A, CN104884789B, EP2906817B1;
• Core document EP3067553A1: US20160265507A1, US9869294B2, EP3067553B1;
• Core document US8534421B2: AU2004308998A1, AU2004308998B2, EP1706636A2, EP1706636B1, NZ548485A, US20090020361A1, US20120090917A1, US8083029B2, WO2005064152A3;
• Core document US8578604B2: CA2764789A1, CA2764789C, CN102734056A, CN102734056B, EP2481912A1, EP2481912B1, US20120192400A1;
• Core document US20160068373A1: WO2014150950A4, EP2969883A2, CN105050935A, CA2867025A1, CA2867025C, CA2867001A1, CA2867001C, CA2866999A1, CA2866999C, CA2866998A1, CA2866998C, CA2849463A1, CA2849463C, US9821984B2, US20180057321A1, EP2969883B1, EP3486207A1, CN105050935B, EP3486207B1, US10435274B2.

Sicherung eines bedieners während wartung einer nabe einer windkraftanlage / en: Protection of a personnel during maintenance of a wind turbine hub / EP2906817B1 / Siemens AG / Publ. date: 27.02.2019. The patent proposes a protective device located in the rotor of a wind turbine to ensure personnel safety. “…The device has a platform with a number of standing surfaces, at least one of the standing surfaces being substantially horizontal when the safety device is used as intended, and also having a securing system for securing the platform to a hub of the rotor and/or to an inner face of a rotor housing of the rotor…”.

                                                                                                                                    Image from US20150354233A1

Safety structure for performing servicing operations in a wind turbine and method for its installation / US9869294B2 / GE Renewable Technologies Wind B.V., ALSTOM RENEWABLE TECHNOLOGIES / Publ. date: 16.01.2018. The present invention discloses an original safety structure that includes a set of specialized rod-shaped elements, safety bars, bar locking mechanisms. The claims specify a list of units and tools used, their configuration, and a method for installing and using the device. “…The safety structure comprises temporarily deployable safety bars that can be attached to a support member associated with at least one of a wind turbine hub, a wind turbine blade, a wind turbine root section, a wind turbine yaw mechanism, a wind turbine tower base, a wind turbine foundation, and a wind turbine nacelle…”.

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Various robotic devices and methods for use thereof proposed in the present group of inventions allow different repair and maintenance procedures to be performed, including those directly on wind turbines. In particular, there are patented variants of wind turbine component inspection by the means of controlled robotic arms, performing cleaning or dosed application of materials on surfaces, capturing and moving individual elements of the structure, controlled bolt tightening, etc. In the selection of documents under review such technical solutions are disclosed, for instance, in the following documents:

•   Core documents US20150028610A1: US9321613B2, EP2832675A1, CN104340861A, EP2832675B1, CN104340861B;
• Core documents US20150267688A1: WO2014059964A1, EP2908987A1, DE112013005873A5, CA2888017A1, AU2013332141A1, AU2013332141B2, US9790923B2, US9915246B2, US20180128248A1, EP2908987B1;
•  Core documents WO2019068299A1: DK201770746A1, CN111263856A, DK180161B1, EP3692260A1, US20200238324A1;
• Core documents US20130289769A1: EP2653273A1, KR20120067562A, KR101194576B1, WO2012081793A1, JP2014506968A, JP5822409B2, CN103534068A, CN103534068B;
• Core documents WO2013113494A3: DE102012001725A1, EP2896823A1, EP2809946A2, US20150090504A1, US9327784B2, EP2809946B1, EP2896823B1.

Robot for inspecting rotor blades of wind energy installations / EP2908987B1 / Krampe Nina Katharina, Krampe Timothy / Publ. date: 13.12.2017. The invention discloses a drone-robot for wind turbine blade condition control: “…a frame construction includes an inner opening surrounding a rotor blade during use and a plurality of propellers for a vertical flying movement of the robot. A rotor blade state detection system disposed at the frame construction detects the state of the rotor blades. Preferably a power and/or data cable is provided for connecting the robot during use to a control and evaluation station provided, for example, on the ground…”.
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Cleaning And Inspecting Apparatus For Wind Turbine And Related Methods / US8641374B2 / Byreddy Chakradhar, Bowyer Robert, Sareen Ashish, Vestas Wind Sys As / Publ. date: 04.02.2014. Equipment and methods for cleaning and inspection of wind turbines proposed in the present invention allow these important operations to be performed directly on the wind turbine by the means of a robotic  arm: “…A maintenance apparatus is provided for use with a wind turbine that has a tower, a hub supported by the tower, and a plurality of blades extending outwardly from the hub. The maintenance apparatus has a mounting element that is configured to be secured to the tower and to be selectively movable along the length thereof. A robotic arm is coupled to the mounting element, and a blade-engaging device is coupled to the robotic arm and is configured to engage one of the blades to effect a maintenance task thereon”.
Image from US8641374B2

CLIMBING ROBOT FOR MASTS /US9327784B2 / Fachhochschule Aachen, Bagheri Mohsen, Dahmann Peter / Publ. date: 03.05.2016. A robotic device proposed in the invention allows elements of a wind turbine to be lifted and lowered down without using large-scale cranes, and thus the problem of timely maintenance operations to be solved, while reducing operational costs. The key element of the invention is: “…A mast-climbing robot has first and load-bearing assemblies, at least one linear actuator connected between the assemblies for changing their vertical spacing, and a respective clamp on each load-bearing assembly that can secure the respective load-bearing assembly on the mast and release the respective load-bearing assembly therefrom…”.
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A complete version of the databases WIND ENERGY. Offshore Wind Turbine and WIND ENERGY. Maintenance, repair and replacement can be found at