The design of a new solution from the early stages to the fully commercial units needs to achieve and overtake the different technology readiness levels (TRL). The floating platforms for offshore wind turbines (FOWTS) are not an exception. Moreover, there are some handicaps for these technology solutions like the high initial investment costs, the low number of available offshore wind turbines for full scale prototypes, or the big differences of the construction and installation between the initial smaller prototypes and the final designs in a commercial stage.
Windcete is a monolithic concrete spar platform, including both the tower and the floater in a unique concrete member of which a proof of concept was developed in the KIC Innoenergy AFOSP project. The monolithic characteristic means that joints are avoided, thus the fatigue resistance is increased since weak points are driven out. The whole structure is in compression state by the use of active reinforcement, and it is designed to avoid traction at any point during the span life of the platform. Furthermore, the use of concrete allows to reduce the Capital Expenditure (CAPEX) because its low cost, and also reduces the Operational Expenditure (OPEX) due to the its high resistance against the marine environment.
This article highlights the scalability of the concept through the main dimensions, construction and installation processes for three different Windcrete units. These units are predesigned for different TRL to compare the evolution from an initial prototype to commercial units for a wind farm.
A 3D aero-hydro-servo-elastic coupled finite element method (FEM)
numerical model in time domain for structural analysis has been
developed at the UPC-BarcelonaTech (FloaWDyn). The code integrates
the environmental forces from the waves and currents as well as the
aerodynamic loads, including the wind turbine, and the mooring
system. As a part of the FloaWDyn numerical code validation, in the
paper is presented the calibration of the numerical model accordingly to
the DeepCwind experimental scaled model, as well as some simulations
of the Phase 2 of the OC5 project, which include the free decay tests
and some coupled wind and waves tests. The simulations are finally
compared to the results obtained in the experimental campaign at
La presente invención se refiere, en estructuras flotantes de soporte de turbinas eólicas, a la materialización mediante una lámina de hormigón pretensado de la zona de transición entre la torre, de menor diámetro, y el flotador de hormigón de mayor diámetro, tanto si la torre es metálica como de hormigón. Dicha lámina de revolución presenta una geometría óptima para la correcta transmisión de esfuerzos entre ambas partes, torre y flotador, con un espesor reducido y sin necesidad de elementos de rigidización y refuerzo exteriores a sus superficies que aumentarían el peso y el coste de la estructura.
WINDCRETE: A new spar-type floating substructure made of concrete for offshore wind turbines could help move wind farms to deeper waters while providing a cost-effective and robust alternative to steel. Called Windcrete, the substructure has been developed by a small group of professors and researchers at the Polytechnic University of Catalonia in Barcelona, Spain.
Campos, A.; Molins, C.; Gironella, X.; Trubat, P. Proceedings of the Institution of Civil Engineers. Maritime engineering Vol. 169, num. 2, p. 49-63 DOI: 10.1680/jmaen.2014.24 Data de publicació: 2016-06 Article en revista
Significant research efforts are now being directed at floating offshore wind turbines. The main challenge posed by floating wind turbines is the high construction and installation costs of the substructure, which make it too expensive for commercial exploitation in the current energy market. With the aim of achieving a cost-effective floating platform for offshore wind turbines, a new concept of a monolithic floating spar buoy is hereby presented. The monolithic concrete structure includes both the tower and the floater, built as a continuous single piece. This new concept offers a significant cost reduction during the construction phase and also while in operation, because the platform becomes almost free of maintenance during its lifetime. The main dimensions and the hydrostatic and hydrodynamic properties are presented, including a basic structural assessment of the platform to ensure its structural integrity. The construction and installation processes are presented, taking into account the special requirements of the monolithic design. Finally, a cost comparison between a steel and an equivalent concrete platform design has been performed, showing a material cost reduction larger than 60% in the case of the concrete design.
A novel concept of a floating platform for supporting wind turbines (named WindCrete) has been developed at the Universitat Politècnica de Catalunya (UPC) in order to substantially reduce the capital expenditure or CAPEX for floating offshore wind turbines. The concept is based on a monolithic full concrete structure, including the tower and the floater, which also allows a significant reduction of the operating expense, or OPEX. The basics of the concept are presented in this article, including the advantages of concrete in the marine environment, the main dimensions and the hydrostatic and hydrodynamic properties of WindCrete.
Nowadays the offshore wind energy market is clearly oriented to be extended around the world. Bottom fixed solutions for supporting offshore wind turbines are useful in shallow waters which are available in a limited extent unless a continental shelf exists. Considering the Oil & Gas background knowledge, move from bottom fixed solutions to floating solutions is not a
technical challenge, but the cost of each structure in terms of industry profit is currently the main issue for its commercial implementation. That point has induced huge research efforts on the topic.
Recently, a new concept consisting of a monolithic concrete SPAR platform was experimentally and numerically studied in the framework of the AFOSP KIC-InnoEnergy project (Alternative Floating Platform Designs for Offshore Wind
Towers using Low Cost Materials). The studies comprised a set of hydrodynamic tests performed in the CIEM wave flume facility at UPC, with a 1:100 scaled model assuming Froude similitude.
The whole test campaign includes free decay tests, RAO’s determination, regular and irregular waves with and without wind mean force. For the determination of the platform RAO’s, a set of 21 regular waves trains with periods ranging from 0.8s up to 4.8s were applied. The 6 DOF motions of the platform were measured with an infrared stereoscopic vision system.
In this paper, a summary of pitch and heave RAO’s tests will be presented with the main objective to calibrate and validate the accuracy of the Morison-based numerical model for floating wind turbine platforms developed at the Universitat Politècnica de Catalunya.
Because the wave flume spatial constraints, both Airy and Stokes wave theories are necessary to reproduce the correct wave kinematics. The numerical model includes both theories and a comparison between them has been done, checking the validity range of each one. The simulations revealed a reasonable good agreement with the experimental results, as well with the computed RAO’s in commercial software.
Preliminary studies of a concept consisting of a monolithic concrete SPAR platform were presented in 2014. The studies were performed in the framework of the AFOSP KIC-InnoEnergy project (Alternative Floating Platform Designs for Offshore Wind Towers using Low Cost Materials) showing significant costs reduction. The experimental phase of the project was developed during 2014.
The experiments comprised a set of hydrodynamic tests performed in the CIEM wave flume facility at the Universitat Politècnica de Catalunya (UPC), with a 1:100 scale model assuming Froude similitude. The complete experimental campaign included free decay tests, a set of 22 regular wave trains of different periods to determine the RAO’s and another set of 21 regular and irregular wave trains in conjunction with a mechanical wind device, simulating the mean thrust force exerted by the wind turbine.
To adjust the weight of the whole system, a set of adjustable weights inside de scale model were designed assuring such properties, particularly the
pitch/roll inertia. The scaled model of the mooring system was carefully studied because the constraints in width of the flume facility. A mechanical wind device
was also specifically designed to ensure an averaged force at the top of the model, simulating the effect of the mean rotor thrust force.
A detailed description of the methodology for the experimental campaign and a summary of the experimental results are presented.
Matha, D.; Sandner, F.; Molins, C.; Campos, A.; Cheng, P. Philosophical transactions of the Royal Society A. Mathematical physical and engineering sciences Vol. 373, num. 2035 DOI: 10.1098/rsta.2014.0350 Data de publicació: 2015-02 Article en revista
The current key challenge in the floating offshore wind turbine industry and research is on designing economic floating systems that can compete with fixed-bottom offshore turbines in terms of levelized cost of energy. The preliminary platform design, as well as early experimental design assessments, are critical elements in the overall design process. In this contribution, a brief review of current floating offshore wind turbine platform pre-design and scaled testing methodologies is provided, with a focus on their ability to accommodate the coupled dynamic behaviour of floating offshore wind systems. The exemplary design and testing methodology for a monolithic concrete spar platform as performed within the European KIC AFOSP project is presented. Results from the experimental tests compared to numerical simulations are presented and analysed and show very good agreement for relevant basic dynamic platform properties. Extreme and fatigue loads and cost analysis of the AFOSP system confirm the viability of the presented design process. In summary, the exemplary application of the reduced design and testing methodology for AFOSP confirms that it represents a viable procedure during pre-design of floating offshore wind turbine platforms.
One of the main aspects when testing floating offshore platforms is the scaled mooring system, particularly with the increased depths where such platforms are intended. The paper proposes the use of truncated mooring systems to emulate the real mooring system by solving an optimization problem. This approach could be an interesting option when the existing testing facilities do not have enough available space. As part of the development of a new spar platform made of concrete for Floating Offshore Wind Turbines (FOWTs), called Windcrete, a station keeping system with catenary shaped lines was selected. The test facility available for the planned experiments had an important width constraint. Then, an algorithm to optimize the design of the scaled truncated mooring system using different weights of lines was developed. The optimization process adjusts the quasi-static behavior of the scaled mooring system as much as possible to the real mooring system within its expected maximum displacement range, where the catenary line provides the restoring forces by its suspended line length.
One of the main aspects when testing floating offshore platforms is the scaled mooring system, particularly with the increased depths where such platforms are intended. When the existing testing facilities do not have enough available space, the use of truncated mooring systems with a similar behaviour to the real mooring system could be an interesting option. As part of the development of SPAR platform made of concrete for FOWTs a station keeping system with catenary shaped lines was selected. The test facility available for the planned experiments presented an important width constraint. Then, an algorithm to optimize the design of the scaled truncated mooring system by using different weights of lines was developed. The optimization process adjusts the quasi-static behaviour of the scaled mooring system as much as possible to the real mooring system within its expected maximum displacement range, where the catenary line provides the restoring forces by its suspended line length.
A new concept of a SPAR floating platform is being developed in the KIC-Innoenergy project AFOSP (Alternative Floating Platform Designs for Offshore Wind Turbines using Low Cost Materials). Members of the consortium are Gas Natural Fenosa, University of Stuttgart and Universitat Politècnica de Catalunya. The main differentiating aspects with respect to other SPAR prototypes are the monolithic nature of the whole structure, including both, the platform and the tower, the use of post-tensioned concrete as main material and the installation process.
A comparison between similar steel and concrete designs demonstrates that the material cost for the concrete structure is around one third of the steel one. Considering that the concrete Oil & Gas platforms are virtually free of maintenance and have an extended lifetime, the real cost is less than 1/3 of the steel one, while the offshore tasks and the moorings systems have similar costs for both alternatives.
Following a hydrostatic pre-design of the structure, coupled aero-servo-hydro-elastic analyses for a 5MW wind turbine have been performed by using an in-house FOWT model with a reduced number of degrees of freedom (DOF) and simplified aero- and hydrodynamics. With the obtained loads, the most relevant structural members have been checked, including a simplified fatigue limit state analysis, obtaining a lifetime over 50 years.
Finally, a comprehensive cost analysis has been performed to obtain the Levelized Cost Of Energy (LCOE) for the developed platform.
A new concept of a SPAR floating platform is being developed in the KIC-Innoenergy project AFOSP (Alternative Floating Platform Designs for Offshore Wind Turbines using Low Cost Materials). Members of the consortium are Gas Natural Fenosa, University of Stuttgart and Universitat Politècnica de Catalunya. The main differentiating aspects with respect to other SPAR prototypes are the monolithic nature of the whole structure, including both, the platform and the tower, the use of post-tensioned concrete as main material and the installation process. A comparison between similar steel and concrete designs demonstrates that the material cost for the concrete structure is around one third of the steel one. Considering that the concrete Oil & Gas platforms are virtually free of maintenance and have an extended lifetime, the real cost is less than 1/3 of the steel one, while the offshore tasks and the moorings systems have similar costs for both alternatives. Following a hydrostatic pre-design of the structure, coupled aero-servo-hydro-elastic analyses for a 5MW wind turbine have been performed by using an in-house FOWT model with a reduced number of degrees of freedom (DOF) and simplified aero- and hydrodynamics. With the obtained loads, the most relevant structural members have been checked, including a simplified fatigue limit state analysis, obtaining a lifetime over 50 years. Finally, a comprehensive cost analysis has been performed to obtain the Levelized Cost Of Energy (LCOE) for the developed platform.
Estructura flotante para soporte de turbinas eólicas marinas y procedimiento para su construcción e instalación.
La estructura flotante para soporte de turbinas eólicas marinas comprende una torre (1) que define una porción superior (1a) donde se puede montar una turbina eólica y una porción inferior (1b) que está sumergida, al menos parcialmente, en el mar, y se caracteriza porque también comprende una plataforma de flotación (2) formada de una sola pieza con dicha torre (1) y que está formada alrededor de dicha porción inferior (1b) de la torre. La invención también se refiere al procedimiento para la construcción de dicha estructura y al procedimiento para su instalación.
Permite sumar las ventajas del reducido coste del hormigón como material, una geometría sencilla y de fácil ejecución en dicho material y un calado suficientemente pequeño para poder instalar la estructura de acuerdo con la presente invención en un amplio rango de profundidades: desde aguas intermedias hasta aguas profundas.
Proceso de sustitución o remoción de aerogenerador en estructuras flotantes monolíticas tipo SPAR.
La presente invención hace referencia al proceso de sustitución de un aerogenerador en una estructura flotante monolítica tipo SPAR fondeada.
La invención se basa en la inundación controlada de la estructura flotante tal que la coronación de la estructura quede situada a una altura sobre el nivel medio del mar (NMM), entre 5 y 20 m, para que la coronación de la estructura y el aerogenerador sean fácilmente accesibles desde la cubierta de una embarcación tipo catamarán que se acople a la estructura y, mediante un sistema de puente grúa o similar, efectuar tareas de mantenimiento y/o sustitución sin necesidad de grúas flotantes. Finalizadas dichas tareas, la estructura se emerge mediante evacuación por bombeo del agua interior, permitiendo también reajustar la línea de flotación y la tensión en los amarres si las nuevas condiciones de masa lo requieren.
Proceso de instalación de estructura flotante monolítica para soporte de aerogenerador en zonas marítimas de gran profundidad y alejadas de la costa que consiste en el fondeo de la estructura desde una posición horizontal de transporte hasta la vertical mediante la inundación controlada de su interior, de forma que el tramo emergente sobre la superficie marina sea mínimo, para que el montaje del aerogenerador a instalar en la coronación se realice a través de una embarcación tipo catamarán o similar y sin necesidad de medios complementarios de elevación. El emergido de la estructura se realiza mediante extracción del agua interior a través de diversas válvulas a lo largo de la altura que se equilibra parcialmente con el lastre tipo granular introducido a través de una apertura lateral. La fuerza en los amarres de sujeción se aplica mediante el ajuste de la línea de flotación de la estructura.
Estructura flotante de hormigón prefabricado para soporte de aerogenerador.
La plataforma objeto de la presente invención se basa en una plataforma monolítica flotante de tipo SPAR, prefabricada en hormigón y precomprimida mediante armaduras activas.
La estructura está formada por un tramo de geometría cilíndrica (13), que hace las funciones de elemento de flotación y otro superior, situado por encima de la superficie marina (12), de forma cilíndrica y/o troncocónica, que sirve para el soporte del aerogenerador.
La fijación de la estructura al fondo marino se realiza mediante líneas 20 de cables, a través de elementos de lastre pesados o pilotes de succión (16), capaces de contrarrestar las componentes vertical y horizontal inducidas por los cables.