Floating Wind Farm Research Articles

Offshore wind farm layout optimization using ensemble methods

When planning wind farms it is important to optimize the layout to increase production and reduce costs. In this paper we minimize the levelized cost of energy (LCOE) for a floating wind farm using wind data in an area around Porto Santo in Portugal. We use ensemble based optimization (EnOpt), which is frequently applied in the geophysical community to find optimal controls of oil reservoirs. EnOpt is usually used for unconstrained optimization problems or for problems with simple constraints, for example upper and lower bounds on the optimization variables. Here we consider a layout problem with many constraints on the distances between turbines. To handle the constraints, we use an extension of EnOpt called EPF-EnOpt, in which the constrained problem is replaced by a series of unconstrained problems with increasing penalty terms. We compare the performance of this method with EnOpt with a fixed penalty term, and with a deterministic gradient method. All the tested methods reduce the LCOE, but EPF-EnOpt gives better results than both a single run of EnOpt with a fixed penalty term and the deterministic gradient method, and at a lower computational cost than using the gradient method. We also consider the problem of maximizing the annual energy production without taking into account any costs. EPF-EnOpt performs the best also for this problem.

Optimization of floating wind farm power collection system using a novel two-layer hybrid method

Deep-sea floating wind farms have gained significant attention in recent years, however, their high construction and operation cost remains a notable challenge. In the floating wind farm, floating wind turbines (WTs) have a certain range of movement, and dynamic cables are used, thus the collection system needs a careful design that relies heavily on iterative optimization. In this study, a life cycle cost model for the collection system of floating wind farms is firstly established considering the floating characteristics. Due to the complexity of the optimization model, the two-layer optimization framework is presented. The upper layer uses Binary Particle Swarm Optimization (BPSO) to determine the optimal connection between the WTs and offshore substations (OSs), while the lower layer optimizes the cable topology between WTs via Improved Monte Carlo Tree Search (IMCTS). Simultaneously, the cable selection scheme corresponding to the obtained topology is optimized by the lower level. Simulations are performed to validate the proposed method. The results demonstrate that the proposed algorithm achieves a minimum optimization cost of 45.277 million euros, and attains significant reductions of 2.31, 0.486 and 1.667 million euros, respectively, compared to Genetic Algorithm (GA), BPSO-Sweep-IMCTS and BPSO-AA-GA. Further, this study evaluates the differences in the optimized structures of the collection system between floating and fixed wind farms, and analyzes the effects of the OS position and environmental factors. The analysis results show that locating OSs at the central position and upstream side reduces the cost of the collection system, and the wind condition has a considerable influence on the design of the collection system.

Experimental comparison of a dual-spar floating wind farm with shared mooring against a single floating wind turbine under wave conditions

Shared mooring can potentially be a cost-reduction factor for future floating wind farms. To assess the effect of shared mooring on the response dynamics of floating wind turbines (FWTs), experiments have been conducted for two spar FWTs with a shared mooring configuration and for a single spar FWT with catenary mooring, both at a scale of 1:47. Various regular and irregular wave conditions were tested and only one wave heading was considered. From the test results, the response amplitude operators and response spectra of platform motions and statistics of mooring tensions are compared for the two configurations. In the extreme wave condition, the shared mooring configuration leads to a 40% increase in the platform surge motion compared with the single spar FWT. Still, the absolute offset is within allowable limits prescribed by power cables. The fairlead tensions of the anchor lines are not significantly increased in the shared mooring configurations, but the shared line shows extreme tension peak events that are seldom present in the anchor lines. This study demonstrates the technological promises and challenges of a shared mooring system from an experimental perspective. Results and videos are made available and can be used to validate numerical models.

Layout optimization of an offshore floating wind farm deployed with novel multi-turbine platforms with the self-adaptive property

To deploy offshore wind in deeper waters, floating offshore wind confronts simultaneously significant opportunities and challenges. For dealing with the power deficit caused by the wake effect, a layout optimization method has been proposed for wind farms under variable wind conditions using the full-field wake model with the capacity to deploy multi-turbine platforms. The joint distribution of wind speed and direction is utilized to consider the variable wind conditions. The layout of an offshore wind farm, comprised of the floating platforms with multiple wind turbines and the wind-orientated ability, i.e., the self-adaptive property, is optimized under different wind conditions. Different numbers of turbines on a platform and platforms in the wind farm are deployed, respectively. The optimization results confirm that the platform with the self-adaptive property has a remarkable advantage to improve the efficiency of the wind farm. More turbines on a platform and less platforms can obtain higher efficiency. The distribution of wind speed and wind direction impacts the optimized layout and power output of the wind farm, simultaneously. The platforms arrange parallel lines which are perpendicular to the wind direction with more frequency and higher speed in the optimized wind farm. The concentration of the wind direction and the orthogonal angle between the wind and the long edge of the wind farm can increase the power output of the wind farm. However, the distribution of the wind speed has the dominant influence on the power output.

Service Operation Vessels Fleet Size and Mix Location Routing for the Maintenance of an Offshore Floating Wind Farm

Mixed-integer linear programming is adopted to translate the routing of service operation vessels that support the logistic aspects of the maintenance of offshore floating wind farms into mathematical language. The models attempt to help the decision-makers by providing quantified tools to screen out the optimal planning for preventive maintenance. The models search for the optimal offshore base location, vessel’s routing per day, vessel’s capacity, and vessel fleet composition that minimize the total fixed and variable infrastructure cost. The integration of the vehicle fleet size and mix problem, facility location–allocation problem, and vehicle-routing problem with time window advances the state of the art. A realistic case study is shown, and the results and discussions demonstrated that the practical insights of the solutions, as well as the identification of the route patterns through a navigation route table, may improve the decision planning of preventive maintenance.

Wake Effects on A Hybrid Semi-Submersible Floating Wind Farm with Multiple Hub Heights

Wake Effects on A Hybrid Semi-Submersible Floating Wind Farm with Multiple Hub Heights

Predictive digital twin for offshore wind farms

As wind turbines continue to grow in size, they are increasingly being deployed offshore. This causes operation and maintenance of wind turbines becoming more challenging. Digitalization is a key enabling technology to manage wind farms in hostile environments and potentially increasing safety and reducing operational and maintenance costs. Digital infrastructure based on Industry 4.0 concept, such as digital twin, enables data collection, visualization, and analysis of wind power analytic at either individual turbine or wind farm level. In this paper, the concept of predictive digital twin for wind farm applications is introduced and demonstrated. To this end, a digital twin platform based on Unity3D for visualization and OPC Unified Architecture (OPC-UA) for data communication is developed. The platform is completed with the Prophet prediction algorithm to detect potential failure of wind turbine components in the near future and presented in augmented reality to enhance user experience. The presentation is intuitive and easy to use. The limitations of the platform include a lack of support for specific features like electronic signature, enhanced failover, and historical data sources. Simulation results based on the Hywind Tampen floating wind farm configuration show our proposed platform has promising potentials for offshore wind farm applications.

Micro sitting of floating wind turbines in a wind farm using a multi-criteria framework

A novel procedure is introduced to optimise floating turbines' placement in a wind farm. In the approach, the ‘Weighted Product Model (WPM)'is used, which is a Multi-Criteria Decision Method (MCDM). The turbine position is made by the mean of technical, economic, and environmental criteria. Moreover, experts' knowledge is introduced in the framework through the Ranking Method (RM). As test cases, two areas previously identified as potential locations for a floating wind farm are grid-characterised on square cells representing the turbine locations. As a result, the methodology proposed presents the optimal arrangement of the wind turbines in the wind farms based on the WPM-RM method. The results confirm the usefulness of the method for wind turbines micro-siting on floating wind farms.

Comparison of Operation and Maintenance of Floating 14 MW Turbines and Twin 10 MW Turbines

Abstract Turbine ratings in the past decade have grown unexpectedly fast. In 2021, Siemens Gamesa and GE revealed their new 14 MW turbine models, and it is predicted that this is not yet the rating limit that turbines can reach. Increased turbine ratings can also be achieved by putting two turbines on a single foundation. This study analyzes how operation and maintenance (O&M) would differ if a floating wind farm had twin 10 MW turbines installed on each substructure, instead of a single 14 MW turbine. This study demonstrates how the strategic O&M simulation tool compass can be used to perform this comparison. Assumptions regarding the O&M of twin turbines were estimated with the major floating twin turbine developer Hexicon AB. This study analyzed four cases—a case with 35 twin 10 MW turbines, and three cases with 50 single 14 MW turbines—to understand the potential effect of increased consumable costs, spare part lead times, and maintenance durations. All cases had the same wind farm capacity of 700 MW. The results show that O&M for cases with single turbines is at least 4.5% more expensive than the case with twin turbines. The case with twin turbines also resulted in a higher availability than any other case. Additionally, results showed that operational expenditure (OPEX) for the cases with single turbines is at least 6.0% higher in scenarios with single turbines than in the twin turbine scenario. The biggest cost contributors to the difference between scenarios were craft costs, particularly cable laying vessels and tugs. Due to the higher number of cables required for the scenario with single turbines, there is more frequent mobilization of cable vessels for cable repairs.

Approach for Installation and Logistics of a Floating Offshore Wind Farm

An approach is developed for floating wind farm installation by creating a model that allows the planning of the main logistics and installation aspects of a floating wind farm. The method aims to preserve the coherency between logistic methods and project performance, as floating wind farm installation is a complex problem, due to the number of components that impose specific constraints in areas such as transportation and manufacturing. The planning tool is developed based on the knowledge about how to use the various approaches and on the analysis of different logistical solutions. A techno-economic view of the logistics and installation involved in the floating wind farm design is the main objective of this study. A case study for the CENTEC TLP concept implemented in Spanish and Irish waters is performed. Case study findings reveal the major aspects that affect the design and logistics factors. The tool is developed for the main types of floating wind platforms and is applicable for the preliminary design of wind farms worldwide. The tool suggests a strategy of design and logistic aspects dependent on a few inputs such as the number of components for installation, distances and the maximum number of turbines. These findings are especially important for the new floating wind farms being positioned further offshore.

Coupled loads analysis of a novel shared-mooring floating wind farm

Shared mooring lines are a method to reduce the stationkeeping cost of floating offshore wind farms; however, their impacts on floating array dynamics are not yet well understood. This article presents advancements to floating wind farm simulation capabilities that allow the dynamic modeling of shared-mooring floating wind arrays—specifically, platform coupling through shared lines and proper phasing of wave loads across the array. These capabilities are demonstrated on a 10-turbine shared-mooring array featuring two staggered rows of wind turbines. A baseline array design with individually moored turbines is used as a basis for comparison. Coupled analysis using FAST.Farm shows that the shared-mooring design has smaller fluctuations in surge when compared to the baseline design. The mean and maximum platform offsets are highest in normal operating conditions, but the maximum mooring line tensions are highest in 50-year storm conditions. Power spectral density analysis of platform surge and sway motions shows that the shared mooring configuration does not introduce any significant inter-platform resonances. The tower-base bending moment statistics and the line tension damage equivalent loads indicate no consequential differences in turbine loading or mooring fatigue life. Anchor load analysis shows that the total required anchor capacity for the shared-mooring array is decreased by approximately 25% when shared anchors are used. Dynamic simulations of the shared mooring system under line failures show that remaining line tensions stay within bounds and that offsets are significantly smaller when compared to the baseline design. Overall, the results show that shared moorings do not introduce any dynamic response concerns in this floating wind array design.

A passively self‐adjusting floating wind farm layout to increase the annual energy production

AbstractWake losses inside a wind farm occur due to the aerodynamic interactions when a downwind turbine is in the wake of upwind turbines. The ability of floating offshore wind turbines (FOWTs) to relocate their positions in the horizontal plane introduces an opportunity to decrease the wake losses in a floating wind farm (FWF). Our goal is to use this ability to passively move the downwind FOWT out of the wake of upwind ones. Since the mooring system (MS) attached to a FOWT is responsible for its station keeping, the horizontal motions of the FOWT depend on the MS design. Hence, if we can design the MS to passively move the FOWT out of the wake, we can increase the FWF annual energy production (AEP). In this paper, we investigate if we can benefit from relocating FOWTs in a FWF and increase its AEP. In addition, we present a novel approach that considers the ability of a FOWT to relocate its position as a new degree of freedom (DoF) in the FWF layout design. This means we will have a self‐adjusting wind farm layout where the FOWTs passively re‐arrange themselves depending on the wind direction and the wind speed. Consequently, we will have a slightly different wind farm layout for every wind direction and every wind speed. To achieve this layout, we include the MS design as part of the FWF's layout design. In a self‐adjusting FWF layout, each FOWT is attached to a customized MS design allowing it to relocate its position in the best way possible according to the wind direction, to increase the overall AEP of the wind farm. The results of one case study show that the novel approach can increase the FWF's AEP by 1.6% when compared with a current state of the art optimized floating wind farm layout. Finally, we implemented our method as an open‐source python tool to be used and enhanced further within the wind energy community.

Energy system design of offshore natural gas hydrates mining platforms considering multi-period floating wind farm optimization and production profile fluctuation

Natural gas hydrate has potentially become a clean energy source that can replace fossil fuels in the future. Offshore natural gas hydrates mining platforms are usually energy-intensive and wind power has been used as the main source of energy supply. However, there have been a limited number of studies investigating the energy systems in these offshore platforms, and the optimal implementation of wind turbines has not been considered. In this work, a floating wind farm is combined with gas turbines to supply energy for the natural gas hydrate mining platform. Since the position of floating wind turbines can be adjusted, a multi-period optimization method is proposed to consider the changes in wind resources and production profiles in different periods. In addition, the performances of different types of wind turbines are also investigated in the optimization. The minimum total cost of energy is set as the objective function in this method. Considering that the number and layout of wind turbines are affected by moving costs. When the moving costs per unit distance is 40 €/MW, the results showed that six wind turbines are required for stable operation of the platform, and the power generated by the wind turbines accounts for 77.59% of the total power supply in the whole period. From the results of case, compared with directly burning natural gas, wind power generation can effectively reduce the power generation cost of the platform.

How Does the Accessibility of Floating Wind Farm Sites Compare to Existing Fixed Bottom Sites?

Offshore wind is poised for huge growth in the coming years, the UK government has set targets of 40 GW of offshore wind, including 1 GW of floating wind, to be installed in the UK by 2030. Many proposed wind development sites are in deeper waters, farther from shore and will therefore need to be developed as floating wind sites. Developing sites in deeper waters provides access to higher, more consistent wind speeds, however this also means increased wave heights and tougher operating conditions. This makes the challenge of site accessibility critical to the goal of lowering the costs of offshore wind. Accessibility is the amount of time that vessels can safely access a given site. The objective of this study was to make a comparison of the accessibility of potential future floating wind sites to existing fixed bottom wind farm sites. Accessibility was calculated by developing Matlab code using established techniques and definitions found in the literature. A case study was then completed using sites in Scottish waters proposed for development as part of the Scotwind leasing plan. The majority of the Scotwind sites will need to be developed as floating wind sites due to the large water depths. This study assesses the accessibility of the Scotwind leasing sites and compares them to a typical fixed bottom site. The study found that accessibility will be a greater challenge for floating farm wind sites compared to fixed bottom sites. Increased access to vessels that can operate in larger wave heights will likely be necessary to operate and maintain floating wind farm sites.

Design and analysis of a ten-turbine floating wind farm with shared mooring lines

This paper discusses the development and analysis of a novel design for a 10-turbine floating wind farm with shared mooring lines. Shared mooring lines tether adjacent floating platforms together, reducing the number of anchors required but increasing system complexity. We present a systematic, multistage design process for shared mooring systems, involving linearized analysis of array layout options, quasi-static mooring line optimization, and design refinement based on coupled dynamic loads analysis. The design developed from this process is thought to represent one of the most advantageous shared-mooring configurations for this scale of floating wind array. It features perpendicular anchor line pairs and allows shared, multiline anchors, making it an example of a shared-mooring-and-anchor array. Comparing the performance and cost characteristics of the shared-mooring design with more conventional three-line individual mooring systems shows equivalent dynamic response characteristics and stationkeeping system cost savings of 25% when using shared mooring lines and shared anchors. The design is also advantageous in the case of a mooring line failure, with offsets and redundancy characteristics similar to four-line individual mooring systems.

Unmoored: a free-floating wind turbine invention and autonomous open-ocean wind farm concept

This paper contributes to emerging deep offshore wind literature by presenting the design for a novel free-floating offshore wind turbine for deep water use. The wind turbine uses one large underwater propeller to maintain its position and move as needed, while two small propellers turn the unit. This allows access to areas of high energy production potential in the open ocean out of reach to contemporary floating wind turbines, which are anchored to the seabed. An autonomous ocean-based wind farm concept is also presented. Together, the semi-autonomous wind turbines form a floating wind farm in the open ocean. A separate unit uses electricity from the wind turbines to produce climate-neutral fuels such as hydrogen (H2) and ammonia (NH3) for transport and eventual use.

Multicriteria Decision Approach to the Design of Floating Wind Farm Export Cables

This paper addresses subsea electric cable routing using the application of decision support systems combined with the experts’ knowledge. The methodology is successfully applied to a case study on the Spanish coast. The ranking method calculates the multiple criteria weights, and the weighted product method determines the most suitable space. The environmental criteria, with a weight of 61.4%, exceed the significance of other essential criteria in the study based on experts’ considerations. These rankings are input into the model to extract the suitable spaces to deploy the underwater cable. The final result accurately highlights an optimal route in alignment with the experts’ preferences.

Technology legitimation and strategic coupling: A cross-national study of floating wind power in Norway and Scotland

Building upon recent work in sustainability transitions studies and economic geography, this paper is concerned with the process of legitimation by which emerging technologies are aligned with broader societal rules and norms. Challenging the assumption of earlier research that legitimation occurs within regional and national borders, the paper views legitimation as set of transregional processes whereby the actors behind emerging technologies seek support from different regional and national organizations on an international basis. Inspired by the Global Production Networks (GPN) approach, the paper argues that technology legitimation can be understood as a trans-regional process of strategic coupling between the strategic needs of the industrial actors advancing new technologies and the efforts of national and regional organizations to promote their territories as leading nodes in emerging production networks. Empirically, the paper adopts a micro-level focus on the legitimation of a particular renewable energy technology: the Hywind floating wind power (FWP) technology, developed by the Norwegian energy firm, Equinor. The paper shows that the FWP technology was gradually legitimated in a pragmatic sense over the three stages of Hywind. The demonstration phase generated a temporary and conditional form of legitimacy at an intra-national scale, while the next phase, Hywind Scotland, generated a stronger and more durable form of legitimacy as the world’s first floating wind farm. This led to the internalisation of legitimacy from outside into the Norwegian energy regime (absorption) in the third stage of Hywind Tampen.

Site selection of floating offshore wind through the levelised cost of energy: A case study in Ireland

Potential areas for the development of a floating offshore wind farm by means of the levelised cost of energy (LCOE) are studied through a case study in the Republic of Ireland. Eligible locations are ascertained by acknowledging the characteristics of the national maritime landscape – areas reserved for aquaculture, natural parks and areas with intense maritime traffic are excluded. A selection of Irish port facilities that could accommodate the operations of a floating wind farm is also presented and incorporated into the cost model. The LCOE is computed and mapped in the areas identified as eligible using a site-specific approach, taking into account the distance to the coast and to adequate port facilities, water depth and wind climate. Among these, the wind climate and the distance to the coast play the main role in the LCOE, affecting the energy production and the cost of the export cable, respectively. The lowest LCOE values (∼100 €/MWh) occur close to the coast of West and North-west Ireland – off Donegal, Mayo and Kerry. Conversely, the highest values of the LCOE (130 €/MWh) occur further offshore. Areas in the Celtic and, especially, Irish Seas (counties of Dublin, Wicklow and Wexford) present relatively high values of the LCOE (∼120 €/MWh) due to a comparatively weaker resource. Besides, many areas in this region are excluded due to intense maritime traffic. Importantly, the distance to adequate port facilities is found to play a lesser role on the LCOE; therefore, ports requiring less investment for offshore wind operations could be employed despite not being the nearest.

A parametric study of the mooring system design parameters to reduce wake losses in a floating wind farm

Wake effects inside a conventional fixed bottom wind farm decrease the power produced by the downwind turbines, hence decreasing the farm’s annual energy production (AEP). However, floating offshore wind turbines (FOWTs) have the ability to relocate their positions laterally through surge and sway motions. This flexibility provides a new degree of freedom (DOF) in the floating wind farm layout, which can be used to decrease the aerodynamic interactions inside the floating wind farm and hence decrease the wake losses. The lateral movement of FOWTs can be passively controlled by the mooring system design. The mooring system’s restoring characteristics allows the FOWT to only move within a specific area in the x-y plane known as the watch circle. Current state of the art mooring system designs are following oil and gas design basis where the floating platforms are not allowed to have large lateral displacements. In this work, we use full factorial design to analyse the effect of different mooring system design parameters on the ability of the floater to relocate its position. The analysis shows that each design parameter has a different way of affecting the FOWT’s response. The mooring lines’ headings control which wind directions cause the biggest displacements in the crosswind direction. The smaller the lines’ diameters the higher the displacements of the FOWT. Finally, the longer the line length the smaller the mooring system’s stiffness and hence the larger the FOWT’s displacement. The results of this study can be used as the basis for floating wind farm optimization, in which the wind turbines are allowed to passively relocate their positions according to the wind speed and wind direction.