Offshore Floating Wind Farms Research Articles

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.

The Use of eDNA to Monitor Pelagic Fish in Offshore Floating Wind Farms

After nearly 30 years of experience with offshore wind energy (OWE), the industry is moving past the initial learning phase and into large-scale development. One of the strongest motivations for OWE is that projects are large enough to replace fossil-fueled electricity production that we know is a primary contributor to the ongoing climate crisis. Environmental concerns are therefore also at the core of OWE development, and environmental research and impact monitoring have been central parts of the industry since its inception. A large volume of science-based knowledge is available about the environmental impacts of OWE on marine ecosystems, from effects on the seafloor sediment infauna beneath the turbines to those on marine mammals that roam the developed seas.

Integrating Blue Energy in Maritime Spatial Planning of Mediterranean Regions

Blue Energy (BE) is expected to play a strategic role in the energy transition of Europe, particularly toward the 2050 horizon. It refers to a set of Marine Energy Sources (MES), including offshore wind, waves, tides, marine currents, sea thermal energy, salinity gradients, and marine biomass, which are exploited by different BE technologies. Nevertheless, the implementation of integrated solutions to exploit MES in marine areas does not just concern technological issues; it requires inclusive planning practices considering different aspects regarding climate and environmental impacts, landscape compatibility, interference with other marine activities (such as shipping, fishing, and tourism), and social acceptance. A replicable BE planning framework has been developed based on interdisciplinary knowledge in three Mediterranean sites in Greece, Croatia, and Cyprus, under the scope of the Interreg Med BLUE DEAL project. It has been implemented by some interdisciplinary experts through a collaborative and iterative process of data elaboration, mapping, evaluation, and visualization. Results concern the localization of suitable sites to install BE plants and the estimation of potential energy production and avoided emissions in selected scenarios. Together with visual simulations, this study shows the potential effects of the implementation of BE in specific marine areas, with a special focus on the most promising offshore floating wind farms and wave energy converters (WECs), as basic information for participative design and stakeholder engagement initiatives, including public authorities, businesses, and citizens.

Benchmarking Marine Energy Technologies Through LCA: Offshore Floating Wind Farms in the Mediterranean

Floating wind turbines are a valid option for offshore wind farms in the Mediterranean, where the sea-floor falls off rapidly with distance from the coastline. The present study concerns a Life Cycle Assessment of the environmental performance of two types of floating wind turbine. Greenhouse gas emissions of two standard models (raft-buoy and spar-buoy, 154 m rotor diameter, 6 MW installed power) were estimated in terms of Global Warming Potential (t CO2eq) with the aim of determining a benchmark for evaluating the performance of similar offshore wind farms. Thus, the aim of the paper was to create a benchmark for the design of innovative technologies, such as those developed by specialist companies, and to verify the validity of new designs and technologies in terms of avoided greenhouse gas emissions. The results show that the Carbon Intensity of Electricity of a single floating wind turbine varies in the range 26–79 g CO2eq·kWh−1, averaging 49 g CO2eq·kWh−1, in line with other studies of offshore wind turbines and other renewable energy sources (such as onshore wind and photovoltaic). Extension of our study to the whole life cycle, including manufacturing, assembly and installation, maintenance and material replacement and a hypothetical decommissioning and end-of-life, showed that wind farms are among the most promising marine renewable energy technologies for the Mediterranean.

Characterization of wake interference between two tandem offshore floating vertical-axis wind turbines: Effect of platform pitch motion

The wake interference within the offshore wind farms, especially with the tandem arrangement scenario, affects the designed total power output. Also, the six degrees of freedom motions of the platforms not only can change the aerodynamics of the offshore floating wind turbines, but also may influence the wake interference between them. In the present study, the effect of the platform pitch motion on the wake interference between two tandem offshore floating vertical-axis wind turbines (VAWTs) is characterized using the improved delayed detached-eddy simulation (IDDES). First, the power performance of the downstream turbine (VAWT Ⅱ) at different separation distances, 2D ≤ LS ≤ 10D, and tip speed ratios, 0.4 ≤ TSRⅡ ≤ 1.5, are analyzed, assuming that the upstream turbine (VAWT Ⅰ) is bottom-fixed and operates at an optimal TSRⅠ of 1.2. Then, the effects of the pitch amplitude, 5° ≤ APⅠ ≤ 15°, and pitch period, 2TⅠ ≤ TPⅠ ≤ 8TⅠ, on the wake interference are characterized by assuming that the platform pitch motion of VAWT Ⅰ follows a prescribed simple harmonic law. The results show that locating VAWT Ⅱ in the medium wake region of VAWT Ⅰ, e.g., LS = 6D, can appropriately balance the power performance and space cost of the bottom-fixed turbine array. Also, the platform pitch motion can reduce the mean velocity deficit in the core wake region of VAWT Ⅰ. The mean wake deficit reduction increases the averaged power coefficient of VAWT Ⅱ, e.g., up to 22.67% when LS = 6D, TSRⅡ = 1.2, APⅠ = 15°, and TPⅠ = 4TⅠ. In addition, relatively larger pitch amplitudes and smaller pitch periods will further alleviate the negative effect of the wake interference. This study may serve as a reference for designing offshore floating wind farms.

Analysing the effectiveness of different offshore maintenance base options for floating wind farms

Abstract. With the growth of the floating wind industry, new operation and maintenance (O&M) research has emerged evaluating tow-to-port strategies (Offshore Wind Innovation Hub, 2020), but limited work has been done on analysing other logistical strategies for offshore floating wind farms. In particular, what logistical solutions are the best for farms located far offshore that cannot be reached by crew transfer vessels (CTVs)? Previous studies have looked at the use of surface effect ships (SES) and CTVs during the operation and maintenance (O&M) of bottom-fixed wind farms, but only some of them included service operation vessels (SOVs). This study analyses two strategies that could be used for floating wind farms located far from shore using ORE Catapult's in-house O&M simulation tool. One strategy comprises of having a SOV performing most of the maintenance on the wind farm, and the other strategy uses an offshore maintenance base (OMB) instead, which would be located next to the offshore substation and would accommodate three CTVs. This paper provides an overview of the tool and the inputs used to run it, including failure rates of floating wind turbine subsea components and their replacement costs. In total six types of simulations were run with two strategies, two different weather limits for CTVs and two weather datasets ERA5 and ERA-20C. The results of this study show that the operational expenditure (OPEX) costs for the strategy with an OMB are 5 %–8 % (depending on the inputs) lower than with SOV, but if capital expenditure (CAPEX) costs are included in the analysis and the net present value (NPV) is taken into account then the fixed costs associated with building the offshore maintenance base have a significant impact on selecting a preferred strategy. It was found that for the case study presented in this paper the OMB would have to share the foundation with a substation in order to be cost competitive with the SOV strategy.

Socio-economic impact of a 200 MW floating wind farm in Gran Canaria

This research analyses the economic impact of a 200 MW offshore floating wind farm in an isolated tourist-led region as the Canary Islands in terms of regional and national gross value added (GVA) and employment. After analysing the value chain of the offshore wind energy industry, the impact of the regional and national economy has been estimated using an input/output model. The main aim is to evaluate this impact in comparison to more industrialized region and to bottom-fixed offshore wind farms. The value chain analysis shows that the floating offshore wind capabilities in Spain are very high. Two different scenarios have been developed to take into account transfers of the value-chain between the regional and the national level. It is concluded that similar level of investment in the Canary Islands and in Mainland-Spain will lead to different impacts in the economy due to their different economic structures. The highly tourism-led Canarian economy, characterised by a marginal industrial sector and overdeveloped services one, will lead to an overall lower GVA and, at the same time, to a higher employment demand. Several indicators have been deployed using the results of this research that show the impact in tourist-led economies and also of floating versus bottom-fixed offshore wind farms. The GVA generated through the whole project is high, reaching 680 million euros at national level, which includes a regional contribution of 365 to 245 million euros, showing the high impact of the project in the national and local economy.

Dynamic Modeling of an Offshore Floating Wind Turbine for Application in the Mediterranean Sea

Wind power is emerging as one of the most sustainable and low-cost options for energy production. Far-offshore floating wind turbines are attractive in view of exploiting high wind availability sites while minimizing environmental and landscape impact. In the last few years, some offshore floating wind farms were deployed in Northern Europe for technology validation, with very promising results. At present time, however, no offshore wind farm installations have been developed in the Mediterranean Sea. The aim of this work is to comprehensively model an offshore floating wind turbine and examine the behavior resulting from a wide spectrum of sea and wind states typical of the Mediterranean Sea. The flexible and accessible in-house model developed for this purpose is compared with the reference model FAST v8.16 for verifying its reliability. Then, a simulation campaign is carried out to estimate the wind turbine LCOE (Levelized Cost of Energy). Based on this, the best substructure is chosen and the convenience of the investment is evaluated.

Bioactive Ceramic Coating Solution for Offshore Floating Wind Farms

Bioactive Ceramic Coating Solution for Offshore Floating Wind Farms

Experimental characterisation of the wake behind paired vertical-axis wind turbines

Two vertical-axis wind turbines (VAWTs) benefit from a power increase when placed side by side in close proximity. To study the potential of paired VAWTs for integration in wind farms, wind tunnel wake measurements of lift-driven VAWTs are compared for isolated and three counter-rotating configurations. Because the wake of an isolated VAWT is deflected, the direction of rotation significantly influences the wake of paired VAWTs. The wake of counter-rotating VAWTs where the adjacent blades move downwind, exhibits a similar length, width and replenishment as the wake of an isolated VAWT. The wake of counter-rotating VAWTs with adjacent upwind moving blades, however, significantly differs from an isolated VAWT wake. While its wake length is similar to an isolated VAWT wake, its width and replenishment are not. Because of appealing wake characteristics, paired VAWTs exhibit unique advantages for wind farm applications, and especially for offshore floating wind farms.

A life cycle cost model for floating offshore wind farms

Over the last few decades, there has been a renewed interest in the offshore wind sector. In particular, floating wind turbines represent the next frontier in the wind power industry. Currently, only research prototypes exist, and few studies are available on their possible investment cost. Therefore, a cost assessment for this technology is necessary to ascertain whether it is economically sustainable. This paper develops a life cycle cost model for floating offshore wind farms, bringing together the most up-to-date data and parametric equations from databases and literature. The cost model considers the key parameters of the wind power economy, namely CAPEX, OPEX, DECEX and LCOE. The proposed model should be helpful for future decision-making, as the wind energy industry is in constant evolution. An application to an offshore floating wind farms is also carried out, in which the three main types of floaters are considered, namely the Semi-Submersible Platform, the Spar Buoy and the Tension Leg Platform. An average LCOE of 9.74 €c/kWh was found, at the lower bound of the typical range applying to fixed base offshore wind farms, and higher than typical values applying to onshore wind farms.

Active structural control of a floating wind turbine with a stroke-limited hybrid mass damper

Floating wind turbines are subjected to more severe structural loads than fixed-bottom wind turbines due to additional degrees of freedom (DOFs) of their floating foundations. It's a promising way of using active structural control method to improve the structural responses of floating wind turbines. This paper investigates an active vibration control strategy for a barge-type floating wind turbine by setting a stroke-limited hybrid mass damper (HMD) in the turbine's nacelle. Firstly, a contact nonlinear modeling method for the floating wind turbine with clearance between the HMD and the stroke limiters is presented based on Euler-Lagrange's equations and an active control model of the whole system is established. The structural parameters are validated for the active control model and an equivalent load coefficient method is presented for identifying the wind and wave disturbances. Then, a state-feedback linear quadratic regulator (LQR) controller is designed to reduce vibration and loads of the wind turbine, and two optimization methods are combined to optimize the weighting coefficients when considering the stroke of the HMD and the active control power consumption as constraints. Finally, the designed controllers are implemented in high fidelity simulations under five typical wind and wave conditions. The results show that active HMD control strategy is shown to be achievable and the designed controllers could further reduce more vibration and loads of the wind turbine under the constraints of stroke limitation and power consumption. “V”-shaped distribution of the TMD suppression effect is inconsistent with the Weibull distribution in practical offshore floating wind farms, and the active HMD control could overcome this shortcoming of the passive TMD.

The impact of wind resource spatial variability on floating offshore wind farms finance

AbstractWind resource availability determines the financial performance of wind farms as it is directly related to production. Offshore wind developers require great investments to design, build, operate and dismantle offshore wind farms. Furthermore, the investments in the offshore floating wind sector are expected to increase in the future. Because of that, the assessment of the variability of the investments, mainly because of the wind resource variability, seems to be a crucial step in the design methodology. Consequently, a flexible methodology for supporting offshore floating wind farm optimal location assessment is presented in this paper. The proposed methodology is focused on including the offshore wind resource variability and its influence on the power production of floating wind farms, as well as on the main financial indicators (internal rate of return, net present value, pay‐back period and cost of energy). The methodology is applied to the north coast of Spain, and it allows to identify the most promising sites for offshore wind farms deployment. Differences on the cost of energy up to 100% can be found in the area under study. The methodology proposed has been conceived to be site‐independent and applied at any spatial and time horizon. Copyright © 2017 John Wiley & Sons, Ltd.

Use of a Vertical Wind Turbine in an Offshore Floating Wind Farm

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper OTC 21705, ’Use of a Vertical Wind Turbine in an Offshore Floating Wind Farm,’ by Marc Cahay and Eric Luquiau, Technip, and Charles Smadja and Frederic Silvert, Nenuphar, originally prepared for the 2011 Offshore Technology Conference, Houston, 2-5 May. The paper has not been peer reviewed. With 2.0 GW already installed and more than 50.0 GW planned in Europe by 2020, as reported by the European Wind-Energy Association, the installation of bottom-mounted offshore wind turbines in very shallow water (less than 40 m) is now well established. The foundation and the offshore installation costs represent approximately 50% of the total development cost of an offshore wind farm, and this proportion increases with the water depth. Hence, floating wind turbines are the solution for deep offshore. Vertiwind Project Coming from a strong and complementary partnership of utilities, industrials, and academics, the Vertiwind project plans to build, install, and operate, in real offshore conditions, a full-scale floating vertical-axis wind turbine (VAWT) of 2 MW. This is a real step change in the technology compared with most offshore wind turbines with horizontal axes. The floater concept retained is of a semisubmersible design and is called “multifloater.” It skillfully combines an out-of-the-wave excitation response, a shallow draft to facilitate fabrication, and a very simple installation procedure requiring only one or two tugs. The VAWT is located in the center of the floater, ensuring that the center of gravity, the buoyancy, and the convergence point of the mooring lines are all on the same axis. This geometrical property highly reduces the sway and yaw response of the floater subject to noncolinearity or heading variation of wave and wind. Because of the architecture and underlying principles of this Darrieus turbine, the power production is not affected by the inclination of the turbine axis relative to the wind direction as a result of the floater motions. The turbine design is carried out in parallel with the floater. It integrates, at an early stage, all requirements of the offshore environment in terms of loads, accessibility, and ease of maintenance. The complete unit will be anchored to the seabed and linked to the network by a compliant subsea cable.

浮体式洋上風力発電ファームにおける風車間の遮蔽影響に関する研究

As the wind power is now considered as one of the most promising renewable energy resources, the total amount of electricity produced worldwide by wind-power generators is increasing quite rapidly. In Japan, since land spaces suitable for wind-power generations are quite limited, the feasibility of wind-power generations in offshore areas is now being studied extensively. Among various possible types of offshore wind-power generations, a floating wind farm, which consists of large floating structures and an array of wind-power generators mounted on each of the floating structures is considered to be an adequate type for Japan because the water depth tends to become large steeply even in the close proximity of shores. It is known that, in such a floating offshore wind farm, the construction cost of the floating structures, on which an array of wind-power generators are to be mounted, accounts for a major part of the total construction cost. It is therefore quite vital for the reduction of the power-generation cost that the number of wind-power generators mounted on a unit area of a floating structure could be increased. On the other hand, however, a larger number of wind-power generators per unit area of a floating structure usually results in the lower amount of average power produced by each generator, because the wind speed incident to power-generating blades tends to be reduced due to the shielding effects among the congregated wind-power generators.In the present study, the shielding effects among the generators in an offshore floating wind farm are investigated through extensive experiments and the trade-off effects on the generation cost due to the increase of the number of generators mounted on a unit area of a floating body and the increase of the shielding effects among generators are quantified. It has been found out through the experiments that the interaction effects between adjacent wind-power generators when they are placed side-by-side against wind direction are much smaller than generally conceived, and thus wind-power generators could be mounted in an offshore wind farm with significantly higher density than that of conventional wind farms.Finally, an offshore floating wind farm free from the shielding effects among the mounted generators is proposed.