Floating Wind Farms Research Articles

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.

An integrated GIS approach for site selection of floating offshore wind farms in the Atlantic continental European coastline

This study presents a novel method for the selection of sites for floating wind farms based on marine spatial optimization. After providing a review of the present state of the art, a tool based on geographic information systems is presented, consisting of three main stages and built in Python language. The first stage collects and analyses the information of the different regulatory bodies, marine spatial planning, maritime concessions and other sources. The second stage excludes not feasible sites for floating wind farms, based mostly on marine space use and on environmental constraints. The third stage characterises the available locations based on five major categories that are spatially dependent: metocean data, viability data, logistics, facilities, marine environment and techno-economic data. The proposed methodology is implemented at the Europe Atlantic coast, with specific reference to Portugal, Spain and France. These three countries together combine 3.362.408 km2 of the Atlantic Exclusive Economic Zone, where in only 0.22% of that area could host floating offshore wind turbines. While further detailed studies about locations and legislative considerations are required, the effort made has contributed to eliminate unsuitable areas and identify those where sustainability can be maximized.

Technology Focus: Field Development (September 2020)

Field developers have shifted the usual approach to planning and operations to a “dare to try” approach, experimenting, piloting, and directly implementing from the start a digital transformation of their activities. Under the mandate of decarbonization and safe operations embraced by many international, national, and service oil companies, there is no turning back on an accelerated journey of field-development projects that are moving toward automatic production optimization and predictive maintenance loops. Real and tangible results are available, proving that shifting the focus on operations to a digital approach, using digital twins, machine learning, and artificial intelligence (AI) truly benefits operators in three main aspects: safety, monetization of investment, and low carbon. Operators who do not engage in this wave most probably will lose competitive advantage soon. Swift innovation in field development was accelerated by the commanding need to reduce operating costs because of low oil prices during the last 2 years and by the imperative urgency of enabling remote and distance-conscious working during the current pandemic. The developments in engineering and digital technology are being integrated to launch solutions never envisioned before, such as wind farms offshore to provide more electricity where it is needed without affecting the environment and North Sea developments modeled on digital twins with little or no staffing. Collaboration among a variety of companies, big and small, is also a preferred approach, leading the way toward the sure digital future in oil and gas. What I consider extremely relevant is the speed with which these improvements are taking place. The selection of articles in this section illustrates three main facets of this vertiginous speed: offshore developments modeled on digital twins that include decarbonization and digitalization implementations that take only months (literally), AI percolating the modeling strategies and consultancy services for large oil and gas operators, and the remarkable innovation of producing electricity with floating wind farms in offshore fields. We live in an exciting transformation era, in which “dare to try” is needed, and we need to learn from any mistakes quickly to shape better field developments that take care of the environment, reduce costs, and increase safety. A failure to dare now will penalize operators who did not grip the imminent change.

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.

Numerical Study of a Proposed Semi-Submersible Floating Platform with Different Numbers of Offset Columns Based on the DeepCwind Prototype for Improving the Wave-Resistance Ability

DeepCwind semi-submersible floating offshore wind turbines have been widely examined, and in some countries this type of floating offshore wind turbine has been adopted in the construction of floating wind farms. However, the DeepCwind semi-submersible floating offshore wind turbines still experience large surge motion that limits their operational time. Therefore, in this study, a semi-submersible floating platform with different numbers of offset columns, but with the same total weight, based on the DeepCwind prototype is proposed. From the free-decay test, it was found that the number of the floating columns will affect the natural frequency of the platform. Furthermore, the regular wave test in the time domain and the irregular wave test in the frequency domain show that increasing the number of the floating columns will reduce the surge motion greatly, while the effects in the heave and pitch motions are not obvious.

Comparison of pilot-scale floating offshore wind farms with shared moorings

As floating wind turbine technology matures and wind farms are considered at larger scales in deeper waters, moorings may take a larger share of the costs. In response, floating wind farms could be designed such that the moorings are shared between turbines, using interconnecting mooring lines between adjacent floating offshore wind turbine platforms and also possibly connecting multiple mooring lines to the same anchor. This may reduce the total length of mooring line, the wind farm footprint, and the number of anchors; worthwhile advantages if not overcome by increases in mooring strength requirements.A design algorithm is presented for preliminary sizing of shared mooring systems for pilot-scale floating offshore wind farms. Quasi-static modelling is used to analyze the performance of shared-mooring systems produced by the algorithm. The model accounts for steady wind thrust forces and nonlinear mooring line reactions. A four-turbine floating wind farm is designed and analyzed with three alternative shared-mooring configurations and four water depths. Results are presented in terms of platform displacements, mooring tensions, and cost, providing an initial comparison of shared mooring options and their potential for cost savings over conventional individually-moored configurations.

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.

Dynamic response signatures of a scaled model platform for floating wind turbines in an ocean wave basin.

Understanding of dynamic behaviour of offshore wind floating substructures is extremely important in relation to design, operation, maintenance and management of floating wind farms. This paper presents assessment of nonlinear signatures of dynamic responses of a scaled tension-leg platform (TLP) in a wave tank exposed to different regular wave conditions and sea states characterized by the Bretschneider, the Pierson-Moskowitz and the JONSWAP spectra. Dynamic responses of the TLP were monitored at different locations using load cells, a camera-based motion recognition system and a laser Doppler vibrometer. The analysis of variability of the TLP responses and statistical quantification of their linearity or nonlinearity, as non-destructive means of structural monitoring from the output-only condition, remains a challenging problem. In this study, the delay vector variance (DVV) method is used to statistically study the degree of nonlinearity of measured response signals from a TLP. DVV is observed to create a marker estimating the degree to which a change in signal nonlinearity reflects real-time behaviour of the structure and also to establish the sensitivity of the instruments employed to these changes. The findings can be helpful in establishing monitoring strategies and control strategies for undesirable levels or types of dynamic response and can help to better estimate changes in system characteristics over the life cycle of the structure.

Coupled Mooring Systems for Floating Wind Farms

In this paper it is investigated if, by coupling the catenary mooring systems of a number of turbines, the number of lines and anchors needed and subsequently the costs could be reduced and what kind of dynamic phenomena such a mooring system will exhibit. A row, triangular and rectangular arrangement of floating wind turbines is analyzed in terms of their cost saving potential and their dynamic properties in the frequency domain. The row arrangement is further investigated in the time domain, with a one dimensional simplified model. The most important forces to evaluate the station keeping performance, except current, are applied. These consist of irregular wave forces, employing the Morison equation, estimated wave drift and wind forces. Diffraction effects have been estimated by employing the McCamy-Fuchs theory. Four operational and a 50-year extreme load case have been applied. The results are showing that significant cost reductions of up to 60% in mooring system and 8% in total system costs could be achieved. The dynamic analysis shows the general feasibility of integrated mooring systems. No resonance problems seem to exist. However displacements are increasing with the number of floaters, and cost savings diminish for larger numbers of turbines, as the required diameters, lengths and costs of mooring chains increase.

Influence of failed blade-pitch-control system to FOWT by aero-elastic-control-floater-mooring coupled dynamic analysis

More FOWTs (floating offshore wind turbines) will be installed as relevant regulations and technological hurdles are removed in the coming years. In the present study, a numerical prediction tool has been developed for the fully coupled dynamic analysis of FOWTs in time domain including aero-loading, tower elasticity, blade-rotor dynamics and control, mooring dynamics, and platform motions so that the influence of rotor-control dynamics on the hull-mooring performance and vice versa can be assessed. The developed coupled analysis program is applied to Hywind spar design with 5 MW turbine. In case of spar-type floaters, the control strategy significantly influences the hull and mooring dynamics. If one of the control systems fails, the entire dynamic responses of FOWT can be significantly different. Therefore, it is important to maintain various control systems in a good operational condition. In this regard, the effects of failed blade pitch control system on FOWT performance including structural and dynamic responses of blades, tower, and floater are systematically investigated. Through this study, it is seen that the failure of one of the blade pitch control system can induce significant dynamic loadings on the other blades and the entire FOWT system. The developed technology and numerical tool are readily applicable to any types of floating wind farms in any combinations of irregular waves, dynamic winds, and steady currents.

Life-cycle cost analysis of floating offshore wind farms

The purpose of this article is to put forward a methodology in order to evaluate the Cost Breakdown Structure (CBS) of a Floating Offshore Wind Farm (FOWF). In this paper CBS is evaluated linked to Life-Cycle Cost System (LCS) and taking into account each of the phases of the FOWF life cycle. In this sense, six phases will be defined: definition, design, manufacturing, installation, exploitation and dismantling. Each and every one of these costs can be subdivided into different sub-costs in order to obtain the key variables that run the life-cycle cost. In addition, three different floating platforms will be considered: semisubmersible, Tensioned Leg Platform (TLP) and spar. Several types of results will be analysed according to each type of floating platform considered: the percentage of the costs, the value of the cost of each phase of the life-cycle and the value of the total cost in each point of the coast. The results obtained allow us to become conscious of what the most important costs are and minimize them, which is one of the most important contributions nowadays. It will be useful to improve the competitiveness of floating wind farms in the future.

Floating 2-MW Turbine Prototype Tests Feasibility of Harnessing Offshore Wind

This article, written by Editorial Manager Adam Wilson, contains highlights of paper OTC 23492, ’Implementation of a 2-MW Floating Wind Turbine Prototype Offshore Portugal,’ by Christian A. Cermelli, Marine Innovation & Technology, and Dominique G. Roddier and Alla Weinstein, Principle Power, prepared for the 2012 Offshore Technology Conference, Houston, 30 April-3 May. The paper has not been peer reviewed. A 2-MW floating offshore wind system prototype was implemented off the coast of Portugal. The project was designed to prove the technical and economic feasibility of floating offshore wind turbines in southern Europe. It is based on the WindFloat concept, a three-column semisubmersible-platform design with water-entrapment plates. Such technology enables deployment of multimegawatt wind-turbine generators at great distances from shore, in any water depth. Synergies with offshore oil and gas platforms have been exploited; however, deployment in an area with no previous offshore oil and gas activities led to unique challenges. Project Design Bases The project design bases were driven by the following principle: The floating wind turbine should be large enough to provide meaningful testing of fabrication, installation, and operation capabilities. Some of the main project design bases were A location in 49-m-deep water, 6 km offshore Aguçadoura, a small town located north of Porto on the west coast of Portugal A wind-turbine size from 2 to 2.3 MW A connection to the country’s main power grid Although no specific targets were set for local content, the drive to maximize work performed locally was also seen as a critical success factor for the project. Previous testing conducted during earlier feasibility studies was performed at a 1/67 scale in a model-testing facility. Intermediate-scale testing (between in-door controlled-environment testing in a wave tank and full-scale prototype) was not seen as a necessary step. Commercial development of floating wind farms will likely be based on the largest available wind turbines. Currently, 3- to 6-MW machines are available for the offshore market; however, because of budgetary limitations and limited experience with wind turbines of such size, the more common and lower-capacity 2- to 2.3-MW turbines were considered optimal for this project. A testing site 6 km off the west coast of Portugal was selected because of the presence of a subsea electrical cable with sufficient capacity to transport power from the WindFloat prototype to shore. The target design life for the plat-form is 5 years, but planned operation should not exceed 2 years.

Preliminary Design of a Floating Wind Turbine Support Structure and Relevant System Cost Assessment

This paper describes the preliminary design of a floating support structure for offshore wind turbines that has been developed by ERSE (former CESI RICERCA). It considered the prospects that this kind of structure could hold for exploiting wind resources in the windiest sea areas along the coasts of Italy (Sardinia, Sicily, Apulia). A review of the various types of floating structure that have been devised worldwide for wind turbines has made it possible to single out the floating structure that looks most interesting from the technical and economic standpoint. Specifically, the selected structure is of the Tension Leg Platform (TLP) type. It consists of a nearly fully submerged hexagonal platform, which carries a 6 MW wind turbine and is linked to the sea bottom by 6 ties, which assure stability and limited tilting, even under the worst loads induced by wind and sea. The construction and installation phases for this structure have been analysed, and the most effective and economically viable techniques chosen. With a view for avoiding the use of expensive sea craft, the floating structure has been designed in such a way that it can be towed to its site with the wind turbine already standing on it. A preliminary dimensioning of the floating structure has been carried out, along with technical verification of the main structural members. This work has been performed in cooperation with the engineering company TECON, which used, among others, the MOSES computation code by Ultramarine. Attention has also been devoted to the most suitable options for mooring the floating structure to the sea bottom. To assess the behaviour of the floating system under the action of wind and waves, the computational code (BM) has been developed by ERSE. This code takes into account the whole “wind turbine + floating platform” system, represented by a scheme featuring 8 degrees of freedom. Using this code no anomalous or unexpected behaviours were observed. The costs of building and installing this floating system have been calculated, drawing on experience gained with similar offshore structures in the oil and gas fields. The unique conditions of Italy as regards shipyards, harbours, electrical grid layout etc. have been taken into account. Along with estimates of operation and maintenance costs, and annual energy yields, these results have allowed the calculation of the probable unit energy production costs of floating wind farms in deep-water coastal areas of Italy.

Turbines take float

Floating wind farms promise to reach the depths that offshore farms can't. But can we afford them asks the author?