Construction Of Offshore Wind Farms Research Articles

Sound exposure in harbour seals during the installation of an offshore wind farm: predictions of auditory damage

Summary With ambitious renewable energy targets, pile driving associated with offshore wind farm construction will become widespread in the marine environment. Many proposed wind farms overlap with the distribution of seals, and sound from pile driving has the potential to cause auditory damage. We report on a behavioural study during the construction of a wind farm using data from GPS/GSM tags on 24 harbour seals Phoca vitulina L. Pile driving data and acoustic propagation models, together with seal movement and dive data, allowed the prediction of auditory damage in each seal. Growth and recovery functions for auditory damage were combined to predict temporary auditory threshold shifts in each seal. Further, M‐weighted cumulative sound exposure levels [cSELs(Mpw)] were calculated and compared to permanent auditory threshold shift exposure criteria for pinnipeds in water exposed to pulsed sounds. The closest distance of each seal to pile driving varied from 4·7 to 40·5 km, and predicted maximum cSELs(Mpw) ranged from 170·7 to 195·3 dB re 1μPa2‐s for individual seals. Comparison to exposure criteria suggests that half of the seals exceeded estimated permanent auditory damage thresholds. Prediction of auditory damage in marine mammals is a rapidly evolving field and has a number of key uncertainties associated with it. These include how sound propagates in shallow water environments and the effects of pulsed sounds on seal hearing; as such, our predictions should be viewed in this context. Policy implications. We predicted that half of the tagged seals received sound levels from pile driving that exceeded auditory damage thresholds for pinnipeds. These results have implications for offshore industry and will be important for policymakers developing guidance for pile driving. Developing engineering solutions to reduce sound levels at source or methods to deter animals from damage risk zones, or changing temporal patterns of piling could potentially reduce auditory damage risk. Future work should focus on validating these predictions by collecting auditory threshold information pre‐ and post‐exposure to pile driving. Ultimately, information on population‐level impacts of exposure to pile driving is required to ensure that offshore industry is developed in an environmentally sustainable manner.

Study on Load-bearing Characteristics of Different Types of Pile Group Foundations for an Offshore Wind Turbine

Lang, R.; Liu, R.; Lian, J., and Ding, H., 2015. Study on load-bearing characteristics of different types of pile group foundations for an offshore wind turbine.Elevated pile-cap foundation is one of the most popular foundation types for offshore wind turbines. Form selection and design are the keys in the construction of offshore wind farms. Because offshore wind turbines are high-rise structures, a reasonable and applicable foundation can ensure the normal operation of wind turbines. Meanwhile, it can decrease the size of foundation and reduce the cost of construction effectively. Four types of pile group foundations named BPG-type, SPG-type, VPG-type, and CPG-type are developed. Combined with laboratory model experiments, a numerical simulation method is established and verified in this paper. The vertical bearing capacity, horizontal bearing capacity and bending bearing capacity are studied comparatively with the numerical simulation method. Combined with practical engineering, the applicability of the foundations is evaluated. The results indicate that BPG-type and SPG-type have the stronger vertical bearing capacity, horizontal bearing capacity and bending bearing capacity than VPG-type and CPG-type in the same amount of steel. In addition, batter piles can effectively increase the bearing capacity of pile foundations. The VPG-type needs to increase the size of foundation to meet the requirements of wind turbine operation. In practical engineering, the combination of vertical piles and batter piles can increase the bearing capacity of pile group foundations and decrease the cost of construction.

Resampling of Data for Offshore Grid Design Based on Kernel Density Estimation and Genetic Algorithm

Offshore wind power has been a major focus in the renewable energy development in recent years, due to better wind speeds and wind energy are available offshore. Since the development (construction and grid connection) of offshore windfarms is relatively more expensive in nature, careful planning and design are needed to maximise the benefits of the offshore wind projects. Optimisation with only one operational state is not sufficient in grid design as the state of power system is not stationary due to the fluctuations of the wind power and power consumption. Eventually this leads to the fluctuation of the base load power generations. To account for this variability, the optimisation has to be done with many operational states. Historical data of power consumption at each load centre and simulation data of wind power have to be used to describe the system states. Ideally, the complete set of data should be used to describe the power system states but this could also lead to unsolvable case as there are too many unknowns involved in the calculation. To keep the number of states as low as possible to reduce the computation time, selection of smaller number of samples that can represent the whole data set has to be carried out. This involves detail studies of the statistical distributions of the data. This study is therefore dedicated to develop a procedure for selecting a set of statistically sound samples to represent the entire data set for grid design purposes.

Towards a numerical model to simulate the observed displacement of harbour porpoises Phocoena phocoena due to pile driving in Belgian waters

The impact of impulsive pile driving on marine mammals is a major environmental concern in offshore wind farm construction. Odontocetes, depending on emission and reception of sound for foraging, spatial orientation and social interactions, are likely to be impacted most. In Belgian and adjacent waters, specific concerns exist about the impact of underwater sound generated during pile driving on the harbour porpoise Phocoena phocoena, the most common cetacean in these waters. The results of visual aerial line-transect surveys performed before and during pile driving at the Thorntonbank (Belgian waters, North Sea) suggested a displacement of porpoises to a distance of around 20 km from the piling location. Such an apparent large-scale avoidance reaction is similar to the one observed in other countries’ waters in the North Sea. Using survey data, we developed a simple numerical model that could reproduce the harbour porpoises’ redistribution pattern during disturbance. The further development of our initial model can be useful to predict or simulate the redistribution of harbour porpoises in cases when field investigations are not possible or impractical, for pre-construction environmental impact assessments and for impact assessments in case of multiple piling operations ongoing in the same area.

Rapid macrobenthic recovery after dredging activities in an offshore wind farm in the Belgian part of the North Sea

The development of offshore wind farms (OWFs) in the North Sea has increased considerably to create alternatives for fossil fuel energy. Activities related to the construction of OWFs, in particular gravity-based foundations (GBFs), are mainly associated to dredging, causing direct effects to the macrofauna in the seabed. The sediment characteristics and macrofauna were studied before and after construction (2005–2010) of six GBFs in an OWF in the Belgian part of the North Sea. We distinguished natural from anthropogenic-related fluctuations in macrofaunal communities by analysing a long-term dataset (1980–2012). The analysed sandbanks are characterised by sandy substrates and a community with low species abundance (180–812 ind m−2) and diversity (6–15 species per 0.1 m2). Strong temporal variations were observed possibly related to variable weather conditions in the area. Significant differences in community composition were observed due to the installation of six GBFs in the construction year of the OWF followed by a rapid recovery a year later and confirmed by the benthic ecosystem quality index BEQI. Even though the construction of GBFs creates a physical disturbance to the seabed, the macrobenthic community of these sediments have illustrated a fast recovery potential.

The significance of parameter uncertainties for the prediction of offshore pile driving noise

Due to the construction of offshore wind farms and its potential effect on marine wildlife, the numerical prediction of pile driving noise over long ranges has recently gained importance. In this contribution, a coupled finite element/wavenumber integration model for noise prediction is presented and validated by measurements. The ocean environment, especially the sea bottom, can only be characterized with limited accuracy in terms of input parameters for the numerical model at hand. Therefore the effect of these parameter uncertainties on the prediction of sound pressure levels (SPLs) in the water column is investigated by a probabilistic approach. In fact, a variation of the bottom material parameters by means of Monte-Carlo simulations shows significant effects on the predicted SPLs. A sensitivity analysis of the model with respect to the single quantities is performed, as well as a global variation. Based on the latter, the probability distribution of the SPLs at an exemplary receiver position is evaluated and compared to measurements. The aim of this procedure is to develop a model to reliably predict an interval for the SPLs, by quantifying the degree of uncertainty of the SPLs with the MC simulations.

Comparison of manual and semi-automatic underwater imagery analyses for monitoring of benthic hard-bottom organisms at offshore renewable energy installations

The construction of new offshore wind farms is one of the strategies to fulfill growing demands for “green” renewable energy. Underwater imagery is an important tool in the environmental monitoring of offshore renewable energy installations, especially in rocky benthic environment where traditional techniques are not applicable. Underwater video from the high energy Norwegian Sea coast was used for this study. Traditional manual point-based benthic cover estimations from selected frames were tested against a semi-automatic approach which involved making mosaic images from underwater videos. The study demonstrates that results of manual and semi-automatic benthic cover estimations are similar, although the manual analysis has a much larger spread in the variability of the data with many outliers due to the limited amount of points used in the analysis. Although the number of benthic features that could be extracted by computer using color is fewer than those that can be detected with the human eye, the described semi-automatic method is less biased and less costly in terms of qualified staff. Implementation of the semi-automatic method does not require any programming skills and has the ability to quickly and simply process larger amount of underwater imagery which would be of decisive advantage to the industry.

Sequence determining of construction of the offshore wind farm construction applying permutation method

Sequence determining of construction of the offshore wind farm construction applying permutation method

Simulation of Sensor Fault Diagnosis for Wind Turbine Generators DFIG and PMSM Using Kalman Filter

The fault detection and isolation of generators used in wind turbines gathering interest as to maximize the reliability and avail of distributed energy systems with recent unmatched growth in construction of offshore wind farms. In particular it is interested in performing fault detection and isolation (FDI) of incipient faults affecting the measurements of the three-phase signals (currents) in a controlled DFIG and PMSG. Although different authors have dealt with FDI for sensors in induction machines and in DFIGs, most of them rely on the machine model with constant parameters. However, the parameter uncertainties due to changes in the operating conditions will produce degradation in the performance of such FDI systems. The robust techniques to detect faults are exist but there is a need of extra sensor. This paper proposed a systematic methodology for the design of sensor FDI systems with the following characteristics: i) capable of detecting and isolating incipient additive (bias) faults, ii) robust against changes in the references/disturbances affecting the controlled DFIG and PMSG as well as modeling/parametric uncertainties, iii) residual generation system based on a multi-observer strategy to enhance the isolation process, The designed sensor FDI systems have been validated using measured voltages, as well as simulated data from a controlled DFIG. First the state space models of DFIG and PMSM explained followed by kalman filter introduction and current sensor fault detection using a bank of kalman filter named dedicated Observer Scheme and generalized Observer scheme to detect simultaneous and multiple faults was theorized and simulated using MATLAB simulation tool .The simulation results were summarized with and without Sensor fault.

The potential of offshore windfarms to act as marine protected areas – A systematic review of current evidence

As offshore windfarm (OWF) construction in the UK is progressing rapidly, monitoring of the economic and ecological effects of these developments is urgently needed. This is to enable both spatial planning and where necessary mitigation in an increasingly crowded marine environment. One approach to mitigation is co-location of OWFs and marine protected areas (MPAs). This systematic review has the objective to inform this co-location proposal and identify areas requiring further research. A limited number of studies addressing marine renewable energy structures and related artificial structures in coastal waters were found. The results of these studies display a change in species assemblages at artificial structures in comparison to naturally occurring habitats. An increase in hard substrata associated species, especially benthic bivalves, crustaceans and reef associated fish and a decrease in algae abundance were the dominant trends. Assemblages associated with complex concrete structures revealed greater similarity to natural hard substrata compared to those around steel structures. To consider marine renewable energy sites, especially large scale OWFs as MPAs, the dissimilar nature of assemblages on the structures themselves to natural communities should be considered. However positive effects were recorded on the abundance of commercially important crustacean species. This suggests potential for incorporation of OWFs as no fishing, or restricted activity zones within a wider MPA to aid fisheries augmentation. The limited available evidence highlights a requirement for significant further research involving long term monitoring at a variety of sites to better inform management options.

Resource Use of Wind Farms in the German North Sea—The Example of Alpha Ventus and Bard Offshore I

The German government aims to obtain at least 40 percent of its electricity from renewable sources by 2030. One of the central steps to reach this target is the construction of deep sea offshore wind farms. The paper presents a material intensity analysis of the offshore wind farms Alpha Ventus and Bard Offshore I under consideration of the grid connection. An additional onshore scenario is considered for comparison. The results show that offshore wind farms have higher resource consumption than onshore farms. In general, and in respect to the resource use of other energy systems, both can be tagged as resource efficient.

Framework for assessing impacts of pile-driving noise from offshore wind farm construction on a harbour seal population

Offshore wind farm developments may impact protected marine mammal populations, requiring appropriate assessment under the EU Habitats Directive. We describe a framework developed to assess population level impacts of disturbance from piling noise on a protected harbour seal population in the vicinity of proposed wind farm developments in NE Scotland. Spatial patterns of seal distribution and received noise levels are integrated with available data on the potential impacts of noise to predict how many individuals are displaced or experience auditory injury. Expert judgement is used to link these impacts to changes in vital rates and applied to population models that compare population changes under baseline and construction scenarios over a 25year period. We use published data and hypothetical piling scenarios to illustrate how the assessment framework has been used to support environmental assessments, explore the sensitivity of the framework to key assumptions, and discuss its potential application to other populations of marine mammals.

Diel variation in feeding and movement patterns of juvenile Atlantic cod at offshore wind farms

Atlantic cod (Gadus morhua) is a commercially important fish species suffering from overexploitation in the North-East Atlantic. In recent years, their natural environment is being intensively altered by the construction of offshore wind farms in many coastal areas. These constructions form artificial reefs influencing local biodiversity and ecosystem functioning. It has been demonstrated that Atlantic cod is present in the vicinity of these constructions. However, empirical data concerning the diel activity and feeding behaviour of Atlantic cod in the vicinity of these artificial reefs is lacking. Atlantic cod has a flexible diel activity cycle linked to spatio-temporal variations in food availability and predation risk. In this study we integrated acoustic telemetry with stomach content analysis to quantify diel activity and evaluate diel feeding patterns at a windmill artificial reef (WAR) in the Belgian part of the North Sea. Atlantic cod exhibited crepuscular movements related to feeding activity; a 12h cycle was found and the highest catch rates and stomach fullness were recorded close to sunset and sunrise. It is suggested that the observed diel movement pattern is related to the prey species community and to predation pressure. Foraging at low ambient light levels (i.e. at dusk and dawn) probably causes a trade-off between foraging success and reducing predation pressure. Fish did not leave the area in-between feeding periods. Hence other benefits (i.e. shelter against currents and predators) besides food availability stimulate the aggregation behaviour at the WARs.

A semi-analytical model for the prediction of underwater noise from offshore pile driving

Underwater noise from offshore pile driving gained considerable attention in recent years mainly due to the large scale construction of offshore wind farms. The most common foundation type of a wind turbine is a monopile, upon which the wind tower rests. The pile is driven into place with the help of hydraulic hammers. During the hammering of the pile, high levels of noise are generated which are known to produce deleterious effects on both mammals and fish. In this work, a linear semi-analytical model is developed for predicting the levels of underwater noise for a wide range of system parameters. The model incorporates all major parts of the system. The hydraulic hammer is substituted by an external force, the pile is described as a thin circular cylindrical shell, the water is modelled as a compressible fluid and the water-saturated seabed is defined by distributed springs and dashpots in all directions. The solution of the coupled vibroacoustic problem is based on the representation of the response of the complete system on the modal basis of the in vacuo shell structure. The influence that the inter-modal coupling, the choice of the soil parameters and the acoustic impedance of the seabed have on the generated noise levels is studied in the frequency domain. Strong and weak points of the present model are discussed on the basis of a comparison with a set of available experimental data. The obtained results show the capability of the model to predict the underwater noise levels both qualitatively and quantitatively.

풍력발전기의 에너지 비용 산출에 대한 고찰

Large offshore wind farms have actively been developed in order to meet the needs for wind energy since the land-based wind farms have almost been fully developed especially in Europe. The key problem for the construction of offshore wind farms may be on the high cost of energy compared to land-based ones. NREL (National Renewable Energy Laboratory) has developed a spreadsheet-based tool to estimate the cost of wind-generated electricity from both land-based and offshore wind turbines. Component formulas for various kinds and scales of wind turbines were made using available field data. In this paper, this NREL estimation model is introduced and applied to the offshore wind turbines now under designing or in production in Korea, and the result is discussed.

Diversity of demersal and megafaunal assemblages inhabiting sandbanks of the Irish Sea

Sandbanks are marine habitats of conservation importance under the EU Habitats Directive. These habitats are becoming subject to impacts of several human activities including fishing, aggregation extraction, and construction of offshore wind farms that may have detrimental effects on their structure and functioning. We characterised and com- pared the diversity and biological traits of demersal fish and megafaunal invertebrate assemblages inhabiting three sand- banks, one in the vicinity of a small existing wind farm and two which are proposed sites for future wind farm installa- tions. Samples in the vicinity of the offshore wind farm were compared with two control sites on the same sandbank. There were significant differences in mean number of taxa, abundance and structure of assemblages between sand- banks. However, biological traits analyses (BTA) showed no differences in the functional traits of assemblages among sandbanks, suggesting functional redundancy. Despite a significant spatial variation in structure and Shannon diver- sity of assemblages between sites within sandbanks, fish and megafaunal assemblage did not differ between sites near wind turbines and the controls. The natural spatial variabil- ity in the diversity and biological traits of demersal and megafaunal assemblages inhabiting this naturally highly disturbed environment is larger than any changes associated with the presence of the wind turbines. This study provides important baseline data against which potential future impacts of human activities can be tested.

Consequences of a cumulative perspective on marine environmental impacts: Offshore wind farming and seabirds at North Sea scale in context of the EU Marine Strategy Framework Directive

Legal requirements in context of the EU Marine Strategy Framework Directive require increased trans-national cooperation on environmental effects induced by marine uses to achieve Good Environmental Status by 2020. Interactions between offshore wind farms and seabirds represent a valuable example of how a changed spatial perspective might influence the assessment of environmental impacts. This paper addresses the potential consequences of offshore wind farm development at the North Sea scale on selected seabird species with high relevance in context of national approval procedures. It provides a new methodology to estimate the cumulative habitat loss due to ongoing and planned offshore wind farm construction activities within the North Sea's exclusive economic zones of Germany, the Netherlands, Belgium and the United Kingdom. In addition to providing information on the seasonal distribution of important species and initial estimates of potential seabird habitat exclusion due to offshore wind farming, this study highlights the need for increased trans-national cooperation among riparian states and harmonization of conservation approaches to successfully implement the Marine Strategy Framework Directive.

Underwater radiated noise and impact assessment of marine piling operations during offshore windfarm construction

In UK waters numerous large scale offshore wind farm developments have been constructed typically using large hollow steel mono-pile foundations with pile diameters varying from a few meters to greater than 6 m diameter and lengths 60-80 m. Piles may be driven 20-30 m into the seabed in water depths from a few meters to greater than 30 m. Typically percussive piling construction operations are used with many thousands of individual strikes over periods of several hours resulting in repetitive high amplitude impulsive sound within the water column that has potential for impact on marine life. Data is presented for in-situ measurements made during installation a range of mono-pile diameters used on offshore windfarms. Full piling sequences were recorded at fixed ranges using fixed autonomous data loggers and sampled range dependent boat based measurements. Simultaneous recordings at multiple ranges varying from 10’s meters to 10’s km were made. Data is analyzed in terms of received levels, spectral and temporal components. Using range dependent propagation loss modeling equivalent mono-pole source levels are estimated. Level dependence on range, hammer energy, etc. are discussed. A Monte Carlo approach is used to obtain total cumulative exposure (SEL) risk for single foundation to whole windfarm construction scenarios.

The Application of Modified Delphi Method in the Topological Optimization Site Selection of Offshore Wind Farm

Core of the topological optimization site selection of offshore wind farm is Delphi method. The paper divides the investigated experts into industry experts and professional experts, which respectively score the weighting coefficient and its value of the influence factors of offshore wind farm. The separate marking scheme can well develop the ability of experts, avoid the specialty bias and thereby improve the assessment accuracy. Another modification is to apply the accumulative vote method in the first stage of topological optimization site selection instead of designers’ own judgments, which gives a good solution to classify the disputed factors, and avoids fault or deviation due to the knowledge deficiency of designers. In addition, the data analysis results should be reassessed by the industry experts. And in company with the reassessment opinion the data analysis results are the basis for designers to determine the best sea area for offshore wind farm construction, which gives an extra guarantee for the scientific site selection.

Using real options to compare the economics of nuclear power and wind power with electricity from natural gas

The real options method provides one objective basis for judging when (if at all) it is reasonable to invest in a product in competition with another, the future price of which may exhibit a high degree of uncertainty. This article uses the real options technique to find the economically desirable start-up dates for three carbon-free methods of generating electricity, nuclear, onshore wind, and offshore wind, when facing competition from electricity generated from natural gas. The fact that the same assessment method has been used for each of the three carbon-free options allows intercomparability of the results. Nuclear power is projected to become competitive with gas-based electricity in 2015, even when no benefit is claimed for its carbon-free properties. Using the same yardstick, unaided onshore wind power first becomes competitive with gas in 2032 and unaided offshore wind power in 2040. There is thus a wide disparity among the dates of competiveness for the three methods of generation considered. Judged on a level playing field for carbon-free technologies, nuclear power emerges as a much better investment than onshore wind, while onshore wind is better than offshore wind. The analysis provides an explanation for the significant number of utilities who have declared an interest in New Nuclear Build in the UK in the near future. It shows that these utilities can be expected to make money immediately after their plants start up, even if they are given no credit for the carbon-free nature of nuclear generation. By contrast, the economics of wind power look more problematic. Even given the current level of intervention, £40/MWh, equivalent to £90/t CO2 avoided, onshore wind farms are not expected to become competitive with gas generation for about 15 years. That timescale stretches to over 20 years if no intervention is made. The situation is worse for offshore wind farms, which do not become competitive until 2028 even when given twice the aid offered to onshore wind farms: £80/MWh, equivalent to £180/t CO2 avoided. Without this high level of support, offshore wind farms are not expected to become competitive with gas generation for nearly 30 years even when allowance is made for the improved technology associated with series build. While wind technology is likely eventually to become competitive with gas, the real options analysis suggests that it would require significant cost reductions for a major, early deployment of wind power to become justified. It would appear to be a particularly questionable use of resources to spend money developing offshore wind farms so far in advance of their likely cost-effectiveness. The real options analysis suggests that large-scale construction of offshore wind farms should be delayed until the late 2030s.