Tidal Energy Projects Research Articles

Review of tidal turbine wake modelling methods

Enabling Future Arrays in Tidal (EnFAIT) is an EU Horizon 2020 flagship tidal energy project. It aims to demonstrate the development, operation and decommissioning of the world’s largest tidal array (six turbines), over a five-year period, to prove a cost reduction pathway for tidal energy and confirm that it can be cost competitive with other forms of renewable energy. To determine the optimal site layout and spacing between turbines within a tidal array, it is essential to accurately characterise tidal turbine wakes and their effects. This paper presents a state-of-the-art review of tidal turbine wake modelling methods, with an overview of the relevant fundamental theories. Numerical and physical modelling research completed by both academia and industry are considered to provide an overview of the contemporary understanding in this area. The scalability of single device modelling techniques to an array situation is discussed, particularly with respect to wake interactions.

Relating fish distributions to physical characteristics of a tidal energy candidate site in the Banks Strait, Australia

With the tidal energy industry moving towards commercial-scale developments, it is important to consider potential interactions between tidal energy converters (TECs) and the marine environment prior to the instalment of large-scale TEC arrays. The Banks Strait, a tidal channel located in the northeast of Tasmania, Australia, was identified as a promising candidate site for tidal energy by the Australian Tidal Energy (AUSTEn) project. To gain an understanding about potential overlap between TEC arrays and fish usage of the Banks Strait tidal channel, fish density distributions were estimated from hydroacoustic surveys during the tidal resource characterization campaign. Differences in fish density were examined according to bottom–depth, bottom – type, current speed, temperature and vertical distribution. Fish densities were significantly higher at night and displayed preferences for depths between 20 – 40 m and current speeds between 1.75 – 2 m/s. Fish density was generally highest in the bottom 10 m from the sea floor at all depths sampled. Variation by temperature and bottom–type sampled was not significant. Future studies involving long-term, stationary surveys of fish densities along with repeated surveys across different seasons would provide a more wholistic picture of fish distributions in the Banks Strait to inform developers about potential device encounter probabilities.

Enhancing local support for tidal energy projects in developing countries: Case study inFlores Timur Regency, Indonesia

AbstractTidal energy is a new renewable energy source that can be used to provide electricity to remote islands, while contributing to climate change mitigation. Like all renewable energy projects, public awareness and support are not only crucial for the successful development of marine renewable energy projects too, but also aid the private sector project developers in making long‐term plans. As information about tidal energy is not easily available, public views toward it are not well known, making it challenging for the project developers to strategize implementation strategies. Moreover, the limited studies focusing on such social aspects of tidal energy come from advanced countries, highlighting the lack of focus on cases from developing countries. Our study fulfills this gap by providing a case study focusing on the social aspects of tidal energy in a developing country, which can be utilized by developers for designing their public engagement strategies. We estimate the public support for tidal energy in eastern Indonesia using two methods: (a) stages of development and (b) information provision. Using the first method, we found that support for tidal energy is lower in the initial stages, but it keeps rising once the public can realize the benefits. The second method shows that though people tend to support tidal energy, the role of information provision is dissimilar compared with western cases. Additionally, Probit modeling shows thatAge,Education,Collective Outcome Favorability, and especially,Individual Outcome Favorabilityare the key factors that positively impact the support for tidal energy in eastern Indonesia.

Public perceptions of tidal energy: Can you predict social acceptability across coastal communities in England?

Early consideration of potential societal issues faced by the nascent tidal industry is important to facilitate public engagement and potentially avoid levels of conflict that have arisen within other renewable energy sectors; general expressions of public support (as reported in national-scale attitude surveys) do not always translate into approval for local developments. It is a very appealing idea that the likely response of different types of communities to marine energy developments can be mapped and used to support planning. This study examined the attitudes of 963 people in South West England to hypothetical local tidal energy projects, analysing the results both by geographic location and according to the coastal community typology developed for England by the Marine Management Organisation. With the exception of age, demographic variables had little influence on the level of opposition to tidal energy, which instead was affected more by factors such as attitudes towards tidal energy in general (in particular its likely environmental impact), activities undertaken at the coast, and place attachment. These significant factors are typically not captured by the national census data used to determine community types. Any predictions about the acceptability of energy projects made as a result of community mapping based on demographic variables will not be a substitute for thorough public engagement and consultation, which should centre on the implications of tidal developments for the environment.

Influence of the 18.6-year lunar nodal cycle on the tidal resource of the Alderney Race, France

Resource assessment is an important phase of tidal energy projects. Extensive literature is nowadays available on this topic with most studies focussing on the time-scales of the tide or the spring-neap cycle. The evolution of the resource over longer time scales has yet received very little attention in the scientific literature. In the present contribution, we investigate the effect of the 18.6 year lunar nodal cycle on the depth-averaged current of the Alderney Race (France). Firstly, we identify the major constituents of the study zone with the UTide Matlab functions. Two datasets are used: a 36.5 day time-series of depth-averaged current and elevations acquired in the Alderney Race and a 24 year times-series of tidal heights acquired in a neighbouring harbour. The analysis shows that the tide is mostly controlled by the semi-diurnal constituents M2, S2 and N2. Secondly, we verify the ability of UTide functions to predict the changes in amplitude of the major components over decadal time-scale. Thirdly, we predict the tidal resource of the Alderney Race over the period 2014 – 2034 and analyse the yearly changes within this period. The results show that the change of resource is of the order of +/-10% and that the next decade (2020–2029) will be characterised by a significant reduction of the resource.

Assessing the consistency of in-stream tidal energy development policy in Nova Scotia, Canada

The provincial government of Nova Scotia, Canada, has provided numerous incentives for developing in-stream tidal energy projects since 2009. These incentives include co-operatively funding the development of the Fundy Ocean Research Centre for Energy with the Canadian federal government and industry partners, extensive funding of environmental impacts monitoring research for tidal energy projects, and offering direct financial incentives for tidal power produced and sold to the grid via feed-in tariffs. However, the provincial government has not treated all scales and types of tidal energy projects equally. Until recently, ambitious targets for hundreds of MW of tidal development by 2020–2025 led to tidal support policies focusing on large, utility-scale projects, with little evidence the tidal energy sector was prepared to pursue such projects in Nova Scotia or elsewhere. Some support was offered to smaller-scale, community-oriented tidal energy projects, but the rules and regulations for such projects were repeatedly changed (and sometimes revoked) between 2012 and 2018. Since the provincial legislature passed the revised Marine Renewable-electricity Act of 2018, a potentially more coherent and consistent tidal energy policy consensus appears to be forming in the province. This paper provides a review of the policies introduced, projects approved and canceled, and sectoral outlook for tidal energy development in Nova Scotia for the period 2009–2018.

Study of a cost model of tidal energy farms in early design phases with parametrization and numerical values. Application to a second-generation device

Tidal Energy Conversion farms are a promising but not yet mature technology whose costs are still highly uncertain. In order to be able to predict costs for early Technology Readiness Level (TRL) phases, this paper presents a cost model in which a detailed parametrization of all Capital Expenditures and Operation and Maintenance items has been carried out, whose results make it possible to select the best design alternative in each case. Each parameter has been updated with numerical values based on both actual and foreseen costs. A generalist tool that integrates all these parameters and that calculates, among other variables, the Levelized Cost of Energy (LCOE) has also been developed. This tool, in which the parameters have been updated, has been applied as a case study to a single-rotor GESMEY-designed generator in the case of both fixed and controllable pitch; the numerical results for the operation parameters selected are also included. The model presented in this paper is proposed in order to compare different design alternatives, under user-defined operation conditions, for tidal energy projects in early TRL phases and the effect on their LCOE.

Optimisation of tidal turbine array layouts whilst limiting their hydro-environmental impact

The economic viability of tidal energy projects will likely require large-scale deployment, with tens, or even hundreds, of turbines positioned in an array. There is limited published research available on the viability of large-scale deployments, which will depend on both the expected energy yield and potential adverse hydro-environmental impacts. This leads to the question of how best to position turbines in large-scale arrays for maximum energy capture with minimal associated hydro-environmental impacts. The primary aim of this research was the further development of an existing two-dimensional tidal flow model for optimising tidal turbine arrays relative to both power output and potential hydro-environmental impacts. Turbine impacts are simulated using a momentum sink approach and an optimisation algorithm was implemented, which determines an optimal array configuration for maximum energy capture, whilst employing spatial and environmental impact constraints. Application of the developed model to an idealised test case demonstrated that a staggered array is optimal, if one considers maximising power capture alone, while a fence layout was optimal, when considering both power output and associated impacts. In both the scenarios, the optimised configurations produced higher efficiencies than symmetrical inline arrays. To demonstrate the model’s applicability to a real tidal environment, it was applied to a case study site; the Shannon Estuary, along the West Coast of Ireland. To the authors’ knowledge, this is the first automated array optimisation model to incorporate hydro-environmental impact constraints with the aim of determining specific optimised array configurations with quantifiable efficiencies. The approach could be extremely useful for determining the economic viability of proposed arrays, enabling determination of ‘environmentally acceptable’ levels of tidal energy extraction, and thereby allowing the completion of realistic and accurate early stage cost–benefit analyses for tidal energy projects. The model is therefore, potentially, a very valuable tool for tidal energy researchers, developers and planners.

Multiresolution Large‐Eddy Simulation of an Array of Hydrokinetic Turbines in a Field‐Scale River: The Roosevelt Island Tidal Energy Project in New York City

AbstractMarine hydrokinetic (MHK) power generation systems enable harvesting energy from waterways without the need for water impoundment. A major research challenge for numerical simulations of field‐scale MHK farms stems from the large disparity in scales between the size of waterway and the energy harvesting device. We propose a large‐eddy simulation (LES) framework to perform high‐fidelity, multiresolution simulations of MHK arrays in a real‐life marine environment using a novel unstructured Cartesian flow solver coupled with a sharp‐interface immersed boundary method. The potential of the method as a powerful engineering design tool is demonstrated by applying it to simulate a 30 turbine MHK array under development in the East River in New York City. A virtual model of the MHK power plant is reconstructed from high‐resolution bathymetry measurements in the East River and the 30 turbines placed in 10 TriFrame arrangements as designed by Verdant Power. A locally refined, near the individual turbines, background unstructured Cartesian grid enables LES across a range of geometric scales of relevance spanning approximately 5 orders of magnitude. The simulated flow field is compared with a baseline LES of the flow in the East River without turbines. While velocity deficits and increased levels of turbulence kinetic energy are observed in the vicinity of the turbine wakes, away from the turbines as well as on the water surface only a small increase in mean momentum is found. Therefore, our results point to the conclusion that MHK energy harvesting from large rivers is possible without a significant disruption of the river flow.

Strategic timing of commercial-scale tidal energy investment

The many uncertainties in tidal energy conversion combine to form a significant barrier to raising private-sector capital. Mitigation and management of risk are essential if the industry is to attract equity investors. One way to manage the risk is through investment timing. The option to time an investment has value, which can be estimated. An analysis of an invest-vs-delay decision revealed a persistent, economicallyrational incentive to delay. Further inquiry identified a strategic rationale for delaying investment in tidal energy projects, given the uncertainty still present in the undertaking. As the largest sensitivity in the value of delay is the volatility of the investment’s expected cash flows, an investigation into the prevalent uncertainties was undertaken.
 This paper summarizes the real option valuation model. It then reports on results of a qualitative study of the predominant uncertainties facing developers and conditions that would help move the industry along. Predominant uncertainties reported revolve around technology reliability; site and resource knowledge; prospects for buildout; predictability of government policy and supports; prospects of off-take agreements; and supply chain capacity and costs. These are related back to the variables in the real option pricing model. The model is relevant for companies wishing to systematically evaluate timing options and communicate project value to the investment community. It can also be used by governments to evaluate the design of policies and financial supports in a way that is consistent with the priorities of financial markets.

Method for the spatial targeting of tidal stream energy policies

Policy making is called to play a decisive role in the commercialisation of tidal stream energy projects. For they are site-specific, spatial targeting of policies is needed, so that tidal stream regulations (financial supporting mechanisms, consenting procedures, etc.) could be concentrated to sites where they can achieve the greatest benefits. With this in view, the aim of this paper is: (i) to develop a new method to delimit the most suitable (target) areas for tidal stream energy policy intervention within a coastal area of interest, and (ii) to apply it to the Bristol Channel and Severn Estuary (UK). The method includes spatial numerical analysis by means of a Matlab-based code coupled with a Navier-Stokes solver. The programme works in steps, in which different constraints are imposed with a view to carry out a zoning process. As a result of this zoning process, four hotspots are selected, for which a set of policy interventions is proposed. This includes the specific levels of subsidisation for closing the grid parity gap of potential projects in each area. The method can be viewed as a supporting decision mechanism for spatially targeted policy-making and management of tidal stream energy across the Bristol Channel and Severn Estuary.

Assessment of Energy Production Potential from Tidal Stream Currents in Morocco

Energy extracted from the ocean can provide a source of regular and foreseeable electrical production at higher energy densities than any other renewable energy resource. The marine current resource is potentially great and is focused in several sites around the world. The knowledge of the energy potential, its constraints and availability are all prerequisites to determine the possibilities for the implementation of infrastructure to produce energy. They are also required to anticipate the structuring of energy routes and to respond to increasing technological needs. Several Moroccan regions want to take advantage by their coastal domain and play a role in the development of the tidal energy sector. They also want to benefit from the associated economic advantages knowing that the Mediterranean coast length is 550 km and the Atlantic length is 3000 km, respectively. The Copernicus Marine Service ocean products provide key input for such technologies, as they can be employed to help evaluate the accessible ocean energy devices and choose the most attractive sites to exploit the tidal energy projects in Morocco. The goal of this research was to evaluate and analyze the tidal marine current resource at the sites which are potentially suitable for the installation of Horizontal Axis Marine Current Turbines in Morocco. Distributions of available power of tidal energy in the Moroccan region are provided, and three possible areas are suggested for installing tidal energy conversion systems.

Cost Assessment Methodology and Economic Viability of Tidal Energy Projects

The exploitation of technologies with which to harness the energy from ocean currents will have considerable possibilities in the future thanks to their enormous potential for electricity production and their high predictability. In this respect, the development of methodologies for the economic viability of these technologies is fundamental to the attainment of a consistent quantification of their costs and the discovery of their economic viability, while simultaneously attracting investment in these technologies. This paper presents a methodology with which to determine the economic viability of tidal energy projects, which includes a technical study of the life-cycle costs into which the development of a tidal farm can be decomposed: concept and definition, design and development, manufacturing, installation, operation and maintenance and dismantling. These cost structures are additionally subdivided by considering their sub-costs and bearing in mind the main components of the tidal farm: the nacelle, the supporting tidal energy converter structure and the export power system. Furthermore, a technical study is developed in order to obtain an estimation of the annual energy produced (and, consequently, the incomes generated if the electric tariff is known) by considering its principal attributes: the characteristics of the current, the ability of the device to capture energy and its ability to convert and export the energy. The methodology has been applied (together with a sensibility analysis) to the particular case of a farm composed of first generation tidal energy converters in one of the Channel Island Races, the Alderney Race, in the U.K., and the results have been attained by means of the computation of engineering indexes, such as the net present value, the internal rate of return, the discounted payback period and the levelized cost of energy, which indicate that the proposed project is economically viable for all the case studies.

Do tidal stream energy projects offer more value than offshore wind farms? A case study in the United Kingdom

Marine-based renewable energy could help the United Kingdom (UK) move towards a more sustainable and low-carbon energy system. Today, offshore wind is the prevailing marine renewable technology but there is growing progress towards developing others, such as tidal stream energy (TSE) turbines which capture kinetic energy from tidal currents. Using historical operations data from 18 wind farms and simulated generation data for two TSE sites in the UK, we estimate that TSE projects offer about $10/MWh more in net social benefits than offshore wind projects. This estimate includes the value of energy generated, value of reduced marginal CO2 emissions, cost of visual changes to the landscape, and cost of energy generation forecast errors. However, relative to offshore wind, the increased cost of TSE projects far outweighs the increased social benefits. The levelized cost of energy (LCOE) of TSE projects is expected to be about $74/MWh to $330/MWh higher than offshore wind projects through 2050. Only with optimistic LCOE projections, small TSE projects (20MW) may be competitive (when including increased net social benefits) with small offshore wind projects by 2020.

A decision support model to optimise the operation and maintenance strategies of an offshore renewable energy farm

In order to accelerate the access into the energy market for ocean renewables, the operation and maintenance (O&M) costs for these technologies must be reduced. In this paper a reliability-based simulation tool for the optimization of the management of an offshore renewable energy (ORE) farm is presented. The proposed tool takes into account the reliability data of the simulated devices and estimations on the energy produced to create a series of results in terms of availability and maintainability of the farm. The information produced supports operational and strategic decision making regarding the O&M for offshore farms. A case study simulating a conceptual tidal energy project, consisting of an array of two tidal turbines located off the north coast of Scotland, is presented to show some of the results achievable with this model. The proposed methodology, although adopted for a tidal farm here, is generally applicable to other kinds of ORE farms.

Quantifying uncertainty in acoustic measurements of tidal flows using a ‘Virtual’ Doppler Current Profiler

Accurate characterisation of flows at tidal sites can enable the developers of tidal stream energy projects to design and model the loads on, and the performance of, tidal energy converters. Acoustic Doppler technology is versatile in the measurement of sea conditions; however, this technology can be limited in its effectiveness at measuring the small-scale kinematic fluctuations caused by waves and turbulence. A Virtual Doppler Current Profiler (VDCP) is used to sample a simulated tidal flow to understand the limitations of this type of measurement instrument whilst recording the small timescale kinematics of waves and turbulence in tidal currents. Results demonstrate the phase dependency of velocity measurements averaged between two acoustic beams and provide a theoretical error for wave and turbulence characteristics sampled under a range of conditions. Spectral moments of the subsurface longitudinal wave orbital velocities recorded by the VDCP can be between 0.1 and 9 times those measured at a point for certain turbulent current conditions, turbulence intensity measurements may vary between 0.2 and 1.5 times the inputted value in low wave conditions and turbulence length scale calculation can also vary hugely dependent on both current and wave conditions. The continuation of this work will enable effective comparison of a linear model for tidal flow kinematics against field measurements from UK tidal site data, and subsequently validate numerical models for the testing of tidal turbines.

Representation and operation of tidal energy impoundments in a coastal hydrodynamic model

A methodology associated with the simulation of tidal range energy projects through a coastal hydrodynamic model is discussed regarding its capabilities and limitations. Particular focus is directed towards the formulations imposed for the representation of hydraulic structures and the corresponding model boundary conditions. Details of refinements are presented that would be applicable in representing the flow (and momentum flux) expected through tidal range turbines to inform the regional modelling of tidal lagoons and barrages. A conceptual tidal lagoon along the North Wales coast, a barrage across the Severn Estuary and the Swansea Bay Lagoon proposal are used to demonstrate the effect of the refinements for projects of a different scale. The hydrodynamic model results indicate that boundary refinements, particularly in the form of accurate momentum conservation, have a noticeable influence on near-field conditions and can be critical when assessing the environmental impact arising from the schemes. Finally, it is shown that these models can be used to guide and improve tidal impoundment proposals.

Capital costs in tidal stream energy projects – A spatial approach

Tidal stream energy projects involve high amounts of capital, for which ex-ante economic assessments are crucial. Unfortunately, the existing models to estimate the capital costs of a tidal stream energy project are often oversimplified. Focused on single estimates on a per installed power basis, such models fail to capture the all-important sensitivity of the capital costs to project site-specific characteristics (water depth, distance to the shoreline, etc.) The objective of this work is twofold: (1) to develop a new formulation for estimating the capital costs of a tidal stream farm, and (2) to implement this formula in a Matlab-based tool coupled with a Navier-Stokes solver and thus deliver the spatial distribution of this cost. As a case study, the new tool is applied to the Bristol Channel – the single largest resource area for tidal energy in the UK. Here, the best sites to install tidal stream farms are identified, with a cost comparable to that of offshore wind energy. Simulation results show that the proposed method is more efficient than the existing approaches. The results of this work have relevant policy implications in that they serve as decision criteria for allocating tidal stream projects and for designating supporting mechanisms.

A correction to the enhanced bottom drag parameterisation of tidal turbines

Hydrodynamic modelling is an important tool for the development of tidal stream energy projects. Many hydrodynamic models incorporate the effect of tidal turbines through an enhanced bottom drag. In this paper we show that although for coarse grid resolutions (kilometre scale) the resulting force exerted on the flow agrees well with the theoretical value, the force starts decreasing with decreasing grid sizes when these become smaller than the length scale of the wake recovery. This is because the assumption that the upstream velocity can be approximated by the local model velocity, is no longer valid. Using linear momentum actuator disc theory however, we derive a relationship between these two velocities and formulate a correction to the enhanced bottom drag formulation that consistently applies a force that remains close to the theoretical value, for all grid sizes down to the turbine scale. In addition, a better understanding of the relation between the model, upstream, and actual turbine velocity, as predicted by actuator disc theory, leads to an improved estimate of the usefully extractable energy. We show how the corrections can be applied (demonstrated here for the models MIKE 21 and Fluidity) by a simple modification of the drag coefficient.

Grid parity in tidal stream energy projects: An assessment of financial, technological and economic LCOE input parameters

Assessments in electricity production technologies are usually supported by a levelised cost of energy (LCOE) analysis. Such cost analyses are riddled with uncertainty, with LCOE values depending on a number of financial, technical and economic variables. When it comes to minimising LCOE, the question arises as to which parameters have a greater bearing — especially if the current grid parity gap between tidal stream energy and conventional sources is to be narrowed. The aim of this study is to investigate the independent effects of the input variables on LCOE values, in order to determine the main drivers in closing the grid parity gap between tidal stream energy costs and traditional grid-power costs. The assessment features six tidal stream farms, in which different numbers of turbines, rows and spacing are considered. Not only are the device interactions of each configuration considered (by means of numerical modelling) but also the impacts of the financial and economic variables. In addition to individual variable sensitivity, a multivariable scenario analysis estimates the combined effect on the projected LCOE of varying an entire set of inputs simultaneously. As a result, it is found that the power coefficient is one of the inputs with the greatest bearing on the LCOE, closely followed by the discount rate and the capital costs (CAPEX). On this basis, a LCOE best-case scenario is constructed, which characterises tidal stream energy projects in terms of economic viability over a variety of conditions in four countries.