Case 13: Ocean Energy ComplexENGM 178 : Technology Assessment

Poseidon Energy Consultants

Alvin OclooEric Hauke

Nalla Harsha

Thayer School of Engineering at Dartmouth College

November 20, 2015

Executive SummaryOur client, Mr. Edward March has enlisted Poseidon Energy Consultants to conduct a

technology assessment of marine energy technologies for integration with offshore wind. Theclient is a believer in the economies of scale principle and has expressed a desire for determiningcost saving opportunities through utilizing shared infrastructure. He believes in the ocean asa valuable energy resource and would like to pioneer the marine technology industry with twopilot projects located in China and Europe.

Global energy demand continues to rise. With the idea of long term sustainability, the worldis depending more on renewable energies as an energy resource. Renewable energies havegrown steadily in all areas except marine energy. Offshore wind is the most widely adoptedmarine energy but cannot compete with onshore alternatives in regard to cost. Therefore,in order to accelerate the adoption of ocean energy, there is a need to improve the financialviability of offshore wind through integration with complimentary marine energy technologies.

This report assesses the integration opportunity of existing marine energy technologieswith offshore wind. An overview and introduction is given for each technology considered. Acriteria for selection was then crafted based on the assessment objectives. Each consideredtechnology was rn through the selection criteria and a leading candidate was chosen. Costsaving opportunities through the sharing of infrastructure were then identified. In addition,further cost savings through infrastructure design and technical decisions were determined.Both of these concepts were then combined to create the recommended energy complexdesign.

It is recommended to integrate offshore wind with wave point absorber technology. Further,a linear output generator point absorber design should be used. This design creates electricitydirectly and eliminates the need for components that convert mechanical energy. This technologywill share infrastructure by sharing the same offshore platform, using a shared HVDC transformer,supplying energy to a common substation, and utilizing the same electric grid cabling andmonitoring systems. In addition, it is recommended to combine these technologies with anocean renewable energy storage system (ORES). This will eliminate any penalties associatedwith forecasting error of these highly variable technologies, thereby increasing the revenuegeneration. As the ORES system is anchored to the ground, further cost can be saved byalso utilizing the ORES as mooring anchors for the platform above. Implementing a two bladedownwind turbine design will further reduce project cost. Installation cost and overall turbineweight will be reduced. This has positive effects regarding cost of the structural platform. A highvoltage DC transmission system is recommended. This system will reduce transmission lossesover large distances thereby increasing the overall energy output efficiency of the complex. Thisalso eliminates the need for robust capacitive correction electrical components.

Lastly, three regions were considered for placement of this project, China, the EU, and SubSaharan Africa. Each region is discussed with pros and cons and the client can choose aregion which best suits his vision.

Contents

1 Introduction 11.1 Client introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Overview of global energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2 Ocean Energy 12.1 Ocean as an energy reservoir . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.2 Ocean energy technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.3 Barriers to adoption of ocean energy . . . . . . . . . . . . . . . . . . . . . . . . . 3

3 Technology Assessment 43.1 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43.2 Objectives of assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53.3 Criteria description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53.4 Application of criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73.5 Wave energy technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

3.5.1 Terminators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83.5.2 Point absorbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93.5.3 Surface attenuators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

4 Ocean Energy Complex 104.1 Offshore wind turbine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104.2 Wave energy converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

4.2.1 Reduce output variability of offshore wind . . . . . . . . . . . . . . . . . . 124.3 Ocean renewable energy storage (ORES) . . . . . . . . . . . . . . . . . . . . . . 134.4 Complex concept design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144.5 Location of the ocean energy complex . . . . . . . . . . . . . . . . . . . . . . . . 14

5 Economies of Scale 155.1 Electrical equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155.2 Structural components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155.3 Operational costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165.4 Ocean energy complex farm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

6 Regional Recommendation 176.1 Overview of Europe Union . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176.2 Overview of China . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186.3 Overview of Africa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

7 Conclusion 19

8 Appendix A 20

List of Figures

1 Ocean energy technology tree . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Comparison of the technology candidates . . . . . . . . . . . . . . . . . . . . . . 33 LCOE of different energy technologies . . . . . . . . . . . . . . . . . . . . . . . . 44 Methodology used for the assessment . . . . . . . . . . . . . . . . . . . . . . . . 55 Summary of the criteria applied on the different technology candidates . . . . . . 86 Wave energy technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 A point absrober with a linear generator . . . . . . . . . . . . . . . . . . . . . . . 118 Error in forecast accuracy increases with the forecast horizon . . . . . . . . . . . 129 The increase in number of operational hours with a more consistent output . . . 1210 Operation cycle of an energy storage system . . . . . . . . . . . . . . . . . . . . 1311 ORES : charging and discharging operations . . . . . . . . . . . . . . . . . . . . 1312 Concept design of Ocean Energy Complex . . . . . . . . . . . . . . . . . . . . . 1413 Shared infrastructure opportunities . . . . . . . . . . . . . . . . . . . . . . . . . . 1514 Cost breakdown of Offshore wind turbines . . . . . . . . . . . . . . . . . . . . . 1615 Global wind speeds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2016 Global wave energy potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2017 Global tidal energy potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2118 Global ocean thermal potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2119 Global ocean current potential(during northern hemishpere winter) . . . . . . . . 2220 Global salinity gradient potential . . . . . . . . . . . . . . . . . . . . . . . . . . . 2221 Technology stage of development . . . . . . . . . . . . . . . . . . . . . . . . . . . 2322 Wind and wave correlation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2323 Different wave energy conversions . . . . . . . . . . . . . . . . . . . . . . . . . . 2424 MVDC vs AC component reduction . . . . . . . . . . . . . . . . . . . . . . . . . . 2425 HVDC vs HVAC transmission - Optimal distance to shore . . . . . . . . . . . . . 2526 Technology costs and performance data for major marine energy technologies . 25

1 Introduction

1.1 Client introduction

Our primary client, Mr. Edward March, is a container shipping magnate who strongly believes inthe untapped potential of the ocean as a renewable energy resource. The client has requestedPoseidon Energy to provide an assessment of marine energy technologies in regards to creatinga hybrid ocean energy complex using offshore wind as a baseline. The client has stressed theimportance of employing the economy of scale principle through designing a complex thatshares key infrastructure components.

The client would like to implement pilot projects in China and the European Union as heis aware of the renewable energy sector’s positive trends in these regions, but is also open toother regional recommendations. The client wishes to pioneer this industry and be among thefirst movers into the hybrid ocean energy business. The client has also expressed that costis not his main concern and more importantly wants to prove the feasibility of a hybrid oceanenergy complex.

1.2 Overview of global energy

Before outlining details of the assessment it is necessary to provide an overview of the currentglobal energy market. Global energy demand is on the rise and is forecasted to increaseby 40% over the next 30 years [1]. Along with this increase in global demand, renewableenergy production has been increasing by more than 15% a year with hydropower, onshorewind energy, and solar leading the way. However, ocean marine energy technologies haveseen less than 1% of the total renewable energy investment in year 2013 [2]. Studies haveshown that the ocean has the potential to produce over 20,000 TWh of energy per year [3].This is compared to the current annual global energy consumption of 16,000 TWh. The oceancould theoretically provide enough energy to power the entire globe. However, there is a keybarrier to the wide spread adoption of ocean energy that need to be addressed before oceanenergy technologies can become a large provider of the worlds energy needs.

2 Ocean Energy

2.1 Ocean as an energy reservoir

Earth’s surface is covered around 65% by the oceans[4]. Oceans play an integral role inthe eco-system of life on earth by influencing critical planetary phenomenon. Global climate,weather, and overall sustenance of life are heavily impacted by the oceans. The sheer vastnessof the oceans makes them susceptible to interactions with the earth’s core and other planetarybodies such as the sun and the moon. These interactions make ocean a vast reservoir ofenergy. Marine energy comprises of the energy carried by the ocean waves, tides, thermaland salinity gradients. There is potential to extract energy from the movement in the oceansas hydro-kinetic energy, the temperature gradient between surface and deep ocean as thermal

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energy, the salinity gradient between different ocean depths as osmotic power.

Also, oceans interact with atmosphere to give rise to powerful winds, which can be used togenerate wind energy. The vast ocean can act as a platform to harvest sun’s radiation as solarenergy. The above two technologies are also forms of ocean energy but not marine energyas they are not directly extracted from the ocean. We can categorize the different energytechnologies based on the source from which energy is extracted. Specific technologies ineach category share most of the advantages and disadvantages associated with the source.

2.2 Ocean energy technologies

Figure 1 below describes the method of generation of each ocean energy technology considered.

Figure 1: Ocean energy technology tree

Figure 2 gives an overview of each marine technology considered. It explains the sourceof energy generation, the advantages and disadvantages of utilizing each technology, and howthe technology compliments with offshore wind.

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Figure 2: Comparison of the technology candidates

2.3 Barriers to adoption of ocean energy

The major barrier to ocean energy adoption is its high levelized cost of energy compared toother existing energy alternatives. Levelized cost of energy (LCOE) is the industry standardfor measuring a technologys energy production efficiency. LCOE is simply the calculation ofa technologies life time cost, including all investment, operational, and fuel costs, and thendividing by the total amount of energy produced in the technologys lifetime. An equation forLCOE can be found below. This calculation includes Investments, It , Operational/MaintenanceCosts, Mt, Fuel Expenditures, Ft, and an Interest Rate r over n number of years.

In figure 3 is a graph comparing the estimated LCOE of several energy technologies. Itis easy to see that many of the current marine technologies including offshore wind are wellbehind onshore alternatives such as gas and coal. Unless costs for these marine energytechnologies can be brought down to levels comparable to onshore alternatives is it unlikelythey will be widely adopted.

There are several reasons marine technologies have high LCOEs compared to onshorealternatives. Firstly, these are still emerging technologies. Many of these have only been in usefor the past 20 or so years while seeing little investment and few new projects. Therefore they

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Figure 3: LCOE of different energy technologies

have not had the chance to develop and bring cost down through technology advancement.

Another reason is the high costs associated with installation and maintenance in an oceanenvironment. Long travel distances by water prove costly compared to roadway transportation.The ocean is a very harsh environment; high waves and storms cause structural damage andthe salt water leads to wide-spread corrosion.

Lastly, the ocean is inherently a highly variable resource. For example, wave sizes fluctuate,winds die down, and currents change with the seasons. High variations in energy output bringin a whole new set of needed infrastructure and costs to handle connection with the mainenergy grid. In addition, with the price of oil at a 5 year low, these offshore energies are at aclear disadvantage. The way to expand the use of the ocean as an energy source is to look forways to bring down the associated costs.

3 Technology Assessment

3.1 Methodology

We have conducted this assessment for both the short-term and long-term targets of thisproject in four steps. These steps can be grouped into Technology and Infrastructure approaches.Each approach starts with a broad field that looks at addressing the need of forming a feasibleocean complex. This is followed by a more comprehensive analysis which introduces boundariesand criteria based on the understanding of the ocean energy ecosystem to select complimentarytechnologies. Both technology and infrastructure integrate to form the final ocean energycomplex recommendation. Figure 4 illustrates the steps.

The first step is to complete a broad research of ocean energy technologies in all stages ofcommercial development. This is followed by shortlisting technologies that satisfy criteria that

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Figure 4: Methodology used for the assessment

favor integration with offshore wind. In parallel with technological decisions, other contributingfactorssuch as infrastructure requirements need to be considered.Both of these progressions,technology and infrastructure, are refined in order to present the final recommendation for ahybrid ocean energy complex.

3.2 Objectives of assessment

The objectives of this assessment can be summarized as below:

• integrate the chosen technology with offshore wind

• reduce cost through economies of scale by sharing infrastructure

• to recommend a regional location and timeline for a pilot project design.

To ensure objectives of the assessment are met, the five criteria described below have beenadopted for shortlisting the best-suited marine energy technology. Each marine technologywas compared against each other and against offshore wind using metrics developed for eachcriterion. The criteria are focused towards creating a successful prototype model, consideringoff-shore wind as a platform around which the ocean energy complex needs to be developed.

3.3 Criteria description

1. Spatial synergy with wind: One of the objectives of this assessment is to integrate marineenergy technology with offshore wind energy platforms and spatial synergy is key to shortlistingtechnologies for integration. To determine spatial synergy, the global generation resourceof each marine technology was overlaid with the global resource potential of wind energy.Refer Appendix A (figure15 to figure 20). Regions with common/overlapping highs in both windenergy and marine energy were observed and technologies were ranked on a metric from Highto Low. A high rated marine technology indicates it shares common resource potentials withwind energy and as a result is more likely to integrate well with an offshore wind platform. This

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will ensure a higher probability of success for the pilot project while avoiding research costs ofdeploying the hybrid complex in unproven environments.

Global marine energy resource maps for the marine technologies were obtained using theweb-GIS (Geographic Information System) tool from Ocean Energy Systems web database[13]. From the marine technologies considered, both Wave Energy and Solar PV performedwell using this criterion.

2. State of technology development: The state of technology development criteria usesthe Technology Maturity Index (TMI index) as a metric to quantify the development of emergingmarine technologies. The TMI index is developed specifically for marine technologies and isa derivation from the widely used Technology Readiness Level (TRL) index [19]. TMI ranksmarine technologies on a scale of 1 to 7 with TMI 1 representing technologies still in theirresearch and concept phase and TMI 7 representing technologies that have fully commercializedarrays. Technologies with high TMI ratings are preferred because the cost involved against thestage of development of a technology are generally lower. See Appendix A (figure 21) for thedescription of the index.

This criterion is important in supporting the assessment objective of deploying a pilot projectwithin a timeline. From the marine technologies considered, Wave Energy and Current Energyhave the highest rating of TMI 5 because of multiple full scale prototypes located in Europe,Asia, and the United States [13]

3. Smoothen output variability of wind energy: Wind is inherently a variable source ofenergy and one of the problems currently facing offshore wind complexes is the high errors inforecasting energy supply to the grid [8]. It is therefore important to select a marine technologyto integrate with offshore wind that compliments the variability of wind as an energy source.This criterion uses the source of generation for each of the marine technologies consideredand analyzes how well each source contributes to smoothening the output variability of windenergy. Three metrics are used to classify each marine technology considered;

Independent: Technologies rated as independent share similar characteristics to offshorewind in that they both utilize variable sources of energy. However, these sources are independentof wind and as a result contribute little to none in smoothing the output variability of wind energy.

Dependent: Technologies rated as dependent share the same source of generation asoffshore wind.

None: Technologies rated as none do not share characteristics in sources of generationwith wind and do not contribute in smoothening the output variability of wind energy.

To ensure that the output of the energy complex is better predicted and more reliable, marineenergy technology which can compensate variation in off-shore wind generation is considered.

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As shown in Appendix A (figure 22), waves are dependent on wind and both Wave and Offshorewind complexes generate energy from the wind. Waves provide an additional advantage in thattheir energy is sustained up to seven hours after winds have passed [8]. This will provide acontinuous generation of energy and better predictability which gives the opportunity to plan foroff-peak wind energy generation.

4. Global generation potential: The pilot project is envisioned to be expanded past theinitial recommendation and as a result, marine technology with more global generation potentialwill present more opportunities for expansion and integration with offshore wind in the future.The theoretical generation potential in terawatt-hour per year (TWh/yr) is used as a metric tocompare each marine technology. Wave energy has the highest theoretical generation potentialbetween 8,000 to 80,000 TWh/yr [7]

5. Opportunity for shared infrastructure: One of the objectives of this assessment is toreduce cost through economies of scale by sharing infrastructure and this criterion evaluatesthe potential of each marine technology considered to share common electrical and structuralcomponents with offshore wind and a proposed Ocean renewable energy storage (ORES) [17]system, discussed later in the report. Marine technologies that can share multiple infrastructurewith both offshore wind the proposed ORES system are rated on a high to low metric. A highrated marine technology easily shares electrical and structural components and this will helpin reducing the overall cost of the hybrid complex. On the other hand, a low rated marinetechnology does not share common infrastructure with offshore wind the proposed ORESsystem. The wave technology is rated high and can share electrical components such ascabling and substation components, and structural components such as platform and mooring.

3.4 Application of criteria

Figure 5 summarizes the performance of all the marine technologies considered following thecriteria outlined for technology selection. Wave energy emerged as the best suited marinetechnology for integrating with offshore wind

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Figure 5: Summary of the criteria applied on the different technology candidates

3.5 Wave energy technology

Wave energy generators have capacity factors comparable to offshore wind between 30% -40%. The three main categories of technology based on method of wave energy extraction areshown in figure below and detailed in the following sections. Point absorber technology is thechosen method for wave energy extraction and for integrating with offshore wind because it isthe most widely adopted method and provides opportunities of sharing infrastructure with theother technologies in the complex. The different types are illustrated in figure 6

Figure 6: Wave energy technologies

3.5.1 Terminators

This technology utilizes a low head system to turn a turbine to generate power. The averagegeneration of a typical terminator system is 450KW [30]. Terminators are placed perpendicular

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to direction of the wave direction. These can be used on shore or off shore applications buttend to be large in size.

3.5.2 Point absorbers

Point absorbers generate power by using a buoy unit which moves on the vertical axis as waveshit the unit. Point absorbers are the most widely used WECs with typical generations of 250KW[30] per buoy unit. Point absorbers have the ability to capture energy in all directions due totheir design. These are preferably installed off-shore locations either on the surface or beneaththe surface.

3.5.3 Surface attenuators

Surface attenuators lie parallel to the wave front and rides the wave to generate power. Theygenerate an average of 750KW [30] of power. Surface attenuators need to be oriented indirection of the waves to generate their maximum potential.

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4 Ocean Energy Complex

A successful integration of off-shore wind energy with a suitable marine energy is essentialtowards realizing the ocean as a cost competitive source of renewable energy. Firstly, theproposed ocean energy complex aims to reduce the intermittency problems of wind energy byintegrating it with wave energy. The complex further minimizes the output variability through theuse of an energy storage system, functioning as an auxiliary energy generator when required.Secondly, the complex gives the opportunity to reduce the project costs through the use ofshared infrastructure such as the platform, mooring and electrical equipment.The proposed ocean energy complex aims to meet the technical objectives of the assessmentrestated below:

• Integrate the chosen marine energy technology with offshore wind energy technology

• Realize economies of scale through the use of shared infrastructure

The design choices of the energy complex have been summarized in the following sections.

4.1 Offshore wind turbine

The design of offshore wind turbines has been traditionally adopted from onshore wind turbinesleading to constraints which limit performance and increase costs in an offshore scenario. Wepropose a customized design and component selection to reduce installation costs, increasegeneration efficiency, and reduce number of system components in the wind turbine. We aim toreduce the capital and operational costs through the design and component selection detailedbelow:

Blade design: We recommend a 2-blade wind turbine design over a traditional 3-bladesystem. The lower number of blades reduces the weight of the rotor which inturn reduces theoverall mechanical loading of the tower, lowering fabrication and material costs [14]. A 2-bladedesign can operate at higher blade tip speeds than those that are possible with a 3-bladedesign [15, 31]. This reduces the size of the gear box needed in the generation system therebylowering both costs and component weight. A 2-blade design also enables pre-assembly ofthe rotor with its blades, eliminating the need of multiple heavy lifiting equipment during on-siteinstallation.

Rotor configuration: A 2-blade design allows for a downwind configuration of the rotor.The downwind configuration allows the sensory equipment to collect wind data without theblade turbulence experienced in the case of a upwind configuration. This improves the generationefficiency of the wind turbine by orienting the system in the most optimal direction of winds.This configuration also offers better structural safety during high winds, as the blades bendaway from the tower during operation. [15]

Turbine generator: We recommend a medium voltage direct current (MVDC) technologyfor the wind turbine. This DC energy collection system eliminates the need for heavy powertransformers which are necessary in an AC collection system. This reduces the number of

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electrical components in the turbine, reducing the overall turbine weight.Refer Appendix A(Figure 24). The MVDC system utilizes DC submarine cables to transfer more power thanan equal capacity AC system. This lowers energy production costs for the wind turbine throughbetter utilization of the cabling infrastructure[28, 16].

4.2 Wave energy converter

As discussed previously, the technology assessment of different marine energy technologieshas yielded wave energy as the most suitable candidate for integration with offshore wind. Wehave chosen point absorber wave technology for integration into the ocean energy complex.The point absorber technology is the most widely adopted among different wave energy technologies.The advantages offered by the selection are detailed below:

Energy absorption: The design of point absorbers allows them to capture energy fromwaves in all directions. This eliminates the need for control systems which align the WECtowards optimal energy capture. The simple design reduces the size and the output capacityof the converters. However, the point absorbers can be delpoyed as a scalable array utilizingeconomies of scale to achieve a higher cummulative output capacity [29]

Shared infrastructure: The point absorber design limits the movement of the WEC, whichallows the placement of the device close to the wind turbine platform. This way the mainplatform mooring can be shared for securing the WECs reducing total mooring costs. Theplatform offers better protection to the WECs in rough ocean environments lowering componentand structural failures.

Figure 7: A point absrober with a linear generator

Energy generation: For converting the wave enetgy into useable power, we recommendusing a linear generator system. This type of generation reduces the number of stages ofconversion compared to traditional mutli-stage energy conversion systems such as hydraulic,rotary and turbine transfer technologies [27].Refer Appendix A (Figure 23).This system alsooffers better efficiency in a larger range of operation compared to traditional options. Also,

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the increased complexity of hydraulic or turbine systems introduces reliability and maintenanceissues which can be prohibitively expensive in an offshore environment [27].

4.2.1 Reduce output variability of offshore wind

A major concern for offshore wind is the intermittent nature of wind over the ocean causingvariablity in the output generated. A grid connected energy generator can incur a 7-8% loss ofrevenue due to inaccurate forecasting of output supply[8]. The graph below illustrates the errorin forecasting against the forecast horizon for different configurations of the energy generationsuch as wind, wave, wave combined and wind integrated with wave.

Figure 8: Error in forecast accuracy increases with the forecast horizon

We see that a wind and wave configuration has a better forecasting accuracy over a standalonewind configuration. Therefore, integrating offshore wind with wave energy would reduce theoutput variability of the combined system. Figure 9 highlights the number of zero outputhours for wind alone, wind plus wave and wave alone along wiht the capacity factor of eachconfiguration. A 75% wind and 25% wave output capacity configuration gives a more base loadlike generation for the wind plus wave system [6].

Figure 9: The increase in number of operational hours with a more consistent output

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However, there still exits a considerable error in the forecast even after integrating wind withwave. To overcome this gap we recommend an energy storage system which can compensatefor the inaccurate prediction of the system by supplying the deficiency in the complex’s output.

4.3 Ocean renewable energy storage (ORES)

An energy storage system is designed to store generated excess energy and when the demandarises, discharge the stored energy to meet the forecasted output. This eliminates the outputvariability of the wind and wave combination by ensuring that the forecasted output of the oceanenegy complex is always met. Figure 10 illustrates this through an example.

Figure 10: Operation cycle of an energy storage system

For the ocean energy complex, we recommend using an ocean renewable enegy storagesystem (ORES) [17]. The ORES uses a hydrokinetic system to generate energy. It comprisesof a concrete shell located on the ocean floor with a pump - turbine system inside it. Thisreversible pump-turbine system acts as a pump when excess energy is available and emptiesthe water stored in the shell. The excess energy is converted into a large water pressure headwhich can be utilized to regenerate energy. When an output deficiency occurs, the water is letback into the shell which causes the turbine to turn generating energy.

Figure 11: ORES : charging and discharging operations

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The concrete shell on the ocean floor also functions as mooring for the entire wind andwave platfom reducing the combined mooring costs of the ocean enegy complex [17].

4.4 Complex concept design

A concept design for the ocean energy complex is depicted in Figure 12.

Figure 12: Concept design of Ocean Energy Complex

4.5 Location of the ocean energy complex

The location of the ocean energy complex will significantly impact the overall feasibility of theproject. We recommend a deep water installation for the complex with distance to shore greaterthan 50km. The associated advantages and challenges are mentioned below.

Advantages

• Winds are stronger and waves are larger further distances from shore

• ORES has higher storage density under greater water pressure [17]

• Less visual impact on the coastline

Constraints

• Installation costs increase (higher output generation should offset the cost)

• Transmission losses are higher (Use of High Voltage Direct Current HVDC transmissioncan offset the losses).Refer Appendix A (Figure 25).

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5 Economies of Scale

The client has expressed his interest in utilizing the economies of scale principle to bring downthe cost of offshore renewable energy. This has been further detailed as utilizing sharedinfrastructures to achieve a higher energy output with lower capital expenditure. One of theselection criteria for our chosen technology was assessing the opportunity for shared infrastructurewhen combining with offshore wind. Wave energy achieved a high metric for this criteriafor several reasons. Combining wind and wave energy with a subterranean storage systempresents several opportunities for sharing electrical and structural infrastructure as well asoperational costs. The table below outlines the areas of opportunity for sharing infrastructurecosts broken down in three categories; electrical, structural, and operational.

Figure 13: Shared infrastructure opportunities

5.1 Electrical equipment

The first category listed is the sharing of electrical infrastructure. This includes things such asthe undersea high capacity cabling, substation components, and the HVDC transformer. Theseare all components that are necessary in a traditional offshore wind farm. However, we able toincrease the complex output by adding additional WECs that can share this core infrastructure.

5.2 Structural components

The next opportunity is for the sharing of structural components. The platform and mooringare our most significant opportunity for cost savings, these two components acount for 22.5%of wind turbine cost [11]. The WECs will be held in place by the same platform structurethat supports the wind turbine. The savings on mooring is twofold. First, the WECs will besecurely moored to ocean floor by the same lines that support the floating platform. Secondly,the mooring anchors will serve a dual purpose. The anchors will be large hollow concretestructures that securely anchor the technologies to the ocean floor but also serve as the neededair storage containers for employing the Ocean Renewable Energy Storage system. Since themooring anchors are already needed, the complex will not incur significant additional cost whileutilizing the benefits of energy storage technology [17]. Included in the structural category is ashared parts inventory and the decreased cost of installation through combining transportationand labor costs.

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A cost breakdown of an offshore wind turbine is shown below in figure 22 . All costsaving opportunities have been highlighted in green, such as the foundation platform cost andsubstation components. When totaled, it was determined that 55% of the total cost of anoffshore wind turbine can be reused when also employing wave energy technology as outlinedin earlier sections.

Figure 14: Cost breakdown of Offshore wind turbines

5.3 Operational costs

The final category, operational, should not be overlooked. There are many benefits to deployingan offshore energy complex utilizing multiple technologies. The cost associated with legalapprovals and licensing will come down compared to going through the process once foreach tech. Maintenance costs will be shared between the technologies such as time paid fortransportation and labor. By having more units in the complex the maintenance team can bemore productive with each visit by servicing multiple pieces of equipment. This same principlegoes for management costs. The costs already required for managing an offshore windfarmcan now be used for managing the wind plus wave.

Many of these costs listed above will have to increase when adding wave technology, butunder the economies of scale principle, the cost increase will be marginal when compared tothis additional energy output of the complex.

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5.4 Ocean energy complex farm

The farm size of the ocean energy complexes and the array configuration will further impacteconomies of scale. The configuration and size of the farm are highly dependent on the locationof the farm and desired final output capacity. These assessments are beyond the scope of theproject and need further research. The potential benefits and the practical constraints of thescaled array are mentioned below:

Advantages

• More opportunities to utilize shared infrastructure

• Improved reliability through redundancy

• Manufacturing costs lowered through economies of scale

Constraints

• Limited by the capacities of HVDC transmission cable and substation equipment

• Individual complexes should be placed at least 7 times the wind turbine diameter to ensureno loss of generation potential

6 Regional Recommendation

The client has expressed interests in implementing the pilot project in the European Union andChina due to the positive investment trends in marine energy in those regions. The client plansto seek government approval and funding to proceed with a pilot project demonstrating theconcept. However, the client has also made it clear that more suitable geographic locationscan be considered if barriers prevent meeting the pilot project timeline. As a result, regionalregulations for each location will be considered keeping in mind the clients motivations forinvesting in the hybrid ocean complex.

6.1 Overview of Europe Union

The European Union (EU) is one of the global leaders in ocean renewable production andinvestments. As of 2013, the region contributed to 6.6 GW of production from offshore windfarms [20]. Regulatory provisions and policies are the driving factors for investments in oceanenergy and there are opportunities for installing the proposed hybrid ocean complex pilotproject in this region. Policies in the recently ratified Treaty on the Functioning of the EuropeanUnion (TEFU 2013) aim to promote new and renewable forms of energy by setting memberstate production targets to 20% of produced energy coming from renewable sources by 2020[21]. The North Sea region in particular is recommended as a prime location in this region forthe hybrid pilot project. A well-established grid infrastructure will also reduce costs in sendinggenerated energy onshore.

Despite several regulatory and policy advancements in both Member Country and EUprimary law, there are barriers that must be highlighted prior to commencing with the pilotproject. The consent and licensing process is a major barrier that slows down fast adoption

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of ocean energy complexes. Stakeholders that influence the consent process are known asmarine spatial planners and involve multiple groups who have a say regarding decisions onhow ocean resources should be used. In England for example, this consent process can takeup to 2 years from the start of the application to the final approval [22].

6.2 Overview of China

In recent years, China has invested heavily in developing commercial grid connected offshorewind projects in order to meet its rising energy demand [23]. The South China Sea region isa recommended location for the proposed pilot project. Financial grants and incentives fromthe Chinese government [24] make this region a good location for the pilot project. Lowermanufacturing and transportation labor cost also make this region attractive for investment.

The major barrier to developing the pilot project in this region is that China lacks the desire toemploy more expensive energy alternatives such as ocean renewables. Chinas energy marketis primarily dependent on cheap fossil fuels, with 86% of total energy consumption coming fromcoal and crude oil in 2014[25]. Unlike the EU, China has no current energy initiative for movingtheir energy reliance away from fossil fuels. Without extensive assistance from the governmentit may prove impossible to see a return on investment in this region as you will not be ableto compete with their onshore alternatives in pricing. The second barrier is that the consentprocess for installing an offshore complex is not fully understood. It is anticipated that severalagencies will take time to come to speed with evaluating the impacts of installing an offshorehybrid complex. There are very few existing ocean energy complexes in this region so theconsent process timeline is not well known. Approval times between 2 to 5 years or possiblylonger can be expected.

6.3 Overview of Africa

The Gulf of Guinea in the West African region of Liberia was also considered as a location forthe proposed pilot project. Though this region was not part of the initial scope of assessment, itwas included because it aligned closely with the clients vision of realizing the untapped potentialof the ocean as an energy source and being a first mover in this field. Liberia has a populationof 4.2 million with less than 2% of the population having access to electricity. The governmentcurrently relies on expensive diesel fuel generators to supply about 23 MW of power to thenational grid [[26] . The government plans to provide access to 35% of the country by 2030[26] This provides a good opportunity for investment because there is a clear need for energyand the energy currently being supplied is already expensive unlike China and EU which willbe competing directly with cheap fossil fuel alternatives. If a Liberia complex is successful, itmay convince neighboring countries to consider adding ocean renewable energy technologiesto their energy production portfolio and provide opportunities for expansion in the future.

The biggest barrier to entering this region is the lack of adequate electrical infrastructureand grid connection needed to accept power from the offshore site to the national grid. Agovernment partnership may be needed to ensure success of the offshore complex. In addition,

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the licensing and consent process for this region is not well-established if at all. It will thereforetake time for the various stakeholders to become knowledgeable in offshore energies in orderto approve the project proposals. Again, government partnerships may expedite this process.

7 Conclusion

Our assessment of different marine energy technologies, with the objectives of integrating withoffshore wind, reducing costs through sharing infrastructure, and recommending pilot projectlocation, has yielded point absorber wave energy technology and an ORES system as the bestcandidates for integration with off-shore wind energy platforms.

For the design of the ocean energy complex we recommend a two-blade, downwind windturbine design with a MVDC turbine generator. A point absorber WEC using a linear generatorsystem and an ORES system is recommended as the complimentary technologies. A HVDCwill be used as the transmission system to onshore sub-station and grid connection.

We recommend sharing cabling, substation components, complex platform, mooring, andparts inventory across primary and complimentary technologies. Operational costs such asmonitoring, maintenance, management, and licensing can also be shared across the complex.

Regulatory and regional requirements were reviewed for the initial assessment regions ofEU and China with positive trends and barriers highlighted in either region. The barriers ofimplementing the renewable energy complex in the South China Sea does not make the regiona desired location for the pilot project. The North Sea region in Europe and the Gulf of Guinearegion in Liberia are recommended as locations for the pilot project. These regions align closelywith the clients vision of being a first mover in realizing the potential of the ocean as an energysource.

We recommend the client commence with the hybrid pilot project within the five years ofreceiving this report. This will allow the two-blade wind turbine design, the ORES system,MVDC turbines, and the linear generator system in the WEC to mature and be more commerciallyaccessible. From our assessment of the marine energy landscape, we advice the client on thepotential of Ocean Current Energy and Ocean Thermal as emerging technologies to combinewith offshore wind within the next 10 to15 years.

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8 Appendix A

Figure 15: Global wind speeds

Figure 16: Global wave energy potential

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Figure 17: Global tidal energy potential

Figure 18: Global ocean thermal potential

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Figure 19: Global ocean current potential(during northern hemishpere winter)

Figure 20: Global salinity gradient potential

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Figure 21: Technology stage of development

Figure 22: Wind and wave correlation

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Figure 23: Different wave energy conversions

Figure 24: MVDC vs AC component reduction

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Figure 25: HVDC vs HVAC transmission - Optimal distance to shore

Figure 26: Technology costs and performance data for major marine energy technologies

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