Concept Development Protocol

The scope of this thesis is to address methodologies of assessment of combined floating wave and wind energy platforms in conjunction with the development of a specific platform which adheres to the specific criteria necessary for the development of a successful hybrid wave-wind device for deployment in high energy sites. This section outlines the development protocol of the IEA-OES, to which both European and American developers are urged to adhere during the process of development of marine energy technologies. Since the device development process extends from applying fundamental laws of physics at the proof of concept stage to implementing heavy offshore engineering design and fabrication at the prototype sea trial stage, it lends itself to following a structured, phased programme similar to the National Aeronautics and Space Administration’s (NASA) Technology Readiness Level (TRL) approach [14]. The principle idea of such a development schedule is to sequence the design development through various levels so the required knowledge is obtained at different stages. In the case of ocean energy devices the stages can conveniently be linked to different device scales by following Froude Similitude Laws and geometric similarity. This scaling law however does not account for all physical phenomena correctly at each scale, hence the various stages of development. The Structured Development Plan proposed is modified slightly from the NASA TRL approach in that some of the TRL levels are grouped into “Stages”, based on the application of Froude scaling to the WEC model, whereby five Stages now form the Structured Development Plan incorporating the nine TRL levels as illustrated in Figure 2-1.

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Figure 2-1: IEA-OES 5 Stage Structured Development Plan [14]

A comprehensive description of each Stage is given in an IEA-OES Annex II report [14]. For clarity and for structure of this chapter, a description of each of the five Stages is included below from the aforementioned report. Reference [15] also outlined the development of wave energy devices in Denmark. The approach is similar to the concept development protocol as outlined.

2.1.1 Stage 1 (TRL 1-3) – Concept Validation

This development stage consists of testing the idea as an idealised small scale (~

1:50) model in a set of monochromatic, regular waves followed by panchromatic, irregular sea states. The former tests are to identify and describe the physical processes in relation to the design variables such that the device geometry can be optimised. The latter are to estimate the performance potential in realistic seaways.

Hull seaworthiness and mooring suitability can also be established.

2.1.2 Stage 2 (TRL 4) Design Validation

This development stage uses a more sophisticated model (~1:10) and tests cover a more extensive range of sea states, including realistic survival conditions. During this phase engineering is introduced in the form of a preliminary design and an elementary costing of the system components is established. Based on the measured power absorption in a range of sea states the annual energy production is calculated using a set of generic wave conditions.

2.1.3 Stage 3 (TRL 5-6) Systems Validation

This development stage includes the testing of all sub-systems incorporating a fully operational power take-off (PTO) that enables demonstration of the energy conversion process from wave to wire. If the projected cost of energy production is acceptable, Stage 3 is entered in more detail with the aim to test the complete wave energy converter at a selected sub-prototype size (~ 1:4) that can safely be deployed

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at sea and produce power. The device is still small enough to facilitate easier handling and operation but large enough to experience deployment, recovery and maintenance techniques at sea. The first involvement with licenses, permissions, certification and environmental requirements will be encountered. Also, design teams will experience manufacturing and production and supply chain issues, though the device may not be grid connected. Productivity remains a key stage gate requirement in these tests.

2.1.4 Stage 4 (TRL 7-8) Device Validation

This development stage is a critical part of the process and covers a solo machine pilot plant validation at sea in a scale approaching the final full scale (~ 1:1). This stage is a proving programme of designs already established rather than actually experimenting with new options. Tests can be initially conducted at a moderate sea state site prior to extending to proving at an exposed ocean location. This is a very exacting requirement however, since it involves all components from each sub-systems conversion process. The device as a whole must be proven fit for purpose before this stage is concluded and must also be grid connected before the end of the proving trials. Heavy engineering operations at sea are involved so health and safety requirements become important, as do O&M of the plant under realistic conditions.

Since only a simple unit is involved, environmental impact will be minimal but monitoring of the machine’s presence in a given location must be undertaken.

2.1.5 Stage 5 (TRL 9) Economics Validation

This final development stage involves multiple device testing, initially in small arrays (~3-5 machines) which can be expanded as appropriate. By the conclusion of the previous sea trials, the technology and engineering of a device should be well established and proven. The technical risk of Stage 5 should, therefore, be minimised. However, the consequence of failure would be significant and the financial risks are less certain since it is the economic potential of the devices deployed as a generating wave park that are under investigation. Initially the hydrodynamic interactions of the devices will be investigated, together with the combined electricity supply stability possible via the power electronics. Availability and service scenarios will be important issues as more machines are deployed as will onshore and offshore O&M requirements. Environmental aspects, both physical and biological, can now be studied in detail as well as the socio-economic effect the wave park will have on the local areas. Early stakeholder involvement is recommended.

It should be noted here that while the above development processes may only refer directly to WECs, they are also the recommended development protocol for floating offshore wind energy converters.

Each of the stages of development described briefly above, incorporate a number of tank testing procedures, mathematical/numerical modelling for power absorption and

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structural analysis as well as economic modelling as detailed in Figure 2-2. The following section of this chapter is dedicated to establishing the state of the art in each of these topics relating specifically to Stage 1 and 2.

This thesis is focussed on the provision of methods of assessment of early stage offshore wind, wave and combined energy devices through LCCA modelling. In the early stages of development of concepts, the information required for LCCA modelling may not be available. This thesis is dedicated to determining the information required and how this information is attained while satisfying the development protocol.

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Figure 2-2: Concept Development Protocol

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