An oscillating water column (OWC) wave energy converter (WEC) is a device designed to extract energy from waves at sea by using the water to move trapped air and thus drive an air turbine. Because the incident waves and the force caused by the power take-off (PTO) interact, control of the power take off (PTO) system can increase the total energy converted. A numerical model was developed to study the interaction of an OWC with the water and other structures around it. ANSYS AQWA is used here to find the effects on the water surface in and around the central column of a five-column, breakwater-mounted OWC. For open OWC structures, coupled modes were seen which lead to sensitivity to incident wave period and direction. The frequency-domain displacements of the internal water surface of the central column were turned into a force-displacement, time-domain model in MATLAB Simulink using a state space approximation. The model of the hydrodynamics was then combined with the thermodynamic and turbine equations for a Wells turbine. A baseline situation was tested for fixed turbine speed operation using a wave climate for a region off the north coast of Devon. A linear feedforward controller and a controller based on maximising turbine efficiency were tested for the system. The linear controller was optimised to find the combination of turbine speed offset and proportional constant that gave maximum energy in the most energy abundant sea state. This increased the converted energy by 31% in comparison to the fixed speed case. For the turbine efficiency control method, the increase was 36%. Energy conversion increases are therefore clearly possible using simple controllers. If increased converted energy is the only criterion for controller choice, then the turbine efficiency control is the best method, however the control action involves using very slow turbine speeds which may not be physically desirable.

Public support for renewable energy projects is important in transitioning towards a more sustainable energy system. However, the literature investigating local energy acceptability has predominantly focused on understanding local opposition to single (wind) energy projects. As a result, it has relatively little to say about the construction of support for such projects, and about the relative acceptability of other local contributions to sustainability. Also, by focusing on oppositional responses to energy projects, the willingness and ability of local communities to contribute constructively to the design of locally-supported energy developments has also been overlooked by many previous studies. In response to these limitations, this research adopted a focus on early stage ‘upstream’ deliberation of multiple local energy alternatives, using the British island of Guernsey as a case study. Informed by social representations theory, three studies investigated how potential future offshore wind, tidal and wave energy projects were represented by Guernsey residents to threaten, enhance or fit place-related values and meanings associated with Guernsey and its coast and sea. Working collaboratively with the Guernsey government’s Renewable Energy Team, a mixed methods approach with a focus on participatory, visual methods was adopted, including auto-photography (Study 1), deliberative focus groups (Study 2) and a questionnaire survey (Study 3). The research found Guernsey and its coast and sea to be meaningful to local residents in many ways and at different scales, including as a unique island in need of more independence, with a coast that is valued for its quietness, wildlife, leisure opportunities, tides, natural beauty and as a space for exploration. Public understandings of tidal and wave energy as a local energy option were highly diverse, and subsequently some but not all local offshore renewable energy options were represented as ‘fitting’ these place-related meanings. In particular, the notion of Guernsey’s local distinctiveness was found to be important; tidal energy projects were represented as enhancing this distinctiveness, while offshore wind energy was instead portrayed as making Guernsey more like everywhere else. Overall, local energy acceptance at such an upstream stage was found to depend to a substantial extent on the technology chosen, the selected site for the project, and on how the project is interpreted relationally within a context of wider energy systems, policies and the perceived availability of (more appealing) local alternatives. This thesis suggests that adopting an upstream, visual, place-based approach could be one way to both achieve a better academic understanding of the acceptability of local energy projects, and to contribute to the development of more acceptable energy development practices in the future.

Offshore renewable energy systems, such as Wave Energy Converters or an Offshore Wind Turbine, must be designed to withstand extremes of the weather environment. For this, it is crucial both to have a good understanding of the wave and wind climate at the intended offshore site, and of the system reaction and possible failures to different weather scenarios. Based on these considerations, the first objective of this thesis was to model and identify the extreme wind speed and significant wave height at an offshore site, based on measured wave and wind data. The extreme wind speeds and wave heights were characterized as return values after 10, 25, 50, and 100 years, using the Generalized Extreme Value method. Based on a literature review, fragility curves for wave and wind energy systems were identified as function of significant wave height and wind speed. For a wave energy system, a varying failure rate as function of the wave height was obtained from the fragility curves, and used to model the resilience of a wave energy farm as a function of the wave climate. The cases of non-constant and constant failure rates were compared, and it was found that the non-constant failure rate had a high impact on the wave energy farm's resilience. When a non-constant failure rate as a function of wave height was applied to the energy wave farm, the number of Wave Energy Converters available in the farm and the absorbed energy from the farm are nearly zero. The cases for non-constant and an averaged constant failure of the instantaneous non-constant failure rate as a function of wave height were also compared, and it was discovered that investigating the resilience of the wave energy farm using the averaged constant failure rate of the non-constant failure rate results in better resilience. So, based on the findings of this thesis, it is recommended that identifying and characterizing offshore extreme weather climates, having a high repair rate, and having a high threshold limit repair vessel to withstand the harsh offshore weather environment.