Mixed wave energy arrays: Going beyond the status quo

Abstract

Wave energy represents a highly predictable and energy-dense renewable resource with the potential to contribute significantly to future low-carbon energy systems. Despite decades of research and the existence of numerous Wave Energy Converter (WEC) concepts, large-scale commercial deployment remains limited. This is primarily due to high capital costs, deployment in adverse offshore conditions, technological uncertainty, and challenges associated with scaling from single devices to array-level deployments. Most existing wave energy arrays are deployed as mono-arrays, consisting of identical devices operating in the same degree of freedom. While this approach simplifies design and control, it may limit flexibility in array design and constrain overall hydrodynamic and economic performance.

This dissertation introduces and systematically investigates the concept of mixed wave energy arrays, in which different types of WECs operating in distinct degrees of freedom are deployed within the same array. The central hypothesis is that combining devices with complementary hydrodynamic characteristics can influence array-level power absorption, directional behaviour, and techno-economic performance relative to conventional mono-arrays. By exploiting differences in resonance behaviour, radiation characteristics, and wave-structure interaction mechanisms, mixed arrays may offer alternative pathways for improving energy capture while balancing spatial and economic constraints.

The thesis begins by introducing an accurate and computationally efficient numerical framework for analysing the hydrodynamic behaviour of both mono and mixed WEC arrays. To this end, the HAMS-MREL solver is formulated, extended, and validated for multi-body and multi-degree-of-freedom systems. The model explicitly accounts for wave-structure interactions, array effects, and directional wave incidence, enabling consistent and systematic assessment of single devices and arrays of increasing complexity. Validation against analytical solutions, experimental data, and established numerical tools, together with parallelised implementations, demonstrates the suitability of the framework for array-scale investigations.

This modelling framework is then applied to examine and compare the hydrodynamic behaviour of mono and mixed arrays in both shallow- and deep-water environments. A broad range of array configurations is considered under regular and irregular wave conditions, allowing the influence of device type, spacing, layout, and wave directionality to be assessed. The analyses provide insight into how hydrodynamic interactions and directional effects differ between mono and mixed arrays, and how these differences influence array-level behaviour across a range of operating conditions.

Finally, the hydrodynamic analyses are integrated with a techno-economic assessment of wave energy arrays. Using representative cost models and site-independent assumptions, the levelised cost of energy of mono and mixed arrays is evaluated alongside spatial performance indicators such as array footprint. This combined assessment enables a consistent comparison of alternative array concepts, highlighting the trade-offs between energy production, spatial efficiency, and economic performance in different deployment contexts.

Overall, the findings of this thesis demonstrate that mixed wave energy arrays constitute a viable alternative to conventional mono-technology deployments and merit consideration in future wave energy farm design. By jointly examining hydrodynamic behaviour, spatial characteristics, and techno-economic implications at the array scale, this work provides a structured framework for evaluating next-generation wave energy arrays. The modelling tools and insights developed in this thesis form a foundation for future optimisation studies, control integration, and site-specific assessments aimed at advancing the commercial viability of wave energy systems.