Modelling of a wave energy converter array with non-linear power take-off using a mixed time-domain/frequency-domain method

A mixed time-domain/frequency-domain method is proposed for modelling dense wave energy converter (WEC) arrays with non-linear power take-off (PTO). The model is based on a harmonic balance method which describes the system response in the frequency domain, while evaluating the non-linear PTO force and solving the system equations of motion in the time domain. The non-linear PTO force is computed with Lagrange multipliers. In order to apply the proposed method for WEC array responses in real sea states, the time series is split into time windows and the simulation is carried out individually per window. The method is demonstrated by investigating the dynamics of the Ocean Grazer WEC array (OG-WEC) with an adaptable piston pumping system. The key parameters thought to possibly influence model accuracy, including the number of harmonic components, the length of the time window and overlay, are discussed. It is shown that the proposed model can significantly reduce the computational cost with an acceptable accuracy penalty

Analysing the influence of power take-off adaptability on the power extraction of dense wave energy converter arrays

The aim of this work is to assess the influence of different degrees of adaptability of the power take-off (PTO) system on the power absorption of dense wave energy converter (WEC) arrays. The adaptability is included in simulations through a transmission ratio that scales the force actuating the PTO relative to the force generated by the motion of a floater. A numerical model is used in which nonlinearities in the PTO and hydrodynamic forces acting on WEC array members are considered. The lower computational cost of this numerical model makes it possible to study the power extraction of a dense WEC array in irregular waves to easily create power matrices and other performance metrics. The methodology is applied to the case study of the Ocean Grazer WEC to showcase the potential performance improvements achieved through the inclusion of a transmission ratio. The analysis shows that including a high degree of adaptability and choosing WEC array configurations and PTO designs specific to potential deployment locations early in the design process can lead to significant increase in extracted power

Techno-Economic Assessment of Offshore Wind and Hybrid Wind-Wave Farms with Energy Storage Systems

Ocean renewables (such as offshore wind and wave) are abundant and essential energy resources for supporting future emission-free targets. However, their energy intermittency and high cost have hindered commercialization and wide-scale implementations of these ocean energy technologies. This paper focuses on both issues and aims to increase the dispatchability of ocean energy farm, by investigating the potential of a hybrid wind and wave energy platform with various energy storage systems (ESSs). In the paper, a novel method is proposed to assess the ESS for an offshore renewable energy farm to guarantee the energy dispatchability to the local demand. The effect of two farm configurations on the ESS capacity is analysed: one involves wind turbines only and the other one uses a hybrid configuration (with wind and wave generation subsystems). Lifecycle cost models of energy farms are developed and the economic feasibility of different energy storage systems are investigated. The sensitivity of energy farm configurations and the energy storage systems to the resource characteristics at multiple locations are also studied. The results indicate that the combined wind and wave energy farm significantly reduces the energy storage system capacity requirement and provides competitive lifecycle costs compared to the stand-alone wind energy farm, though the amount of these benefits vary on the local resource characteristics. In addition, it was concluded that the Lithium-ion battery option in a combined energy farm offers better overall performance over the other storage options considered

Techno-financial assessment of offshore hybrid renewable energy systems:The performance of wave energy converter arrays and the sizing of renewable energy systems including generation and storage subsystems

With the environmental goals set by governmental agencies for the years 2030 and 2050 in mind, this thesis’ aim is to enhance the reliability, efficiency, and financial viability of offshore hybrid renewable energy systems and to contribute to the knowledge base available for future investments and projects in the offshore environment.The research presented in this thesis focuses on two main objectives: Improving the performance of a specific technology extracting energy from ocean waves: The technology is designed and through extensive simulations the power extraction is assessed with varying technical parameters.Quantifying the value of diversifying the energy generation technologies included in a renewable energy system: The system’s context and application is taken into account and the subsystems comprising the offshore hybrid renewable energy system are sized based on techno-financial metrics

Analysis of the impact of floater interactions on the power extraction of a dense WEC array with adaptable nonlinear PTO

This research focuses on studying the interactions between a closely spaced wave energy converter (WEC) array with an adaptable hydraulic power take-off (PTO) system. The boundary element method is used to extract the hydrodynamic and hydrostatic coefficients, while the power extraction and hydrodynamic behaviour of the array are simulated in irregular waves with a mixed frequency-time-domain (MFT) model to include the nonlinear PTO forces of each array element. The interactions between floaters are assessed and the influence of adaptability on the behaviour of the total array and its elements in comparison to single floater performance (i.e., the q factor) is analysed. The differences in performance of the WEC array are assessed with three levels of adaptability: no adaptability, adaptability per sea state and adaptability per incoming wave

Analysis of power take-off adaptability in dense wave energy converter arrays

extended abstrac