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With larger shares of renewable energy sources in the generation mix, their inherent variability and intermittency increasingly challenge power system stability. One strategy to mitigate the variability of renewable energy sources is to co-locate complementary energy sources. This article reviews the concept of renewable energy complementarity, with a particular focus on metrics for complementarity assessment. Twelve distinct metrics are identified and classified into four groups: statistical, fluctuation-based, event-based, and effectiveness metrics. Of the reviewed articles, approximately one-third employed the Pearson correlation coefficient, and more than half focused on wind-photovoltaic (PV) combinations. The identified metrics are compared in this study using both synthetic test data and meteorological reanalysis data. Our analysis reveals that metrics designed for more than two sources tend to overestimate complementarity, and no single metric consistently captures all relevant aspects. We recommend the combined use of multiple metrics, chosen for the intended application, to ensure a robust and transparent assessment.

The Nordic synchronous area strives to achieve a fossil-free energy system, requiring significant expansion of renewable electricity generation. While onshore wind power is technologically mature, offshore wind, particularly floating installations, offers access to stronger and more consistent wind resources in deeper waters. In this study, the potential of floating offshore wind power in the Nordic synchronous area is evaluated through a 21-year (2004-2024) wind resource analysis using ERA5 reanalysis data for 11 geographically distributed sites across several seas. A MATLAB-based model was developed to simulate the wind power generation. Simulating local compressed air energy storage at each site and centralized hydropower storage, the total losses and curtailments of the proposed system are determined. A system with both local and centralized storage demonstrates greater reliability in providing a baseload to the grid than a system with only local storage. Additionally, the geographical smoothing significantly reduces variability, with correlation between sites decaying exponentially with distance. The system has the potential to provide 187.3 TWh annually. Furthermore, the seasonal variation in the Nordic synchronous area was integrated into the model. It showed higher demand during the winter and lower demand during the summer, and demonstrated reliability in providing a baseload to the grid, with an annual output of 189.5 TWh. Floating offshore wind, combined with local storage and existing hydropower flexibility, can contribute to the Nordic synchronous area for baseload supply and enhance system reliability while expanding generation and supporting the region's decarbonization goals.

The large-scale deployment of renewable energy at sea offers an opportunity to combine complementary resources within shared offshore infrastructure. While co-location of wind, wave, and solar energy has been proposed as a means to reduce variability and costs, the global conditions under which hybrid offshore power parks are economically preferable remain poorly understood. This study performs a global, temporally high-resolved, techno-economic assessment of offshore wind, wave, and floating solar power, both as stand-alone and co-located systems. Using hourly ERA5 reanalysis data for the period 2020–2024, energy generation from each technology is modelled, and the levelized cost of energy (LCOE) for hybrid parks is minimized subject to shared grid infrastructure and curtailment. The optimization is performed for two cost scenarios representing present-day and near-future capital expenditure levels. Results show that LCOE ranges from 0.04–0.16 €/kWh under present-day conditions and 0.02–0.09 €/kWh under near-future scenarios. Co-location is rarely cost-optimal in regions with excellent single-resource conditions, but can yield lower LCOE than single-technology deployment in locations with moderate and complementary resources. Negative correlations between hourly energy profiles, even when weak (−0.3 to −0.2), are shown to systematically reduce LCOE in mixed systems. While the optimal technology mix is sensitive to assumed cost levels, the underlying drivers (solar capacity factor, resource availability and intersource correlation) for co-location remain robust. These findings provide a global perspective on where and why hybrid offshore energy systems can contribute to a cost-efficient and resilient future energy supply.

As the world transitions to renewable electrification to reduce CO2 emissions, remote island electrification remains a challenge. Although some islands are connected to the grid, many still rely on fossil fuels for electricity generation. Several studies indicate that renewable energy sources, such as wave energy, have the potential to make these islands self-reliant because of their substantial power potential. However, research on the control of power electronics converters for these systems remains limited. This paper proposes isolated grid-forming control for island electrification to address this gap using a wave energy converter and an energy storage system. Resistive loading control is implemented to optimize the power absorption of the generator. The result illustrates the establishment of the required AC voltage and 50 Hz frequency in the island load, ensuring harmonics compliance with the recommended standards. Experiments were conducted to test and validate the operation of different converter controls. The results also demonstrate the converter's ability to black-start the island load and automatically transition the load current with varying loads in a few milliseconds. Furthermore, the power quality produced by the wave energy converter presents one of its significant challenges. Therefore, the performance of two distinct converter technologies was compared. The performance of the IGBT converter was evaluated against that of the SiC-based converter in terms of power quality. The study demonstrates that the use of SiC enhances power quality in all switching frequencies tested, achieving the most significant reduction of 78% in current THD and 92% in voltage THD at the 25 kHz switching frequency, thus validating its advantages for wave energy converter applications.

One of the key problems with integrating renewable energy in the power grid is the inherent variability and uncertainty. One way of mitigating this issue is using complementary energy sources, that when combined reduce variability and increase system reliability or optimize resource utilization. In this paper, various metrics for renewable energy complementarity are reviewed. Definitions, methodologies and interpretations of the metrics are provided.

A particular focus is placed on the implications of the metrics for wave energy. The temporal characteristics of wave energy is often similar to that of wind power, with a time delay. Therefore, combining wave energy with wind energy as well as other energy sources offer opportunities for synergetic co-location strategies.

The paper acts as a reference map for when to use which complementarity metric, and what the metric means. Our finding underscores the importance of leveraging energy complementarity, and aids to avoid pitfalls in wrongly assessing complementarity.

With the recent advancements in the development of hybrid offshore parks and the expected large-scale implementation of them in the near future, it becomes paramount to investigate proper energy management strategies to improve the integrability of these parks into the power systems. This paper addresses a multiobjective energy management approach using a hybrid energy storage system comprising batteries and hydrogen/fuel-cell systems applied to multi-source wind-wave and wind-solar offshore parks to maximize the delivered energy while minimizing the variations of the power output. To find the solution of the optimization problem defined for energy management, a strategy is proposed based on the examination of a set of weighting factors to form the Pareto front while the problem associated with each of them is assessed in a mixed-integer linear programming framework. Subsequently, fuzzy decision making is applied to select the final solution among the ones existing in the Pareto front. The studies are implemented in different locations considering scenarios for electrical system limitation and the place of the storage units. According to the results, applying the proposed multiobjective framework successfully addresses the enhancement of energy delivery and the decrease in power output fluctuations in the hybrid offshore parks across all scenarios of electrical system limitation and combinational storage locations. Based on the results, in addition to the increase in delivered energy, a decrease in power variations by around 40 % up to over 80 % is observed in the studied cases.

In this study, the impact of data time resolution on long-term voltage stability assessment of a power grid with high penetration of wind-solar hybrid power plants is investigated. Historical and synthetic wind data as well as solar irradiance are used to calculate power output from hypothetical offshore wind-solar hybrid power plants, geographically located off the coast of Massachusetts, USA. The results show that using hourly input data can overestimate the long-term voltage stability, compared with using minute data. However, the relative difference in terms of voltage mean value and standard deviation is marginal whilst the most significant difference is the intensity of the voltage fluctuations. The main drawback of using high-resolution data is the execution time, increasing proportionally with the number of time steps. Thus, it is argued that the choice of da ta time resolution should be based on the aspects of long-term voltage stability and the size of the power grid to be studied.

This article presents the state-of-the-art and challenges related to the optimization and grid integration of farms of wave energy converters (WECs). Various physical and electrical circuit layouts have been proposed to interconnect WECs. The grid impact of wave power farms (WPFs) is associated with energy variability in ocean waves. Although fluctuations in the WPF output power might be reduced due to the farm aggregation effect, it remains highly variable, changing from minimum to maximum within several seconds. Parameters assessing the grid impact of farms of WECs are presented here, and various solutions to reduce the grid impact from WPFs are summarized.

This study uses a genetic algorithm(GA) to investigate the practicality of optimizing the geometry and dimensions of a floating platform, which houses pitching wave energy converters (WEC). Using frequency- domain analysis, sensitivity tests for the search start point, choice of optimized variable, number of iterations, simulation time, and contents of the search space are made. Results show that the required number of iterations to convergence increases with an increased number of optimized variables. Furthermore, for the studied platform geometry, no single global optimum exists. Instead, various combinations of characteristic features can lead to comparable performances of the integrated wave absorber. Finally, it is observed that when the solution space is controlled and made to contain a subset of potential solutions known to improve the system performance, computation time, absorption efficiency and range are observed to improve. Additionally, the GA optimum tends towards platform geometries for which the wave absorber's resonance response corresponds to the dominating wave climate frequencies. A key contribution of this study is the controlled manipulation of the solution space to contain a subset of potential solutions that enhance system performance. This controlled approach leads to improvements in computation time, absorption efficiency, and range of the system.

As the share of renewable energy sources in the energy mix increases, weather-dependent variations in several time scales will have a significant impact on the power system. One way of mitigating these variations is to co-locate complementary energy sources at the same location. In this study, the complementarity between offshore floating photovoltaics, wave, and wind power is analyzed and the grid impact of such co-located energy sources is addressed using capacity credit. Additionally, the possibility of installing supplementary generation capacity within existing offshore wind power farms is investigated. It is found that co-locating wave power with offshore wind results in increased capacity credit compared to stand-alone wind power farms and that in all analyzed cases, the capacity credit of the co-located energy sources exceeds the capacity credit contribution of the separate energy sources. Co-locating photovoltaics with offshore wind brings little benefit to the capacity credit, but shows potential in increasing the utilization of the transmission cable.