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Marine energy resources could be crucial in meeting the increased demand for clean electricity. To enable the use of marine energy resources, developing efficient and durable offshore electrical systems is vital. Currently, there are no large-scale commercial projects with marine energy resources, and the question of how to design such electrical systems is still not settled. A natural starting point in investigating this is to draw on experiences and research from offshore wind power. This article reviews different collection grid topologies and key components for AC and DC grid structures. The review covers aspects such as the type of components, operation and estimated costs of commercially available components. A DC collection grid can be especially suitable for offshore marine energy resources, since the transmission losses are expected to be lower, and the electrical components could possibly be made smaller. Therefore, five DC collection grid topologies are proposed and qualitatively evaluated for marine energy resources using submerged and non-submerged marine energy converters. The properties, advantages and disadvantages of the proposed topologies are discussed, and it is concluded that a suitable electrical system for a marine energy farm will most surely be based on a site-specific techno-economic analysis.

This paper discusses the article "Assessing temporal complementarity between three variable energy sources through correlation and compromise programming." The discussed paper proposes a novel method of assessing comple-mentarity between three energy sources using correlation, compromise programming, and normalization. The method is then used to calculate a complementarity index which is applied to a case study in Poland. However, upon inspection, the normalization of the index overestimates the complementarity potential. This issue is dis-cussed in detail in this paper, and an alternative way of calculating the index is proposed, eliminating the issue of overestimating complementarity.

An important aspect in designing co-located wind and solar photovoltaic hybrid power plants is the sizing of the energy converters to achieve as efficient power smoothening as possible. In this study, the ratio of wind- and photovoltaic energy converters in a hybrid power plant is determined by minimizing the overall stored energy that is needed to facilitate constant power output. Using Fourier transform the variability is isolated at predefined time scales that are relevant for grid integration. For the investigated time scales, energy and power ratings for energy storages are determined to counteract the variability. The resulting configuration is the one that is able to achieve constant power output with minimum stored energy. It is shown that co-locating wind- and photovoltaic energy converters smoothen seasonal energy generation, and reduce the energy storage need in both the diurnal and seasonal time scales. A case study for south-eastern Sweden is presented where the wind- \& solar hybrid plant configuration that minimizes the energy storage need and therefore most closely resembles constant output power is determined. It is found that a ratio of approximately 40-45\% wind power in the hybrid power plant yields the lowest need for energy storage. The presented method is valid for any number of co-located energy sources, and can also be extended to sizing of hybrid power systems.

Co-locating renewable energy sources such aswave power, solar photovoltaic and wind power, forminga hybrid power plant, may reduce the overall variability,increase the utilization of the transmission system, and reduce the needed physical area. An important topic to address regarding the formation of hybrid power plants is which energy sources to co-locate, and to what proportions these energy sources should be included in the hybrid power plant. In this study, offshore hybrid power plants are analyzed in the North Sea region. By minimizing the plant variability the proportions of each energy source are found, forming the plant with minimal need for energy storage for constant power output operation. The added grid value of such plants is analyzed in terms of electrical infrastructure utilization and power production ramping. It is found that in conditions suitable for the wave energy converter used in the study, a plant configuration of 23% wave power, 22% wind power and 55% solar minimizes the need for energy storage. It is shown that the inclusion of wave power in a hybrid power plant lowers ramping of power generation, increases the capacity factor and provides an overall higher grid value compared to stand-alone installations.

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.

Flexibility has increasingly gained attention within the field of electrification and energy transition where a common objective is to reduce the electricity consumption peaks. However, flexibility can increase the risk of grid congestion depending on where and when and it is used, thus an overall system perspective needs to be considered to ensure an effective energy transition. This paper presents a framework to assess electricity users' contributions to grid load peaks by splitting electricity consumption data into subsets based on time and temperature. The data in each subset is separately correlated with the grid load using three correlation measures to assess how the user's consumption changes at the same time as typical grid peak loads occur. The framework is implemented on four different types of business activities at Uppsala municipality in Sweden, which is a large public entity, to explore their behaviors and assess their grid peak load contributions. The results of this study conclude that all four activities generally contribute to the grid peak loads, but that differences exist. These differences are not visible without splitting the data, and not doing so can lead to unrepresentative conclusions. The presented framework can identify activities that contribute the most to unfavorable grid peaks, providing a tool for decision-makers to enable an accelerated energy transition.