The share of renewables in the power system is increasing rapidly. Large offshore wind power plants (OWPPs) are developed at a high pace and conventional fossil fuel-based plants are decommissioned. If the OWPP gets islanded due to any contingency or in the event of a blackout, the whole OWPP will be shutdown. This paper proposes a STATCOM with a battery storage that is located at the point of common connection to an OWPP to enable OWPP energization from a fully discharged state to operate in islanded mode. The STATCOM functionality provides fast and dynamic reactive power management and the battery unit provides active power balancing capability to regulate the frequency in the island. The concept is demonstrated through time-domain simulations on an OWPP model in PSCAD. The results confirm the technical feasibility of the system.
This paper presents the methods developed and key findings of the IWEC project performed by Ocean Harvesting Technologies AB (OHT). It aimed to reduce the levelized cost of energy (LCoE) of OHT’s wave energy converter InfinityWEC, by analysing how different key parameters impact cost and annual output using a model of a 100-MW array installation. Component-level cost functions were developed and mapped to key parameters and constraints of the system. A large number of system configurations were then evaluated with a numerically efficient 3 degree-of-freedom (DoF) nonlinear radiationdiffraction model in WEC-Sim along with OHT’s sea statetuned polynomial reactive control (PRC). The most promising configurations were identified and investigated in more detail. The configuration with the best LCoE were finally identified and analysed further, including estimation of the effect of changing the PRC to model predictive control, which resulted in 17-34% higher annual output and 12-23% lower LCoE. The final LCoE was found to be 93-162 EUR MWh at 100 MW installed capacity. An important finding from the study is that using simplified metrics such as CAPEX/ton was found to be irrelevant. Numerical wave tank testing, high-fidelity computational fluid dynamics (CFD), were used to tune the viscous drag of the 3 DoF WEC-Sim model. Applying verification and validation (V&V) techniques the CFD simulations showed a relatively large numerical uncertainty, but the average power and the motion responses were found to be sufficiently accurate.
Offshore wind energy production has seen a significant expansion in the past decade and has become one of the most important maritime activities. However, the implications of offshore wind farm expansion for maritime security have, so far, received sparse attention in the literature. In this article we conduct one of the first thorough analyses of the security of offshore wind farms and related installations, such as underwater electricity cables, energy islands, and hydrogen plants.
Offshore wind energy production has seen a significant expansion in recent years. With technologies rapidly improving and prices dropping, it is now one of the key instruments in the green energy transition. The implications of offshore wind farm expansion for maritime security and ocean governance have, so far, received sparse attention in the literature. This article offers one of the first thorough analyses of the security of offshore wind farms and related installations, such as underwater electricity cables, energy islands, and hydrogen plants. The technical vulnerabilities of wind farm systems is reviewed and threats from terrorism, crime and State hostilities, including physical and cyber risk scenarios, are discussed. The expansion of green offshore energy production must keep pace with the changing threat landscape that follows from it. Prospective solutions for the protection of wind farms systems, including surveillance, patrols and self-protection are discussed. The current repertoire of maritime security solutions is in many ways capable of dealing with the threats and risks effectively if adjusted accordingly. The analysis builds important new bridges between debates in energy security and maritime security, as well as the implications of climate change adaption and mitigation for security at sea.
This report provides an assessment on the prospects for the microgrids at large ports. A survey has been developed to this end and has been evaluated by respondents to crowdsource a forecasted time horizon to implementation and its potential as an opportunity for the maritime and offshore industries. The report is produced by the PERISCOPE Group at Aarhus University for the PERISCOPE network.
Several large offshore wind power plants (WPP) are planned in the seas around Europe. VSC-HVDC is a suitable means of integrating such large and distant offshore WPP which need long submarine cable transmission to the onshore grid. Recent trend is to use large wind turbine generators with full scale converters to achieve an optimal operation over a wide speed range. The offshore grid then becomes very much different from the conventional power system grid, in the sense that it is connected to power electronic converters only. A model of the wind power plant with VSC-HVDC connection is developed in PSCAD for time-domain dynamic simulation. This paper presents the modeling and simulation of such a system. A single line to ground fault has been simulated and fault currents for the grounded and ungrounded offshore grid system are obtained through simulation and then compared.
This paper explores the application of modular multi-level converters (MMC) as a means for harnessing the power from off-shore wind power plants. The MMC consists of a large number of simple voltage sourced converter (VSC) submodules
that can be easily assembled into a converter for high-voltage and high power. The paper shows that the MMC converter has a fast response and low harmonic content in comparison with a two-level VSC option. The paper discusses the modeling approach used, including a solution to the modeling challenge imposed by the very large number of switching devices in the MMC.
In a number of experiments and field tests of point absorbers, snap loads have been identified to cause damage on the mooring cables. Snap loads are basically propagating shock waves, which require special care in the numerical modeling of the mooring cable dynamics. In this paper we present a mooring cable model based on a conservative formulation, discretized using the Runge-Kutta discontinuous Galerkin method. The numerical model is thus well suited for correctly capturing snap loads. The numerical model is verified and validated using analytic and experimental data and the computed results are satisfactory.
Taking concrete steps towards a carbon-free society, the Danish Parliament has recently approved the establishment of the world's first two offshore energy hubs on Bornholm and on an artificial island in the North Sea. Being the two first-of-their-kind projects, several aspects related to the inclusion of these “energy islands” in the current market setup are still under discussion. To this end, this paper presents a first large-scale impact analysis of offshore hubs on the whole European power system and electricity market. Our study shows that energy hubs in the North Sea contribute to increase social welfare in Europe. However, when considering the impact on each country, benefits are not shared equally. To help the development of such projects, we focus on the identification of the challenges arising from the hubs. From a market perspective, we show how exporting countries are affected by the lower electricity prices and we point at heterogeneous consequences induced by new transmission capacity installed in the North Sea. From a system point of view, we show how the large amount of wind energy stresses conventional generators, which are required to become more flexible, and national grids, which cannot always accommodate large imports from the hubs.
In 2017, Energinet and TenneT, the Danish and Dutch Transmission System Operators (TSOs), have announced the North Sea Wind Power Hub (NSWPH) project. The project aims at increasing by 36 GW the North Sea offshore wind capacity, with an artificial island collecting all the power produced by wind turbines and several HVDC links transmitting this power to the onshore grids. This project brings together new opportunities and new challenges, both from a technical and economic point of view. In this regard, this paper presents three analyses regarding the design and operation of such an offshore system. First, we perform a techno-economic assessment of different grid configurations for the collection of the power produced by wind farms and its transmission to the hub. In this analysis, two frequencies and two voltage levels for the operation of the offshore grid are investigated. Our findings show that the nominal-frequency high-voltage option is the more suitable, as lowfrequency does not bring any advantage and low-voltage would results in higher costs. The second analysis is related to the differences in operating the system with low- or zero-inertia; different dynamic studies are performed for each configuration to identify proper control actions and their stability properties. Comparing the outcomes of the simulations, we observed that voltage and frequency oscillations are better damped in the zero-inertia system; however, the risk of propagating offshore faults in the connected onshore grids is mitigated with the inclusion of the synchronous condensers. Lastly, a comparison of ElectroMagnetic Transient (EMT) and phasor-mode (also known as RMS) models is presented, in order to understand their appropriateness of simulating low- and zeroinertia systems. The results show that phasor approximation modelling can be used, as long as eigen-frequencies in power network are well damped.