Review of Grid Code Requirements for Cost Optimization of Offshore Energy Hubs
02 HYB24-70
Presented by: Daniela Pagnani
Denmark is planning the world’s two first energy islands, also known as offshore energy hubs (OEHs), which will mark the beginning of a new era for the integration of large-scale offshore wind power. This decision is a cornerstone in reaching Denmark’s climate targets as by 2050, the Danish target is climate neutrality. One OEH is planned on the island of Bornholm (2 GW) and one in the North Sea (3 GW with later expansion to 10 GW). One of the main objectives of the research project called “Offshore Energy Hubs (OEHs)” is to develop technical solutions for the cost-efficient design of wind power plants (WPPs) connected to the OEH. As part of the project, possible cost reduction for the WPP design is investigated by reviewing grid code requirements (GCRs) and assessing their potential shift and relaxation, while maintaining the same level of operational security. In particular, it is addressed how substantial cost optimizations can be obtained by shifting relevant GCRs from the individual WPPs to the hub high-voltage direct current (HVDC) terminal.
In this paper, the main state-of-the-art review of current GCRs will be shown as well as a discussion on how the selected GCRs impact the costs related to the design and operation of the OWF. The PROMOTioN project found that for meeting the stringent GCRs in HVDC-connected WPPs, the electrical components of WTs are oversized and/or additional devices like STATCOMS are installed at the WPP grid connection point, adding to their cost. These components and costs can be reduced by shifting the GCRs. The OEH project exploits these findings to realize cost-optimized WPPs. The core idea is to create room for substantial design optimizations of WPPs by shifting GCRs from the individual WPPs to the central OEH structure. The grid code shift is possible because the WPP is only connected to the hub and not directly to the onshore transmission grid in an OEH. The state-of-the-art is extended by obtaining a holistic view of the overall GCRs and assessing which of them have the potential to be relaxed. One example is to shift the GCR about reactive power injection to create room for enhancing the production capability of the individual production WTs. Furthermore, the importance of limiting the single-phase earth fault current by having an impedance in the neutral earthing of the array cable system, thereby avoiding increased costs of array cables, is also investigated. The shifting of the GCRs has to be done while preserving the security of the supply level. Therefore, new requirements will be also investigated, e.g., grid-forming functionality. Moreover, the cost impact of DC-link chopper costs in each WT versus a few centralized AC choppers to dissipate power in case of HVDC link faults/fault ride-through situation is discussed. To conclude, a brief overview of proposed recommendations for future grid codes and standards will be given. Future work will aim to determine if the modified GCRs have an impact on the hub operation and vice versa.
In this paper, the main state-of-the-art review of current GCRs will be shown as well as a discussion on how the selected GCRs impact the costs related to the design and operation of the OWF. The PROMOTioN project found that for meeting the stringent GCRs in HVDC-connected WPPs, the electrical components of WTs are oversized and/or additional devices like STATCOMS are installed at the WPP grid connection point, adding to their cost. These components and costs can be reduced by shifting the GCRs. The OEH project exploits these findings to realize cost-optimized WPPs. The core idea is to create room for substantial design optimizations of WPPs by shifting GCRs from the individual WPPs to the central OEH structure. The grid code shift is possible because the WPP is only connected to the hub and not directly to the onshore transmission grid in an OEH. The state-of-the-art is extended by obtaining a holistic view of the overall GCRs and assessing which of them have the potential to be relaxed. One example is to shift the GCR about reactive power injection to create room for enhancing the production capability of the individual production WTs. Furthermore, the importance of limiting the single-phase earth fault current by having an impedance in the neutral earthing of the array cable system, thereby avoiding increased costs of array cables, is also investigated. The shifting of the GCRs has to be done while preserving the security of the supply level. Therefore, new requirements will be also investigated, e.g., grid-forming functionality. Moreover, the cost impact of DC-link chopper costs in each WT versus a few centralized AC choppers to dissipate power in case of HVDC link faults/fault ride-through situation is discussed. To conclude, a brief overview of proposed recommendations for future grid codes and standards will be given. Future work will aim to determine if the modified GCRs have an impact on the hub operation and vice versa.