Abstract
Anholt Offshore Windfarm (ANH01), commissioned in 2013, is showing degradation of existing cable protection systems (CPS) associated inter-array cables and platform connector cables. Thus, Ørsted is planning to undertake cable stabilisation around 42 wind turbine monopiles, and 14 cables at the offshore substation (OSS) in 2023.
A continued degradation of the inter-array cables as a result of unrestrained lateral motions combined with abrasion of the CPS on the already installed rock scour foundations will occur (which could result in power transmission loss, and subsequent emergency cable repairs). The risk of degradation in the CPS and associated cable systems can be mitigated by the introduction of stabilisation by means of rock berms on the existing scour protected sites. The objective of the planned work is therefore to
conduct stabilisation from the seabed touch down point of the CPS at the foundation, out to the seabed burial point, stopping the systems from moving and sliding. This mitigation action will reduce the risk of cable/CPS abrasion and fatigue and subsequent cable failures. It is expected that this precautionary measure will minimize the likelihood of future works, specifically cable replacements. In effect, conducting the stabilisation works now will result in reduced environmental effects at the seabed compared to a full cable replacement campaign.
The planned stabilisation includes placement of permanent rock berms since rock placement is expected to be the best solution, providing most stability for the CPS and associated array cables and allowing the most accurate placement.
According to Section 25 of the Renewable Energy Act (VE-loven) significant changes to existing installations can only be carried out with the prior permission of the Minister for Climate, Energy and Utilities (Klima-, Energi- og Forsyningsministeren), represented by the Danish Energy Agency (DEA) (Energistyrelsen). Moreover, according to Annex 2, no. 13a, in the Environmental Assessment Act, amendments or extensions to projects in Annex 1 (which are not covered by Annex 1, no. 29) or Annex 2 that have already been approved, have been carried out or are in the process of being carried out must undergo screening when they may have significant adverse effects on the environment.
This document contains a description of the planned stabilisation by rock placement on the CPS and associated array cables at the scour protected wind turbine positions and the offshore substation. In addition, it presents an assessment of the potential environmental effects, and any impacts, from the planned stabilisation (‘screening’). Therefore, the document is intended to provide sufficient information to the Danish Energy Agency to enable them to decide whether the planned work constitute a significant change to the existing Anholt Offshore Windfarm and whether a detailed Environmental Impact Assessment is required.