Technical and spatial planning criteriaIn order to carry out grid planning, it is necessary to develop technical and spatial planning criteria. Technical criteria are rules which apply to the construction or placement of cables which are usually industry standards or determined by marine licence conditions. Spatial planning criteria on the other hand are principles applied to spatial position of cables.
Grid planning differs between North Sea countries, with Germany having well-established planning criteria compared to limited criteria in other NSR countries. There is also a difference between criteria being Government-led or Industry-led. For example, in Germany, the Government have defined planning principles and criteria for both offshore wind farms and for interconnectors in their designated Spatial Offshore Grid Plan, however they both follow similar principles. On the other hand, in Scotland planning principles are classed more as ‘rules of thumb’ by Industry and adherence to the principles is dependent on risk.
With regard to technical planning criteria for cables, suitability of seabed conditions is one of the most important issues to consider. However, there are solutions to overcome difficult ground conditions when laying cables, it is more a question of the technique of cable laying/cable securing. Techniques such as cable protection measures such as concrete mattresses or rock armour and specific depths for cable burial (for example 1 meter or 1.5 meters depending on risks) are important from the perspective of the shipping and fishing sector. Technical planning criteria for cables also includes the use of HVDC and HVAC technology for different connections as it is relevant for the capacity of the cable and therefore determines the number of cables required to transmit a certain capacity. The technical specification of the grid connection systems of offshore wind farms depends on the distance to shore. For example, longer connections such as wind farms further away from shore or interconnectors are usually HVDC cable systems as they enable transport of electricity over larger distances while featuring lower energy losses. Requirements for bundling of cables as a technical specification is also important in helping to minimise negative effects from magnetic fields on sensitive species.
Besides these technical planning criteria, countries can also determine spatial planning criteria. These can contain restrictions, guidelines or specifications for interconnectors and cables in general. A specific planning principle which is used by most NSR countries is planning cable corridors. However this involves several spatial considerations, for example, space is needed for the cable itself and its laying, for a safety or buffer zone around it to ensure sufficient space for potential repairs and ship manoeuvring, space at cable crossing areas and specific distances in case of parallel routing with other marine uses. Necessary distances between cables and other marine uses depend on the water depth, sites specific ground conditions and technical required distances for cable laying and cable repairs. Regarding the question of appropriate distances guidelines of the International Cable Protection Committee (ICPC) and the European Subsea Cables Association (ESCA) can give helpful advice. As for offshore energy cables, the International Cable Protection Committee (ICPC) recommends that existing cables in shallower waters (up to a depth of 75m) are given a default 500m exclusion zone on either side. The actual distance varies between single countries. In general, offshore renewable energy infrastructure and cable corridors should be integrated whenever possible to maximize concentration of sea uses.
One of the main advantages of spatial planning criteria is to avoid conflict with other marine users, protected or commercially important areas. For example, designated cable corridors are essential in the Netherlands as they need to route their cables around economically important near-shore sand extraction zones. Cable corridors are also useful for encouraging bundling of cables which, in terms of space, is an advantageous planning criteria. Germany and the Netherlands encourage bundling of cables where possible and in Belgium, pipelines are also clustered into corridors. Planning principles also help to select preferred routes for passing through areas such as shipping lanes or fishing areas and can advise cables to be routed to accommodate certain safety distances from shipping lanes or to run in parallel and only cross waterways in the shortest and straightest possible way.
For a full list of countries technical and spatial planning criteria see Annex 1.