Decreasing the environmental impact of grid connections

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TenneT TSO is a grid operator in the Netherlands and Germany and therefore has a crucial role to play in the energy transition. The company is currently developing grid connections for several offshore wind parks that will be built in the coming years. To transport the renewable electricity generated by a wind park to the user as efficiently as possible via the electricity grid, (offshore) transformer stations and transport cables are required.

Constructing these assets requires materials such as steel, copper, aluminium and plastics. The production and processing of these materials has an impact on the environment – for example, through the emission of greenhouse gases. Using these assets also has both a direct and an indirect environmental impact through emissions and the loss of generated electricity.


TenneT TSO has formulated objectives for reducing greenhouse gases (science-based targets) as well as environmental impact in a broader sense. To effect the concrete application of these objectives, environmental impact has been chosen as a principal consideration in all new offshore tenders. With this, TenneT is taking a big step towards realising a more sustainable electricity grid.

TenneT has entered a collaboration with Aratis and Witteveen+Bos to achieve this aim. Witteveen+Bos provided reference calculations for the environmental impact; Aratis is implementing these as part of TenneT’s sustainability programme and applying them practically in tenders such as those for offshore activities in the Netherlands and Germany.

'TenneT commits to reduce absolute scope 1 and 2 GHG emissions 95 % by 2030 from a 2019 base year. TenneT also commits to reduce absolute scope 3 GHG emissions from purchased goods and services and capital goods 30 % within the same timeframe.'


The efforts to reducing environmental impact focus on stimulating the entire supply chain, starting with TenneT’s direct suppliers. They are stimulated to provide their goods and/or services with the lowest possible environmental impact. Life Cycle Assessment (LCA) is performed using reference designs, providing insight into various environmental impacts (e.g. climate change, eutrophication, acidification). The scope of these reference designs encompasses aspects that can be influenced by the supplier.

The environmental impacts are then converted into a single score indicator following the weighting of the Environmental Cost Indicator (ECI). The ECI is determined for various possible scenarios regarding the composition and source of the materials in, for example, a transformer platform or transport cable.

The maximum and minimum values form upper and lower limits for a fictional discount on a tender application. The lower the supplier bids, the higher the fictional discount will be, in accordance  with the MEAT (Most Economically Advantageous Tender) criteria for the tender. In this way, the supplier with the most sustainable design can distinguish itself from the rest of the market and be rewarded for doing so.


The 2GW High Voltage Direct Current (HVDC) offshore transformer platforms and HVDC transport cables are being analysed by Witteveen+Bos using the ECI method. This has revealed that, for offshore platforms, the source of the bulk material (construction steel) is very important. A higher proportion of recycled steel, for example, would mean a large reduction in environmental impact; and the producer of primary steel – via technology and regulations – can have a big influence.

During the use phase, the emission of insulator gas (sulphur hexafluoride, SF6) amounts to greenhouse gas emissions. This gas is only occasionally released, but it can have a significant influence on the total environmental impact. Alternative insulator gases and vacuum switches offer solutions, but they also present new challenges – alternative insulator gases, for example, are designated as hazardous PFASs (poly- and perfluoroalkyl substances).

For cables, the conductor – copper in most cases – is highly influential on the ECI. This applies both to the construction (resource extraction, processing, and production) and use phases (transmission losses). Again, the source of the copper is important, but there is also a trade-off where the use of more copper leads to fewer transmissions losses.


Applying ECI in tender criteria has the potential to be broadly applied throughout TenneT projects. It allows TenneT to have an even bigger effect on reducing environmental impact across the entire chain. In light of the imminent increase in number of wind parks, Witteveen+Bos will be continuing its reference calculations for transformer stations and transport cables for large offshore energy projects. The same applies to onshore cable routes. Additionally, electrotechnical installations (transformers) will be assessed for environmental impact using the ECI methodology.

Essential materials, too, such as conductors (copper, aluminium) and construction material (steel), offer much room for reductions in environmental impact and will therefore remain subjects of a discussion in which the whole chain will be involved.