Aratis and Witteveen+Bos aid TenneT in making environmental impact criteria in offshore tenders

TenneT has developed goals for reducing greenhouse gases (with a scientific foundation) and environmental impact in general.

It has been decided to emphasize environmental impact in all new offshore tenders in order to give this concrete substance. To achieve this, TenneT has partnered with the consulting firms Aratis and Witteveen+Bos.

The environmental impact reference calculations were provided by Witteveen+Bos. The calculations from TenneT’s sustainability program are put into practice by Aratis and used, among other things, in the tenders for the offshore activities in the Netherlands and Germany.


The strategy for lessening the impact on the environment concentrates on energizing the entire supply chain, beginning with TenneT’s direct suppliers. They are urged to provide the products and/or services with the least amount of environmental impact possible. In order to achieve this, a life cycle analysis (LCA) is carried out based on reference designs, allowing for the transparency of the various environmental effects (such as climate change, eutrophication, and acidification). The focus of these reference designs is on elements under the offering party’s control.

According to the weightings in the Environmental Cost Indicator, these environmental effects are then converted into a “single score indicator” (MKI). The composition and origin of the materials in a transformer platform or, for instance, a transport cable, are taken into account when determining this MKI for various conceivable scenarios.

The maximum and minimum values serve as the upper and lower bounds for a hypothetical subscription discount. According to the MEAT (Economically Most Advantageous Tender) of the relevant tender, the notional discount will increase the lower the offer. In this way, the supplier with the most environmentally friendly design can stand out from the competition and profit from it.


Witteveen+Bos used the MKI method to determine the 2 GW High Voltage Direct Current (HVDC) offshore transformer platforms and HVDC transmission cables. It has become clear that the bulk material’s (structural steel’s) place of origin is crucial for offshore platforms. For instance, a higher percentage of recycled steel can result in a more significant reduction in the environmental impact, and due to technology and regulations, the producer has a significant impact on primary steel.

Greenhouse gases are released during the use phase as a result of the emission of the insulator gas sulfur hexafluoride (SF6). Although this gas is inadvertently released, it has the potential to significantly affect the overall environmental impact. Vacuum switches and alternative insulator gases present solutions but also new problems because, for instance, alternative insulator gases are classified as PFAS.

The conductor, which is frequently made of copper, has a significant impact on cables. This holds true for both the realization phase (the gathering and production of raw materials) and the use phase (cable losses). Once more, the place of origin of the copper is crucial, but there are also trade-offs where using more copper results in fewer cable losses.

Going forward

There is a lot of room for expanding the use of the MKI in TenneT project tender criteria. In this way, the business can intensify its efforts to lower environmental impact along the entire supply chain. Witteveen+Bos will continue the reference calculations for transformer stations and transport cables for significant offshore energy projects in light of the impending expansion of offshore wind farms. Onshore cable routes are also covered by this. Additionally, the MKI method will be used to evaluate the environmental impact of electrical installations (transformers).

The environmental impact of fundamental materials like conductors (copper, aluminum) and building materials (steel) also offers a lot of room for reduction, so they will continue to be discussed. Witteveen + Bos, cited.

Image source: TenneT

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