The pumped storage power plant of Etzelwerk AG consists of the reservoir (Sihlsee) created in the high valley of the Sihl river to the northeast of Einsiedeln, the headrace tunnel and the penstock as well as the control centre near Altendorf on the upper part of Lake Zurich. Swiss Federal Railways (SBB) has been the sole owner of Etzelwerk AG since 1987. The Etzelwerk concession expired in 2017 and was secured with a transitional concession until 2022. In addition to the concession renewal, the technology at the Etzel plant is also to be updated (e.g. partial replacement of the turbines, replacement of the penstock). A two-stage environmental impact assessment must also be carried out in the concession/planning approval procedure.

In its client-support role, TBF is providing technical and administrative support to the overall project management of SBB in the preliminary project and construction project. This is in the areas of project management, environment and BIM as well as in the tender process and coordination of the numerous stakeholders.