By deploying storage at the right nodes in the electricity grid, our projects actively help reduce grid congestion and make better use of existing infrastructure.

Our batteries increase the flexibility of the energy system, support the integration of renewable energy, and deliver demonstrable social value. In doing so we strengthen security of supply,and accelerate the energy transition — in balance with the local community and in cooperation with local and public partners. We develop projects in the Netherlands and Belgium.

In 2025, Tethys and Kallista Energy entered into a strategic partnership for the development, construction and operation of BESS projects in the Netherlands. The Tethys BESS projects will be further developed jointly with Kallista. Upon completion, the objective of Kallista Energy is to become the owner and operator of the BESS projects. Kallista Energy is a European energy company with activities in wind, solar, e-mobility and BESS. Kallista Energy is backed by APG, one of the main pension fund managers in the Netherlands.