Tethys Energy Storage is a professional project developer of sustainable energy storage. As our energy system changes, there is increasing variation in the amount of energy available at any given moment. We develop battery energy storage systems (BESS) in the Netherlands and Belgium at strategic locations within the energy system: exactly where they are most effective.

 

In 2025, Tethys and Kallista Energy entered into a strategic partnership for the development, construction, and operation of battery projects in the Netherlands. The Tethys BESS projects are being further developed jointly with Kallista Energy. 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, the largest pension fund manager in the Netherlands.

 

The Tethys and Kallista Energy team consists of professionals in the world of energy transition who know how to drive projects forward. Together, we develop projects in a sustainable manner.

Battery Projects (BESS)

Due to the increasingly changing energy system, batteries are essential. These can be connected behind-the-meter, but can also operate stand-alone. Tethys develops battery projects from A to Z that fit within the energy system and the landscape.

Sustainable Development

The current energy system runs largely on fossil fuels. Energy storage can ensure greater use of renewable sources. In addition, sustainable project development, with a focus on people, the environment, and nature, is central to our approach.

Stronger Together

Tethys was founded by individuals and companies who have long been active in the energy transition and believe in the shift toward a sustainable energy system. We look beyond the issues of the day and are committed to a mission of sustainable project development with social added value.

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