A decade-long flexibility partnership will support the deployment of 55 MW / 220 MWh of battery storage in Spain’s Basque Country. The full tolling agreement provides long-term revenue certainty for Return while enabling ENGIE to optimize the assets across wholesale and ancillary electricity markets from late 2027.
Return, an independent energy storage developer, and ENGIE, a global energy company focused on the energy transition, have signed a ten-year flexibility agreement covering a portfolio of battery energy storage projects in Spain. The agreement marks a significant step in the country's evolving battery storage market by establishing a long-term commercial framework designed to accelerate investment in grid-scale energy storage.
The agreement covers three battery energy storage projects located in Spain's Basque Country with a combined installed capacity of 55 MW / 220 MWh. Structured as a full tolling agreement, Return will develop, own and operate the battery assets while ENGIE will optimize their participation across Spain's wholesale electricity and ancillary services markets. Commercial operations are expected to begin by the end of 2027.
The alliance is based on an already established cooperation in Germany and extended into a second market of Europe. It shows how contractual agreements may help lower the risks of investments due to predictable incomes along with maximizing the efficiency of batteries with the help of professional energy traders.
The potential of renewable energy production in Spain keeps growing; thus, there arises the necessity to have technologies that would allow controlling the energy flow and make it stable. Batteries can perform this function because they will be able to save excess power generated through renewables and then use it when it is necessary.
The three battery projects will provide grid balancing services, improve renewable energy integration and strengthen electricity system reliability. The long-term agreement also creates greater financing confidence for storage developers by improving revenue visibility throughout the project lifecycle.
For ENGIE, the partnership expands its portfolio of flexible energy resources that support wholesale market participation, ancillary services and its broader ambition to provide around-the-clock carbon-free energy solutions to customers. The agreement reflects growing interest in long-duration commercial partnerships as battery storage becomes an increasingly valuable asset within European electricity markets.
Construction of all three battery storage facilities is already underway. Once commissioned, they will contribute to Spain's transition toward a more resilient, flexible and decarbonized electricity system. Both companies also see opportunities to replicate similar long-term tolling structures across additional European markets, supporting wider deployment of battery energy storage while combining investment certainty with advanced energy management expertise.