Stem wins deal to add 160 MWh of battery storage to Hungary solar plants

Stem, Inc. (NYSE: STEM) announced that Solarmarkt Group has selected its PowerTrack Energy Management System to manage the addition of battery storage to two operating utility-scale solar plants in Hungary.

Under a five-year agreement, a 40 MW / 80 MWh battery energy storage system will be added to each of Solarmarkt Group's existing 60 MWp solar facilities, one located in Szihalom and one in Hódmezővásárhely. The projects will bring total new storage capacity to 160 MWh across the two sites. Commercial operation of the hybridized assets is expected by September 2026.

Pannonwatt Energetikai Megoldások Zrt. is serving as the engineering, procurement, and construction partner for both projects. Stem previously supplied power plant control capabilities for the solar facilities using its PowerTrack platform, which it describes as designed to support future battery integration.

At each site, PowerTrack will coordinate solar generation, battery dispatch, grid constraints, and market instructions while maintaining compliance with E.ON distribution-system requirements. The initial commercial strategy will target Hungary's automatic Frequency Restoration Reserve market, with the platform intended to support additional reserve services over time.

"This project demonstrates how operating solar plants can evolve into hybrid assets without replacing the existing controls foundation," said Matt Tappin, President of Software at Stem.

Miklos Mormer, Chief Technology Officer at Solarmarkt Group, said PowerTrack provides "transparency into the performance and economics of both the solar and battery systems at each site, while allowing them to operate as coordinated hybrid assets."

The hybridization also supports Solarmarkt Group's Green Cloud Platform, which connects renewable generation with corporate energy consumers. According to the press release, the platform offers traceable, auditable physical green-energy solutions aimed at supporting corporate decarbonization goals.

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