Texas Energy Storage Boom: $400M Investment Portfolio Unites Stem, Regis Energy Partners, and Excelsior Capital

A major renewable energy initiative has taken shape in Texas, with three major players joining forces to build out a significant battery storage portfolio. Stem (NYSE: STEM), the AI-driven clean energy software company, has partnered with Regis Energy Partners LP and Excelsior Energy Capital to develop a series of grid-scale energy storage projects across the ERCOT region.

The Deal: Four Projects, One Vision

The partnership kicks off with four standalone battery energy storage systems (BESS), each rated at 9.9 megawatts, currently under construction and expected to begin operations in 2023. This marks the first phase of a $400 million equity commitment from REX Storage Holdings—a joint venture between Regis Energy Partners and Excelsior Energy Capital—aimed at acquiring additional construction-ready projects from Regis’ development pipeline. ERCOT, which serves over 26 million customers and accounts for roughly 90 percent of Texas’ electricity demand, represents both a lucrative and strategically important market for energy storage deployment.

Why This Matters for Texas Grid

The distributed energy storage strategy leverages Stem’s expertise and its proprietary Athena® AI platform to optimize project performance and returns throughout their operational lifetimes. Regis Energy Partners, known for identifying high-value development opportunities at distribution-level nodes across the grid, handles project oversight, while Stem provides the battery technology, software platform, consulting services, and ongoing optimization support.

“The merchant revenue opportunities in ERCOT have attracted serious investors,” explained industry participants involved in the project. The projects position themselves to capture value through multiple revenue streams in a market that continues to evolve rapidly.

The Players Behind the Partnership

Stem brings a decade of experience helping developers and IPPs (independent power producers) optimize clean energy projects through AI software and project management. Its Athena platform, alongside complementary offerings like AlsoEnergy’s PowerTrack asset management system, enables operators to maximize returns while managing complex multi-asset portfolios.

Regis Energy Partners specializes in utility-scale energy storage development, using a unique approach to identify volatile, high-demand locations where distributed assets make more economic sense than large transmission-scale projects. This strategy positions projects for resilience and profitability.

Excelsior Energy Capital is a North America-focused infrastructure fund bringing over 100 years of combined experience to renewable energy investments. The firm has established itself as a trusted manager for institutional capital in the wind and solar sectors, now expanding into battery storage.

What’s Next

The partnership underscores a broader shift toward distributed energy storage in competitive electricity markets. As Texas continues to modernize its grid infrastructure, projects like these demonstrate the economic viability of merchant battery storage outside of traditional utility models. The 2023 online date puts these systems in position to capture near-term market opportunities while building a replicable model for future expansion across ERCOT territory.