Tucson Electric Power (TEP) has announced its second battery energy storage system (BESS) in southeast Tucson in the US state of Arizona to store solar renewable energy until later in the day to satisfy customers' peak energy needs. The battery project in the southeast-side TEP substation is likely to be commissioned by the start of 2026. 

According to the power company, The 200 MW 'Roadrunner Reserve II' system will store 800 MWh of energy, enough to serve approximately 42,000 homes for four hours when deployed at full capacity. The system is to be located on the same site as the previously announced Roadrunner Reserve BESS that may begin its operations next year. 

The co-location of these two BESS will be the largest energy storage resources in TEP's portfolio, even among the largest in Arizona. TEP expects to charge both grid-connected batteries in the morning and early afternoon, when solar resources produce the most energy. Stored energy will be delivered later in the day when energy use typically is at its highest.

Susan Gray, TEP's President and CEO, commented on the battery system, "Our new Roadrunner Reserve II system will help us make the most of intermittent resources, especially during the summer when usage is highest and customers are counting on us the most. We need additional energy storage as part of a diverse energy portfolio to support service reliability."

The utility claims that the battery systems with help utilities make better use of wind and solar resources by "shifting" their output to periods of greatest need. They also can help smooth out imbalances throughout the day as clouds block the sun or wind patterns shift, reducing the amount of clean energy produced by renewable resources.