Battery energy storage [/ˈbætəri ˈɛnərʤi ˈstɔrɪʤ/] n - The Uninterruptible power supply holds no energy of its own; it draws upon a battery system for the seconds-to-minutes window before the The Standby Engine takes the load. Sizing is a deliberate trade: just enough runtime (often 5–15 minutes) to cover generator start, plus a margin of safety.

Of VRLA and Lithium-Ion

• VRLA (valve-regulated lead-acid). [/ˈvrlæ ˈvælvɛrɛgʌlætɛd ˈlɪːdækɪd/] n Cheap and familiar, yet heavy, with a 3–5 year service life and a tenderness toward heat. Long the default.
• Lithium-ion. [/ˈlɪthɪʌmɪɒn/] n 2–3× the energy density, a 10–15 year life, a smaller footprint, and a built-in battery management system. Dearer at first, and swiftly becoming the norm.

Batteries are wired into long strings to reach the DC bus voltage the UPS inverter requires, itself a consequence of the The Current That Comes in Threes output it must synthesize. Because a battery system is a single point of failure for its UPS, strings are deployed redundantly, in keeping with the site’s Redundancy topologies.

More and more, the same plant serves peak shaving and grid services when no backup is wanted, blurring the line between a UPS battery and a grid-scale storage asset.

Part of The Engines of the Hall.