Energy Storage Is a Core Power Strategy for Next-Generation Data Centers

Overview

This 2025 white paper by Justin Gruetzner and Joshua Tucker was published by Burns & McDonnell. It treats battery energy storage systems as a campus-scale power asset for hyperscale and AI data centres. It sets out use cases from interconnection support and load smoothing to spinning reserve, black start and campus-level UPS, and explains which are sized on MW and which on MWh.

On sizing, most commercial BESS offer 2-4 h duration, and data centres usually prioritise MW capacity over duration. Load smoothing is sized on MW, while spinning reserve and backup are sized on MWh from ramp rates, start times and required ride-through. Degradation is handled by initial overbuild plus augmentation, often in years 3-5, and 20-25 year performance guarantees are common.

On chemistry, LFP is preferred over NMC because thermal runaway starts at a higher temperature and propagation risk is lower. On electrical architecture, current data centre BESS connect AC at medium voltage, typically 34.5 kV, while 800 V DC buses are emerging. Alternatives such as sodium, flow batteries and flywheels are treated as complementary rather than near-term replacements. These architectural choices directly affect site layout and the connection point.

The primary codes are NFPA 855, UL 9540 and the UL 9540A large-scale fire tests, which drive layout spacing; NFPA 72 is used for detection. NFPA 75 is also among the related standards. The document is a consultancy white paper, so it needs vendor- and project-specific verification, and its figures are given under particular assumptions. Even so, the MW versus MWh distinction and the code requirements give teams bringing BESS into the design a practical framework.

Key points

1. Most commercial BESS offer 2-4 h duration; data centres usually prioritise MW capacity over duration.
2. Load smoothing is sized on MW; spinning reserve and backup on MWh, from ramp rates, start times and required ride-through.
3. Degradation is handled by initial overbuild plus augmentation, often in years 3-5; 20-25 year performance guarantees are common.
4. LFP is preferred over NMC because thermal runaway starts at a higher temperature and propagation risk is lower.
5. Current data centre BESS connect AC at medium voltage, typically 34.5 kV; 800 V DC buses are emerging.
6. Primary codes: NFPA 855, UL 9540 and UL 9540A large-scale fire tests (which drive layout spacing); NFPA 72 for detection.
7. Sodium, flow batteries and flywheels are treated as complementary, not near-term replacements.
8. Use cases include interconnection support, load smoothing, spinning reserve, black start and campus-level UPS.

Using it in design

• Add a BESS catalogue type with chemistry, MW, MWh, connection voltage and UL 9540A test reference.
• Define separate sizing rules for MW-driven and MWh-driven use cases.
• Apply NFPA 855 spacing and exposure checks in site layout.
• Warn when NMC is chosen near occupied buildings.

Who should read it

Electrical engineers, energy consultants and fire-safety specialists planning BESS for hyperscale and AI data centres.

Related standards

• NFPA 855
• UL 9540
• UL 9540A
• NFPA 72
• NFPA 75

Publication details

Authors

Justin Gruetzner; Joshua Tucker

Publisher

Burns & McDonnell

Year

2025

Document number

10791403663

Document language

English

Source type

Expert / community

Access

Free to read

Licence

Copyright retained; citation only — the publisher’s terms apply to the original document

Citation