How to Select the Right C&I Battery Storage System: A Step-by-Step Sizing Guide
Undersize a battery and it never pays back; oversize it and the payback stretches for years. This guide walks through the five numbers that actually decide your C&I storage configuration.
Every week we meet plant managers who were quoted three different battery sizes by three different vendors — for the same factory. The spread is rarely about technology; it is about who actually did the sizing maths.
The good news: with one year of electricity bills and an afternoon, you can do that maths yourself. Here is the exact sequence our engineers follow.
What you need before you start
12 months of utility bills, your tariff sheet (peak/off-peak hours and demand charges), and a one-line diagram of the plant. That is all.
Step 1 — Read your load profile, not your intuition
Step 2 — Size energy from the gap you actually shift
Plot a typical weekday. The area between your evening peak and the off-peak valley is the energy you can arbitrage — not your transformer rating, not the roof size.
For most two-shift factories this lands between 1.5 and 2.5 hours of average load, which is exactly why 215 kWh cabinets pair so naturally with 100 kW power blocks.
Step 3 — Run the five-number checklist
- Peak/valley price spread — below ¥0.6/kWh, look at demand charges first
- Daily shiftable energy (kWh) — from the Step-2 curve
- Transformer headroom — charging must fit inside the night valley
- Cycles per day — two-cycle tariffs halve the payback time
- Floor space and access — a 215 kWh cabinet needs about 1.7 m × 1.3 m
The most expensive battery is not the oversized one — it is the one sized from a brochure instead of a load curve.
Step 4 — Sanity-check the payback
Multiply daily shiftable energy by the price spread and by 330 working days, subtract roughly 12% for round-trip losses and auxiliary power, then divide the system price by the result. Anything under five years is solid for a 10-year-warranty LFP system; under four years means you probably found free money.
When to bring in an engineer
If your plant has demand charges above 30% of the bill, on-site solar, or backup-power requirements, the spreadsheet stops being enough — those cases need simulation against your actual 15-minute interval data. Send us the bills and we will run it free of charge, usually within two working days.
