🔋 Battery Sizing Calculator
Size a LiFePO4 battery for backup or peak-shaving: required capacity from load and autonomy, series/parallel configuration, DoD-driven cycle life and a matching PCS, with a bill of materials.
🔋 Load & Autonomy
📊 Battery Design
For solar and storage designers sizing batteries and power conversion systems.
How it is calculated
· Required capacity: E = Load (kW) × hours ÷ DoD ÷ efficiency.
· Series cells: series = V_system ÷ 3.2 (LFP cell).
· C-rate check: load ÷ capacity ≤ 1.0 C recommended.
Referenced standards
| Standard | Scope |
|---|---|
| IEC 61427 | Secondary cells for renewable energy storage |
| IEC 62619 | Safety of secondary lithium cells and batteries |
Worked example — 10 kW for 4 h → 46.8 kWh
1. Load 10 kW, backup 4 h, DoD 90%, efficiency 95%.
2. Required = 10 × 4 ÷ 0.90 ÷ 0.95 = 46.8 kWh.
3. 51.2 V system → 16 cells in series; nearest cluster configuration selected.
4. C-rate = 10 ÷ 46.8 = 0.21 C (within 0.5–1.0 C); matching PCS selected.
FAQ
How do I size a battery from load and autonomy?
Battery energy = daily load kWh x autonomy days / depth of discharge / round-trip efficiency. For 20 kWh/day load, 1 day autonomy, 80% DoD and 90% efficiency: 20 / 0.8 / 0.9 = 27.8 kWh, so select a 30 kWh bank. The calculator computes capacity and matches standard rack/cabinet sizes.
What is depth of discharge and why does it matter?
Depth of discharge is the fraction of capacity used per cycle. LFP batteries tolerate 80-90% DoD for 6,000+ cycles; lead-acid lasts longest at 50% DoD. Deeper discharge shortens cycle life, so the battery is oversized to respect the DoD limit. The calculator applies DoD to the usable-capacity calculation.
How long does a battery last in cycle life?
LFP cells deliver 6,000-8,000 cycles at 80% DoD (roughly 15-20 years at one cycle/day), while NMC gives 3,000-5,000 and lead-acid 500-1,200. Calendar life and temperature also matter — operating above 35 deg C accelerates degradation. The calculator reports cycle-life implications for the sized bank.
How do I match a PCS to the battery?
The PCS power rating must cover the peak load and charge rate, and its DC voltage range must match the battery string. For a 30 kWh bank serving a 10 kW peak load, select a 10-15 kW PCS. The calculator matches PCS power and battery DC voltage to the sized bank.
What battery capacity do I need for peak-shaving?
For peak-shaving, the battery must cover the peak demand above the target for the duration of the peak window, usually 2-4 hours. Shaving 100 kW for 3 hours needs 300 kWh usable, or ~375 kWh at 80% DoD. The calculator sizes the bank for the shaving window and quantifies demand-charge savings.
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