IEC 62933-2-1 · BESS sizing

BESS Battery Sizing Calculator

Required nameplate kWh accounting for usable DoD window, BoL→EoL capacity fade, round-trip efficiency chain and AC auxiliary loads. LFP · NMC · LTO.

C_nameplate = E_required / (DoD × η_AC) η_AC = η_cell² × η_inv² × (1 − η_aux) C-rate = P_kW / C_kWh SoH_EoL governs sizing
Enter project parameters and click "Calculate" to see sizing results.

Worked Example — 1 MW / 2 h LFP Peak-Shaving System

Step-by-step walkthrough of the sizing formula for a utility-scale peak-shaving BESS.

Step 1
Given
P = 1000 kW, duration = 2 h → E_required = 2000 kWh
Step 2
Chemistry
LFP: η_cell = 96%, DoD = 80%, N_ref = 4000 cycles
Step 3
η_RTE
η_RTE = 0.96² × 0.98² = 0.883 (88.3%)
Step 4
Aux derating
η_ac = 0.883 × (1 − 0.025) = 0.861 (86.1%)
Step 5
BoL nameplate
C_BoL = 2000 / (0.80 × 0.861) = 2904 kWh
Step 6
Degradation
LFP @ 250 cyc/yr, 15 yr: final SoH ≈ 80% → governs
Step 7
EoL nameplate
C_EoL = 2000 / (0.80 × 0.861 × 0.80) = 3630 kWh
Step 8
C-rate check
C-rate = 1000 kW / 3630 kWh = 0.28C ≤ 1.0C ✓
Step 9
Annual throughput
3630 kWh × 0.80 × 250 cyc = 726 MWh/yr
Step 10
Topology
16S × 280Ah = 14.3 kWh/rack → 254 racks → 16 containers

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Frequently Asked Questions

How is the BESS nameplate capacity calculated?

C_nameplate = E_required / (DoD × η_RTE) at BoL, then increased so that EoL performance (at 80% SoH after degradation) still meets E_required. The governing (larger) figure is reported.

What does round-trip efficiency include?

η_RTE = η_cell² × η_inverter² accounts for cell-level charge and discharge losses plus inverter losses in both directions. Auxiliary loads (HVAC, BMS) are an additional deduction on AC-side energy.

Which IEC standard is used?

IEC 62933-2-1 provides the unit parameter and testing framework. Degradation curves follow Wang 2014 (LFP) and Schmalstieg 2014 (NMC) empirical fits. LTO uses manufacturer data (N_ref = 15 000 cycles).

What is C-rate and why does it matter?

C-rate = P_kW / C_kWh. A 1C rate fully charges or discharges the battery in one hour. Exceeding the sustained C-rate limit increases heat generation and accelerates degradation. LFP tolerates 1C sustained; NMC should stay ≤ 0.5C for stationary use.

How are rack and container counts calculated?

Using 280 Ah prismatic reference cells (IEC 62619 grade for stationary). Cells are arranged in series to reach ~48V per rack. Rack count = C_nameplate / kWh_per_rack. Container count assumes 16 racks per standard enclosure (~200 kWh).

When should I use LTO instead of LFP?

LTO is preferred for frequency regulation (FCR/aFRR) requiring >1C rates and high cycle counts (>700 cycles/yr). It costs 2–3× more per kWh but tolerates 15 000+ cycles vs. 4 000 for LFP. For peak shaving or solar applications, LFP is typically optimal.