About the SoC Window Optimization

SoC (State of Charge) window optimisation sets the upper and lower SoC limits for BESS operation to balance cycle life against usable energy. A narrower window (e.g. 20–80% SoC) extends battery life; a wider window (10–90%) maximises usable energy per cycle at the cost of faster fade.

Formula

How to calculate it

1. 1Determine the use case: backup systems benefit from a higher SoC_max (ready for emergency); cycling systems benefit from a tighter window for longevity.
2. 2Set SoC_max: LFP is relatively tolerant of 100% SoC but manufacturers often recommend 90–95% for longevity.
3. 3Set SoC_min: most manufacturers recommend ≥10% SoC to protect against over-discharge, particularly at low temperatures.
4. 4Model the annual cycles × usable window to calculate lifetime throughput at that setting.
5. 5Optimise: test 60–100% vs 10–90% windows using the manufacturer's cycle-life curve to find the window that maximises lifetime throughput and LCOS.

Worked example

LFP battery: 10–90% window → 80% DoD, 4,500 cycle life → lifetime throughput = 4,500 × 80% = 3,600 equivalent full cycles. 20–80% window → 60% DoD, 6,000 cycles → 3,600 equivalent full cycles. In this case, both windows deliver similar lifetime throughput — the wider window is preferred for more energy per day.

What you can calculate

• Min/max SoC %
• Cycle life trade-off
• Revenue impact
• LFP/NMC optimum

Frequently asked questions