A 100 kW, 2-hour backup requirement sized up to nameplate battery energy, checked against C-rate and PCS voltage window, and carried through to an actual AC cable size.
| Chemistry | Lithium-ion (90% DoD, 92% round-trip efficiency) |
| Load power / backup duration | 100 kW for 2 hours |
| C-rate | 0.5 C |
| Nominal DC voltage / PCS window | 700 V nominal, 600–850 V PCS operating range |
| PCS rated AC power | 100 kW, 400 V three-phase |
| AC cable | Copper, Method C, 20 m run, 30°C ambient |
| Check | Requirement | Actual | Status |
|---|---|---|---|
| C-rate delivers enough power for the load | maxPower ≥ 100 kW | 120.8 kW | ✓ PASS |
| Nominal DC voltage within PCS window | 600–850 V | 700 V | ✓ PASS |
| AC output cable ampacity | ≥ 180.4 A | 229 A (70 mm² Cu) | ✓ PASS |
| AC output cable voltage drop | ≤ 3% | 0.98% | ✓ PASS |
Key insight: The gap between usable energy (200 kWh) and nameplate energy (241.5 kWh) — a 20.75% uplift — comes entirely from depth of discharge and round-trip efficiency, both genuine physical characteristics of the battery chemistry, not safety margin in the traditional sense. A lead-acid system with this app's default 50% DoD and 85% efficiency would need a dramatically larger nameplate rating (about 470 kWh) for the identical 200 kWh usable requirement, which is a big part of why lithium-ion has become the default choice for space- and weight-constrained BESS applications.
Every input in this example is editable in the live calculator — free, no signup.
Open Energy Storage (BESS) calculator →This mirrors the same NEC-style continuous-load convention used throughout this suite's cable-sizing calculators — a source that can run continuously at its full rated output (like a PCS/inverter operating for the full backup duration) is treated the same way a continuous load is, with a 125% factor applied before selecting cable ampacity, to build in margin for genuinely continuous full-power operation rather than a brief peak.
In this example, the battery's C-rate-limited power (120.8 kW) comfortably exceeds both the 100 kW load and the 100 kW PCS rating, so neither the battery nor the inverter is the bottleneck — but for a system with a much lower C-rate (energy-optimized rather than power-optimized battery chemistry) or a smaller PCS relative to nameplate energy, either check could become the actual limiting factor, which is exactly why both are verified independently rather than assuming one implies the other.