String Sizer
Safe min/max modules per series string
Free · No sign-up · Computed instantly on your device
Inverter & Module Data
Voc/Vmp are prefilled for a typical 545 Wp Mono PERC module — edit them from your module datasheet for exact results.
Assumes a 1100 V max-DC string inverter with a 200–1000 V MPPT window, site temperature range 0–75 °C (cell), voltage coefficient −0.27%/°C, and a DC/AC oversizing ratio of 1.35. Always confirm against the specific inverter datasheet before ordering.
Minimum modules / string
6
Keeps hot-weather string Vmp ≥ 200 V (217 V at 6 modules)
Maximum modules / string
20
Keeps cold-morning string Voc ≤ 1100 V (1,059 V at 20 modules)
Corrected voltages
- Voc at 0 °C
- 52.9 V
- Vmp at 75 °C cell
- 36.2 V
Array-level guide
- Max total modules (DC/AC 1.35)
- 123
- ≈ Strings at max length
- 6
About This Calculator
String sizing is where paper designs fail in the field. Too many modules in series and the cold-morning open-circuit voltage (Voc) exceeds the inverter’s maximum DC input — a safety violation that can destroy the inverter. Too few, and the hot-afternoon operating voltage (Vmp) sags below the MPPT window, collapsing generation exactly when the sun is strongest.
This calculator applies the standard temperature-correction method: Voc is scaled up for the coldest expected morning and checked against the inverter’s DC limit; Vmp is scaled down for peak cell temperature and checked against the MPPT minimum. Module Voc/Vmp fields come prefilled with typical 545 Wp Mono PERC values — replace them with your module’s datasheet numbers for exact results.
Frequently Asked Questions
- Why Does Temperature Matter in String Sizing?
- Silicon voltage rises when cold and falls when hot (≈ −0.27%/°C). A string that measures 950 V at 25 °C can exceed 1,020 V on a cold winter morning — which is why calculations must use temperature-corrected voltages, not STC datasheet values.
- Can Strings of Different Lengths Connect to One Inverter?
- Only on separate MPPT inputs. Strings paralleled on the same MPPT must be identical in module count, model, and orientation, or mismatch losses and reverse-current risks follow.