Help CenterInverters
DC input voltage and MPPT window
Inverter4 min readUpdated: 2026-08
A panel's open-circuit voltage (Voc) rises as temperature drops. A string sized for the maximum input voltage of the inverter/controller can exceed it in cold weather, damaging the equipment.
Voc_corrected = Voc_STC × (1 + temp_coeff × (T_min − 25))temp_coeff typically −0.30%/°C for a monocrystalline panel (negative value, so Voc rises as T drops)
| Coldest site temp | Voc correction (mono, −0.30%/°C) | Impact |
|---|---|---|
| 25°C (reference) | +0% | None |
| 10°C | +4.5% | Low |
| 0°C | +7.5% | Check on a long string |
| −10°C | +10.5% | Risk of exceeding the MPPT window |
In Europe, clear cold winter mornings are the worst case — Voc peaks just before sunrise when production begins. In Africa this risk is generally low except at altitude (Lesotho, Ethiopia, the Moroccan Atlas).
The MPPT window (optimal operating voltage) is narrower than the absolute maximum input voltage. A string whose Vmp falls outside the MPPT window loses efficiency even without exceeding the safety limit.
Common mistakes
- Sizing the number of panels in series using Voc at 25°C without cold correction
- Ignoring altitude and winter climate for a European project
- Confusing maximum input voltage (hardware limit) with the MPPT window (optimal efficiency range)