The voltages on a panel's label are measured with the panel at 25°C (77°F). When the panel is colder than that, its voltage goes up. On a winter morning a panel can make a few volts more than its label says, and a string of panels in Series Panels chained + to -. Voltages add, current stays the same. adds those extra volts together.
How much it rises
Each panel has a temperature coefficient for Voc Open-circuit voltage. The highest voltage a panel makes, with nothing connected. Rises in cold.. A typical value is about 0.3% for every °C below 25°C. A panel's own number is in its manual: Jackery's SolarSaga 200 manual gives -0.27% per °C.
cold Voc = Voc x (1 + 0.003 x (25 - °C))
50 V at 0°F (-18°C): 50 x (1 + 0.003 x 42.8) = 56.4 V
That is 6.4 V more than the label. On a station with a 55 V or 60 V limit, that can be the whole margin.
When it matters
A panel sits at its open-circuit voltage whenever the station is not drawing current from it, for example the moment you plug it in, or when the battery is full. The coldest moment of the day is usually early morning, as the sun comes up. That is when the voltage is highest.
What the manuals say
EcoFlow's DELTA 3 Plus manual: keep the total open-circuit voltage within 60 V and the short-circuit current within 15 A on each input.
EcoFlow's DELTA Pro 3 manual warns that open-circuit voltage changes with temperature. It gives overvoltage protection of 155 V on the High-PV input and 62 V on the Low-PV input, just above their 150 V and 60 V input ranges.
BLUETTI's manuals say panels above the open-circuit voltage limit damage the station, and the warranty does not cover it.
Jackery rates its inputs by working voltage, not open-circuit voltage. The checker still tells you when a cold morning pushes Voc past the input's top number.
A real example
The EcoFlow RIVER 3 Plus takes up to 55 V. The Anker SOLIX PS200 Bifacial lists a Voc of 57.6 V Shop listing, not yet confirmed. That is over the limit even on a mild day. On a 20°F morning it would reach about 63.1 V. The checker says Don't connect. Try your own pair below.
Calculator
Your panels on a cold morning
Panels in series
Voc at 20°F63.1 V1 x 57.6 V on the label = 57.6 V at 77°F
Input limit55 VRated against open-circuit voltage.
Input limit, 55 VVoc of 1 panel in series, by temperature
66-10°F
6410°F
61.932°F
60.250°F
57.677°F
Checker, 1 in series at 20°FDon't connect
Open-circuit voltage 57.6V is above the station's 55V limit. The manual warns this can damage the station.
Uses a typical 0.30% per °C. This panel's own value is not published. Panel numbers: Shop listing, not yet confirmedOpen in the checker
Leave room
Set the checker to the coldest morning you expect where you will use the panels, not today's weather.
If a series string comes close to the limit at that temperature, use one fewer panel in series, or wire in parallel if the current limit allows it.
When a panel's own coefficient is not published, we use 0.30% per °C and say so in the checker's assumptions.
