PV string calculator for Deye and Felicity Solar inverters

Longest string: Voc at the lowest ambient temperature (at dawn the cells are as cold as the air) = Voc × (1 + βVoc × (Tmin − 25°C)). The string Voc must stay at or below the inverter's maximum DC input voltage and the module's maximum system voltage.

Shortest string: Vmp at the highest cell temperature = Vmp × (1 + βVmp × (Tcell − 25°C)). The string must stay above the MPPT minimum and the start-up voltage, whichever is higher. Few datasheets give βVmp, so we derive it as γPmax − αIsc: slightly more negative than γPmax, which keeps the minimum on the safe side.

On cold days the string Vmp should stay below the MPPT ceiling; if it does not, you get a remark, not an error. Where the datasheet gives a full-load MPPT range, we also check the string Vmp at 25°C against it.

Strings in parallel: the short-circuit current at the highest cell temperature, Isc × (1 + αIsc × (Tcell − 25°C)), must not exceed the tracker's maximum short-circuit current, and the strings must not outnumber its inputs. We also apply the IEC 62548 design margin, Isc × 1.25, which covers irradiance above 1000W/m² and bifacial gain: exceeding it gives a remark. If the module's αIsc is missing, the 1.25 rule becomes the limit. An operating current (Imp) above the tracker's maximum is a remark: the inverter caps the current.

Array size: the STC power must not exceed the maximum PV power in the datasheet (Deye calls it PV access power, Felicity Solar DC access power or recommended PV power). Above the PV input power the inverter limits output in the sunniest hours.

Inverter values come from the official Deye and Felicity Solar datasheets linked above, module values from the manufacturers' datasheets linked on our product pages. When a value is missing we do not estimate it: the check shows “data not available” and we answer by e-mail.