String Inverter Input Planner

Checks which strings sit on which MPP input: current per input, string voltage, array power, DC/AC ratio and the share of the array behind each input.

Design aid, not a substitute for the inverter manual, the adopted code or your AHJ. The defaults are the Fronius Symo Advanced 10.0-3-M help-page limits and Qcells 425 W datasheet values. The temperatures (-10 °C cold, 70 °C hot cell) and the roof (E 11, W 11, S 12 modules) are invented. The Vmp coefficient is an estimate (Pmax minus Isc coefficient) because the module sheet prints none. Use the datasheet of your exact model and variant.

Examples:

Module (STC datasheet values)

Voc (V) Vmp (V) Isc (A) Imp (A) Pmax (W) Voc coefficient (%/K, negative) Pmax coefficient (%/K) Isc coefficient (%/K) Vmp coefficient (%/K, blank = estimate)

Site (invented stand-ins)

Cold cell temperature (°C) Hot cell temperature (°C)

Inverter (shared limits)

Max DC input voltage (V) MPP range, lower (V) MPP range, upper (V) Start-up voltage (V, blank = none) Max PV power (Wp, blank = none) Rated AC power (W)

Per MPP input: limits (blank = no such input)

Input 1 max current (A) Input 1 max short-circuit (A) Input 2 max current (A) Input 2 max short-circuit (A) Input 3 max current (A) Input 3 max short-circuit (A)

Layout: modules in each string (blank = no string)

Input 1, string 1 Input 1, string 2 Input 1, string 3 Input 2, string 1 Input 2, string 2 Input 2, string 3 Input 3, string 1 Input 3, string 2 Input 3, string 3

Check	Design value	Limit	Result

Method: voltage at cell temperature T = STC value x (1 + coefficient x (T - 25)). Voltage rows use the worst string on each input. Current is strings x Imp (or Isc) on that input. The share is modules on the input divided by all modules; it is arithmetic on the layout, not a failure rate. Unequal lengths on one input are not a datasheet fail; see the MPPT page for the loss. Numbers: type 10,000 or 10 000 for ten thousand and 0,25 for a quarter. A value such as 1.000 is ambiguous and is rejected; type 1 instead.