Square field from the DC nameplate

Method

The number of rows is estimated from the DC nameplate alone. The array is taken as 300 W modules in a square field, with as many rows as modules along a row (1, 2). The modules up a row are two on fixed racks and one on a tracker. The DC nameplate is the number of modules of the Racking tab times the module's nameplate. A 1 MW array gives 41 rows on fixed racks and 58 on trackers. This is the layout PVWatts version 8 assumes.

The math

1. Modules
2. Rows

$$n_{mod} = \max\!\left(1,\ \left\lceil \frac{P_{dc0}}{300\ \text{W}} \right\rceil\right),\qquad P_{dc0} = N_{str}\,N_{s}\,N_{inv}\,P_{nom} \tag{1}$$ $$N_{rows} = \left\lceil \sqrt{n_{mod} / n_y} \right\rceil \tag{2}$$

where

Symbol	Meaning	Unit
$n_{mod}$	the number of 300 W modules of the estimate	—
$P_{dc0}$	the DC nameplate of the array	W
$N_{s}$	the modules in series per string	—
$N_{str}$	the strings per inverter	—
$N_{inv}$	the number of inverters	—
$P_{nom}$	the module's nameplate power	W
$N_{rows}$	the number of rows the self-shading counts	—
$n_y$	the modules up a row: 2 on fixed racks, 1 on a tracker	—

References

1. NREL SAM Simulation Core (SSC) source code, release 2026.7.3, github.com/NatLabRockies/ssc: ssc/cmod_pvwattsv8.cpp, the estimated system layout in exec()

API

array.row_count = square_field

Symbols follow the symbol registry.