Sequential flat derates

Method

The flat derates act in two places. In the loss diagram each takes its fraction of the running DC total, in this order: the module quality, the light-induced degradation, the light soaking (CIS and CIGS modules only), then the module and string mismatch combined. On the array's current-voltage curve, which the inverter reads when it moves away from the maximum-power point, their product scales the current and the voltage alike, each by its square root. The curve's maximum power is then scaled by the product itself.

The math

1. Combined derate
2. Derated array curve

$$f_{dc} = (1 + g_q)(1 - \text{LID})(1 + g_{ls})(1 - m_{mod})(1 - m_{str}) \tag{1}$$ $$I_d\big(\sqrt{f_{dc}}\,V\big) = \sqrt{f_{dc}}\,I(V) \tag{2}$$

where

Symbol	Meaning	Unit
$f_{dc}$	the combined DC derate	—
$g_q$	the module quality gain: the quality loss input with its sign reversed	—
$\text{LID}$	the light-induced degradation fraction	—
$g_{ls}$	the light-soaking gain; 0 for modules other than CIS and CIGS	—
$m_{mod}$	the module mismatch fraction	—
$m_{str}$	the string mismatch fraction	—
$I_d(V)$	the derated array current at voltage $V$	A
$I(V)$	the array current at voltage $V$ before the flat derates	A

API

dc_losses.quality_loss, dc_losses.lid_loss, dc_losses.light_soaking_gain, dc_losses.module_mismatch_loss, dc_losses.string_mismatch_loss

Symbols follow the symbol registry.