No - derating factor is different from the safety factor. The derating factor is used as the basis of calculation to determine worst-case performance for EOL voltages: when the batteries are at the end of their life expectancy (5 years) and the battery output voltage has decreased (15%) the result is the panel's output voltage will similarly be reduced (unless it is documented by UL to have compensation circuitry). Accordingly, circuits that used to be calculated using 24VDC are now calculated using 20.4VDC as the base voltage. Then the circuit load calculations are done using the UL max current draws - which are measured at the lowest listed operating voltage (typically 16VDC).
The safety factor is to provide additional power beyond what the minimum calculations show will be required to operate the system, to compensate for minor system additions or changes. (2010 at 10.5.6.3.1)
The de-rating factor is applied to the voltage, the safety factor is applied to the amperage.
The Safety factor is upping the battery capacity after calculating the proper standby and alarm capacity needed to operate a system
