Can an impact driver replace the specified torque check on solar mounting fasteners?

Not by default. Use an impact driver only for the steps permitted by the specific component’s installation instructions. IronRidge’s XR Flush Mount manual lists an impact driver for lag bolts, but separately lists a torque wrench and connection-specific torque values. Unirac’s SolarMount guide gives a limited impact-driver instruction for an end-clamp installation; that is not permission to apply the same method to every fastener. Do not treat a driver’s power setting, run time or a “tight” feel as a universal torque measurement. Complete the manufacturer-specified final tightening and any required torque measurement or recheck using the prescribed tool and procedure. A purpose-designed controlled-torque tool is not automatically approved for every joint. If the instructions are unclear, confirm the method with the mounting-system supplier before proceeding.

Sources: IronRidge, XR Flush Mount Installation Manual, Tools Required and module-clamp installation: https://files.ironridge.com/pitched-roof-mounting/resources/brochures/IronRidge_Flush_Mount_Installation_Manual.pdf Unirac, SM SolarMount Installation Guide, printed pages K, M and T (LA County archive of manufacturer document): https://dpw.lacounty.gov/bsd/lib/fp/Small%20Residential%20Rooftop%20Solar%20Energy%20Systems/LA%20County%20Recognized%20UL%202703%20Racking%20Systems/Unirac%20SM%20SolarMount%20Installation%20Guide.pdf