A modular ballistic barrier assembly for deployment in proximity to a protected high value asset such as electrical grid equipment. A ballistic barrier assembly comprises a plurality of prefabricated ballistic barrier panel units that can be stacked on top of each other. Each panel unit is made of spaced apart angled steel louvers or slats, arranged in one or more sections. The louvers are arranged in one or more vertically extending, spaced apart rows, having an outwardly facing row of louvers presenting a downwardly angled surface to an approaching projectile, and an inwardly facing row of louvers presenting a second layer of ballistics protection. Steel I-beam support columns are provided at spaced apart intervals to receive and support a stack of panel units. The panel units are made to interlock with vertically adjacent, stacked panels, so that multiple panel units can be stacked.