Void shield generators. Atomantic pavises. Flare shield projectors. Ion palisades. Whatever the specifics, the Solar Auxilia should make reasonably widespread use of portable shield projection systems.
The Solar Auxilia are a (comparatively) lightly armoured force who descend onto planets en-masse to create and expand fortified landing zones, and fight in advancing close-order infantry blocks, with "aggressive defence" being a preferred tactical approach.
Mobile (but sluggish, vulnerable, and unreliable) area-of-effect shield projectors would not only be a great tactical addition, they'd be perfectly in-theme for how they operate.
Imagine something like an oversized Rapier platform fitted with a bulky cluster of flare shields instead of a gun or seat. Two void-suited technicians are tending to its reactor and adjusting its field output, with a tercio vexilla fluttering atop its chassis. It rumbles steadily forward between the sections of its tercio, projecting a defensive aura that's even more effective against dispersed blasts that would otherwise wipe out whole sections. If it remains stationary, the technicians can strengthen its output further, or focus its energies toward a specific direction for a more efficient shield effect.
I appreciate that the Legiones Astartes get all the shiny toys, but they have so much less doctrinal need for mobile shield-bubble projectors that it's kind of baffling they get so many of them compared to the Auxilia. The old Deredeo atomantic pavise, the Legions Imperialis Palisade Drop Pods, the Araknae's own atomantic pavise, etc; give some similar tools to the Solar Auxilia and it'd do amazing work.