T1 Energy in Texas is producing solar panels and systems including batteries at gigawatt(about 3 currently, but they're expanding) scales.

Illuminate USA in Ohio claims to be going even bigger than T1. Over 5 GW/year (10 million panels). But they just seem to manufacture panels and not batteries.

Some others include: Tesla, Qcells, Mission Solar, First Solar, Ambri, Enphase, Ørsted, TotalEnergies, and Generac.

Not all are fully vertically integrated and many still rely on global supply chains...