Roof direction, tilt, obstructions and shade influence the sunlight reaching the modules. Ground mounts offer different layout choices when land and approvals permit.
The season & equipment
Daylight, clouds, temperature and snow affect generation. Equipment conversion, wiring and other system losses also belong in an annual production estimate.
Compare annual production with annual consumption, and review the assumptions behind the estimate. A battery shifts when available energy is used; it does not create additional solar generation.