Rooftop and ground-mounted systems solve different site problems. A rooftop array uses space that already exists but depends on a building designed for something else. A ground-mounted array gets a purpose-designed frame, but its foundations, layout and access depend on the land.
Neither is automatically simpler or cheaper. The structural questions are just different.
What decides each option
For a roof, the questions are the building's structural system and condition, how the array is anchored, what the waterproofing allows and how wind forces reach the supporting frames and foundations. For ground mounting, they are soil investigation, the choice between piles, screws and footings, terrain, drainage and whether installation equipment can reach the whole field.
Wind drives the design of both, but the load path differs. On a roof, anchors pass force into the building. On the ground, supports pass reactions into piles or footings and then into the soil. The design basis should say which applies.
- Rooftop: existing drawings, condition survey and anchorage details.
- Ground-mounted: survey and geotechnical coverage across the whole footprint.
- Both: access for installation, cleaning and maintenance.
Compare them on equal terms
Use the same capacity and the same site constraints, then list the extra work each option needs. A roof may need assessment or strengthening. A ground site may need extra surveys, ground improvement, access tracks or drainage works. Compare the complete scope, not the headline equipment price.
- Identify the surveys and checks each option needs.
- Confirm waterproofing or groundworks interfaces.
- Include inspection and maintenance in the comparison.
- Record why the chosen option fits the site.