Roof Mount vs Ground Mount vs Carport For Shaded Lot Decision Matrix
Why this matters
On a lot where the roof is shaded by trees or neighboring structures, the mounting decision is really a site-energy decision: where on the property can panels see unobstructed sun for the most hours? Roof mount is cheapest and simplest when the roof is good and clear, but a shaded roof forfeits that advantage. Ground mount and carport relocate the array to better solar access at higher structural and trenching cost. Choosing the wrong mount on a shaded lot either buries the array under the same trees that shaded the roof or spends ground-mount money where a clear roof plane existed all along. This matrix gives the tech a structured way to weigh solar access, structure, code, and cost.
The options
Roof mount. Modules on rails attached to the roof structure via flashed mounts into rafters/trusses. Lowest cost, no separate foundation, uses otherwise unused space, and keeps conductor runs short. On a shaded lot its viability depends entirely on whether any roof plane has good access; a shaded south plane may yield less than a clear ground array. Adds dead load and requires the roof to have remaining service life, since re-roofing under an array is costly.
Ground mount. A standalone racking structure on driven piles, ground screws, or concrete footings in an open area of the lot. Frees the design from roof geometry and shade, allows optimal tilt and azimuth, and simplifies future service (no roof access). Costs more for foundation, trenching, conductor runs, and often a larger required clear footprint. Subject to setback, fence/guarding, and sometimes accessibility requirements; raised arrays may need fall protection considerations during service.
Carport (solar structure over parking). A purpose-built canopy that both shades vehicles and hosts the array, elevated above ground-level obstructions. Useful when the lot's only unshaded open space is the driveway/parking, when the owner wants the dual benefit, or when ground space is paved. Highest structural cost (engineered steel, larger foundations, wind/snow load on a tall structure) and the most permitting complexity, but excellent solar access above low obstructions.
When A/B/C wins
Roof mount wins when at least one roof plane has good solar access (acceptable shade for only a small part of the day), the roof has ample remaining life, and the structure can carry the load. On a shaded lot this is the winner only if a usable clear plane actually exists; do not default to roof out of habit if a shade study shows the roof is the worst place on the property.
Ground mount wins when an open, unshaded area of the lot exists, the owner can give up that footprint, and the energy gain from optimal tilt/azimuth and clear sun outweighs the foundation and trenching cost. It is the typical answer when trees shade the whole roof but a field or yard is clear. It also wins where future roof maintenance access is a concern.
Carport wins when the only meaningfully unshaded space is paved (driveway, parking lot), when low ground obstructions (fences, shrubs, vehicles) would shade a ground array but not an elevated canopy, or when the owner values vehicle shade/EV charging integration enough to absorb the structural premium.
A solar-access ranking, not a cost ranking, should drive the first cut on a shaded lot: instrument each candidate location, then let cost break ties between locations that deliver similar harvest.
Field decision flow
- Run a solar-access study at every candidate surface: each roof plane, the open ground, and the proposed canopy height. Record unobstructed sun hours, not just azimuth.
- Eliminate any location whose access is poor regardless of mount type. A shaded roof plane is out even though roof is cheapest.
- Among locations with good access, rank by harvest, then by cost to reach with conductors and foundation.
- Check structure. Roof: remaining roof life and load capacity. Ground/carport: soil/foundation suitability and wind/snow loading.
- Check code and site constraints: setbacks, guarding/fencing for ground mounts, height limits and engineered design for carports, and conductor/trench routing and fire-service access per the applicable code.
- Confirm rapid-shutdown and conductor protection requirements apply to whatever is mounted on or near a building; ground-mount arrays not on a building have different 690.12 applicability than roof and building-attached carports.
- Choose the mount that serves the highest-access location at the lowest lifecycle cost, and document the shade study that justified moving off the roof if you did.
References
- NEC (NFPA 70) Article 690.12, Rapid Shutdown of PV Systems on Buildings
- NEC (NFPA 70) Article 690.31, Wiring Methods (and conductor protection)
- IEC 62446-1, Photovoltaic (PV) systems - Requirements for testing, documentation and maintenance
- NEC (NFPA 70) Article 690.4, General Requirements for PV Systems