Non-penetrating trays or frames
Best suited to firm, level or properly prepared surfaces where excavation is undesirable. Quick and potentially removable, but heavy, material-intensive and sensitive to settlement and wind design.
Ground-mount design
Ground-mounted solar on uneven land: ballast, posts or ground screws?
Ballast trays are simple on flat, prepared ground. Once the land slopes, undulates or drains poorly, an adjustable post-and-rail structure is usually the more convincing engineering route.
The practical answer
Do not make ballast compensate for unsuitable ground.
Ballasted trays avoid penetrating the ground, but they need stable support and enough accurately distributed mass to resist wind. On uneven ground, levelling individual trays can create inconsistent angles, point loading, settlement and awkward drainage.
Driven posts or ground screws create adjustable foundation points. Rails can then be levelled across modest changes in height while maintaining a consistent panel plane and clearance.
Uneven is not the same as unstable. A frame can bridge height differences; it cannot make peat, made ground, loose fill or a landslip safe without engineering.
Three approaches
Choose the foundation, then design the frame around it.
Steel piles or posts
Efficient for suitable soils and repeated rows. Adjustable heads and rails handle varying levels. Installation can be rapid, but refusal on rock and pull-out capacity must be addressed.
Helical or screw foundations
Useful where excavation and concrete are undesirable. They can suit slopes and be removable, but require verified torque/capacity, correct corrosion protection and suitable ground.
Comparison
What changes the decision?
| Question | Ballast | Posts | Ground screws |
|---|---|---|---|
| Uneven levels | Usually requires prepared pads or grading | Good adjustment through post height and rails | Good adjustment with engineered heads |
| Ground penetration | None | Yes | Yes |
| Weight and transport | Often high | Usually lower | Usually lower |
| Rocky ground | May avoid refusal if surface is stable | Risk of refusal | Specialist pre-drilling may be needed |
| Removal | Generally straightforward | Possible but site-dependent | Often reversible |
| Engineering evidence | Ballast and bearing calculations | Drive and pull-out capacity | Installation torque and pull-out capacity |
Survey before specification
The land needs its own evidence pack.
✓ measured slope, contours and row-to-row shading;
✓ soil type, made ground, peat, rock and drainage;
✓ buried electrical, water, gas and drainage services;
✓ wind exposure, altitude and shelter;
✓ frost, erosion, livestock and vegetation management;
✓ access for piling or screw-driving machinery;
✓ cable route, inverter location and earthing design.
A trial pile or screw and pull-out test may be more valuable than guessing from the surface.
Layout on a slope
Consistent panel geometry matters more than making every post identical.
The structure can step with the terrain or use varied post heights to create aligned rows. The engineer must control ground clearance, maximum post projection, rail spans and bracing.
Rows also need enough separation to prevent one row shading the next when the sun is low. On south-facing slopes this may be favourable; on north-facing slopes the geometry can become much less productive.
Drainage must remain natural or be deliberately managed. Concentrated runoff and newly compacted tracks can create erosion around foundations.
Planning and ecology
Check permission before ordering a mounting system.
Scottish permitted-development rules include a route for some free-standing domestic solar installations, but limits and exclusions apply. Listed buildings, conservation considerations, scale, location and non-domestic use can change the answer.
Ground arrays may also affect trees, habitats, archaeology, agricultural use, drainage and neighbours. Obtain written confirmation from the planning authority where there is doubt.
Recommendation
For genuinely uneven ground, start by pricing an engineered post or ground-screw system.
Use ballast where avoiding ground penetration is important and a stable, reasonably level bearing surface exists. Use posts or screws where levels vary and the ground can provide verified structural capacity.
The cheapest frame is not the cheapest solution if it first requires extensive levelling, imported ballast and future settlement repairs.
Planning reference
Confirm the exact site rules.
- Scottish Government: householder solar permitted-development guidance
- Scottish Government: Planning Circular 1/2024
Guide checked 25 September 2026. Final structural and foundation design belongs with the mounting supplier and appropriately competent engineer.