Short answer: on hillsides, let the structure absorb the slope instead of grading the ground flat. Use fixed terrain-following tables beyond about 15 % north–south slope, where single-axis trackers reach their published limits. Space rows by slope direction: equator-facing slopes allow tighter rows, pole-facing slopes need much wider ones. Choose foundations from pull-out tests, and design edge rows for higher wind.
Flat land near the grid is getting scarce, so more utility-scale plants are going onto hillsides, ridges and plateaus. These sites work well with the right structure. Our structures carry 12 utility-scale plants of 50–210 MW in Yunnan, much of it on uneven ground, and these are the points we check first.
Key numbers
- Our fixed ground-mount systems accept slopes up to 30° north–south and 20° east–west.
- Terrain-following single-axis trackers are published at about 15 % north–south (8.5°); one manufacturer allows up to 2° of bend between adjacent posts.
- Early users of one terrain-following tracker reported 30–90 % less grading on undulating sites (manufacturer-reported).
- In our worked example below, a 10° equator-facing slope cuts row pitch by about 14 %; a 10° pole-facing slope adds about 30 %.
1. Follow the terrain, keep earthworks minimal
Grading a hillside flat is expensive, slow and causes erosion. A terrain-following structure leaves the ground as it is: posts of different lengths, adjustable post-to-rafter connections and purlins that tolerate small angle changes. Beyond 30° north–south or 20° east–west, split long tables into shorter ones that step down the slope, or leave the steepest areas out of the layout.
Trackers are possible on gentle hills. Terrain-following designs bend the torque tube a little at each post so a row can follow undulating ground, within about 15 % overall north–south slope. On steeper or broken ground, fixed-tilt is usually the practical choice; see fixed-tilt vs tracker.
2. Row spacing depends on which way the slope faces
On a slope facing the equator (south-facing in the northern hemisphere), each row stands higher than the one in front, so rows can be closer without shading. On a slope facing away from the equator, the row behind sits lower and rows must be much further apart. This simplified calculation shows the size of the effect.
For a table whose top edge stands h above its bottom edge, the gap needed to avoid shading at a design sun altitude α is:
- Flat ground: gap = h ÷ tan α
- Equator-facing slope of angle β: gap = h ÷ (tan α + tan β)
- Pole-facing slope of angle β: gap = h ÷ (tan α − tan β)
| Worked example (latitude 25°, two modules in portrait, 4.6 m table at 25° tilt) | Flat | 10° equator-facing | 10° pole-facing |
|---|---|---|---|
| Table height h = 4.6 × sin 25° | 1.94 m | ||
| Table depth = 4.6 × cos 25° | 4.17 m | ||
| Design sun altitude (winter solstice, 9:00 solar time) | about 25° | ||
| Gap between rows (horizontal) | 4.16 m | 3.02 m | 6.69 m |
| Row pitch (depth + gap) | 8.33 m | 7.19 m (−14 %) | 10.86 m (+30 %) |
The example ignores the sun’s azimuth at 9:00, so it is conservative. Use it to judge which parts of a site are worth building on, then run the full shading model on the topographic survey. East–west slopes cause morning or evening shading between neighbouring tables and need the same check.
3. Choose the foundation from the geotechnical report
| Ground | Typical foundation |
|---|---|
| Soil without large stones | Driven steel pile or PHC pile |
| Stony soil, weathered rock | Pre-drilled hole with steel pile, or cast-in-place pile |
| Sound rock | Drilled anchors or small cast-in-place piles |
| Very loose or mixed ground | Independent concrete footings |
Mountain sites often change ground type within a few metres. Plan pull-out and lateral load tests at several points across the site, and keep two foundation designs ready. Tolerance in the post-to-rafter connection absorbs the height and position errors that uneven ground causes.
4. Wind is stronger on ridges and slope edges
Wind speeds up as it crosses a ridge, an escarpment or the top of a slope. Loading codes account for this with a topography factor: the orography factor in Eurocode EN 1991-1-4, or the topographic factor in ASCE 7. Edge and corner rows of an array also carry higher loads than the middle. Design to the local code at the actual site, and use heavier sections or extra bracing in edge zones rather than over-designing the whole plant.
5. Drainage, corrosion and access
- Drainage. Keep natural drainage paths open. Concentrated runoff from module edges can erode the ground around foundations; plan gravel or vegetation along drip lines on steep sections.
- Corrosion. High-altitude sites have strong UV and large temperature swings; humid valleys can be more corrosive than they look. Match the zinc coating to the site, see our galvanizing guide.
- Access. Mountain roads limit truck size, and parts are often carried by hand on the last stretch. Short members, light sections and a clear marking system make installation faster.
- Survey first. A topographic survey before final design gives accurate post lengths and reduces cutting on site.
FAQ
What is the maximum slope for a fixed PV structure?
It depends on the design. Our fixed ground-mount systems accept up to 30° north–south and 20° east–west; steeper areas are handled with stepped tables or left out of the layout.
Can single-axis trackers be used on hills?
On gentle, undulating ground, yes: terrain-following trackers are published at about 15 % north–south slope. Steeper or broken terrain usually calls for fixed-tilt structures.
Are pole-facing slopes worth building on?
Gentle ones can be, with wider row spacing; in the example above a 10° pole-facing slope needs about 30 % more pitch than flat ground. Steep pole-facing slopes are usually excluded.
Which foundation works in rock?
Drilled anchors or small cast-in-place piles in sound rock, and pre-drilled holes with steel piles in weathered rock. Confirm with pull-out tests on site.
Working with us
We design terrain-following fixed, adjustable-tilt and tracking structures to the site survey, geotechnical report and loading code, and supply them from our roll-forming and hot-dip galvanizing lines near Kunming. Send us the layout, module data and site loads for a structure proposal.
Sources: our fixed-structure slope limits from our structure catalogue; terrain-following tracker data from manufacturers’ announcements reported by pv magazine and pv magazine (2026); Eurocode EN 1991-1-4 and ASCE 7 for topography factors. Row-spacing figures are our own worked example and are simplified. Related: our projects, all mounting systems.