How to Verify Pile Elevations on Solar Farms

Why Pile Elevation Verification Matters on Solar Sites

Solar racking systems are designed to specific pile top elevations that position panels at the correct height above finish grade for clearance, drainage, and structural performance. Piles driven too high or too low create misaligned chord members that are difficult to clamp, require additional hardware to accommodate, or in the worst cases require the racking row to be torn down and re-driven.

On a utility-scale solar site with 20,000–100,000 piles, even a 5% out-of-tolerance rate means 1,000–5,000 piles needing some form of corrective action. Catching pile elevation problems before racking starts is the difference between a relatively cheap correction (field cut or extension) and an expensive rework (removing installed racking to access non-conforming piles). Verification surveying is one of the highest-ROI QC activities on a solar construction site.

GPS Setup for Pile Elevation Surveys

RTK GPS is the standard tool for solar pile surveys because it allows one operator to cover large areas quickly. On open terrain without canopy or structure obstruction, a GPS rover with a reliable correction source achieves ±0.05 ft vertical accuracy — adequate for the ±1 inch (±0.08 ft) tolerance used by most racking manufacturers.

Base station setup options: (1) local base station over a project control point with known coordinates and elevation, (2) network RTK subscription (VRS or similar) if the project is within the network's coverage area. Network RTK eliminates the need to set up and move a local base station across the site. Verify the chosen correction source achieves the required vertical accuracy on your site — test it on two known control points before starting the pile survey.

On large solar sites, establish multiple check points across the project area. Move between check points every few hours to verify the GPS solution has not drifted. Document each check point verification in Sitemark — this is part of the survey quality record.

Loading Design Pile Elevations into Sitemark

Before starting the pile survey, load your design pile top elevations into Sitemark. On a typical utility-scale solar project, pile top elevations vary across the site to follow the finish grade profile — piles on higher ground are driven shallower (same stick-up from grade) than piles in low areas. The design pile top elevation for each pile is calculated from the design finish grade at each pile location plus the design stick-up height.

Design pile top elevations are typically available from the civil engineer's pile schedule or from the racking engineering package. They can be imported into Sitemark as a CSV file organized by pile ID, or entered manually for smaller sections. Having design elevations loaded before going to the field is essential — without them, the GPS rover is collecting raw elevation data that requires a separate comparison step later.

Surveying the Piles

Work systematically through each row section, placing the rover pole on the top of each pile cap. The rover pole tip must contact the pile cap squarely — any tilt in the pole introduces error equal to the pole lean times the pole height. Most experienced GPS operators keep the pole within 3–5 degrees of vertical for routine shots. Use a bull's-eye level on the pole for critical or borderline shots.

In Sitemark, select the pile ID and log the measurement. The app shows the deviation from design immediately. Most GPS rovers with RTK achieve a measurement in 2–3 seconds when the fixed solution is confirmed. A well-organized one-person GPS survey covers 300–500 piles per hour on open terrain, meaning a 500-pile block can be surveyed and reported in roughly 1–2 hours.

Corrective Actions for Out-of-Tolerance Piles

When a pile is out of tolerance, the correction depends on whether it is too high or too low:

• Pile too tall (above design elevation) — Field cut the pile to the design elevation. Mark the cut line with the calculated cut dimension (as-built elevation minus design elevation), cut with an angle grinder or portable bandsaw, and deburr the cut end. Re-survey the pile after cutting to confirm compliance. Document the corrective action and the confirmed-corrected elevation in Sitemark.
• Pile too short (below design elevation) — Install a pile coupler extension. The extension must be rated by the manufacturer for the racking system's structural loads. The extension length is calculated as design elevation minus as-built elevation, plus a splice overlap per the manufacturer's specification. Verify the extension installation brings the pile top within tolerance before the racking crew arrives.
• Pile significantly out of tolerance (more than 3–4 inches) — Notify the EPC contractor's engineer before taking corrective action. Large deviations may indicate a pile installation problem (improper template setup, GPS error during driving) that requires a different resolution than a standard cut or extension.

Handoff to the Racking Installation Crew

When a row section passes pile verification (or after all corrections are confirmed), generate the pile survey report from Sitemark and provide it to the racking installation crew and EPC superintendent. The report shows each pile number with its verified elevation, deviation, and pass/fail status, organized by row and section.

The racking crew uses the report to pre-plan any remaining adjustment at the clamp level — many racking systems allow ±0.5 to ±1 inch of field adjustment in the clamp without structural consequences. Knowing in advance which piles are at the edge of tolerance helps the crew plan their installation sequence and avoid surprises.