The short answer
Area grading reshapes every part of the boundary that is steeper than the threshold slopes you set, and it smooths that ground together with its neighbours until nothing is over the limit. If the limits are tighter than the racks need, or the boundary covers ground no rack needs moved, the volume grows quickly. On most sites the fix is to set the thresholds to what your racks actually tolerate, and to move ground only where piles need it, with Collision Analysis or Adapt Terrain to Pile, instead of grading the whole area.
1. Your slope limits are tighter than the terrain
The Grading dialog has an NS Threshold Slope (%) and an EW Threshold Slope (%), both 10% by default. Only ground steeper than these values is graded, so the lower you set them, the more of the site is reshaped. To make sure the result passes, the solver aims slightly below the value you enter. Limits of 1% or less turn the area into a flat platform at its average elevation, which is almost never what a solar site needs.
The grading limits are separate from the slope limits the layout uses (N (%), S (%) and EW (%) in Build Layout). Nothing copies one into the other.
What to do: set the grading thresholds from the rack or tracker supplier’s slope tolerance, not lower. Use Separate North / South limits when north-facing and south-facing slopes have different limits. Before grading, turn on Show Directional Slope Map (EW/NS) on the Terrain Settings tab to see how much of the site is actually over the limit. See Terrain Grading and Multi-Directional Terrain Analysis.
2. You graded the whole area when only some racks needed it
PVX.AI has three ways to move ground, and they produce very different volumes:
- Area grading (Civil sub-tab > Earthworks > Grading): reshapes the whole boundary to the slope limits, whether or not a rack stands there. Use it when the site needs one continuous buildable surface, for example steep ground or a client specification.
- Adapt Terrain to Pile (Layout > Collision Analysis dropdown): moves ground so every pile’s reveal stays inside the pile length or rack height limits you set. On tracker areas it solves for the least cut and fill that keeps each pile in its band.
- Collision Analysis > Fix collisions: first lifts each rack where a lift alone reaches the pile reveal band and clearance, and grades only the rows that still miss. It shows an Estimated earthwork figure before you run it.
What to do: place the racks first, run Collision Analysis to see which racks really need ground moved, and fix those. Keep Grade the terrain first on in Adapt Terrain to Pile unless you have a reason to turn it off: on one test site, skipping the grading step raised fill from about 28,000 m³ to about 217,000 m³. See Adapting Terrain to Piles.
3. The boundary is bigger than the ground you need to move
Grading works inside the area you pick with Select Area. With Soft Slope Transition (the default) it also blends the edge into the surrounding ground over a band just outside the boundary. A boundary drawn around the whole land parcel, including corridors, setbacks and ground outside the racks, adds volume no one will build on.
What to do: grade by PV area, or draw a tighter boundary around the rows that need it. Use Hard Slope Transition when the edge must not touch ground outside the boundary.
4. The cut/fill balance setting is pushing volume one way
Under Cut/Fill Balance, the Cut/Fill Ratio slider balances cut and fill when centered, and biases the result toward more cut or more fill when moved. Max fill height caps fill depth instead. Capping fill moves volume into cut, so total excavation goes up.
What to do: start with the slider centered. Use Max fill height only when imported fill or fill depth is a real constraint on the project, and compare the totals with and without it.
5. The terrain is too coarse for a take-off
Grading has no grid setting of its own. It works on the terrain grid you chose when you imported the terrain, and that grid is locked for the drawing once terrain exists. Elevation data downloaded for a KML boundary comes from a 30 m source, so volumes from it are a feasibility estimate, not a quantity you can price.
What to do: for numbers you will quote, import survey data (contours, a point cloud or survey points) at a grid resolution close to your pile spacing. See Which coordinate system and grid resolution should I use?
6. You are reading volumes from several runs added together
Cubage Breakdown and the Cut Amount and Fill Amount on the Info Screen compare the original imported terrain with the current terrain. Every grading and adapt run since the import is included. Grading again on top of graded ground, or trying several settings one after another, adds up.
What to do: before trying new settings, click Reset Terrain on the Terrain panel to go back to the imported ground, then run one grading with the new settings. Reset can be undone with Ctrl+Z. See Resetting the Terrain.
How to check the result against your own estimate
- Run Cubage Breakdown over the area in question to see the cut/fill map and the before and after table. See Cut/Fill Application Map.
- Use Generate Terrain Profile to look at the original and graded ground along a line. See Cut/Fill Before and After Comparison.
- If an engineer compares the PVX.AI surface with their own survey, give them the graded-zone contours and outline drawn by Contours & Spot Elevations, so they compare only the ground that was moved.
- Run the same settings on a past project whose earthworks you know. If PVX.AI matches that project, the difference on the new site comes from the site or the settings, not the tool.
- Check the units: imperial drawings report volumes in cubic yards (cy), metric drawings in m³.
For background on choosing a grading approach, see the grading guide on pvx.ai.