A SECI tender for a ground-mounted solar PV plant does not buy a layout. It buys a Balance of System package, and inside that package the module mounting structure (MMS), the piles that carry it, the ground it stands on and the DC cabling between the strings are priced as one scope. The modules are tendered separately. What your engineers decide about steel, earth and copper is the part of the bid still yours to win or lose.
Why the Balance of System package decides the tender margin
SECI and NTPC float Balance of System as a standalone package, separate from module supply, with the scope written as design, engineering, supply other than the PV modules, construction, erection, testing and commissioning. That wording is the whole argument. Module pricing is a market you follow. Earthwork volume, pile length and cable cross section are numbers your design office sets.
Two PVX.AI project results show the size of the swing. Choosing between three grading approaches on one site changed earthwork volume by 70 percent and saved $727K. On a 130 MWp plant, changing only the DC cable topology shortened cable runs 14 percent and saved $430K.
Those decisions usually live in different files: a DWG, a civil consultant’s spreadsheet, a separate cable schedule. By revision three they disagree.
What a SECI tender or an NTPC tender asks the designer to produce
Strip the procurement language and four deliverables remain.
The DPR. The Detailed Project Report carries the layout drawing, the earthwork quantities, the cable schedule and the single line diagram. All four are downstream of the same geometry, so all four go stale when the layout moves a row. The question is not how fast you draw them, it is how fast you redraw them.
The GTP. The Guaranteed Technical Particulars fix the values your structure must honour: module orientation and tilt, pile embedment, the allowed reveal band, the minimum ground clearance. They are the limits your drawing has to be checked against, per structure type, because a site with two MMS specs has two sets of limits.
The BoQ. The bill of quantities is where the design becomes a price: cut and fill, site preparation, roads, cable trenches, earthing, cable lengths by cross section. Quantities from a separate take-off trace back to nothing.
The pull-out test. The tender asks for pile testing on site. For the designer that is a consequence of the pile schedule: which pile, at which location, at which length and embedment. If the reveal on a row is out of band before anyone drives a pile, a passing test on a neighbouring pile proves nothing about it.
Module mounting structure (MMS) on real ground: piles, reveal and clearance
The structure is the same steel the West calls racking, and it fails the same way: a pile short of its reveal band on a slope, a low module edge closer to the ground than the spec allows, a ditch between two piles no flat-plane drawing showed.
PVX.Cad places the MMS on the real 3D terrain surface, then checks it. Collision Analysis measures three things per table against that table’s own spec: pile reveal against the allowed band, ground clearance along the whole underside rather than at the pile positions alone, and slope along and across the structure. Multi-row tracker groups linked by drive shafts are judged as one unit, because the field builds them as one unit.
One run on a sample project: 534 tracker tables scanned, 377 violating. The fix ladder runs cheapest remedy first. 90 tables cleared with a rigid vertical lift and no ground moved. The remaining 311 had their rows regraded as one continuous, buildable surface with the least cut and fill that clears every table. Cut 35,505 m3, fill 1,970 m3. The re-scan returned 0 violating.
That scan exports both deliverables the structural reviewer asks for: a pile schedule CSV with one row per pile and its verdict, and a run report stating the measurements, the limits and the fixes applied. Full walkthrough in the collision analysis post.
Grading three ways, and the cut and fill your quantities depend on
Not every earthwork problem deserves the same earthwork. PVX.AI grades three ways. Area grading reshapes a whole PV area to slope targets set per direction, with cut and fill balance under your control, and can generate the site roads in the same run. Pad grading cuts a real, level pad under each table and seats the table on it. Targeted terrain adaptation is the surgical option used by the collision fix above: it touches only the rows that failed.
All three report total cut and fill, colour a per-triangle map, keep the original terrain as a hidden baseline, and feed the civil works sheet of the BoQ alongside site preparation, roads, cable trenches and earthing. Because every candidate surface is built and measured the same way, comparing strategies is a build-and-read exercise. That comparison produced the $727K: earthwork down from 118,225 m3 to 34,819 m3, a 70 percent reduction.
DC cabling and the single line diagram: per-string voltage drop, Line, U and Leapfrog
Electrical design runs on the same drawing. String the structures from a reusable preset, set the scope, configure the hierarchy from string to inverter to transformer, place the devices, then generate trenches and cables.
Cables are sized to a voltage drop target rather than a fixed gauge. You set the standard (IEC or NEC), the conductor (copper or aluminium), the target voltage drop percentage and the system voltage, and the output reports cross sections, cable lengths and voltage drop per group. An undersized run shows up in the report, not after the cable order goes out. Trench lanes follow IEC separation rules, and the 3D drape gives true cable lengths over the ground the cable crosses.
Topology is the lever that moved $430K. On that 130 MWp plant, Line, U and Leapfrog were compared against the same transformer, inverter and DC box layout, and the winning topology shortened the loop length enough to cut 14 percent of the cable run while holding voltage drop inside target.
Generate SLD then draws an IEC-60617 single line diagram onto its own paper-space layout tab, aggregated for a printable sheet or in full detail for verification. It is generated from the design, so it cannot describe a plant the drawing no longer contains.
One DWG, one data model, one revision cycle
These three sections belong in one post because in PVX.Cad they belong to one file. Terrain, structures, graded surface, piles, trenches and cables are native objects in the same AutoCAD drawing, so a boundary change propagates instead of being re-entered.
Move a row and the pile lengths change. Regrade and every structure re-fits to the current surface in one command. Re-run the scan and the pile schedule reflects the new ground. Re-run the cabling and the lengths and cross sections follow. The DPR attachments stop being four documents reconciled by hand, and every BoQ quantity has a drawing behind it when the client’s engineer asks.
Frequently asked questions
What does a Balance of System package cover in a SECI or NTPC tender? Everything around the modules: design, engineering, supply other than the PV modules, construction, erection, testing and commissioning. For the design office: the MMS and its piles, the grading, the trenches and the cabling.
How do you design a module mounting structure (MMS) on sloping ground? Place it on the real 3D terrain surface, then check every table against its own spec: pile reveal against the allowed band, ground clearance along the whole underside, and slope along and across the table. Collision Analysis ranks failures worst first.
Where do the cut and fill quantities for the bill of quantities come from? From the graded surface. Every grading run reports total cut and fill and feeds the civil works sheet alongside site preparation, roads, trenches and earthing.
Can the DC cabling and the single line diagram come from the same drawing as the layout? Yes. Cables are sized to a voltage drop target under IEC or NEC rules, and Generate SLD draws an IEC-60617 diagram from the same design.
- Start a free trial of PVX.Cad and run the MMS check, the grading comparison and the cable sizing on your own site, inside your own AutoCAD.
- Book a demo and bring a DWG from a live bid. The scan, the fix and the cut and fill numbers run on your terrain in the call.
