Most Indian EPC founders manage solar engineering the same way they started: whoever can AutoCAD does the SLD, the site supervisor handles the structural sign-off by knowing the right person, and the DISCOM submission is assembled in a hurry two days before the deadline. This approach works at 1–2 MW per month. It fails structurally at 5 MW and above — not because the EPC is incompetent but because the engineering workflow was never designed for volume. Errors compound. Revision cycles overlap. The CEIG queue stretches. Projects that should close in 90 days close in 140.
This guide is the complete engineering workflow for Indian EPCs — from the moment a project enters the bid stage to the point where the as-built drawings are filed and the commissioning certificate is signed. It covers deliverables, responsible parties, quality gates, and the integration points where outsourced engineering plugs into your internal operations.
Direct answer. The complete solar engineering workflow for Indian EPCs spans seven phases: bid-stage pre-feasibility, detailed engineering (IFC-grade), structural and civil design, CEIG drawing preparation and approval, DISCOM net-metering submission, construction supervision support, and as-built documentation. Each phase has defined deliverables, quality gates, and a responsible engineering party. The 7-Phase EPC Engineering Cascade (defined in this guide) maps each deliverable to its approval authority and the typical turnaround timeline for outsourced production.
According to MNRE data, India’s C&I rooftop and ground-mount pipeline is running at record volume in 2026 — with the ministry targeting 500 GW of total solar by 2030. The EPCs winning in this environment are those that can bid competitively, win consistently, and execute without the engineering bottlenecks that turn 90-day projects into 140-day problems.
Phase Overview — The 7-Phase EPC Engineering Cascade
Bid Stage — Pre-Feasibility and Proposal Engineering
The engineering work that goes into winning the project. Output: 3D layout, preliminary yield estimate, indicative BOQ, and structural feasibility confirmation. Timeline: 24–72 hours from site data receipt. Owner: sales team with engineering input.
Detailed Engineering (IFC) — Design for Construction
Issued for Construction (IFC) drawings — the engineering set that procurement, civil, and electrical teams execute against. Output: GA, SLD, cable schedule, mounting layout, BOQ (final). Timeline: 5–10 business days after site survey. Owner: design firm.
Structural and Civil Engineering
Foundation design, mounting structure specification, and load calculations. Output: STAAD Pro report, foundation drawing, roof load certificate. Timeline: 5–10 business days concurrent with Phase 2. Required for: building permit, CEIG submission, lender technical due diligence.
CEIG Drawing Preparation and Approval
Chief Electrical Inspector to Government (CEIG) approval is required for grid-connected solar installations above certain capacity thresholds (varies by state: 10–500 kW). Output: CEIG-format electrical drawings, signed by a licensed electrical engineer. Timeline: 5–7 days to prepare drawings; state CEIG approval: 15–45 days.
DISCOM Net-Metering Submission
DISCOM-format drawing package, net-metering application form, and annexures submitted to the distribution company for grid connectivity approval. Output: Technical Feasibility Report (TFR) approval from DISCOM, metering infrastructure order. Timeline: DISCOM review takes 15–60 days (varies significantly by state and DISCOM).
Construction Supervision Engineering Support
Site engineering queries, material substitution approvals, and RFI (Request for Information) resolution during construction. Output: marked-up drawings, substitution approvals, site query responses. Timeline: on-demand during construction (typically 30–90 days for a C&I project).
As-Built Documentation and Commissioning
Post-commissioning as-built drawings reflect any field changes made during construction. Output: as-built SLD, as-built GA, commissioning checklist, O&M manual, handover package. Timeline: 5–10 business days post-commissioning. Required for: DISCOM commissioning certificate, warranty activation, O&M handover.
Phase 1 — Bid-Stage Engineering: Winning Projects With Engineering Data
The bid stage is where most EPCs underinvest in engineering. A 3D layout and a preliminary yield estimate turn a price-per-watt conversation into a per-kWh generation value conversation — shifting the client’s decision criteria from initial cost to lifecycle return.
What you need at bid stage:
- A 3D layout showing module count, row spacing, and approximate yield
- Shading analysis for the site (confirmed shadow-free zone for 09:00–15:00)
- Indicative BOQ with cable quantity estimate and mounting type
- Structural feasibility statement (rooftop load-bearing vs. ground-mount foundation type)
Definition. A 3D solar pre-design is a preliminary layout produced before the IFC engineering phase begins — typically from drone photos, satellite imagery, and utility bill data. It shows the client what the installed system will look like and provides a preliminary yield estimate to support the purchase decision. It is not a construction document and should not be used as the basis for procurement.
The bid-stage engineering package takes 24–72 hours from a good site data set. The solar 3D pre-design service delivers bid-stage layouts in 48 hours — which gives EPC sales teams the data they need to close the same week they survey the site, rather than waiting for the full engineering cycle.
Phase 2 — IFC Engineering: The Design Set That Builds the Project
The Issued for Construction (IFC) package is the engineering set that procurement, civil works, and electrical installation execute against. It must be complete, accurate, and DISCOM-format-ready before construction begins — not assembled in pieces as the project moves forward.
IFC deliverable checklist for a C&I rooftop project:
| Deliverable | Contents | Who needs it |
|---|---|---|
| GA (General Arrangement) | Panel layout, row spacing, cable tray positions, access paths, labels | Civil team, client, DISCOM |
| SLD (Single-Line Diagram) | AC + DC SLD, protection, metering point, inverter spec, earthing | Electrical team, DISCOM, CEIG |
| Mounting Layout | Anchor positions, rail layout, module orientation, clearances | Civil / structural team |
| Cable Schedule | DC string cables, AC feeder, earthing — size, route, length | Procurement, electrical team |
| BOQ | Module, inverter, cable (DC/AC/earth), mounting, BOS, protection | Procurement, client |
| PVsyst Simulation | Energy yield, P50, loss waterfall, performance ratio | Client, lender |
Watch out. Construction started on a bid-stage layout (without an IFC package) is the leading cause of field variation orders in Indian solar projects. When the civil team works from a 3D model that has not been verified against DISCOM clearances, CEIG earthing requirements, and actual roof structure load limits, they create deviations that require expensive as-built amendments — sometimes including DISCOM resubmission.
Phase 3 — Structural and Civil Engineering: The Phase Most EPCs Skip
Structural engineering is the most frequently skipped phase in Indian EPC workflows — and the most expensive to skip when something goes wrong. Two categories of structural failure affect solar projects in India.
Category A: Insufficient wind resistance. Monopitch rooftops in coastal zones (Gujarat, Maharashtra coast, Tamil Nadu) face wind loads significantly above the IS 875 Part 3 defaults for inland locations. A mounting structure designed for Zone II wind load (39 m/s basic wind speed) will fail structurally in a Zone V location (50 m/s basic wind speed). IS 875 Part 3 maps India into five wind zones — and the correct zone must be confirmed from the site coordinates, not assumed from the state.
Category B: Roof overloading. Factory rooftops and warehouse structures built before 2010 frequently have lower live load ratings than assumed. A 20 kg/m² uniform load from solar panels (including mounting) can exceed the permitted live load on older industrial structures with 15 kg/m² rating — particularly for tin shed structures without purlins.
A STAAD Pro structural report confirms both: the IS 875 wind load for the site location, and the roof structure’s capacity to carry the panel and mounting dead load. States including Maharashtra, Gujarat, and Tamil Nadu require a structural stability certificate from a licensed structural engineer as part of the CEIG submission. Without it, the CEIG drawing is rejected on first submission.
For STAAD Pro report production, the STAAD Pro report service covers IS 875 Part 3 compliant reports for rooftop and ground-mount structures.
Phase 4 — CEIG Drawing Approval: State-by-State Variation
The Chief Electrical Inspector to Government (CEIG) is the state authority responsible for certifying that a solar installation’s electrical design complies with the CEA Connectivity Regulations 2019, IS standards, and state electrical safety rules. CEIG approval is a pre-commissioning requirement in most Indian states.
| State | CEIG approval threshold | Typical timeline | Format requirements |
|---|---|---|---|
| Gujarat | Above 10 kW grid-connected | 15–30 days | GUVNL-format SLD + structural certificate |
| Maharashtra | Above 10 kW for LT; HT above 66 kV | 20–45 days | MSEDCL electrical schedule + IS compliance note |
| Tamil Nadu | Above 50 kW | 15–30 days | TANGEDCO SLD + CEA connectivity annex |
| Karnataka | Above 10 kW | 20–35 days | BESCOM format; earthing certificate required |
| Rajasthan | Above 100 kW | 30–60 days | RVPN format for HT; DISCOM format for LT |
Field tip. CEIG drawing approval runs on the state authority's calendar, not yours. Submit the CEIG application at the same time as the DISCOM net-metering application — not after it. Running these two approval tracks in parallel saves 15–30 days on the critical path. Many EPCs submit them sequentially and absorb a 4–8 week delay unnecessarily.
The CEIG electrical drawings service covers CEIG-ready drawing preparation for all major Indian states, including the format-specific requirements and submission documentation.
Phase 5 — DISCOM Net-Metering Submission: The Critical Path Gate
The DISCOM net-metering approval is the administrative gate that determines when the system can be commissioned and the net-metering agreement signed. In most states, commissioning without net-metering approval means the client cannot export excess generation — eliminating the financial case for the investment.
The DISCOM submission package for a C&I rooftop in Gujarat (UGVCL / MGVCL / PGVCL):
- Completed net-metering application form (DISCOM portal)
- GA drawing in DISCOM format (state-specific)
- SLD in DISCOM format with bidirectional meter callout
- Technical specification sheets: inverter (with BIS/MCS certification reference), modules (with ALMM registration number)
- Structural stability certificate (from a licensed structural engineer)
- Utility bill (last 3 months) and sanctioned load letter
- PAN card and GST certificate of the applicant
The DISCOM Technical Feasibility Report (TFR) review — the first step in the process — takes 15–30 days in Gujarat and Maharashtra, 30–60 days in some states (Rajasthan, UP). The timeline cannot be accelerated by the EPC, but it can be delayed by submitting an incomplete or incorrect package. A rejected first submission adds the full review cycle to the timeline.
For the detailed state-by-state DISCOM process — including the specific form numbers, portal links, and drawing format requirements for each DISCOM — the complete guide to solar permits in India covers 12 major states.
Phase 6 — Construction Support Engineering: Resolving Field Queries Without Stopping Work
Construction moves faster than the original engineering anticipated. Material substitutions (a specified cable gauge is unavailable; the planned inverter has a 6-week delivery lead time), field conditions that differ from the design survey (a structural beam in a different position than the drawing), and DISCOM comments requiring mid-construction changes all require engineering response — quickly.
The construction support protocol:
- All field queries logged in a single RFI register (not handled via WhatsApp group)
- Design firm responds to RFIs within 24 hours (4 hours for urgent site-stop queries)
- Material substitution approvals documented with a formal substitution note (not verbal)
- Design changes issued as drawing revisions (Rev B, Rev C) — not as annotations on the original
An EPC that manages RFIs informally (WhatsApp, phone calls) loses the documentation trail needed for: client variations, DISCOM resubmission, warranty claims, and O&M handover. The RFI register is also the primary source document for the Phase 7 as-built drawings.
Phase 7 — As-Built Documentation: The Deliverable Most EPCs Forget
As-built drawings are the record of what was actually installed — incorporating all field changes, material substitutions, and design revisions that occurred during construction. They are required for:
- DISCOM commissioning certificate (many states require as-built SLD at commissioning inspection)
- Client handover and warranty activation
- O&M contractor reference (performance monitoring and fault diagnosis rely on accurate single-line and GA)
- Insurance coverage (equipment breakdown policies require accurate plant documentation)
| As-built deliverable | Source documents | Turnaround |
|---|---|---|
| As-built SLD | IFC SLD + all RFI resolutions + material substitutions | 3–5 days post-commissioning |
| As-built GA | IFC GA + field measurement record | 3–5 days post-commissioning |
| Test and commissioning record | Commissioning checklist (Voc, Isc, IR, performance ratio) | Same day as commissioning |
| O&M manual | Equipment manuals + plant-specific operating procedures | 5–7 days post-commissioning |
The solar post-design service covers as-built drawing production, commissioning documentation, and handover package assembly for completed projects.
Where Outsourced Engineering Integrates Into the EPC Workflow
For an EPC running multiple C&I projects concurrently, the practical integration question is: which phases do you keep in-house and which do you outsource?
KEEP IN-HOUSE
- Site survey and data collection
- Client relationship management
- DISCOM submission follow-up
- Construction supervision
- Commissioning sign-off
OUTSOURCE TO SPECIALIST FIRM
- 3D pre-design and yield simulation
- IFC drawing set (GA, SLD, cable schedule)
- Structural calculations (STAAD Pro)
- CEIG-format drawings
- DISCOM drawing package production
- As-built documentation
The EPC’s in-house team owns the client relationship and project management. The outsourced firm owns the technical deliverables. This division produces the best outcome: your site team’s local knowledge combined with a specialist firm’s format mastery and drawing quality.
For an analysis of the cost and throughput impact of this model, the in-house vs. outsourcing solar design guide provides the full P&L comparison.
How Heaven Designs Covers Every Phase of the EPC Engineering Workflow
Heaven Designs is structured as a full-phase engineering partner — from bid-stage 3D pre-design through to as-built documentation and commissioning support.
- Solar 3D Pre-Design — Phase 1: bid-stage layout and yield estimate in 48 hours from site data.
- Solar Rooftop Detailed Engineering Design — Phase 2: IFC-grade GA, SLD, cable schedule, BOQ, DISCOM drawings.
- Solar Civil and Structural Engineering — Phase 3: IS 875 structural analysis, STAAD Pro report, foundation design.
- Electrical CEIG Drawings — Phase 4: CEIG-format electrical drawings for all major Indian states.
- Solar Ground Mount Design — Phases 2–3: utility-scale and ground-mount IFC + structural packages.
- Solar Post-Design — Phase 7: as-built drawings, commissioning support, handover documentation.
- Download a sample deliverable — See IFC-grade drawings from a completed C&I rooftop project.
Contact us to map your current project pipeline against the 7-Phase Cascade and identify which phases your team should outsource first.
FAQ
What is the difference between IFC drawings and DISCOM-format drawings?
IFC (Issued for Construction) drawings are the engineering set used by the civil and electrical construction teams — they are designed for execution accuracy. DISCOM-format drawings are a subset of the IFC set, reformatted to match the specific drawing standard, title block, revision history, and annexure requirements of the local distribution company — they are designed for regulatory approval. A professional design firm produces both from the same source file, ensuring consistency between what is built and what is submitted to the DISCOM.
Is CEIG approval mandatory for all solar projects in India?
CEIG approval thresholds vary by state. In most states, any grid-connected solar installation above 10 kW requires CEIG approval before commissioning. Some states have higher thresholds (100 kW in Rajasthan for LT connection). Additionally, projects connecting at HT (11 kV and above) always require CEIG clearance regardless of capacity. The specific requirement for your project state should be confirmed at the IFC engineering stage — not at the commissioning stage, where a missing CEIG approval delays energisation.
How does the DISCOM approval timeline fit into the overall project schedule?
DISCOM TFR review takes 15–60 days depending on the state and DISCOM. This is the longest approval gate in the project timeline — and it cannot be compressed by the EPC. The practical implication is that the DISCOM submission must be made as early as possible in the project timeline: ideally within 2–3 weeks of signing the client contract, before construction begins. EPCs that submit to the DISCOM after construction is complete face a 1–2 month delay between mechanical completion and commissioning.
What engineering deliverables does a lender require for a C&I project in India?
For a MSME or C&I project seeking bank financing, the standard lender requirement set is: PVsyst simulation report, SLD, structural stability certificate, BOQ, and a techno-commercial report from an independent engineer. For projects above 1 MW seeking institutional lending (IREDA, PFC), the requirement expands to include a full bankable EYA, an independent structural report, and a technical due diligence report from the lender’s appointed IE.
How do I manage engineering quality when outsourcing across multiple concurrent projects?
The most effective method is a standardised brief form that captures all site data consistently, combined with a project-specific quality checklist that your internal coordinator runs before accepting each deliverable. Track four metrics per project: on-time delivery rate, revision count, first-pass DISCOM acceptance rate, and field query count during construction (high field query counts indicate IFC quality problems). Review these metrics monthly with your design partner and address systematic issues before they become project risks.
