Compare rooftop-solar quotes line by line, not by ₹/kW alone. A useful quote identifies the exact module and inverter models, DC/AC capacity, structure and wind assumptions, protections, cable scope, approvals, warranties, generation assumptions, exclusions and payment milestones.
Turn three different-looking quotes into one comparable sheet
1. Normalize system size
Record module DC capacity and inverter AC capacity separately. Two “5 kW” quotes may not describe the same DC/AC design.
2. Lock exact equipment models
Ask for manufacturer, model number, quantity, ratings and warranty documents. Reject vague labels such as “Tier-1 panel” without a model.
3. Compare structural and electrical scope
Review mounting material, roof attachment, corrosion protection, cable lengths, isolators, earthing, surge protection, monitoring and shutdown labels.
4. Separate approvals from promises
List what the vendor will actually handle for DISCOM, net metering or scheme workflow and what remains your responsibility. Never treat an unapproved subsidy as guaranteed cash.
5. Compare payment and warranty risk
Prefer milestone-linked payments with clear deliverables. Check who provides product warranty, workmanship warranty and local service after installation.
A quote-comparison table that exposes hidden differences
| Line item | What to demand | Red flag |
|---|---|---|
| Modules | Exact model, wattage, quantity, technology and warranty | “Premium panel” with no model. |
| Inverter | Exact model, AC rating, MPPTs, warranty and monitoring | Model substitution allowed without approval. |
| Structure | Material, coating, attachment method and design assumptions | No roof-specific structural scope. |
| Electrical BOS | DC/AC cable, connectors, isolators, earthing and surge protection scope | “All accessories included” with no schedule. |
| Generation estimate | Assumptions for irradiation, shade, orientation and losses | Guaranteed annual units with no methodology. |
| Approvals | Exact vendor responsibility and fees | “Subsidy guaranteed.” |
| Payment | Milestones tied to equipment, installation and commissioning | Full advance with weak contractual safeguards. |
Compare warranty responsibility, not just warranty years
Module product warranty, module performance warranty, inverter warranty and installer workmanship warranty are different promises. Ask who receives the claim, who pays removal/reinstallation or transport, and whether the installer will handle manufacturer paperwork.
A long manufacturer warranty is less useful if the model serials are not documented or no local service path exists. Request serial-number records and invoices at handover.
Generation estimates need assumptions
Ask each vendor to state roof orientation, tilt, shade, system losses and DC/AC sizing used in the estimate. Compare the assumptions before comparing annual kWh. Do not rank quotes by the highest predicted generation if one estimate is simply more optimistic.
What should be fixed before you pay the next milestone
- Approved final equipment list and any substitution process.
- As-built single-line diagram after installation.
- Roof penetration and waterproofing responsibility.
- Commissioning and test records.
- Monitoring login and owner access.
- Warranty certificates, serials and service contacts.
- Approval/net-metering handover evidence included in scope.