Sizing, Payback Examples and Checklists
Rooftop solar quotation checklist: how to compare vendors line by line
What a rooftop solar quotation in India must include, how to compare two vendors fairly, red flags, payment terms and the documents to collect, with a worked comparison.
A good rooftop solar quotation names every component by make, model and rating, states that the modules are DCR, shows GST separately, gives warranty and maintenance terms in writing, and states who handles and pays for DISCOM approvals and the net meter. If a quote says only "3 kW solar system, Tier-1 panels, ₹X", you cannot compare it and you cannot enforce it. For PM Surya Ghar, choose from the vendors registered for your DISCOM on the national portal, get at least two written quotations, and compare them on the same scope. This guide gives the checklist, the red flags and a worked comparison.
What every quotation should contain
| Item | What to look for |
|---|---|
| Vendor details | Legal name, address, GSTIN, portal registration for your DISCOM, contact for service |
| System capacity | kWp of modules and kW of inverter |
| Modules | Make, model, wattage, number of modules, DCR, technology (e.g. mono PERC, TOPCon) |
| Inverter | Make, model, rating, type (grid-tie or hybrid), number of MPPTs, monitoring (Wi-Fi app) |
| Mounting structure | Material (hot-dip galvanised steel or aluminium), height, anchoring or ballast, wind design |
| Electrical | DC and AC cable size and type, conduits, DC and AC distribution boxes, surge protection, isolators |
| Earthing and lightning protection | Number and type of earthing pits; lightning arrester where specified |
| Installation and commissioning | Included work; any civil work |
| DISCOM work | Who files the net meter application, who pays the meter and testing fees |
| Price | Pre-tax price, GST rate and amount, total |
| Payment schedule | Milestones linked to delivery, installation and commissioning |
| Warranty | Module product and performance warranty; inverter warranty; structure and workmanship |
| Maintenance | Five-year maintenance commitment under the scheme; visits per year; response time |
| Generation estimate | Expected annual units and the assumptions used |
| Timeline | Days from order to installation |
Red flags
- No module or inverter make named, or "equivalent" substitution allowed without your consent.
- No mention of DCR, or "subsidy guaranteed" with non-DCR modules.
- Full payment in advance.
- Registration or subsidy-processing fees paid to the vendor or an agent: registration on the portal is free.
- Generation promises far above around 4.5 units per kW per day without a site-specific calculation.
- No GSTIN or a request to pay in cash without a bill.
- Pressure tactics: "offer ends today", "subsidy closing this week".
If someone claims to be from PM Surya Ghar or the ministry, see PM Surya Ghar scams and fake websites.
Worked comparison (illustrative)
| Vendor A | Vendor B | |
|---|---|---|
| Total price incl. GST | ₹1,80,000 | ₹1,68,000 |
| Modules | 6 × 545 Wp DCR, named make | "540 Wp DCR, Tier-1" |
| Inverter | 3 kW, named make, 2 MPPT, app | 3 kW "reputed brand" |
| Structure | Hot-dip galvanised, 1.5 m raised | GI, height not stated |
| Earthing | 3 pits | "As per norms" |
| Net meter fees | Included | Customer to pay |
| Payment | 20% / 60% / 20% | 90% advance |
| Maintenance | 5 years, 2 visits/yr | Not stated |
Vendor B looks ₹12,000 cheaper. But if you add an illustrative ₹4,000–6,000 for net meter fees and testing, and the cost of a raised structure if the low one blocks terrace use, the gap narrows. Vendor B's unnamed components and 90% advance carry risk that is hard to price. Ask Vendor B to name every component and match the scope; only then compare prices.
Payment terms that protect you
A common, fair pattern is a modest advance on order, the main payment on delivery and installation, and a final instalment after commissioning and net metering. If you take a bank loan, the bank may pay the vendor in stages. Avoid paying the final amount before the DISCOM has inspected the system and the net meter is working.
Documents to collect at handover
- Tax invoice with GST details.
- DCR certificate listing your module serial numbers.
- Module and inverter warranty cards, registered where the maker requires it.
- Single-line diagram and layout.
- Test and commissioning report.
- Maintenance schedule and service contact.
- Login for the inverter monitoring app.
These are needed for the subsidy, for warranty claims and if you sell the house. See solar warranty claims.
Questions to ask on the site visit
- Where will each row of modules go, and what will shade them through the day and the year?
- How will the structure be anchored without damaging waterproofing?
- Where will the inverter be mounted (shaded, ventilated, accessible)?
- How long are the cable runs, and where will the earthing pits be?
- How will cleaning be done safely?
Use the rooftop solar checklist as your record.
Back to the pillar guide: how many kW of solar you need. Related: solar panel and inverter types, DCR modules, ALMM and BIS.
Frequently asked questions
How many quotations should I get?
At least two, ideally three, from vendors registered for your DISCOM, all on the same written scope.
Is the cheapest registered vendor good enough?
Registration is a minimum, not a quality rating. Compare components, structure, earthing, warranty and service, and ask neighbours with installed systems about their experience.
Can the vendor change the module brand later?
Only with your written consent and a revised quotation. Write this into the order.
Should the quotation include the subsidy?
It may show the expected CFA for information, but the CFA is credited to your account by the government, not paid by the vendor.
Official sources
- PM Surya Ghar national portal — registered vendors for your DISCOM
- GST portal — check a vendor's GSTIN
- Ministry of New and Renewable Energy — technical specifications for scheme systems
