Getting GST Right on Solar Invoices: HSN-Wise Rates, CGST, SGST and IGST

One Invoice, Two Different GST Treatments

A typical rooftop solar invoice contains goods and services with different GST classifications: panels and PV equipment on one side, mounting structures, civil work and installation on the other. Treating the whole invoice as one rate is the most common — and most expensive — invoicing mistake in solar.

Assign the Rate Where the Item Is

Each invoice line carries its own HSN classification and the rate that follows from it. A blended single percentage across the whole invoice misstates both the tax and the totals — and does not survive a departmental query.

Rule of thumb for your own checks: if your quotation and your invoice show the same blended GST percentage on every line, revisit both.

CGST + SGST or IGST — Decided by the Customer's State

• Same state as your supply location: charge CGST and SGST, split between the two.
• Different state: charge IGST.

For EPCs working across state borders, this is a daily decision. A tax invoice system that derives the split from the customer's state — as Doctor Solar Wala's invoicing does — removes the manual error entirely.

What a Compliant Solar Invoice Should Carry

1. Seller and buyer GSTINs
2. Invoice number and date, in sequence
3. Line items with HSN codes and the rate applicable to each
4. CGST/SGST or IGST breakdown
5. Total in figures and words
6. Payment terms and any applicable e-way bill details for movement of goods

Where Most EPCs Go Wrong

• One blended GST percentage across all lines (wrong totals, weak audit position)
• CGST/SGST charged where IGST applied, or vice versa
• Quotation GST that does not match the invoice GST for the same job
• HSN codes omitted or reused across dissimilar items

The fix is systemic, not clerical: assign rates per line at quotation time and carry them through to the invoice unchanged. That flow is described on the Solar ERP page, and the plans that include it are on pricing.