Solar quotations

Solar quotation vs proforma invoice

Author: to be added

Published 10 Oct 2026

A solar quotation is an offer with a price and terms. A proforma invoice is a pre-sale bill used for advance payment or approvals but is not a tax invoice. A tax invoice is the final legal document issued on supply. Use each at the right stage and keep references consistent.

What each document is for

Installers use three documents around a sale, and they are often confused. A quotation is an offer: it states what you will supply, at what price, on what terms, and for how long the offer stands. A proforma invoice is a preliminary bill that lets the customer arrange funds or approvals before the supply happens. A tax invoice is the final document issued when the supply is made, and it carries the tax details your accountant needs. Each has a different job, so each should be issued at a different moment.

When to use which

Send a quotation when the customer is still deciding. Keep it open to revision, and tie each revision to the same customer record so the history is clear; the revisions and status tracking feature does this. Once the customer accepts, a proforma invoice can support a bank request, an employer reimbursement or an advance payment. When the goods are supplied and the service is delivered, issue the tax invoice.

How tax shows up on each

A quotation should show the tax lines you expect to charge, split correctly between the supplier and customer states. That is why the supplier's tax registration and its state code matter, and the GSTIN and state code entry explains how the state is read from the number. A GST-ready quotation calculates the split for you so the document already looks like the invoice that will follow.

The proforma should repeat the same figures, marked clearly as not a tax invoice. The tax invoice then follows the accepted terms, with any approved changes. If the quotation, proforma and tax invoice disagree without a recorded reason, the customer will notice.

Keep the terms consistent

Terms agreed in the quotation should carry through. Payment schedule, warranty and exclusions belong in one reusable set, such as the solar terms and conditions template, so the paper trail tells one story.

Common mistakes

• Calling a proforma a tax invoice

  A pre-sale bill should be marked as such so nobody treats it as the final legal document.

• Different numbers on each document

  Quantities and prices should reconcile to the accepted quotation. Record approved changes in writing.

• Accepting money without a reference

  Advances should point to the quotation number so everyone knows what they were paid against.

• Leaving the quotation open forever

  An offer without a validity date can be accepted long after your costs have changed.

• Issuing the tax invoice early

  Timing matters for tax. Check with your accountant before invoicing ahead of supply.

What to check before you send

Before any of the three goes out, confirm the document type is printed in the title, the reference number links to the accepted quotation, the supplier and customer tax registration details are correct, the tax split matches the two states, and the totals reconcile to the previous document. For the invoice stage, check the timing with your accountant instead of guessing.