GST on Solar Power in India Fell to an Effective 8.9% on a Project — Here's the CFO Math

On 3 September 2025, India's GST Council recommended a rate cut on renewable-energy devices as part of the wider "GST 2.0" rationalisation. The Central Board of Indirect Taxes and Customs (CBIC) gave it legal effect through Notification No. 9/2025 — Integrated Tax (Rate), dated 17 September 2025, which moved solar modules, wind-turbine components, inverters and battery storage to a uniform 5% rate, effective 22 September 2025.

The headline most coverage ran with was "12% to 5%." For a CFO signing a power-purchase agreement, that number is incomplete. A solar project is not a box of modules you buy at one rate. It is a composite supply — goods and installation services bundled into one contract — and the blended rate is what actually lands on the project cost.

Why the real number is 8.9%, not 5%

Under GST, an EPC solar contract is treated as a composite supply with a principal supply of goods. In practice the cost splits roughly 70% goods, 30% services. The goods leg moved from 12% to 5%; the services leg is taxed at the standard 18%. Blend them and the effective project GST is not 5% — it is the weighted average.

Before the change, that weighted figure sat at about 13.8%. After 22 September 2025, it falls to about 8.9%. That single shift — roughly five percentage points off the effective rate — is what the rest of the math runs on.

The number that matters on a PPA is not the rate on a module. It is the effective rate on the whole project after the 70/30 composite-supply blend — and that moved from 13.8% to 8.9%.

What it does to a 50 MW open-access project

Work it through on an indicative 50 MW open-access project. The component cuts compound into a project-level saving and then into the tariff a corporate buyer signs:

The mechanics are simple once the rate is right. Cutting the goods-leg rate from 12% to 5% — a 7-point fall on roughly 70% of project value — removes about ₹5 Cr of tax on every ₹100 Cr of project cost. On the 50 MW case, the GST burden falls from about ₹20.3 Cr to ₹12.4 Cr. That flows into a tariff roughly 10 paise/unit lower and an IRR roughly 1.2 points higher — and across a 25-year offtake, an indicative corporate-buyer saving of about ₹24.1 Cr.

The catch CFOs miss: who actually captures the saving

Here is the part the rate-cut headlines skip. A lower effective GST does not automatically reach the buyer's tariff. Whether it does is decided by contract language, not by the notification.

If you are signing a new PPA after 22 September 2025, the lower rate should already be priced into the developer's tariff build-up — and the buy-side job is to confirm it actually was, rather than being quietly retained as developer margin. If you hold an existing PPA or EPC contract that straddles the change, the saving accrues to whoever the change-in-law clause assigns it to. A well-drafted clause passes a statutory rate reduction through to the buyer; a poorly drafted one lets the counterparty keep it. We see the same pattern when a state tariff order shifts mid-contract — the clause, not the headline, decides who gains.

This is the recurring lesson from advising on 150+ PPAs across 19 states: a favourable policy change is only worth what your contract lets you keep. The rate moved for everyone on the same day; the savings did not land evenly, because the contracts were not drafted evenly.

What to do before you sign

• Re-price live tenders. Any EPC or PPA quote dated before 22 September 2025 is built on the old 13.8% effective rate. Ask for a re-issued cost sheet at 8.9% before you compare bids.
• Read the change-in-law clause first. Confirm in writing that a statutory GST reduction flows to you, the buyer — not to the developer's retained margin.
• Check the IRR you are being shown. A tariff that ignores the new rate is overpriced; an IRR that quietly banks the saving for the developer is mispriced in their favour.
• Lock the rate basis in the contract. State the effective GST assumption explicitly so a future rate change is governed by a clause, not by a negotiation you have already lost.

The 8.9% effective rate is real, durable and verifiable against a single CBIC notification. What it is worth to your business is a contracting question — and that is the buy-side read worth getting before the signature, not after.