70:30 GST rule for solar EPC: partial scope (structure excluded) on an existing plant

The 70:30 deeming provision (effective GST rate of 13.8%) applies to single lump-sum solar EPC contracts even when mounting structures are excluded. For trade-ins, the 70:30 split applies to the gross consideration (cash plus scrap value) under Rule 27, and the Place of Supply for B2C billing is the location of the rooftop installation.

So, it means whenever we supply those renewable energy devices as notified along with other taxable supply, it will attract 70:30 Valuation effectively 8.9% blended GST rate.

Quick arithmetic check first: 70% of value at 5% plus 30% at 18% works out to 3.5 + 5.4 = 8.9% of the gross consideration, so the 13.8% figure in the earlier reply does not follow from the rule.

On your points, as I read it:
- The deeming applies to a composite supply of the notified renewable energy devices with the installation and commissioning services for a single contract value. Whether it carries over when the structure is outside your scope is the open part. The wording is about the supply of devices plus related services, not about who supplied the structure, so a retrofit is arguable, but I would not call it settled without a clarification or ruling on partial scope. Please check the exact explanation text in the notification and the Circular 163/19/2021-GST.
- If the 70:30 split is the prescribed valuation for that supply, it is not an option you pick. Paying 5% on the whole amount or using actual values is a different position that would need a ruling or a reasoned view on whether the supply is outside the deeming. Keep the contract and invoice descripttions clean either way.
- Old panels or inverter taken as part payment: consideration not wholly in money goes through Rule 27 of the CGST Rules, so the open market value of the scrap is added to the cash to get the gross value, and the split is then applied on that gross. Show it as a separate line in the contract so the value is traceable.
- Earlier order billed on actual values: look at whether it was a single composite contract or separate supply and install contracts. If it was genuinely separate, actual values may stand. If it was one lump sum, the exposure is the differential tax, so reconcile before a department query arrives.

Place of supply for installation on the customer's rooftop is where it is installed, so the UP site decides CGST+SGST vs IGST.

I agree that notification wording is supply those entry items along with other taxable supply attract that 70 30 split. But in some projects the 5% tax rate component costing is itself 80% of the total project than why we give that tax at service rate for that Goods excess 10% component.