An unchallenged regulatory tariff order attains finality and bars subsequent re-litigation under res judicata.

Haryana Power Purchase Centre (“HPPC”) and M/s Siwana Solar Power Projects Ltd. (“Siwana”) executed a Power Purchase Agreement (“PPA”) dated 21 February 2014 for procurement of solar power from Siwana’s 5 MW project for 25 years.

Clause 4.1 of the PPA prescribed the lowest of the generic tariff, the tariff discovered in HPPC’s first long-term competitive bid, or the tariff discovered through HAREDA’s reverse-bidding process.

HPPC initially paid Siwana at Rs. 6.44/kWh, being the tariff discovered in HPPC’s competitive bidding process.

HERC upheld this tariff in its order dated 20 January 2016, directing that the year-to-year tariff corresponding to a levelised tariff of Rs. 6.44/kWh be paid.

Siwana’s appeal against that order was dismissed by the Tribunal on 27 May 2019, thereby upholding the applicability of Rs. 6.44/kWh to Siwana’s project.

Separately, in proceedings concerning four other solar developers, the Tribunal approved a tariff of Rs. 5.68/kWh.

HERC subsequently permitted HPPC to pay Siwana at the year-to-year rate corresponding to Rs. 5.68/kWh as an interim arrangement, subject to the outcome of proceedings before the Supreme Court.

Siwana and HPPC later reached a settlement concerning pending arrears, recorded by HERC on 29 September 2020.

Challenges to that settlement were dismissed by HERC, the Tribunal and the Supreme Court.

Siwana thereafter filed Petition No. 26 of 2024 seeking implementation of the Rs. 6.44/kWh tariff and payment of the differential amount over Rs. 5.68/kWh.

HERC dismissed the petition on 12 November 2024, holding that the issue had attained finality and was barred by res judicata.

Siwana did not challenge that order.

Siwana subsequently filed Petition No. 78 of 2025 seeking substantially identical relief.

HERC allowed the petition by order dated 14 May 2026 and directed HPPC to pay the year-to-year tariff corresponding to Rs. 6.44/kWh from 1 April 2019 onwards, together with differential tariff, interest and applicable late payment surcharge.

HPPC challenged that order before the Tribunal.

1. Whether the tariff of Rs. 6.44/kWh applicable to Siwana’s project had been replaced by the tariff of Rs. 5.68/kWh?

2. Whether Siwana’s Petition No. 78 of 2025 was barred by res judicata in view of HERC’s unchallenged order dated 12 November 2024 in Petition No. 26 of 2024?

3. Whether the petition was barred by limitation and whether the settlement dated 29 September 2020 affected Siwana’s claim for tariff after 1 April 2019?

The Tribunal applied Section 11 of the Code of Civil Procedure, 1908, including the principles of actual and constructive res judicata: an issue directly and substantially decided between the same parties by a competent forum cannot be re-agitated, and matters that might and ought to have been raised earlier are deemed to have been in issue.

The Tribunal relied on Syed Mohd. Salie Labbai v. Mohd. Hanifa, (1976) 4 SCC 780, concerning the conditions for res judicata; Satyadhyan Ghosal v. Deorajin Debi, 1960 SCC OnLine SC 15, on the finality of adjudication; Sulochana Amma v. Narayanan Nair, (1994) 2 SCC 14; Swamy Atmananda v. Sri Ramakrishna Tapovanam, (2005) 10 SCC 51; Bhanu Kumar Jain v. Archana Kumar, (2005) 1 SCC 787; and M. Nagabhushana v. State of Karnataka, (2011) 3 SCC 408, establishing that a final determination must be challenged in appeal or review and cannot be reopened through fresh proceedings.

The Tribunal also considered the binding effect of the earlier tariff orders under the PPA and the principle that an unchallenged judicial or quasi-judicial determination attains finality between the parties.

The Tribunal acknowledged that its judgment dated 27 May 2019 had upheld the Rs. 6.44/kWh tariff for Siwana’s project and that the Rs. 5.68/kWh tariff arose in separate proceedings involving four other developers.

However, it held that the decisive consideration was HERC’s subsequent order dated 12 November 2024, which expressly held that Siwana’s entitlement to the Rs. 6.44/kWh tariff had been resolved, had attained finality, and was barred by res judicata.

The prayers in Petition No. 26 of 2024 and Petition No. 78 of 2025 were materially identical: both sought implementation of the Rs. 6.44/kWh tariff and payment of the differential over Rs. 5.68/kWh.

Since the 2024 order was not appealed, it became binding inter partes.

The distinction drawn by HERC between settled past arrears and an allegedly continuing prospective tariff claim was therefore rejected; the earlier order conclusively determined the tariff issue itself, not merely the historical arrears.

Having reached this conclusion, the Tribunal found it unnecessary to decide the separate issues of limitation and the legal effect of the settlement.

Siwana’s attempt to re-agitate entitlement to Rs. 6.44/kWh in Petition No. 78 of 2025 was barred by res judicata under Section 11 CPC.

The Tribunal consequently set aside HERC’s order dated 14 May 2026, allowed HPPC’s appeal, and disposed of the pending interlocutory applications.