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India’s 6-Hour Solar-Storage Bet: How SECI Is Moving Beyond Daytime Solar Photograph: (AI)
With its latest 1,200 MW solar-plus-storage tender, SECI is procuring renewable power that can be delivered when the grid needs it most. The strong developer response and sharply lower tariffs point to a major shift in India’s renewable energy procurement strategy. For more than a decade, India’s solar story has largely been defined by scale and falling costs. The objective was straightforward: add as much low-cost solar generation as possible and bring down the cost of electricity.
But as solar penetration increases, another challenge is becoming harder to ignore. Solar generation is abundant during the day, while some of the grid’s highest demand comes later in the day, when solar output begins to decline. This is where energy storage is increasingly becoming part of the solar procurement equation.
The Solar Energy Corporation of India’s (SECI) latest tender for 1,200 MW of interstate transmission system (ISTS)-connected solar PV projects with 600 MW/3,600 MWh of energy storage systems (ESS) is a clear example of this transition. The projects have been awarded at tariffs of ₹3.12-3.13/kWh and are designed to provide firm and dispatchable renewable power rather than simply daytime solar generation.
India’s move towards storage-backed renewable power did not begin with the latest SECI tender. One of the earliest major experiments came in 2020, when SECI conducted a 1,200 MW renewable energy tender requiring six hours of peak power supply. Greenko won 900 MW using pumped-hydro storage at around ₹6.12/kWh, while ReNew won 300 MW using battery energy storage at around ₹6.85/kWh. The latest tender therefore represents an important change in the economics of the model. Five to six years after that early six-hour procurement, successful bids have come in at just ₹3.12-3.13/kWh.
The comparison is not completely like-for-like because the tender structures and market conditions are different. But the headline numbers nevertheless illustrate how dramatically the economics and competitiveness of storage-backed renewable power have evolved.
SECI itself has continued to expand its procurement of renewable energy coupled with storage, including a 1,200 MW solar-plus-1,200 MWh ESS tender issued in 2024. Its subsequent tenders have increasingly focused on firm and dispatchable renewable energy rather than generation alone.
SECI’s Tranche-XXI tender, issued in June 2025, sought 1,200 MW of ISTS-connected solar PV capacity along with 600 MW/3,600 MWh of ESS under a build-own-operate model. The headline number of 600 MW of storage capacity, however, does not tell the complete story. The tender requires at least 0.5 MW/3 MWh of ESS for every 1 MW of contracted project capacity. That translates into six hours of storage at the ESS’s rated discharge capacity. In other words, the requirement is not simply to install batteries alongside a solar plant. The developer has to combine renewable generation and storage in a manner that allows the contracted power to be supplied during the hours specified by the buyer.
The buyer can schedule six peak hours for drawing power from the storage system. The contracted energy requirement is 3 MWh for every 1 MW of project capacity across those hours. For the overall tender, that translates into 600 MW of ESS power capacity and 3,600 MWh of energy capacity.
The significance of the tender lies less in the number six and more in what those six hours represent. Traditional solar projects sell generation when the sun is available. A storage-backed solar project, by contrast, is being asked to reshape that generation profile. The objective is to make renewable power available closer to the period when the grid needs it.
This changes the commercial proposition for developers. They are no longer competing solely on the cost of solar generation. They have to optimise the combination of solar capacity, storage capacity, charging strategy, degradation, financing and power-delivery obligations. It also explains why the tender specifies penalties for shortfalls. Developers are responsible for meeting the contracted supply profile, with the applicable shortfall penalty going up to 1.5 times the tariff for electricity not supplied during the contracted period.
The selected projects are also required to enter into 25-year power purchase agreements, giving developers a long-term revenue framework against which the substantial investment in generation and storage can be financed.
The market response was significant. SECI received 24 bids representing an aggregate 6,150 MW against the 1,200 MW capacity on offer. That means the tender attracted more than five times the capacity being procured. Following technical and commercial evaluation, 23 bidders representing 6,060 MW were shortlisted for the electronic reverse auction.
The result is particularly notable because the initial financial bids ranged from ₹3.40/kWh to ₹5.40/kWh, before competition through the reverse auction brought the winning tariffs down to ₹3.12-3.13/kWh. Interestingly, Oriana Power had bid for 300 MW but ultimately received 100 MW, while the other three successful bidders were awarded their full bid capacities.
It is not necessarily a “BESS-only” story
There is an important distinction in how the tender should be described. Although battery energy storage is likely to be a major technology for such projects, SECI’s requirement is for an energy storage system rather than exclusively a battery energy storage system. The tender is technology-agnostic, meaning developers can potentially use different commercially established storage technologies as long as they meet the contractual requirements.
This is significant because six-hour storage sits at a point where technology selection becomes more consequential. Batteries can provide fast response and modular deployment, while longer-duration technologies such as pumped hydro can offer different economics and operational characteristics. The tender therefore represents a procurement requirement for a particular power-delivery profile rather than a government decision in favour of one storage technology.
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