The Indian state of Tamil Nadu has made battery storage mandatory for new solar and solar-hybrid projects of 1 MW and above, under a new Battery Energy Storage Systems Policy, 2026, Mercom India and EQ Magazine reported on 29 October.
New projects must install storage equal to 10% of their solar capacity, with a four-hour duration. The policy also sets a first-phase procurement target of 2.5 GW / 10 GWh and offers a 10-year waiver of transmission and wheeling charges for storage that discharges outside solar hours.
The 10% rule
Under the policy, new solar or solar-hybrid projects of 1 MW or more must include battery storage of at least 10% of installed capacity, with four hours of duration. For a 100 MW solar plant, that means 10 MW / 40 MWh of storage.
The requirement applies to applications made on or after notification, or to projects commissioned on or after 1 April 2027. According to EQ Magazine, applications that do not comply will not be considered by the State Nodal Agency.
The policy runs for three years from notification or until 10 GWh of battery capacity is commissioned, whichever comes first. It takes effect on publication in the Tamil Nadu Government Gazette.
Substations and procurement
New renewable energy pooling substations will need standalone storage of at least 10% of their sanctioned capacity, again with four hours of duration. Existing pooling substations must reach a cumulative 10%, phased as 5% by FY 2027-28 and a further 5% by FY 2028-29, subject to technical feasibility and connectivity approvals.
For the first phase, the state distribution company TNPDCL will procure 2.5 GW / 10 GWh through competitive bidding at tariffs approved by the Tamil Nadu Electricity Regulatory Commission.
Incentives and rules for operators
Co-located and standalone battery systems of 1 MW or more that are commissioned within the policy window will get a 100% waiver of transmission and wheeling charges for 10 years. To qualify, they must discharge during non-solar hours, and the energy must be consumed in Tamil Nadu. The incentive is capped at 10 GWh.
Co-located storage may not exceed 100% of the sanctioned renewable capacity, and injection must go through the same interconnection point. Standalone batteries will be treated as de-licensed independent power assets, on par with a generating company.
The State Load Despatch Centre will direct a charging preference during the 10 AM to 2 PM solar window and will control dispatch. Developers must maintain 95% annual availability, with mandatory availability from 1 March to 30 June and from 1 September to 31 October.
Other requirements include real-time telemetry to the load despatch centre at the developer's cost, indigenous energy management systems, compliance with safety regulations and battery recycling rules, and end-of-life decommissioning.
Tamil Nadu Green Energy Corporation Limited (TNGECL) will act as the State Nodal Agency and run a single-window portal for registration and tracking.
What it means for Asia-Pacific developers
Tamil Nadu is turning storage from an option into a condition of grid access. For solar developers in the state, every new project of 1 MW or more now needs a four-hour battery sized at 10% of capacity, which adds cost but also shifts part of the output into the evening, when solar cannot supply. The transmission and wheeling waiver, the 10 GWh cap and the 2.5 GW / 10 GWh tender create a clear, time-limited market for battery suppliers and integrators. Developers planning projects for commissioning after April 2027 will need to build storage into their designs and financing now.
Source: Mercom India, 29 October 2026; EQ Magazine, 29 October 2026
