Grid-Forming BESS: Why India's Inverter-Dominated Grid Needs It Now
India's power grid is in the middle of a structural transformation. In 2015, conventional thermal and hydro generators — which are large synchronous machines physically coupled to the grid — accounted for over 90% of installed capacity. By 2026, solar and wind account for over 30% of capacity, rising to 40%+ in Rajasthan and Gujarat. By 2030, India's plans call for renewable energy to reach 50% of generation.
This transformation has an underappreciated consequence: the disappearance of synchronous inertia from the Indian grid, and the emergence of a new type of grid stability challenge that battery storage — specifically, grid-forming battery storage — is uniquely positioned to address.
What Synchronous Inertia Is and Why India Is Losing It
A conventional thermal generator (coal, gas, nuclear) or hydro generator has a large spinning rotor physically connected to the electrical grid through magnetic coupling. This rotor stores kinetic energy — the energy of a massive machine spinning at 3,000 RPM (for 50 Hz grids). When generation suddenly drops or load suddenly increases, this kinetic energy acts as a buffer: it is automatically and instantaneously transferred to the electrical system, buying time for fast-response generators to ramp up.
This behaviour is called synchronous inertia. It is a physical property of synchronous machines — it does not require control systems, communication, or decision-making. It happens automatically because the machine is physically coupled to the grid.
Solar panels and wind turbines do not have synchronous inertia. They connect to the grid through power electronics (inverters), not through physical rotation. When solar generation collapses — during cloud cover, sudden curtailment, or grid fault — there is no kinetic energy reserve. The system's frequency begins to fall immediately, and the rate of fall is determined by how much remaining inertia the system has.
India's power system inertia is falling as coal plant retirement accelerates and renewable penetration grows. POSOCO's grid frequency data shows increasing ROCOF (Rate of Change of Frequency) events during solar hours in western and southern India — events that would not have reached the same severity a decade ago with a higher proportion of synchronous generation.
Grid-Following vs. Grid-Forming Inverters: The Critical Distinction
The inverters used in virtually all solar, wind, and BESS systems today are grid-following inverters. A grid-following inverter uses a phase-locked loop (PLL) to synchronise with the grid voltage. It measures the grid frequency and voltage, then injects current at the appropriate phase angle to deliver its commanded active and reactive power.
Grid-following inverters are efficient and reliable in grids with adequate synchronous inertia — they follow the grid voltage like a boat following a river's current. But they have a fundamental limitation: they cannot operate as voltage sources. They require a reference signal (the grid voltage) to follow. In a grid with very low inertia — where frequency can change rapidly and voltage can swing widely during disturbances — grid-following inverters can destabilise the system by responding in ways that amplify rather than dampen oscillations.
Grid-forming inverters are fundamentally different. Instead of following the grid voltage, they establish a voltage reference and operate as voltage sources. They determine their own frequency and voltage output based on an internal reference, and the grid current flows in response to the voltage difference. This is how synchronous generators behave — they are voltage sources, and the grid organises around them.
Grid-forming inverters can provide:
Synthetic inertia: By modifying active power output in response to ROCOF (measuring rate of frequency change and responding proportionally), a grid-forming BESS can mimic the inertial response of a synchronous generator. The response is not physical — there is no rotating mass — but electrically, it looks identical to a synchronous machine's inertial response.
Fast frequency response: Grid-forming inverters can respond to frequency deviations within milliseconds — faster than any thermal generator and faster than most grid-following inverters with frequency droop control.
Voltage formation: In island mode or weak grid conditions, grid-forming inverters can establish voltage and frequency from scratch — something grid-following inverters cannot do. This enables black start capability from a BESS system, reducing dependence on dedicated black start diesel generators.
Stability in weak grids: In areas of India's grid with high impedance transmission (remote regions, island grids, new renewable-heavy substations), grid-forming inverters dramatically improve voltage stability.
India's Current BESS Deployments: Almost All Grid-Following
Here is the uncomfortable truth for India's BESS sector: the majority of BESS systems currently commissioned or under procurement in India use grid-following PCS (Power Conversion System). The SECI VGF tender specifications, as of their 2026 RfS, do not mandate grid-forming capability. MSEDCL's tender does not mandate it. GUVNL's tender does not mandate it.
CERC's 2026 updated grid code requires BESS to provide fast frequency response (within 500 ms) and ROCOF ride-through — but these can be achieved with advanced grid-following inverters with droop control. True grid-forming capability is not yet mandated.
This means India is deploying significant storage capacity that addresses energy shifting and frequency regulation, but is not systematically deploying the synthetic inertia capability that the grid will need as renewable penetration rises above 40%.
POSOCO and PGCIL are aware of this gap. POSOCO's technical reports from 2024–2025 identify synchronous condenser installation (large spinning machines that provide inertia without generating power) and grid-forming BESS as the two primary tools for addressing the inertia decline. India has begun procuring synchronous condensers for high-penetration RE regions. Grid-forming BESS is on the horizon.
When Will India Mandate Grid-Forming?
Based on the regulatory trajectory, our assessment:
2026–2027: CERC issues amended grid code provisions requiring grid-forming capability for BESS above 20 MW in specific high-penetration renewable zones (Rajasthan western grid, Gujarat northern grid, Tamil Nadu Tirunelveli corridor). Not a nationwide mandate yet.
2027–2028: SECI's storage tender specifications begin requiring grid-forming PCS as a mandatory technical requirement for projects above 100 MW in identified stability zones.
2029–2030: Grid-forming becomes a standard requirement for all new grid-scale BESS above 10 MW, following the pattern of European regulatory evolution where ENTSO-E mandated grid-forming for new storage in 2025.
For developers planning projects with 2026–2027 commissioning, grid-forming is not yet mandatory. But selecting PCS with grid-forming capability — or firmware-upgradeable PCS that can be updated to grid-forming operation — is forward-looking procurement practice.
The Technology: What Is Available Now
Several PCS manufacturers offer grid-forming inverters or PCS with firmware-switchable grid-following/grid-forming modes:
ABB (Hitachi Energy FREQCON): Commercial grid-forming BESS-PCS, deployed in Borssele (Netherlands) and Hawaii. Available in India through Hitachi ABB Power Grids.
Sungrow: Announced grid-forming capability in their ST2752UX modular BESS in 2024. Available in India, though Indian grid code compliance profile requires verification.
GE Vernova: Grid-forming products available for utility scale, higher cost point.
CATL/BYD integrated BESS systems: Some newer integrated systems (from CATL and BYD) include grid-forming PCS options, typically at a 5–8% premium over grid-following equivalents.
The cost premium for grid-forming PCS versus grid-following at equivalent power rating is currently 5–12%. As the technology matures and volumes increase, this premium will compress — mirroring the pattern seen in grid-following inverters themselves over the past decade.
What Developers Should Do Today
For projects commissioning in 2026–2027, specifying PCS with grid-forming capability is optional but prudent where budget allows. More importantly: avoid procuring PCS that is hardware-locked to grid-following operation, as future regulatory changes could require upgrades or replacements.
For projects in planning stages with commissioning in 2028–2030, factor grid-forming PCS into your base specification. The regulatory requirement will likely exist by the time these projects commission.
SilicIndia Energies' BESS systems are designed with PCS selection flexibility — we specify from the range of qualified grid-forming and firmware-upgradeable PCS suppliers, matching the specification to the project's technical requirements and the applicable grid code. For projects in Rajasthan or Gujarat where POSOCO has flagged grid stability concerns, we recommend grid-forming PCS as standard. Contact our engineering team to discuss PCS specification for your project.
