Two ways an inverter can talk to the grid
Every battery energy storage system (BESS) connects to the grid through a power conversion system (PCS) — the inverter that turns the battery’s DC into grid AC and back again. What is easy to miss is that not all inverters relate to the grid in the same way. There are two families, and the difference has quietly become one of the most important choices in a large storage project.
- A grid-following inverter is a follower. It watches the grid’s existing voltage and frequency, locks onto that reference, and injects power in step with it. If the reference disappears — the grid goes weak or collapses — it has nothing to follow, so it backs off or trips.
- A grid-forming inverter is a leader. It behaves like a voltage source: it creates its own voltage and frequency reference and holds it steady, the way a conventional turbine-driven generator does. It can keep a section of grid alive on its own, ride through disturbances, and even start a dead grid from black.
For decades almost every solar plant, wind farm and battery in India used grid-following inverters. That worked because coal, gas and hydro machines — big spinning masses — were always there to set the beat. As those machines make up less of the grid, the beat gets shakier, and that is where grid-forming comes in.
What grid-forming actually adds
A grid-forming PCS is not just a firmware tweak; it changes what the battery can do for the grid. In plain terms it adds four things:
- A voltage and frequency reference. It holds voltage and frequency steady by itself, rather than borrowing them from the grid.
- Synthetic (virtual) inertia. Spinning generators resist sudden frequency changes because of their physical mass. A grid-forming inverter mimics that damping electronically, slowing down frequency swings in the critical first moments of a disturbance.
- Ride-through, not trip. When voltage or frequency wobbles, a grid-forming unit is designed to stay connected and support the grid instead of disconnecting.
- Black-start capability. Because it can build voltage from nothing, it can help restart a grid — or run an island or microgrid with no grid at all.
Why India is moving to mandate it
This stopped being an academic debate on 13 May 2026. At 14:09 hours, the Khavda renewable complex in Gujarat suffered a fault that knocked out three pooling stations with a combined 15.9 GW of installed capacity, causing roughly 9,000 MW of generation to vanish in one event — which GRID-India described as the largest single-event generation loss in the history of the Indian grid. Automatic load shedding of around 6,000 MW followed to keep the rest of the system standing.
An event like that is exactly what grid-forming resources are meant to blunt. In response, the Central Electricity Authority (CEA) decided to move grid-forming from “nice to have” to “required.” Under the emerging rule, grid-forming inverters would be mandatory for all new transmission-connected BESS above 50 MW, and for at least 25% of the installed capacity of new renewable energy plants. GRID-India had already recommended in early 2026 that all new BESS of 50 MW and above carry grid-forming capability as a condition of connectivity. The CEA’s Grid Management Division is expected to issue an Office Memorandum and then fold the requirement into the Connectivity Standards.
Because policies and technical standards change by notification, treat the exact thresholds and dates above as the current direction of travel rather than settled final rules, and verify the latest CEA/GRID-India notification before you design or bid a project.
Standards behind the scenes
Grid-forming does not stand alone; it sits on top of the grid-code compliance every large Indian BESS already has to meet. The CEA’s connectivity standards (amended in 2023) require detailed simulation-based proof of behaviour using RMS and electromagnetic-transient (EMT) models, and the CERC’s Grid Code (IEGC 2023) sets a tight normal frequency band of 49.95–50.05 Hz with ride-through out to 47.5–52 Hz. Internationally, the IEEE 2800 standard for inverter-based resources is being amended (IEEE 2800a) specifically to reduce barriers for equipment with grid-forming capability — a sign the whole industry is converging on the same direction. A well-chosen PCS is therefore central to how a battery earns its keep in ancillary services and frequency regulation, not just how it stores energy.
Does every project need grid-forming?
Not necessarily. The proposed Indian rules are aimed at large, transmission-connected systems, because that is where a trip cascades into a grid-wide problem. A small commercial or industrial cabinet doing peak shaving behind the meter has very different stakes, and grid-following is often perfectly adequate there. The honest answer for most buyers is: match the inverter to the job.
| Grid-following | Grid-forming | |
|---|---|---|
| Needs a live grid to run | Yes | No — can form its own |
| Provides synthetic inertia | No | Yes |
| Black-start / island capable | No | Yes |
| Typical fit | Behind-the-meter, strong grids | Large utility BESS, weak grids, microgrids |
| Relative cost & control complexity | Lower | Higher |
What this means for you
If you are a developer bidding utility-scale storage, assume grid-forming is heading toward being a hard requirement above 50 MW — price the PCS and its controls accordingly, and ask suppliers for simulation-backed proof of grid-forming behaviour, not just a datasheet claim. If you are a C&I buyer sizing a battery for demand charges or backup, you probably do not need grid-forming today, but you should still confirm your inverter meets your DISCOM’s connection rules. Grid-forming capability is one of the features that turns a battery from a passive energy store into a genuine grid-stabilisation asset — the same thinking behind our Grid-Block product line. To talk through the right PCS choice for a specific project or tender, get in touch with our team.
Technical and policy snapshot as of July 2026. Grid-forming mandates in India are still being formalised through CEA/GRID-India notifications; thresholds and timelines can change — verify current rules before financial or design decisions.