The grid runs on a heartbeat
India’s grid, like every alternating-current grid, runs at a target frequency of 50 hertz (Hz) — the electrical “heartbeat” that keeps every generator and motor in step. That frequency only holds steady when the power being generated exactly matches the power being consumed, moment to moment. When a large plant trips or demand suddenly jumps, generation falls short and the frequency dips below 50 Hz; when there is too much power, it rises above.
The grid operator’s job is to correct these imbalances in seconds, before they cascade into blackouts. The tools it uses to do that are called ancillary services — the fast, on-call reserves of power that get injected or absorbed to hold the frequency in its allowed band. Traditionally this was done by keeping thermal plants running below full output so they could ramp up or down on command.
A battery energy storage system (BESS) does this better than almost anything else — and India’s rules now pay it to. That payment is a second revenue stream, earned on top of the battery’s main job of buying energy when it is cheap and selling when it is dear.
Why a battery is built for this job
Frequency regulation rewards two things: speed and the ability to work in both directions. A BESS is uniquely good at both.
- Speed. A thermal plant takes minutes to change its output. A battery, switching through its power electronics, can go from idle to full injection in well under a second — fast enough to catch a frequency dip almost as it starts.
- Both directions. When the grid has too little power, the battery discharges; when it has too much, it charges. A generator can only add power. This two-way capability makes a BESS ideal for the constant small corrections that frequency regulation demands.
- No fuel penalty. A part-loaded thermal plant burns fuel just to stay ready. A battery sits at zero cost until it is called, then earns for every correction it makes.
The trade-off is that every charge and discharge uses a little of the battery’s cycle life, so operators weigh ancillary earnings against wear — a calculation that ties directly to round-trip efficiency and degradation.
The three reserves, from fastest to slowest
India’s framework, set by the Central Electricity Regulatory Commission (CERC), divides these reserves into three tiers by how quickly they respond. Think of them as three lines of defence after a disturbance.
- Primary Reserve Ancillary Service (PRAS) acts automatically within seconds to arrest a falling frequency — the first catch.
- Secondary Reserve Ancillary Service (SRAS) follows over the next tens of seconds to minutes, steering the frequency back to 50 Hz.
- Tertiary Reserve Ancillary Service (TRAS) comes in later, over roughly fifteen minutes onward, to replace the faster reserves so they are ready for the next event.
Speed is exactly why storage fits: a BESS is naturally suited to the two fast tiers, and can bid into the slower one as well.
The rules that let a BESS get paid
For years, only conventional generators could provide these reserves. That changed with the CERC (Ancillary Services) Regulations, 2022, notified on 31 January 2022 with most provisions taking effect from 5 December 2022. Two things in those rules matter for storage:
- Storage is explicitly eligible. The regulations name entities with energy storage resources — alongside generators and demand-response providers — as qualified to supply secondary and tertiary reserves. For the first time, a standalone battery could be a paid grid-balancing resource, not just an energy trader.
- A market, not just an instruction. Tertiary reserves moved to a market-based mechanism, and a Tertiary Reserve Ancillary Services segment was introduced on the power exchanges (launched on the Indian Energy Exchange from 1 June 2023), with a higher price cap for the ancillary segment — reported around ₹50 per unit against ₹12 for the day-ahead energy market — reflecting the premium the grid places on fast, on-call capacity.
This regulatory shift is part of the same policy push behind India’s 74 GW / 411 GWh storage target for 2032: the grid cannot absorb that much variable solar and wind without fast reserves, and batteries are the cheapest way to provide them.
Stacking revenue: the real economics
The reason ancillary services matter to a buyer is that they stack on top of a battery’s primary income. A BESS bought to do energy arbitrage — charging on cheap midday solar, discharging into the evening peak — is idle for part of every day. Those idle hours are exactly when it can stand ready to provide frequency support and earn for it.
| Revenue layer | What the battery does | When it earns |
|---|---|---|
| Energy arbitrage / peak shaving | Shifts energy from cheap to expensive hours | Daily, on a schedule |
| Ancillary services | Injects or absorbs to hold 50 Hz | On call, when the grid needs it |
| Capacity / tender contract | Provides assured capacity under a PPA | Per the contract term |
No battery captures all of these at once — energy stored for arbitrage is energy not available for a reserve call, and operators must choose how to allocate capacity. But the ability to earn across more than one market is what improves a storage project’s returns, and it is a large part of why standalone-storage business models are becoming bankable in India. Our guides to grid-stabilization solutions and to SECI’s standalone storage tenders cover how these roles are contracted.
What this means for you
If you are evaluating a battery project, ancillary services are a reason the numbers may work better than a simple arbitrage spreadsheet suggests — but treat them as upside, not certainty:
- Model your primary use first. Size and justify the battery on its core job — peak shaving, arbitrage or a firm-power contract. Let ancillary earnings be the bonus that shortens the payback, not the assumption the whole case rests on.
- Check what your connection allows. Participating in reserve markets depends on your grid connection level, metering and registration as a qualified provider — a genuinely grid-connected standalone BESS is set up for it in a way a behind-the-meter cabinet may not be.
- Weigh the wear. Frequent shallow cycling for frequency support is gentle, but it still consumes cycle life — factor it into the warranty and degradation conversation with your supplier.
A necessary caveat: ancillary-service rules, eligibility conditions, price caps and market segments are set by CERC and revised by regulation and order — the framework here is the current picture, but verify the provisions in force before building a business case on them. When you want to put your own load, tariff and duty cycle against a specific configuration and see where the revenue could come from, talk to our team and we will model it with you.
Regulatory and market snapshot as of July 2026. Ancillary-service regulations, price caps and market rules change by notification; verify the currently notified provisions before financial decisions.