Solar Plus BESS for Peak Shaving: When a Factory's Demand Charges Justify Battery Storage

Battery storage justifies itself for a factory when demand charges or contract-demand penalties are large and the peak is short. A battery can shave a peak lasting minutes to a few hours, so the test is simple: kW above your target, multiplied by the hours it lasts, against the monthly demand charge you would avoid. Solar alone cannot be relied on to cut the monthly maximum.

Why rooftop solar does not remove the demand charge

Solar cuts energy units. A demand charge is levied on the highest demand recorded in the billing month, usually averaged over a fixed interval set by the tariff order. One heavy interval sets the charge for the whole month. If that interval falls on a cloudy morning, during a second-shift start-up or after sunset, the solar plant contributed nothing to it.

That is why a plant with a large solar array can still show an unchanged maximum demand. Before you consider storage, pull your last twelve bills and, if your smart meter allows, the interval data. Look at three things: the date and time of each month's maximum demand, how far it exceeds the level at which the other days sit, and whether you pay a penalty above contract demand. Smart metering has changed one rule here. The Ministry of Power's 2023 amendment says that after a smart meter is installed, no penalty is levied on maximum demand recorded for the period before installation, and the sanctioned load is revised upward only if it was exceeded at least three times in a financial year. Confirm how your state applies this.

The demand-charge arithmetic, with assumed numbers

The figures below are assumed for illustration. They are not any DISCOM's tariff. Replace each with a value from your own bill.

The saving is capped by the kVA you shave, so the answer to "does it pay" is whether a battery of that size costs less than the stream of savings over its warranted life. We do not price battery systems on this page, and we are not suggesting a figure. Get firm quotes for the same kW and kWh and compare them with your own saving. If the demand charge in your tariff is low, or your peaks are long and wide, a battery will not pay on demand alone.

Sizing: kW and kWh are different questions

Power (kW) decides whether the battery can cut the sharpest peak. Energy (kWh) decides how long it can hold the cut. A battery short of kW leaves the peak standing; one short of kWh runs out partway through it, and the recorded maximum is set by the last, un-shaved interval.

• Add margin: peaks are not forecast to the minute. Size for the longest excess in the data, then add margin for the day it is longer.
• Usable, not nameplate: batteries are warranted for a usable depth of discharge. Size from usable kWh at the end of the warranty, when capacity has faded.
• Cycle life: datasheets quote cycles at a stated depth of discharge and temperature, and warranties are written in years or in energy throughput. A daily-cycling battery uses its throughput faster than a backup one. Read the warranty terms, not the headline cycle count.
• Round-trip efficiency: some energy is lost in each charge and discharge. Ask for the AC-to-AC figure including the power conversion system and auxiliary load such as cooling.
• Power factor: the demand charge may be on kVA, while the battery's rating is in kW. Check that the inverter can support the reactive power you need.

Our solar battery storage calculator gives a first sizing; it is not a replacement for load-profile analysis.

Time-of-day tariffs add a second value stream

Under the Electricity (Rights of Consumers) Amendment Rules, 2023, time-of-day tariffs apply to commercial and industrial consumers with maximum demand above 10 kW from 1 April 2024 at the latest. The Ministry's release describes a lower tariff during solar hours, an eight-hour window set by the state commission, and a tariff 10 to 20 per cent higher at peak hours. Exact percentages and hours are in your state's tariff order.

For a factory this creates a second value: charge the battery from solar in the cheap window and discharge it in the evening peak. Work this out with your own rates, because the energy shifted per day is small beside what a battery of that size costs. Time-of-day arbitrage tends to support a case already made by demand charges or DG avoidance rather than make it alone. Also check the risk the other way: a battery charged from the grid at peak hours defeats the purpose.

Safety, fire code and approvals for a lithium system

A lithium battery container is a significant fire load. The Ministry of Power told the Rajya Sabha on 27 July 2026 that the Central Electricity Authority's Measures relating to Safety and Electric Supply amendment, which includes safety requirements for battery storage, was notified on 30 March 2026, and that a separate amendment to the construction standards has also been notified. A Ministry release of 30 March 2026 still described the regulations as drafts that had been issued, so official documents differ on the sequence. Press reports say the safety provisions take effect from 1 April 2027 and cover protection design, hazard detection, automatic fire suppression in containers, separation distances and third-party fire audits. We have not read the gazette text, so ask your supplier to show which clauses apply to your voltage and capacity.

In practice, plan three things at the layout stage: separation distance from buildings and from the solar plant's electrical room, detection and suppression designed for lithium thermal runaway, and the fire authority's view on the location. Our NBC fire and life safety guide and Fire NOC assistance pages explain how a fire file is built. The Electricity Rules were also amended in September 2025 to allow energy storage to be owned, leased or operated by consumers, so an owner-operated or leased model is now possible. The viability gap funding schemes the Ministry describes are for utility-scale storage; we have not found a subsidy for a factory's own battery, so confirm before counting one.

How Secured Engineers helps

We design in-house and take MEPF and solar under one contract, so the battery container position, the electrical tie-in and the fire scope are designed together. Fire NOC, CEIG and DISCOM net-metering applications are filed in-house. We work from offices in Noida (Delhi NCR) and Ludhiana, with 535+ projects across 18+ states and 89.77% repeat clients. We have no battery storage project to cite and we do not publish a price for one; we start from your interval data and tariff and tell you whether a battery pays.

Read how we scope storage on the battery energy storage system page. If you are sizing solar first, WhatsApp us your bills, call +91 70099 85817, or ask for a free proposal.