In short
- What pays: cutting demand spikes. TNEB charges ₹608 per kVA a month on the higher of your recorded maximum demand or 90% of your contracted demand. Shaving 200 kVA of spikes is worth about ₹15 lakh a year.
- What barely pays: peak-rate shifting. On HT I the gap between the peak and night rate is ₹2.25 a unit; after battery losses and tax, averaged over two cycles a day, a battery earns about ₹1.10 for each unit it delivers — and only if it may charge from the grid, which is not settled in Tamil Nadu.
- Also worth counting: backup instead of diesel, and moving your own solar into the evening.
- Safety rules are coming: from 1 April 2027, CEA rules for battery systems above 650 V require a two-fault-safe design, fire suppression and an independent fire safety audit.
- No subsidy found yet: we have found no Tamil Nadu subsidy for factory or commercial batteries. A state battery policy was announced in the August 2026 budget but has not been notified.
- Our offer: send 12 months of HT bills and your 15-minute demand data. We tell you whether a battery pays before anyone quotes you a price.
Rates from TNERC Tariff Order No. 6 of 2025, checked 2 October 2026. Illustrative default values — request a site-specific quotation.
Four things a battery can do on an HT bill
Cut demand spikes
Discharge during short spikes so your recorded maximum demand stays lower. Usually the biggest saving.
Back up the plant
Keep critical loads running through cuts instead of starting the diesel generator.
Move solar into the evening
Store daytime solar and use it in the 6–10 pm peak instead of losing or under-selling it.
Shift to peak hours
Charge when power is cheaper, use it when it costs 25% more. A small extra, rarely enough on its own.
The demand charge: where the money is
Your HT bill charges ₹608 per kVA every month on whichever is higher: your highest 15-minute demand that month, or 90% of your contracted demand (TNERC Tariff Order No. 6 of 2025). A few minutes of a big motor starting, or air-conditioning kicking in on a hot afternoon, can set the bill for the whole month.
A battery can cover those spikes. Two examples, with 5% electricity tax included:
The catch: demand is read every 15 minutes, and one missed spike sets the whole month's bill. The battery has to keep enough charge in reserve every day. That is why it must be sized to your spikes, from your own 15-minute meter data, not to how many units you use. These savings assume the spike would happen every month.
Illustrative default values — request a site-specific quotation. Your bill decides.
Peak-rate shifting: the honest numbers
HT tariffs charge 25% more from 6–10 am and 6–10 pm, and 5% less from 10 pm to 5 am. A battery can buy at the lower rate and use the power in the peak, up to twice a day.
| Per unit | Peak | Normal | Night | A 0.5 MW / 1 MWh battery would earn, if it may charge from the grid |
|---|---|---|---|---|
| Factory (HT I) | ₹9.38 | ₹7.50 | ₹7.13 | about ₹6.6 lakh a year |
| Commercial (HT III) | ₹11.75 | ₹9.40 | ₹8.93 | about ₹8.3–9.2 lakh a year |
That is roughly ₹1.10 a unit delivered for a factory and ₹1.40 for a commercial building. On its own, that rarely pays for a battery. Added to a demand-charge saving, it helps. A 0.5 MW / 1 MWh battery in the factory example above could earn up to about ₹22–26 lakh a year from both together if grid charging is allowed, and about ₹15–19 lakh from the demand charge alone. In practice it is less: charge kept back for spikes cannot also be cycled, and charging the battery also counts towards your recorded demand, so it has to charge when your load is low.
Grid charging is not settled. Whether a battery at an HT connection may charge from the grid is not settled in the Tamil Nadu rules we have found. The only precedent we know of (TNERC, April 2023, a 2 MW captive solar plant with a 4 MWh battery) was for a battery charged from that solar plant, and reportedly with no grid charging. We ask TNPDCL (the TNEB distribution company) about your connection before counting any grid-charged saving.
Solar plus battery
If you have rooftop solar or buy solar through open access, a battery can move daytime solar into the evening peak.
- Third-party open access gets no banking under the 2025 regulations, so surplus solar is not credited to you. What a battery is worth then depends on your power agreement: it pays most where you would otherwise pay for units you can't use.
- Group captive already banks normal-hour and night units within the month (8% kept by the grid; unused units paid at 75% of the solar tariff). On HT I, a battery adds about ₹1.60 a unit for solar it moves into the 6–10 pm peak. Illustrative default values — request a site-specific quotation.
- No export: we have found no Tamil Nadu rule that lets a factory battery export power, and we design for no export. Under the rooftop solar rules, battery backup must stay inside your own network, and battery or generator power must not reach TNPDCL's grid when grid supply fails.
What to ask any battery supplier
Grid battery tariffs and container prices rose in 2026 after falling through 2025, and China is cutting its battery export tax rebate to 0% from January 2027. Get firm, dated quotes and check these before you sign:
- Test reports for the battery and system: IEC 62619, IEC 62933-5-2 and UL 9540A fire testing, and BIS registration where it applies.
- The cell maker and where the cells are made.
- A written warranty covering years, guaranteed cycles or MWh delivered, capacity left at the end, round-trip efficiency and availability.
- Safety design to the new CEA rules (Chapter XA of the CEA Safety Regulations, in force from 1 April 2027 for systems above 650 V, as reported): a design that stays safe through two faults, gas and smoke detection, automatic fire suppression, forced ventilation, and an independent fire safety audit.
- How long the quote holds, and what happens if duties or GST change.
How we work
- You send 12 months of HT bills and, if you can, the 15-minute demand data from your TNEB meter or your energy monitor.
- We work out what a battery would earn on your site: demand-charge cut, backup, solar shifting and peak shifting, each shown separately. If it doesn't pay, we say so.
- If it does, we size it to your spikes and get firm quotes for certified partner batteries.
- We design and install the system with our partners, to the CEA safety rules as published, and connect it to your solar and load. We tell you which approvals your site needs.
- We agree the upkeep with you and the battery partner, and you see what the battery actually saves.
Building a grid-scale battery project?
Developers and EPC companies building battery projects at Tamil Nadu substations: see how we work as a local engineering partner →
Common questions
Does Aran make batteries?
No. Aran works with certified partner batteries and designs the battery system around your load and your solar. We make solar trackers and mounting structures in Coimbatore. We tell you at the start which parts we deliver ourselves and which through partners.
Will a battery cut my TNEB HT bill?
Mainly through the demand charge, and only if your recorded maximum demand has spikes above 90% of your contracted demand. Peak-rate shifting adds a little, about ₹1.10 a unit delivered on HT I averaged over two cycles a day, and only if the battery may charge from the grid. Backup and storing your own solar can add more. We work it out from your own bills before anyone quotes a price.
Can my battery charge from the grid at night in Tamil Nadu?
It is not settled in the Tamil Nadu rules we have found. The only precedent we know of (TNERC, April 2023, a 2 MW captive solar plant with a 4 MWh battery) was for a battery charged from that solar plant, and reportedly with no grid charging. We ask TNPDCL about your connection before counting any grid-charged saving.
Can a factory battery send power back to the grid?
We have found no Tamil Nadu rule that lets a factory battery export power, and we design for no export. Under the rooftop solar rules, battery backup must stay inside your own network, and battery or generator power must not reach TNPDCL's grid when grid supply fails.
What safety rules apply to a factory battery?
From 1 April 2027, as reported, Chapter XA of the CEA Safety Regulations applies to battery systems above 650 V. It requires a design that stays safe through two faults, gas and smoke detection, automatic fire suppression, forced ventilation and an independent fire safety audit. We plan systems to these rules as published.
What warranty should I ask for?
Ask for it in writing: the number of years, the guaranteed cycles or MWh delivered, the capacity left at the end of the warranty, the round-trip efficiency and the availability. Ask who makes the cells and for the test reports.
Is there a Tamil Nadu subsidy for batteries?
We have found none yet for factory or commercial batteries. A Tamil Nadu battery storage policy was announced in the August 2026 budget, but it had not been notified when we last checked. The national grant (viability gap funding) is for grid-scale projects.
Is solar plus battery worth it under group captive?
Banking already covers normal-hour and night units within the month, so a battery mainly adds the value of moving solar into the 6–10 pm peak: on HT I about ₹1.60 a unit (illustrative). Under third-party open access, which has no banking, it depends on what your power agreement says about surplus units.
Where these numbers come from
- TNERC Suo-motu Tariff Order No. 6 of 2025 (30 June 2025) — HT energy charges, time-of-day rates, demand charge and the 90% rule.
- Tamil Nadu Tax on Consumption or Sale of Electricity Act, 2003 — 5% electricity tax.
- TNERC Green Energy Open Access Regulations 2025 (notified 18 September 2025) — banking.
- CEA (Measures relating to Safety and Electric Supply) Amendment Regulations 2026, Chapter XA — battery safety from 1 April 2027 (as reported by Mercom, 2 April 2026).
- TNERC order of 25 April 2023 on a 2 MW captive solar plant with a 4 MWh battery (Dollar Industries; as reported by Mercom).
- TNEB rooftop solar "Salient Features", item 15 — battery backup restricted to the consumer's network.
- Saur Energy, 7 August 2026 — Tamil Nadu battery storage policy announced, not yet notified.
- Our own arithmetic for every saving on this page.
Get a free battery check
Tell us about your site. The quickest way is to WhatsApp 12 months of HT bills; add your 15-minute demand data if you have it. No obligation.
Thanks, we've got your details. The fastest next step: send 12 months of HT bills on WhatsApp.
Send bills on WhatsApp