Transformer Capacity for Rooftop Solar: The Secret Check Before You Install (Tamil Nadu & Kerala 2026)

• You’ve measured the roof, compared panel brands and chosen a system size.
• Then the DISCOM says no. Not because of your roof or your paperwork, but because of a grey box on an electricity pole down your street.
• Transformer capacity for rooftop solar is the check most homeowners and businesses never hear about until it delays or blocks their application.

In this guide, Kondaas founder Sanjay explains what that check is, why the DISCOM applies it, the limits that apply in Tamil Nadu and Kerala in 2026, and how to find out whether your area has room before you pay an advance.

In 60 Seconds

Why your local transformer can stop a solar approval. View the Reel

What Is the Transformer Check?

Every rooftop solar system connects to the grid through your area’s distribution transformer (DT). To keep that transformer safe, DISCOMs limit the total solar capacity connected to each transformer. In both Tamil Nadu and Kerala, that limit is 90% of the transformer’s capacity. Once the solar already connected (and approved) on your transformer reaches it, new solar connections on that transformer can be refused or delayed until capacity is added.

	Tamil Nadu (TANGEDCO / TNPDCL)	Kerala (KSEB)
Transformer limit for rooftop solar	Up to 90% of transformer capacity (TNERC order, May 2024)	90% of transformer capacity (KSERC Regulation 14(2), as amended in 2024)
Small systems	Technical feasibility study not required up to 10 kW (TNERC, May 2024)	Feasibility issued through KSEB’s process
Check online	Ask your section office or installer	KSEB publishes transformer-wise balance online

Rooftop solar for homes in Coimbatore & India. On-Grid, Hybrid & Off-Grid systems with govt subsidy support.

Why Does a Transformer Limit Solar?

A distribution transformer is built to step voltage down from the high-voltage line to the 230/415 V supply your home uses. During the day, rooftop systems in your area can generate more power than the homes nearby are using. That surplus flows backwards through the transformer onto the grid.

When too much solar sits on one transformer, especially at midday:

• Voltage on the local line can rise above safe levels, which can trip inverters and damage appliances.
• The transformer can be overloaded in reverse, shortening its life.
• Protection settings designed for one-way power flow may not work as intended.

That’s why regulators set a ceiling. It protects the transformer, the line and every home connected to it, including yours.

The Limits in Tamil Nadu and Kerala

Tamil Nadu

In an order dated 23 May 2024, the Tamil Nadu Electricity Regulatory Commission (TNERC), as reported by DT Next, directed that:

• Rooftop solar connections on a transformer can go up to 90% of its capacity.
• Systems up to 10 kW don’t need a technical feasibility study. The section officer is to sanction them and inform the applicant within 10 days.

This follows the Ministry of Power’s February 2024 amendment to the Electricity (Rights of Consumers) Rules, under which systems up to 10 kW are deemed accepted without a feasibility study.

What this means for homeowners: most home systems are under 10 kW, so the separate feasibility study is gone. But the transformer’s overall 90% ceiling still matters in areas where many homes have already gone solar. Ask your section office or installer about your transformer before you commit.

Kerala

• Under Regulation 14(2) of the KSERC (Renewable Energy and Net Metering) Regulations, 2020, as amended in August 2024, the total renewable energy capacity connected to a distribution transformer shall not exceed 90% of its capacity. The limit was 75% before that amendment.
• In April 2026, Kerala Kaumudi reported that many urban areas had already reached this ceiling, with KSEB installing new transformers in areas of growing demand. For the full Kerala process, including how to check your transformer online.

kVA vs kW: How the Limit Works in Practice

Transformers are rated in kVA (kilovolt-amperes). Solar systems are rated in kW (kilowatts). The two are linked by the power factor: kW = kVA × power factor.

Worked example (100 kVA transformer):

Step	Value
Transformer rating	100 kVA
90% limit	90 kVA
In kW, at a power factor of 0.9	About 81 kW of solar

• Kerala Kaumudi’s April 2026 report gives the same example for KSEB: a 100 kVA transformer allows about 81 kW of solar-to-grid connections.
• So if the homes on a 100 kVA transformer already have about 81 kW of solar connected or approved, the next application on that transformer can be held up, even if it’s only a 3 kW system.
• Important: each DISCOM decides how it counts connected and approved capacity, and which power factor it applies. Always confirm the figure for your transformer with your section office.

To understand kVA and kW on the system side, see our 5kW solar system design guide, which explains the difference for inverters and sanctioned load.

Why This Check Matters Before You Pay

Many families find out about the transformer limit after paying an advance, when the application stalls. Checking first protects you from:

• Money locked with an installer while the application waits for transformer capacity.
• Missing a subsidy window. PM Surya Ghar’s implementation period under MNRE’s guidelines runs until 31 March 2027, and a long transformer delay eats into that time.
• Buying the wrong size. If only 2 kW of headroom remains, a 5 kW quote won’t help you.

How to Check Your Transformer’s Capacity

In Kerala: online

KSEB publishes a transformer-wise list showing the 90% limit, the feasibility already issued, the capacity connected and the balance available.

Our KSEB feasibility guide shows each step.

In Tamil Nadu: ask before you apply

There isn’t an equivalent public, transformer-wise page that we can point you to for Tamil Nadu, so:

1. Find your transformer. It’s usually the pole-mounted or plinth transformer nearest your home. Your section office can tell you which one supplies your connection.
2. Ask the section office whether that transformer has room for more rooftop solar.
3. Ask your installer whether they’ve recently connected systems on the same transformer, and whether any applications were delayed.
4. Watch for local signs: if many homes on your street already have solar, ask about headroom before signing.

For the full Tamil Nadu application process, see our TANGEDCO net metering application guide.

What to Do If Your Transformer Is Full

A full transformer isn’t always a dead end. Your options:

Option	When it works	What to keep in mind
Install a smaller system	Some headroom remains, but less than planned	Size to the balance available. A smaller system still earns savings and the subsidy
Wait and recheck	Approved applications may lapse, or new capacity may be added	Check periodically. Don’t pay a large advance while you wait
Ask about augmentation	Your area is due for a transformer upgrade	Ask your section office about plans and timelines, and whether any cost falls on you. Get the answer in writing
Use more of your solar yourself	Exports are the main concern	A hybrid system with a battery stores daytime surplus. Ask your DISCOM how it treats such systems for approval
Dedicated transformer (larger businesses)	Large commercial or industrial loads	Larger connections may be supplied through their own transformer. Ask your DISCOM about the requirements

Avoid any installer who tells you to “install now and sort out the transformer later”. Without DISCOM approval, the system can’t be net-metered, and the subsidy won’t be released.

For Businesses: Why the Transformer Check Is Bigger

For shops, offices, schools and factories, the transformer question becomes more important:

• Systems above 10 kW don’t fall under Tamil Nadu’s small-system exemption from the technical feasibility study, so DISCOM checks apply.
• A commercial system can use a large share of a transformer’s headroom. A 50 kW system on a 100 kVA shared transformer takes much of the capacity on its own.
• Many larger commercial and industrial sites have higher-capacity connections, sometimes with their own transformer. That changes how the limit applies and what approvals are needed.

The good news for businesses: daytime loads such as machines, air conditioning and lighting usually use most of the solar on site, so far less is exported back through the transformer. A system sized to your daytime load is easier on the grid, and usually earns a better return anyway.

See our commercial solar solutions for how we plan large systems around DISCOM approval.

Three Real-World Scenarios

These examples show how the same rule plays out differently depending on where you live. They’re illustrations, not specific cases.

• Scenario 1: A new house in a growing suburb
  • A family in a new layout on the edge of Coimbatore wants a 3 kW system. Few homes on their transformer have solar yet, so plenty of headroom remains. Because the system is under 10 kW, no separate technical feasibility study is needed, and the application moves through the normal steps.
  • Lesson: in areas with little existing solar, the transformer limit rarely gets in the way. It’s still worth a quick question to the section office.
• Scenario 2: A street where most homes already have solar
  • A homeowner in an established neighbourhood wants 5 kW, but many neighbours installed solar over the past two years. The transformer is close to its limit, and only about 2 kW of headroom remains.
  • Lesson: a 2 kW system may still be approved and still earn the ₹60,000 central subsidy. Waiting for a 5 kW approval could take much longer. Size to what’s available now, and add capacity later if the transformer is upgraded and your sanctioned load allows it.
• Scenario 3: A small factory on a shared transformer
  • A workshop plans a 40 kW rooftop system. Its connection shares a transformer with nearby homes and shops. At 40 kW, the system needs DISCOM checks, and it would take a large share of the transformer’s remaining headroom.
  • Lesson: for business systems, check transformer capacity and connection type at the design stage, before finalising size and budget. Designing the system around daytime consumption keeps exports, and grid stress, low.

Common Myths About the Transformer Limit

• “Only big systems are affected.” No. The limit applies to the total solar on the transformer. A small 2 kW application can be held up if the transformer is already full.
• “If my neighbour got approval, I will too.” Not necessarily. Your neighbour may have connected before the transformer reached its limit.
• “The installer can get around it.” No legitimate installer can bypass the DISCOM’s transformer limit. What a good installer can do is check headroom early, size your system to fit and follow up on approvals.
• “Under 10 kW means no checks at all.” In Tamil Nadu, systems up to 10 kW don’t need a separate technical feasibility study. But the DISCOM still approves the connection and fits the net meter, and the transformer’s overall limit still applies.

A Simple Pre-Installation Checklist

Before you sign with any installer, confirm:

1. Your sanctioned load allows the system size you want.
2. Your transformer has headroom for that size (checked online in Kerala, or with the section office in Tamil Nadu).
3. The installer is a registered PM Surya Ghar vendor for your area, if you want the subsidy. Check this on pmsuryaghar.gov.in.
4. The payment schedule keeps most of the payment until after approval and installation.
5. The quote names the panels and inverter, and includes the net meter process.

Conclusion

The transformer check is the one step that can stop a well-planned solar installation, and it has nothing to do with your roof or your budget. In Tamil Nadu and Kerala, total rooftop solar on a transformer is capped at 90% of its capacity. Check your transformer’s headroom before you pay, size your system to what’s available, and work with an installer who raises this question upfront.

Want to know if your area has room for solar? Kondaas checks transformer capacity and sanctioned load before quoting, so you don’t pay for a system that can’t be connected.

Book a free site and feasibility check with our team.

Frequently Asked Questions about transformer load