Net Metering vs Net Billing | TNERC 2026 Rules

Quick Answer: Tamil Nadu currently uses net metering (1:1 credit) for residential solar under 10kW. You get full credit for every unit exported to the TANGEDCO grid. Net billing (different buy/sell rates) applies to larger systems. Under current TNERC rules, net metering provides the best ROI for homeowners.

If you are considering rooftop solar in Tamil Nadu, you have probably heard the terms "net metering" and "net billing" used interchangeably. They are not the same thing — and the difference directly impacts how much money your solar system saves you every year.

This guide explains both mechanisms under the current TNERC (Tamil Nadu Electricity Regulatory Commission) regulations, shows you exactly which one applies to your situation, and walks through real billing examples so you can make an informed decision.

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What Is Net Metering?

Net metering is the simplest and most homeowner-friendly solar compensation mechanism. It works on a 1:1 credit basis — every unit of solar electricity you export to the TANGEDCO grid offsets one unit you consume from it.

How It Works

1. Your rooftop solar system generates electricity during the day
2. You consume what you need in real time (self-consumption)
3. Any surplus is exported to the TANGEDCO grid through your bi-directional meter
4. In the evening and at night, you draw power from the grid as usual
5. At billing time, TANGEDCO calculates: Units Imported - Units Exported = Net Consumption
6. You are billed only for the net consumption

Simple Example

Meter Reading	Units
Total imported from grid	400
Total exported to grid	350
Net consumption	50 units
Bill amount	Based on 50-unit slab rate

Under net metering, the 350 units you exported are valued at the same retail tariff rate as the units you imported. This is the key advantage — you are effectively "storing" electricity in the grid and getting full value back.

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What Is Net Billing?

Net billing (sometimes called "net feed-in" or "gross billing with netting") is a different mechanism where the export and import of electricity are valued at different rates.

How It Works

1. You generate solar electricity and consume what you need (same as net metering)
2. Surplus is exported to the grid (same as net metering)
3. However, at billing time, imports and exports are valued separately:
   • Imports are charged at the full retail tariff (TANGEDCO domestic rates)
   • Exports are credited at a lower feed-in rate (typically the APPC rate or a regulated buy-back rate)
4. Your bill = (Import charges at retail rate) - (Export credits at feed-in rate)

Simple Example

Component	Units	Rate	Amount
Imported from grid	400	₹4.50/unit (average)	₹1,800
Exported to grid	350	₹3.50/unit (APPC rate)	₹1,225
Net bill			₹575

Compare this to net metering, where the same scenario would result in a bill for just 50 units (approximately ₹112). The difference is significant: ₹575 vs ₹112 for the exact same generation and consumption pattern.

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The Critical Difference: A Side-by-Side Comparison

Feature	Net Metering	Net Billing
Export credit rate	Same as retail tariff (1:1)	Lower feed-in rate (APPC/regulated)
Effective value of exported unit	₹2.25–₹11.00 (depends on slab)	₹3.50–₹4.00 (fixed)
Billing calculation	Import minus Export = Net units	Separate valuation of import and export
Benefit to homeowner	Higher	Lower
Benefit to DISCOM	Lower	Higher
Encourages self-consumption	Moderate	Strong
Typical saving (3kW system)	₹2,000–₹3,000/month	₹1,200–₹2,000/month

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TNERC 2026 Regulations: What Currently Applies in Tamil Nadu

As of March 2026, here are the operative rules under TNERC's solar rooftop regulations:

For Residential Consumers (LT Domestic)

• Net metering applies for systems up to 10 kW
• Bi-directional meter is mandatory and installed by TANGEDCO
• Export credits are carried forward on a monthly basis
• Annual settlement of excess credits at the APPC rate (currently ₹3.50–₹4.00 per unit)
• The system size cannot exceed your sanctioned load

For Commercial and Industrial Consumers (LT/HT)

• Net metering applies for systems up to the sanctioned load or contract demand
• For HT consumers, TNERC regulations allow net metering up to 1 MW
• Excess generation beyond consumption is settled at the APPC rate
• Time-of-day (ToD) tariffs may apply for HT consumers, which affects the value of net metering credits

Key Regulatory Reference

The operative regulation is the TNERC (Grid Interactive Solar Energy Generating Systems) Regulations, most recently amended in 2025. The commission has maintained net metering as the primary mechanism for rooftop solar in Tamil Nadu, though industry observers note that a shift toward net billing for larger systems is being discussed nationally.

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Which One Applies to You?

Here is a quick decision tree:

Your Situation	Mechanism	Notes
Residential, system up to 10 kW	Net metering	Best case scenario — full 1:1 credit
Commercial LT, system up to sanctioned load	Net metering	Same benefit as residential
Industrial HT, system up to contract demand	Net metering	ToD adjustments may apply
System exceeds sanctioned load	Not permitted	TANGEDCO will not approve
Group housing / apartment (common system)	Net metering	Applied at the society level

For most Tamil Nadu homeowners installing 3–5 kW systems, net metering is the applicable mechanism — and it is the most financially advantageous one.

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Settlement Periods: Monthly vs. Annual

Understanding settlement periods is crucial for maximising your solar investment.

Monthly Billing Cycle

• TANGEDCO reads your bi-directional meter every billing cycle (bimonthly in most areas)
• If you exported more than you imported: the excess units carry forward as credit to the next cycle
• If you imported more than you exported: you pay for the net import at the applicable tariff slab

Annual Settlement (End of Financial Year)

At the end of each financial year (March 31), TANGEDCO performs an annual settlement:

Scenario	What Happens
You have accumulated export credits	Credits are "cashed out" at the APPC rate (₹3.50–₹4.00/unit)
You have no accumulated credits	Nothing happens — you have already been billed for net imports

Why This Matters

The annual settlement rate (APPC) is much lower than the retail tariff. This means:

• Units credited 1:1 during the year are worth ₹2.25–₹11.00 each (depending on your consumption slab)
• Units settled at year-end are worth only ₹3.50–₹4.00 each

Strategy: Size your solar system to match your annual consumption as closely as possible. Over-sizing leads to excess credits that are settled at the lower APPC rate, reducing your ROI.

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How Excess Credits Are Handled at Year End

Let us walk through a detailed example:

Scenario: 3 kW System, 300 Units Monthly Consumption

Month	Generation	Consumption	Net	Cumulative Credit
April	400	300	+100	100
May	420	350	+70	170
June	380	300	+80	250
July	360	280	+80	330
August	350	280	+70	400
September	340	290	+50	450
October	300	310	-10	440
November	250	300	-50	390
December	260	320	-60	330
January	320	300	+20	350
February	370	290	+80	430
March	390	280	+110	540

At the end of March, this homeowner has 540 units of accumulated export credit.

Annual settlement:

• 540 units × ₹3.75 (APPC rate) = ₹2,025 credited to the consumer's account
• Compare: If those 540 units had been consumed (offsetting grid imports), they would have been worth approximately ₹2,430–₹3,500 depending on the tariff slab

Lost value: ₹400–₹1,475 per year due to over-sizing

This is why right-sizing your system is so important. Use our Solar Savings Calculator to find the optimal system size for your consumption pattern.

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Billing Examples with Actual TANGEDCO Tariff Rates

Example 1: Perfect Match (Net Metering)

Consumer: 350 units/month consumption, 3 kW system generating 350 units/month

Item	Amount
Gross import	400 units (evening/night consumption)
Gross export	400 units (daytime surplus)
Net consumption	0 units
Energy charges	₹0
Fixed/demand charges	₹50
Total bill	₹50

Without solar: ₹1,350/month Monthly savings: ₹1,300

Example 2: Moderate Mismatch (Net Metering)

Consumer: 450 units/month consumption, 3 kW system generating 350 units/month

Item	Amount
Gross import	500 units
Gross export	400 units
Net consumption	100 units
Energy charges (100 units at first slab)	₹0 (free slab)
Fixed/demand charges	₹50
Total bill	₹50

Without solar: ₹2,100/month Monthly savings: ₹2,050

Example 3: Hypothetical Net Billing Scenario

Same consumer as Example 2, but under net billing:

Item	Units	Rate	Amount
Import charges	500	₹4.50 avg	₹2,250
Export credit	400	₹3.75	-₹1,500
Net bill			₹750
Fixed charges			₹50
Total bill			₹800

The difference: ₹50 (net metering) vs ₹800 (net billing) for the same system and consumption. This is why net metering is so valuable and why Tamil Nadu homeowners should install while it is still the operative mechanism.

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Impact on Your ROI

The metering mechanism directly affects your payback period:

Scenario (3 kW system, ₹1.22 lakh net cost)	Monthly Savings	Payback Period
Net metering (current TN rules)	₹2,000	3 years
Net billing (hypothetical)	₹1,300	4.6 years
No export mechanism (self-consumption only)	₹900	6.7 years

Net metering gives you the best ROI. If regulations shift to net billing in the future, systems already installed under net metering rules may be grandfathered — another reason to install sooner rather than later.

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What Might Change in Future Regulations

While Tamil Nadu currently maintains favourable net metering policies, here is what the national regulatory landscape suggests:

Trends to Watch

1. National push toward net billing: Several state electricity regulatory commissions (SERCs) have moved or are considering moving from net metering to net billing for new installations. Gujarat and Maharashtra have already made partial shifts.

2. System size thresholds: Some states apply net metering only up to a certain size (e.g., 5 kW) and net billing for larger systems. TNERC has not yet adopted this but it remains a possibility.

3. Time-of-day (ToD) metering: As smart meters roll out, ToD-based billing could change the value proposition. Solar exports during midday (when grid demand is moderate) may be valued differently from evening imports (when demand peaks).

4. Grandfathering clauses: Most regulatory changes include grandfathering provisions, meaning systems installed under current rules continue to enjoy net metering for a fixed period (typically 15–25 years).

What This Means for You

• Install now to lock in net metering benefits under current TNERC regulations
• Choose the right system size to maximize self-consumption and minimize reliance on export credits
• Document everything — your approval letter, net metering agreement, and commissioning date are your proof of grandfathering eligibility

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How to Maximize Benefits Under Current Rules

1. Right-Size Your System

Match your system to your annual consumption. A system that generates exactly what you consume throughout the year maximises the 1:1 net metering benefit and minimises low-value annual settlement.

2. Shift Heavy Loads to Daytime

Run washing machines, water heaters, and air conditioners during peak solar hours (10 AM – 3 PM) to maximize self-consumption. Every unit you consume directly is worth the full retail tariff — no metering mechanism needed.

3. Monitor Your Generation

Install a generation monitoring system (most modern inverters include WiFi monitoring). Track your monthly generation vs consumption and adjust usage patterns accordingly.

4. Maintain Your Panels

Dusty panels generate less power, which means less export credit and more grid import. Clean panels every 2–4 weeks for optimal performance. In Tamil Nadu's dusty climate, this alone can improve generation by 5–10%.

5. Consider a Battery (Future-Proofing)

If regulations shift to net billing, a battery storage system allows you to store daytime surplus and use it at night — bypassing the export mechanism entirely. While batteries are not cost-effective for most homeowners today, prices are dropping rapidly.

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Understanding Your Bi-Directional Meter

When you go solar with net metering, TANGEDCO replaces your existing unidirectional meter with a bi-directional (import/export) meter.

What It Measures

Reading	Meaning
KWh Import	Total units drawn from the TANGEDCO grid
KWh Export	Total units sent to the TANGEDCO grid
Net (Import - Export)	Your billable consumption

Key Points

• The meter is provided and installed by TANGEDCO (you may need to pay a meter cost of ₹2,000–₹3,000)
• It is a digital meter with an LCD display showing both import and export readings
• The display cycles between readings automatically — learn to read both values
• Take a photo of your meter readings before each billing cycle for your own records
• If the meter malfunctions, contact TANGEDCO immediately — you may be billed on estimated consumption without export credits

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Frequently Asked Questions

Can I have net metering without the PM Surya Ghar subsidy?

Yes. Net metering and the PM Surya Ghar subsidy are independent mechanisms. You can have net metering without applying for the subsidy (though there is no reason to skip the subsidy if you are eligible).

What happens if I change my TANGEDCO connection type?

If you change from domestic to commercial, your net metering agreement remains valid but the applicable tariff rates change. Inform TANGEDCO and update your agreement.

Can I switch from net metering to net billing (or vice versa)?

Under current TNERC rules, the mechanism is determined by regulation, not consumer choice. Residential consumers up to 10 kW are automatically under net metering.

Is net metering available for agricultural connections?

Yes, but the process and applicable rates differ. Contact your local TANGEDCO office for agricultural connection-specific guidance.

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Next Steps

Net metering in Tamil Nadu remains one of the most homeowner-friendly solar policies in India. The 1:1 credit mechanism, combined with the PM Surya Ghar subsidy, makes rooftop solar one of the best investments available to Tamil Nadu residents in 2026.

1. Calculate your optimal system size with our Solar Savings Calculator — it factors in net metering benefits automatically
2. Speak with a solar expert at Tristar Energy — Contact us for a free consultation on system sizing, net metering, and subsidy application

The window for net metering at current terms is open. Smart homeowners are installing now to lock in 25 years of 1:1 credit benefits before any policy changes.