How Net Feed-in Actually Works Under TNERC Regulations
In Tamil Nadu, grid-interactive rooftop solar PV systems operate under the Commission's Grid Interactive Solar PV Energy Generating Systems Regulations, 2021. For residential domestic consumers, billing is administered through the Net Feed-in framework. Unlike primitive gross metering where all generated electricity is sold away at low wholesale rates, Net Feed-in operates on a 4-step progressive model:
On-Site Consumption First
During daylight hours, electricity generated by your rooftop panels flows directly to your running appliances (refrigerator, fans, washing machine, daytime air conditioning) through your inverter. This power never enters the TNPDCL grid meter and is 100% free of transmission charges and taxes.
Surplus Exported to the Grid
When solar generation exceeds instantaneous home demand, surplus power automatically feeds back into the local distribution transformer. Your TNPDCL bidirectional digital meter records this cumulative active export in kWh.
Export Credited at Feed-in Rate
Under the Commission's Grid Interactive Solar PV Energy Generating Systems Regulations, 2021, surplus solar export is credited on consumer bills. Net-metering credit rates and tariff tiers have been revised multiple times since 2021 (including proposed 2024 updates for group and virtual net metering); actual settlement rates must be confirmed directly with TNPDCL/TNERC rather than assumed as a static benchmark.
Net Billed Consumption Slabs
TNPDCL reads your gross import (units pulled from grid during night/cloudy hours) minus self-consumption. This net import is then billed under the standard domestic telescopic tariff — benefiting fully from state subsidy allowances.
Worked Example: 3 kW Rooftop Solar System on a 600-Unit Baseline
To illustrate the combined economic impact of self-consumption and export credits, let's examine a typical Tamil Nadu suburban home with a 3 kW grid-connected solar installation (the standard benchmark capacity in the PM Surya Ghar Solar Calculator).
Case Study: 3 kW Solar System Performance Over a 60-Day Billing Cycle
Bi-Monthly AnalysisCrosses 500u ceiling; drops to 100 free units:
Net grid import drops to 300u (Unlocks 200 Free Units!):
The "Double Benefit" of Crossing Back Under 500 Units
This is the single most valuable financial dynamic for homeowners in Tamil Nadu consuming between 501 and 700 units bi-monthly, yet it is rarely highlighted in generic solar brochures:
Under the Tamil Nadu Government order effective 10 May 2026 (detailed in our TNEB Old vs New Tariff 2026 Analysis), crossing above 500 units in a bi-monthly cycle creates a severe cliff-edge: you lose 100 units of free power and revert to paying ₹2.35/unit on units 101–200, plus ₹8.40/unit on units above 500.
Numerical Proof: Offsetting Just 100 Units Saves ₹970.00
Solar System Sizing & PM Surya Ghar Subsidy in Tamil Nadu
Under the Government of India's flagship PM Surya Ghar: Muft Bijli Yojana, domestic households installing grid-connected rooftop solar receive direct benefit transfer (DBT) central financial assistance:
| System Capacity | Avg 60-Day Generation | Target Bi-Monthly Consumption | PM Surya Ghar Subsidy |
|---|---|---|---|
| 1 kW System | ~240 kWh | 300 – 450 units | ₹30,000 |
| 2 kW System | ~480 kWh | 450 – 600 units | ₹60,000 |
| 3 kW System | ~720 kWh | 600 – 900 units | ₹78,000 (Maximum) |
For detailed rooftop area calculations (requiring roughly 100 sq ft shadow-free area per 1 kW), system capital cost estimates, and payback schedules (typically 3.2 to 4.1 years in Tamil Nadu), use our dedicated Solar Rooftop Sizing & Subsidy Calculator.
Do I Still Need a Smart / Bidirectional Meter?
Yes. Standard unidirectional meters cannot distinguish between electricity drawn from the grid and electricity exported to the grid. If you install solar panels without a bidirectional meter, the spinning disc or digital counter will actually treat your clean solar export as additional consumption and bill you for it!
When your rooftop solar installation completes structural inspection, TNPDCL's local section engineer will conduct a commissioning test and replace your existing meter with an approved bidirectional net meter. The meter has two active energy registers:
- Register 1 (Import - kWh): Measures grid electricity consumed when solar output is insufficient.
- Register 2 (Export - kWh): Measures surplus solar energy delivered into the distribution grid.
Both registers are printed on your physical TNPDCL white meter card and the digital bill view on the official portal.
Frequently Asked Questions: TNEB Solar Billing & Net Metering
Detailed answers regarding subsidies, billing mechanics, and grid interconnection in Tamil Nadu.
Do solar households still get the 200 free units subsidy?
Yes. The 200/100 free-units subsidy is based on your net billed consumption imported from TNPDCL, identical to any standard domestic consumer. Having a rooftop solar system does not disqualify you — and because self-consumed solar power lowers your net grid import, it actively helps borderline households stay under the 500-unit ceiling to qualify for the higher 200 free units benefit.
How is the solar export credit calculated in Tamil Nadu?
Surplus electricity exported to the grid is credited under the Commission's Grid Interactive Solar PV Energy Generating Systems Regulations, 2021. Net-metering credit rates and tariff tiers have been revised multiple times since 2021 (including proposed 2024 updates for group and virtual net metering) and must be confirmed directly with TNPDCL/TNERC. Approved credits are deducted directly from your bi-monthly electricity bill, and any excess unadjusted credit carries forward to subsequent billing cycles.
Do I need a special meter for rooftop solar with TNEB?
Yes. TNPDCL requires a bidirectional (net) digital meter that separately tracks both Import (electricity drawn from the grid during nighttime or overcast periods) and Export (surplus solar generation sent to the grid). The meter is calibrated, tested, and installed by TNPDCL during the technical grid synchronization phase.
Does a 3 kW solar system fully eliminate my TNEB bill?
For many moderate-consumption households (using 500–650 units bi-monthly), a 3 kW system generating approximately 720 units per cycle can reduce the net payable bill to ₹0.00 when self-consumption savings and export credits are combined. However, heavy nighttime power users or households running multiple air conditioners may still incur modest net grid import charges.
Is the solar feed-in credit the same as the 200 free units subsidy?
No, they operate as two separate calculations. The 200/100 free-units subsidy applies exclusively to your net imported units from the grid under state welfare policy. The solar feed-in credit is a financial payment from TNPDCL for the tangible green kilowatt-hours you fed back into their transmission network.