Solar Apartments & Virtual Net Metering | Tamil Nadu

Apartment living in Tamil Nadu presents a unique challenge for solar adoption. Individual flat owners rarely have exclusive access to the terrace, and a single rooftop system cannot be directly connected to dozens of individual EB meters. This is where virtual net metering (VNM) — also called group net metering — changes the equation entirely.

Virtual net metering allows a housing society to install one solar system on the common terrace and distribute the generation credits across multiple individual flat owners' TANGEDCO meters. Each flat owner sees a reduced electricity bill without any equipment inside their flat.

This guide explains how VNM works under TNERC regulations, the TANGEDCO application process, cost-sharing models, and practical considerations for apartment associations in Tamil Nadu.

---

What is Virtual Net Metering?

In standard net metering, one solar system is connected to one EB meter. The surplus generation is credited against that single meter's consumption.

Virtual net metering (VNM) extends this concept: one solar system generates electricity, and the credits from that generation are distributed across multiple EB meters — even though those meters are not physically connected to the solar system.

How VNM Differs from Standard Net Metering

Feature	Standard Net Metering	Virtual Net Metering
Solar system	Connected to one meter	Connected to one meter (common area)
Credit distribution	One meter only	Multiple meters (individual flats)
Physical connection	Direct	Through TANGEDCO's billing system
Ownership	Individual	Society/association
Applicable for	Independent houses, individual units	Apartments, group housing, commercial complexes

---

TNERC Regulations for Virtual Net Metering in Tamil Nadu

The Tamil Nadu Electricity Regulatory Commission (TNERC) has provisions for group net metering and virtual net metering under its solar energy regulations. Key regulatory points:

Eligibility

• The solar system must be installed on the premises of the registered electricity consumer (the housing society's common area connection)
• All beneficiary meters must be within the same TANGEDCO distribution zone
• The total solar capacity cannot exceed the aggregate sanctioned load of all participating meters
• Minimum system size: typically 1kW per participating unit (no fixed minimum, but practical economics dictate at least 10kW for apartment systems)

Credit Allocation

• The society specifies the allocation ratio at the time of application
• Allocation can be modified once per financial year
• Credits that exceed a beneficiary's consumption in a billing cycle are carried forward for up to 12 months
• At the end of the settlement period (12 months), excess credits are settled at the APPC (Average Pooled Purchase Cost) rate — currently around Rs.3.50-4.00/unit

System Capacity Limits

• Residential VNM: up to 100% of aggregate sanctioned load
• The system must be installed by an MNRE-approved vendor
• Equipment must meet TANGEDCO's technical specifications (DCR-compliant panels, BIS-certified inverter)

---

How VNM Works for Apartments: Step by Step

The Setup

Consider a 50-flat apartment complex in Coimbatore:

1. The housing society installs a 50kW solar system on the common terrace
2. The system is connected to the society's common area EB meter (used for lifts, water pumps, corridor lighting, CCTV)
3. Solar generation is first consumed by common area loads
4. Surplus generation credits are allocated to individual flat owners' meters based on a pre-agreed ratio

Credit Flow

• Monthly solar generation: 50kW system generates approximately 5,500-6,500 units/month in Tamil Nadu
• Common area consumption: Typically 1,500-2,500 units/month (lifts, pumps, lighting, CCTV)
• Surplus for distribution: 3,000-5,000 units/month
• Per flat credit: 60-100 units/month (for 50 flats with equal allocation)

Impact on Individual Flat Owner's Bill

A flat consuming 300 units/month with a 80-unit solar credit:

• Without solar: 300 units consumed, bill approximately Rs.1,200-1,400
• With VNM credit: 300 - 80 = 220 units net consumption, bill approximately Rs.770-900
• Monthly savings per flat: Rs.400-500
• Annual savings per flat: Rs.4,800-6,000

---

Allocation Methods for Housing Societies

The society must decide how to distribute solar credits among participating flat owners. Three common models:

1. Equal Share

Every participating flat receives an equal share of the surplus credits.

• Example: 4,000 surplus units / 50 flats = 80 units per flat
• Best for: Apartments where all flats are the same size
• Advantage: Simple, transparent, easy to manage
• Disadvantage: Unfair if flat sizes vary significantly (a 3BHK subsidises a 1BHK)

2. Proportional to Flat Size (Super Built-Up Area)

Credits are distributed based on each flat's share of total built-up area.

• Example: A 1,500 sq ft flat in a complex with 75,000 sq ft total gets 2% of surplus credits
• Best for: Mixed-size apartments (1BHK, 2BHK, 3BHK in the same complex)
• Advantage: Fair — larger flats that typically consume more get more credits
• Disadvantage: More complex to calculate and explain

3. Proportional to Investment

Credits are distributed based on each flat owner's share of the solar system's cost.

• Example: Owner who contributed Rs.1,00,000 towards a Rs.25,00,000 system gets 4% of credits
• Best for: Societies where not all owners want to participate
• Advantage: Only investors benefit — no free riders
• Disadvantage: Creates a two-tier system within the society; requires tracking individual investments

Recommended Approach

For most Tamil Nadu apartment complexes, proportional to flat size is the fairest and most widely accepted model. It aligns with how maintenance charges are typically calculated, so residents are already familiar with the concept.

---

TANGEDCO Application Process for Group Net Metering

Prerequisites

1. Registered housing society or apartment owners' association
2. Society resolution approving solar installation and VNM arrangement
3. All participating flat owners' consent (signed consent forms)
4. Quotation from MNRE-approved solar vendor
5. Structural feasibility report for terrace installation

Application Steps

1. Society resolution: Pass a resolution in the general body meeting or managing committee meeting approving:

   • Installation of solar system on common terrace
   • Budget allocation or funding mechanism
   • Credit allocation method
   • Maintenance responsibility assignment

2. Vendor selection: Obtain quotations from at least 2-3 MNRE-approved vendors. Select based on equipment quality, installation track record, and warranty terms

3. TANGEDCO application: Submit application to the local TANGEDCO AE (Assistant Engineer) office with:

   • Society registration certificate
   • General body resolution copy
   • List of participating meters with service connection numbers
   • Proposed credit allocation ratio
   • Vendor quotation with technical specifications
   • Structural feasibility certificate
   • Roof ownership/access proof

4. Technical feasibility: TANGEDCO inspects the premises for:

   • Terrace structural adequacy
   • Electrical infrastructure compatibility
   • Transformer capacity in the area
   • Meter accessibility

5. Approval and agreement: TANGEDCO issues approval and the society signs a VNM agreement specifying the credit allocation

6. Installation and commissioning: The vendor installs the system and TANGEDCO installs bi-directional meters

7. Timeline: The entire process typically takes 45-90 days from application to commissioning

---

Cost Sharing Models for Housing Societies

Model 1: Society Fund

The society uses its corpus fund or maintenance reserve to pay for the solar system.

• Advantage: No individual collection needed; quick decision-making
• Disadvantage: Depletes reserves; may face opposition from owners who do not see immediate benefit
• Best for: Well-funded societies with healthy reserves

Model 2: One-Time Collection

A one-time special contribution collected from all participating flat owners.

• Per-flat cost example: Rs.25,00,000 system / 50 flats = Rs.50,000 per flat
• Advantage: Clear investment-return calculation for each owner
• Disadvantage: Some owners may refuse to participate
• Best for: Societies where most owners are resident (not tenanted)

Model 3: Monthly EMI Model

The society takes a loan or arranges vendor financing, repaid through a monthly solar surcharge on maintenance.

• Monthly surcharge example: Rs.800-1,200 per flat for 36-48 months
• Advantage: No large upfront payment; monthly surcharge is offset by electricity savings from month one
• Disadvantage: Interest costs; longer payback period
• Best for: Societies where owners are price-sensitive about large one-time payments

Model 4: RESCO (Rental/PPA) Model

A solar company installs the system at zero cost to the society and sells the generated electricity at a rate lower than TANGEDCO's tariff.

• PPA rate: Typically Rs.3.50-4.50/unit (vs TANGEDCO's Rs.4.60-8.05/unit)
• Contract period: 15-25 years
• Advantage: Zero investment by society; immediate savings; maintenance included
• Disadvantage: Lower savings than ownership model; long-term contract; system ownership remains with RESCO provider
• Best for: Societies that want zero risk and zero investment

---

Common Area Solar: Immediate Benefits

Even before VNM credit distribution, the solar system directly powers common area loads:

Typical Common Area Loads in a 50-Flat Apartment

Load	Quantity	Power (kW)	Daily Hours	Daily Units
Lifts	2	7.5 each	6	90
Water pump (borewell)	1	5.0	4	20
Water pump (sump to OHT)	1	3.0	3	9
Corridor and staircase lighting	40 points	0.6 total	12	7.2
Parking area lighting	20 points	0.4 total	12	4.8
CCTV system	1	0.2	24	4.8
Intercom system	1	0.1	24	2.4
STP (sewage treatment)	1	2.0	8	16
Total				154 units/day

Monthly common area consumption: approximately 4,600 units Monthly common area EB bill: Rs.35,000-45,000 (at commercial tariff rates)

A 50kW solar system generating 5,500-6,500 units/month can fully offset common area consumption and still have 900-1,900 units surplus for VNM distribution — or directly reduce maintenance charges by Rs.35,000-45,000/month.

---

Challenges and How to Address Them

Roof Ownership and Access

• Challenge: In many apartments, the terrace is technically common property but may have informal usage by top-floor residents
• Solution: Society resolution clearly designating the solar zone as common area; compensate top-floor residents if they lose usable terrace space

Committee Approval and Owner Consensus

• Challenge: Getting majority approval in a diverse owner group
• Solution: Present clear financial analysis showing per-flat savings and payback. Start with common area solar (which directly reduces maintenance) as it is easier to approve than VNM

Maintenance Responsibility

• Challenge: Who cleans panels, monitors generation, handles repairs?
• Solution: Include an Annual Maintenance Contract (AMC) in the vendor agreement (typically Rs.5,000-8,000/year for a 50kW system). Assign maintenance monitoring to one committee member

Tenant vs Owner Benefit

• Challenge: Tenants benefit from reduced EB bills but did not invest. Owners who rent out their flats see no direct benefit
• Solution: Factor solar benefit into rent pricing; or allocate credits only to owner-occupied flats and redirect rented flats' share to common area savings

---

Case Example: 50-Flat Apartment in Chennai with 50kW System

Project Specifications

• Location: OMR, Chennai
• Apartments: 50 flats (20 x 2BHK, 30 x 3BHK)
• System size: 50kW (125 panels x 400W)
• Terrace area used: 4,500 sq ft
• Total cost: Rs.27,00,000
• Funding: One-time collection (Rs.54,000 per flat)

Monthly Performance

• Solar generation: 5,800 units/month (average)
• Common area consumption offset: 4,200 units/month
• Common area bill savings: Rs.34,000/month
• Surplus for VNM distribution: 1,600 units/month
• Per-flat VNM credit: 32 units/month (equal allocation)

Financial Returns

• Monthly maintenance reduction: Rs.680/flat (from common area savings)
• Monthly EB bill reduction: Rs.200-250/flat (from VNM credits)
• Total monthly benefit per flat: Rs.880-930
• Annual benefit per flat: Rs.10,500-11,200
• Payback per flat: Rs.54,000 / Rs.10,850 = 5.0 years
• 25-year benefit per flat: Rs.2,70,000+ (accounting for tariff increases)

---

Alternative: Individual Balcony Solar (Limited but Possible)

For flat owners who cannot wait for society-level decisions, individual balcony solar panels are an emerging option:

• Capacity: 400W-1kW (1-3 panels on balcony railing or wall mount)
• Generation: 40-120 units/month
• Cost: Rs.25,000-60,000
• Connection: Plug-in micro-inverter connected to a regular socket (no net metering)
• Limitation: Cannot export to grid; only offsets real-time consumption while panels are generating
• Best for: Reducing daytime consumption (when WFH, running AC during afternoon)

This is a stopgap measure, not a replacement for a proper rooftop VNM system. But for apartments where society-level solar is years away, it provides immediate (if modest) savings.

---

Getting Started: Next Steps for Your Apartment Society

1. Gauge interest: Informally survey flat owners about solar interest. You need a majority for the society resolution
2. Calculate potential: Use our solar calculator to estimate generation based on your terrace area and flat count
3. Request a proposal: Contact our team for a customised proposal including system design, cost breakdown, per-flat savings calculation, and TANGEDCO application assistance
4. Present to society: We provide presentation materials that make it easy to explain the financial case to your fellow owners
5. Decide and execute: Once approved, the installation process takes 2-3 weeks; TANGEDCO commissioning takes an additional 4-6 weeks

Virtual net metering transforms apartment solar from impossible to practical. If your housing society has a common terrace and a willing committee, solar is no longer just for independent house owners.