When a medium-sized textile mill owner in Tiruppur tells me his monthly TANGEDCO bill is ₹18–20 lakhs, I tell him: you do not have to pay that. Not all of it. Open access solar is how Tamil Nadu's smart industrial operators are cutting their electricity costs by 30–50% — not by reducing production, but by switching to a different source for a significant portion of their power.

This article explains exactly how open access solar works, who qualifies, what it costs to set up, and what the realistic savings look like for a typical large commercial or industrial consumer in Tamil Nadu.

What Is Open Access Solar?

Open access is a provision under the Electricity Act 2003 that allows large electricity consumers to purchase power from generators other than their local distribution company (DISCOM), using the existing electricity grid as the transmission pathway.

In simple terms: instead of buying all your power from TANGEDCO at HT (High Tension) tariff rates of ₹6.50–₹8.00/unit, you can contract directly with a solar power project developer who sells you power at ₹3.50–₹5.00/unit. The solar plant might be located 50–200 km away in a high-irradiance location (Tirunelveli, Thoothukudi, or Ramanathapuram districts are preferred for large solar farms in Tamil Nadu). The power travels through TANGEDCO's transmission network, and you pay TANGEDCO only for the wheeling service (using their wires), not for the power itself.

This is fundamentally different from rooftop solar, where the generation happens at your own premises. Open access works at a larger scale and serves consumers whose rooftop area is insufficient to meet their full demand.

Regulatory Framework: TNERC Open Access Regulations

Open access in Tamil Nadu is governed by:

Electricity Act 2003 (Central legislation) — establishes the right to open access
TNERC Open Access Regulations 2005 (as amended) — Tamil Nadu-specific implementation rules issued by the Tamil Nadu Electricity Regulatory Commission
TANGEDCO/TNTRANSCO as the wheeling agency
SLDC (State Load Despatch Centre) — manages scheduling and metering

Who Is Eligible?

Short-term open access: Consumers with 1 MW or higher sanctioned demand on HT connections. As of 2024, TNERC regulations allow short-term open access for periods from 15 minutes to 1 year.

Long-term open access: For contracted periods of more than 1 year, consumers must typically have 1 MW+ demand and enter into a formal Power Purchase Agreement (PPA) with the generator for a term of 10–25 years.

Practical reality in 2025: Most large industrial open access consumers in Tamil Nadu are in the 1–10 MW demand range — textile mills, auto component manufacturers, cement plants, cold chains, large data centres, and commercial complexes with significant HVAC loads.

The Costs: What You Pay to Use Open Access

Open access is not free wheeling. There are several charges stacked on top of the solar power tariff:

Charge	Description	Approximate Rate (Tamil Nadu, 2025)
Solar power tariff	Price you pay the solar generator	₹3.20–₹4.50/kWh (PPA-based, 25yr)
Transmission charges	TANTRANSCO's network usage fee	₹0.55–₹0.75/kWh
Wheeling charges	TANGEDCO distribution network	₹0.85–₹1.20/kWh
Wheeling losses	Energy adjustment for line losses	3–7% of units (varies by voltage level)
Cross-subsidy surcharge (CSS)	Paid to TANGEDCO; partially offsets subsidy cross-subsidisation	₹0.80–₹1.50/kWh
Additional surcharge	Applicable in some cases for stranded costs	₹0.00–₹0.40/kWh
Scheduling / SLDC charges	State Load Despatch Centre fees	₹0.02–₹0.05/kWh
Total landed cost	All-in cost of open access solar power	₹5.50–₹7.50/kWh

Compare this to TANGEDCO HT-1 tariff (general commercial/industrial, 2024–25): ₹7.50–₹9.50/kWh when you include demand charges, fuel surcharge adjustments, and other levies on the full bill.

Net saving: ₹1.50–₹3.50/kWh depending on consumer category and the specific charges applicable. For a factory consuming 5,00,000 units/month, this translates to ₹7.5 lakhs–₹17.5 lakhs per month in savings.

Banking Provisions

Tamil Nadu allows monthly banking of open access solar units under TNERC regulations. This means:

Solar generation injected into the grid during daytime (when your factory may be at partial load or when solar output exceeds your instantaneous consumption) is credited to your account
You can draw these credited units during night hours or on days when solar generation was low
Banking charges apply: approximately 2% of banked units as a banking fee in Tamil Nadu
Banking typically has a 30-day carry-forward limit — unused banked units at the end of the month may lapse or be paid at a low rate (approximately ₹2.00–₹2.50/unit buyback rate)

Implication for system sizing: Open access solar systems should be sized to ensure most banked units are consumed within the same billing month. Chronic over-generation relative to consumption reduces the effective realised savings.

Group Captive Model: An Alternative Structure

If you do not want to set up your own solar plant (which requires EPC costs, land, and developer expertise) but cannot find a third-party generator willing to set up specifically for your load, the Group Captive model is an increasingly popular middle path:

Under Group Captive:

A group of consumers collectively own at least 26% equity in a solar power project
They consume at least 51% of the project's output
The remaining equity and output can be sold to third parties
Group captive consumers are eligible for significantly reduced open access charges — the cross-subsidy surcharge is waived for captive consumers

Why this matters: The CSS (₹0.80–₹1.50/kWh) is one of the most significant charges on open access transactions. Eliminating it under the Group Captive structure can reduce total landed cost by an additional ₹0.80–₹1.50/kWh compared to a pure open access PPA.

Several solar developers in Tamil Nadu offer group captive participation to industrial consumers with as little as ₹25–₹50 lakhs of equity investment, providing proportional power offtake rights.

Process to Obtain Open Access Permission

Getting started on open access in Tamil Nadu involves a structured regulatory process:

Step 1: Identify a Solar Generator / Developer

Work with a reputable solar developer or advisory firm. Negotiate a draft PPA term sheet including tariff, escalation clause (if any — fixed tariffs are increasingly common for long-term PPAs), banking provisions, and metering responsibilities.

Step 2: Apply for Long-Term Open Access with TNERC

Submit the application to TNERC (for long-term open access above 1 year). Documents required:

Draft PPA with the generator
Latest TANGEDCO HT connection details (account number, sanctioned demand, consumption history)
Company registration documents
Technical study report (your energy consultant prepares this)

TNERC processing time: 60–90 days for most cases, subject to any clarifications sought.

Step 3: Obtain SLDC Scheduling Approval

Once TNERC grants in-principle approval, register with Tamil Nadu's SLDC for scheduling. Submit day-ahead generation schedules (your developer's SCADA system typically handles this automatically).

Step 4: Metering and Billing Changeover

TANGEDCO installs ABT (Availability Based Tariff) compatible energy meters at your premises. These record 15-minute interval data enabling accurate open access accounting. Your bill now has two components: TANGEDCO bill (demand charges + wheeling/transmission charges + any non-open-access consumption) and the solar developer's PPA invoice.

Total timeline from initiation to first open access unit: typically 4–8 months for a greenfield application in Tamil Nadu. Experienced consultants who handle the regulatory pathway can compress this.

Advantages Over Rooftop for Large Industrial Units

Aspect	Rooftop Solar	Open Access Solar
Scale	Limited by roof area (typically up to 1–2 MWp)	Essentially unlimited; 5 MW, 20 MW possible
Own land/roof required	Yes	No — generator's land is used
Generation profile dependency	Only daytime, weather-dependent at your location	Same weather dependency, but banking smooths this
Upfront capital required	High (own the asset)	Low (pay per unit under PPA) or equity stake in group captive
Balance of plant responsibility	Owner	Developer/generator
Subsidy eligibility	PM Surya Ghar and MNRE subsidies applicable	Not directly applicable to open access
Grid independence	Zero — fully grid-connected	Zero — fully grid-connected
Maximum practical saving vs TANGEDCO	60–80% of bill	30–50% of bill (after open access charges)

For a factory consuming 10 lakh units/month with an 8,000 sq.m roof, a 1 MWp rooftop system covers roughly 12–13 lakh kWh/year — about 10% of annual load. A 5 MW open access PPA could cover 60–65% of annual load. The two approaches are complementary, not mutually exclusive.

2024–25 Policy Context: Key Changes to Know

Cross-Subsidy Surcharge Revisions

TNERC revised its open access charges in 2023–24. The CSS for HT-1 consumers was adjusted upward slightly, which modestly reduced the savings advantage of open access. However, the fundamental economics remain strongly positive for consumers on tariff categories above ₹7/kWh.

Renewable Purchase Obligation (RPO)

Tamil Nadu's RPO trajectory (mandating that DISCOMs and large consumers procure a defined percentage of renewable energy) creates an additional compliance reason for large industrials to adopt open access solar. Failure to meet RPO targets results in penalties. Open access solar units purchased under PPA count toward the consumer's RPO compliance — an increasingly important consideration as RPO targets rise toward 43% by 2030 under national policy.

PM Surya Ghar Clarification

The PM Surya Ghar scheme (2024) focuses on residential rooftop and does not apply to open access commercial arrangements. Large industrial consumers do not benefit from PM Surya Ghar subsidies but may benefit from MNRE's PM KUSUM Component C for agricultural extensions.

Case Study: A 500 kW Factory in Tiruppur

Consider a mid-sized spinning mill in Tiruppur with the following profile:

Sanctioned demand: 1,200 kVA (approximately 1 MW)
Monthly consumption: 6,50,000 kWh
Current TANGEDCO HT-1 monthly bill: ₹49–₹52 lakhs
Open access solar PPA arrangement: 2 MWp solar project, 25-year PPA at ₹3.75/kWh, covering 3,00,000–3,50,000 kWh/month (approximately 50% of monthly consumption)

Monthly open access savings calculation:

Item	Per Unit	Monthly (3,25,000 kWh)
TANGEDCO HT-1 tariff (avoided)	₹8.20/kWh	₹26.65 lakhs
Open access solar PPA tariff	₹3.75/kWh	₹12.19 lakhs
Transmission + wheeling charges	₹1.70/kWh	₹5.53 lakhs
Cross-subsidy surcharge	₹1.20/kWh	₹3.90 lakhs
Other charges (banking, SLDC)	₹0.10/kWh	₹0.33 lakhs
Total open access cost	₹6.75/kWh	₹21.94 lakhs
Monthly savings	₹1.45/kWh	₹4.71 lakhs

Annual savings: approximately ₹56 lakhs. Over a 10-year PPA with nominal escalation, the cumulative savings exceed ₹6 crores — with zero capital investment from the factory (the developer owns and operates the solar plant).

Is Open Access Right for Your Business?

Open access is best suited for:

Industrial or commercial consumers with sanctioned HT demand of 1 MW or more
Operations running at 60%+ load factor (high monthly unit consumption relative to sanctioned demand)
Businesses with a stable, long-term commitment to their current location (25-year PPAs do not make sense for businesses that might relocate)
Consumers looking to meet CSR/ESG/sustainability targets through verifiable renewable energy procurement

Start Saving More on Your Electricity Bills

Open access solar is not a simple transaction — it involves regulatory approvals, generator selection, PPA negotiation, and metering changeover. But with the right advisory partner, the process is entirely manageable and the financial returns are compelling.

Tristar Green Energy Solutions advises large commercial and industrial consumers in Tamil Nadu on open access solar strategies, from initial feasibility analysis and developer shortlisting through to TNERC application support and post-commissioning monitoring. Our team is based in Coimbatore and has worked with manufacturers, hospitals, educational institutions, and commercial complexes across the state.

If your monthly electricity bill is above ₹5 lakhs, contact us for a free open access feasibility analysis — we will tell you honestly whether it makes sense for your specific situation and what savings you can realistically expect.

Open Access Solar: Benefits for Commercial Users