Solar PPA (Power Purchase Agreement): How It Works for TN Businesses

A Solar Power Purchase Agreement (PPA) allows businesses to go solar with zero upfront investment. Instead of buying a solar system, you buy the electricity it produces — at a rate lower than what you pay TANGEDCO. For many Tamil Nadu businesses, this is the simplest path to reduced electricity costs. This guide explains exactly how solar PPAs work, what the contract terms mean, and how to evaluate whether a PPA is the right model for your company.

What Is a Solar PPA?

A Solar Power Purchase Agreement is a contract between a business (the consumer) and a solar developer (the producer). The developer installs, owns, and maintains a solar system on your rooftop or premises. You agree to purchase the electricity generated at a pre-agreed tariff for a fixed period — typically 15 to 25 years.

The core proposition:

• You pay: A fixed per-unit rate for solar electricity (lower than TANGEDCO tariff)
• Developer pays: All capital costs, installation, insurance, and maintenance
• You provide: Rooftop space and a long-term purchase commitment

Think of it as renting out your roof in exchange for cheaper electricity.

How the PPA Model Works: Step by Step

1. Site assessment and system design

The solar developer surveys your rooftop, analyses your electricity consumption patterns, and designs a system sized to offset a portion of your TANGEDCO bill. Most PPA systems are designed to cover 50–80% of your daytime consumption.

2. Contract negotiation

The PPA contract specifies:

• Tariff rate: The per-unit price you pay for solar electricity (typically Rs 3.00–4.50 per unit)
• Escalation clause: Annual increase in tariff (typically 1–3% per year)
• Contract duration: Usually 15–25 years
• Minimum offtake: Some contracts require you to purchase a minimum amount of generated electricity
• Termination clauses: Conditions under which either party can exit

3. Installation and commissioning

The developer handles everything — procurement, installation, TANGEDCO approvals, net metering setup. You provide site access and any necessary permissions.

4. Electricity generation and billing

Once operational, you consume the solar electricity first. Any excess is exported to the grid under net metering. The developer bills you monthly for the solar units consumed at the agreed PPA rate.

5. Maintenance and monitoring

The developer is responsible for all maintenance — cleaning, repairs, inverter replacements, monitoring — for the contract duration. Your only obligation is paying for the electricity consumed.

PPA Tariff vs. TANGEDCO Tariff: The Savings Math

The financial advantage of a PPA comes from the gap between the PPA tariff and your TANGEDCO tariff.

Consumer Type	TANGEDCO Tariff (2026)	Typical PPA Tariff	Savings per Unit
Commercial (LT3)	Rs 6.35–7.50	Rs 3.50–4.50	Rs 2.00–3.50
Industrial LT (LT4/5)	Rs 5.75–6.50	Rs 3.00–4.00	Rs 1.75–3.00
Industrial HT	Rs 5.50–7.00	Rs 2.80–3.80	Rs 1.70–3.20

Example: Commercial establishment

A commercial office consuming 5,000 units per month at Rs 6.75 per unit installs a 50 kW PPA system generating approximately 5,500 units per month.

• Without solar: 5,000 x Rs 6.75 = Rs 33,750/month
• With PPA (80% self-consumption at Rs 4.00): 4,400 x Rs 4.00 + 600 x Rs 6.75 = Rs 17,600 + Rs 4,050 = Rs 21,650/month
• Monthly savings: Rs 12,100
• Annual savings: Rs 1,45,200

Over 20 years, even with a 2% annual escalation in PPA tariff and a 5% annual increase in TANGEDCO tariff, the cumulative savings can exceed Rs 40–50 lakhs for a mid-sized commercial consumer.

Key Contract Terms to Negotiate

Tariff escalation

This is the most critical clause. A PPA with a low starting tariff but 5% annual escalation will become expensive within 8–10 years. Aim for:

• Ideal: 0–1.5% annual escalation
• Acceptable: 1.5–3% annual escalation
• Avoid: More than 3% annual escalation

Compare the escalated PPA tariff against projected TANGEDCO tariff increases. TANGEDCO tariffs have historically increased 3–6% annually, so a PPA with 1–2% escalation maintains its advantage over time.

Performance guarantee

A good PPA contract includes a minimum generation guarantee — typically 1,400–1,500 units per kW per year for Tamil Nadu. If the system underperforms, the developer should compensate you (usually as a credit or tariff reduction).

Insurance and force majeure

The developer should carry comprehensive insurance covering equipment damage, natural disasters, and theft. Understand what qualifies as force majeure and how it affects your obligations.

Termination and buyout options

Most PPAs include:

• Early termination fee: A penalty for exiting before the contract ends (often the remaining value of the system)
• Buyout option: The ability to purchase the system at depreciated value after a specified period (typically Year 7–10)
• End-of-contract transfer: What happens at contract end — does the system transfer to you, get removed, or does the contract renew?

Negotiate for: A buyout option at fair market value after Year 7, and automatic ownership transfer at contract end.

Rooftop lease terms

Since the developer's equipment sits on your roof, the contract will include rooftop lease provisions. Key points:

• You generally cannot make rooftop modifications that affect the solar system
• The developer has access rights for maintenance
• If you sell the property, the PPA obligation typically transfers to the new owner (this should be clearly stated)

PPA vs. Other Solar Models

Factor	PPA (Zero Upfront)	CAPEX (Self-Owned)	Solar Loan
Upfront cost	Zero	Rs 45,000–55,000 per kW	Low (EMI)
Per-unit savings	Moderate (Rs 2–3.50)	Maximum (Rs 4–6)	Good (Rs 3–5 after EMI)
Maintenance responsibility	Developer	You	You
System ownership	Developer (until contract end)	You (from Day 1)	You (from Day 1)
Tax benefits (depreciation)	Developer claims	You claim (40% AD)	You claim
Contract lock-in	15–25 years	None	Loan tenure (5–8 years)
Best suited for	Cash-conservative businesses	Businesses wanting max ROI	Homeowners, SMEs

When a PPA makes sense

• You want to reduce electricity costs with zero capital expenditure
• Your business prefers operating expenses (OPEX) over capital expenses (CAPEX)
• You do not want the hassle of system maintenance and monitoring
• You are a tenant or lessee with a long remaining lease period (matching PPA duration)
• Your company cannot fully utilise accelerated depreciation benefits

When self-ownership is better

• You have available capital or can access low-interest solar loans
• Your business can benefit from 40% accelerated depreciation in Year 1
• You want maximum per-unit savings and fastest payback
• You prefer no long-term contractual obligations

Common PPA Pitfalls in Tamil Nadu

1. Overlooking the escalation clause

A 3% annual escalation on a Rs 4.00 starting tariff reaches Rs 7.22 per unit by Year 20. If TANGEDCO tariffs do not rise proportionally, your PPA may become more expensive than grid power in later years.

2. Inadequate performance guarantees

Some developers offer vague generation promises. Insist on specific annual kWh guarantees with measurable penalties for shortfalls.

3. Roof structural requirements

The developer will assess your roof, but ensure this assessment is thorough. If structural reinforcement is needed, clarify who bears the cost — it should be the developer.

4. Net metering complications

Under Tamil Nadu's current net metering policy, the TANGEDCO connection must be in the consumer's name. Ensure the PPA structure complies with TNERC regulations for third-party ownership with net metering.

5. Property sale complications

If you sell your property mid-contract, the PPA obligation transfers. This can complicate property transactions. Understand the transfer mechanism and any associated fees.

How to Evaluate PPA Proposals

When comparing PPA offers from multiple developers, create a standardised comparison on:

1. Year 1 tariff and escalation rate — calculate the effective tariff at Year 10 and Year 20
2. System size and guaranteed generation — units per kW per year
3. Equipment quality — panel and inverter brands, ALMM compliance
4. Maintenance SLA — response time, cleaning frequency, monitoring
5. Buyout terms — when and at what price you can purchase the system
6. Developer track record — installed capacity in Tamil Nadu, financial stability, references

Use our solar savings calculator to model the financial impact of different PPA tariffs against your current TANGEDCO consumption.

Next Steps

A Solar PPA can be a powerful tool for Tamil Nadu businesses looking to cut electricity costs without capital investment. But the 15–25 year commitment means the contract terms matter enormously.

Contact our team for a detailed PPA analysis based on your business's electricity consumption, roof specifications, and financial objectives. We will help you compare PPA offers against self-ownership and loan models to find the approach that delivers the best long-term value for your specific situation.