Quick Facts
What the OPEX model is
The OPEX model in solar is a business arrangement where a developer owns, installs, operates, and maintains a solar plant at the customer’s site, while the customer simply buys the generated electricity at a fixed per-kWh tariff. Also called the RESCO model (Renewable Energy Service Company) or zero-CAPEX model, OPEX requires no upfront capital outlay from the customer.
The model unbundles solar adoption into a service consumption rather than an asset purchase. The customer benefits from reduced electricity costs without taking on the technical, financial, or operational burden of owning a solar plant. The developer benefits from a stable long-term revenue stream and the tax incentives of solar asset ownership.
OPEX has become the dominant model for commercial and industrial solar adoption in India among customers without strong tax-paying profiles or without preference for asset ownership. Estimated 50% to 70% of new C&I rooftop solar installations in 2026 are structured as OPEX.
How the OPEX model works
The mechanics involve four stages.
Customer selection: The developer (RESCO) evaluates the customer’s electricity consumption profile, credit quality, roof area or land, and willingness to commit to a long-term PPA. Customer-side requirements include sufficient consumption to absorb the solar generation and adequate creditworthiness.
System design and financing: The developer designs the solar plant, arranges financing (mix of equity and debt), and arranges all approvals (DISCOM, net metering, structural).
Installation and commissioning: The developer installs the solar plant at the customer’s site. The customer’s role is limited to providing access, basic facilities, and approvals.
Operation and billing: For the PPA term (typically 15 to 25 years), the developer operates and maintains the plant. The customer is billed at the contracted tariff for the energy generated. The customer pays only for what the system actually produces.
At the end of the PPA term, ownership typically transfers to the customer (free or for nominal payment). Some contracts include buyout options at intermediate years.
Contract structure
A typical OPEX PPA includes:
Capacity and configuration: The size of the solar plant, technology used, and configuration.
Tariff: Fixed per-kWh price, often with annual escalation of 1% to 3%.
PPA term: Duration of the contract, typically 15 to 25 years.
Roof or land access: Terms under which the developer accesses the customer’s site.
Minimum offtake: The customer’s obligation to consume the energy generated (typically 80% to 90% of expected generation).
Buyout option: Conditions and price at which the customer can buy out the plant.
Performance guarantee: The developer’s commitment on plant availability and performance (typically 95% to 98% availability).
Force majeure and termination: Standard provisions.
Credit security: Bank guarantees, letters of credit, or escrow accounts to secure payments.
Change in law: Protection against regulatory changes affecting tariff or operations.
The PPA is typically a 50 to 200 page document drafted by experienced solar lawyers. Standardisation has improved through MNRE model PPAs and industry practice.
OPEX tariff economics
Indian OPEX rooftop solar tariffs in 2026 typically range:
| Customer Profile | PPA Term | Indicative Tariff (Rs/kWh) |
|---|---|---|
| Large corporate (5 to 50 MW) | 25 years | 3.50 to 4.20 |
| Mid commercial (500 kW to 5 MW) | 20 years | 3.80 to 4.50 |
| Small commercial (100 to 500 kW) | 15 to 20 years | 4.20 to 5.00 |
| Smaller commercial (under 100 kW) | 10 to 15 years | 4.50 to 5.50 |
| Government institutions | 10 to 25 years | 3.80 to 4.80 |
Compared to typical C&I grid tariffs of Rs 8 to Rs 12 per kWh, OPEX delivers 30% to 50% savings. Over a 25-year PPA, total savings can reach Rs 10 to Rs 25 lakh per kW installed, depending on grid tariff trajectory.
OPEX versus CAPEX
| Factor | OPEX | CAPEX |
|---|---|---|
| Upfront cost | Zero | Full system cost |
| Ownership | Developer | Customer |
| Tax benefits | Developer claims AD, GST input credit | Customer claims AD, GST input credit |
| O&M responsibility | Developer | Customer |
| Roof or land | Customer provides | Customer owns |
| Long-term IRR | Effective discount on grid power | Full project IRR (15% to 25% typical) |
| Risk | Developer takes performance and credit risk | Customer takes performance risk |
| Best for | Customers without capital or tax position | Taxable corporates with strong financials |
The choice depends on customer profile. A profitable corporate buyer with capital available usually does better on CAPEX. A government institution, a non-profit, or a financially constrained business usually does better on OPEX.
Common Indian OPEX players
The Indian OPEX solar market has grown significantly. Major RESCO operators in 2026 include:
CleanMax: One of the largest pure-play RESCO operators in India.
Amplus Solar: Significant rooftop OPEX presence.
Fourth Partner Energy: Focused on commercial and industrial OPEX.
ReNew: Large diversified renewable, with rooftop OPEX as one segment.
Tata Power Solar: Rooftop OPEX integrated with broader Tata Power presence.
Adani Green: Utility and rooftop with OPEX offerings.
Hero Future Energies: Rooftop and ground-mount OPEX.
Smaller players and integrators handle local and mid-size opportunities.
Common mistakes when entering OPEX
Comparing OPEX tariff in isolation without considering grid tariff escalation. Solar PPAs typically have lower escalation than grid tariffs, so the savings widen over time.
Signing a PPA without checking the developer’s financial strength and operational track record. A developer default mid-contract is a serious risk.
Not negotiating the buyout option carefully. The buyout price can range from book value to a premium, with significant impact on long-term cost.
Overlooking the minimum offtake clause. If the customer’s load reduces (say, due to business changes), they may be charged for energy they cannot consume.
Forgetting that AD and GST input credit benefits accrue to the developer, not the customer. The lower OPEX tariff already accounts for these.
Best practices
Evaluate OPEX versus CAPEX on a 25-year NPV basis, not just first-year cost.
Choose developers with strong financial credentials and operational track record.
Insist on clear performance guarantees and termination clauses in the PPA.
Include a buyout option, even if you do not plan to exercise it immediately. The optionality has value.
Verify the developer’s compliance with ALMM, MNRE empanelment, and BIS requirements.
For multi-site operations, consider aggregated OPEX deals with a single developer for volume discount.
Standards and references
OPEX PPAs are governed by the Electricity Act 2003, state SERC orders on rooftop solar net metering, and contract law under the Indian Contract Act. MNRE has issued model PPAs for various scheme structures. Industry associations such as Solar Power Developers Association (SPDA) and Indian Solar Manufacturers Association (ISMA) provide guidance documents.
Related glossary terms
- CAPEX Model
- RESCO Model
- Power Purchase Agreement
- Group Captive
- Accelerated Depreciation
- IRR
- Payback Period
- Open Access Solar
Key takeaways
The OPEX model in solar is a zero-CAPEX arrangement where the developer owns, installs, operates, and maintains the solar plant at the customer’s site, while the customer buys only the generated electricity at a fixed tariff. Indian OPEX tariffs typically range from Rs 3.50 to Rs 5.50 per kWh, delivering 30% to 50% savings versus grid power. OPEX is the dominant model for C&I rooftop solar in India in 2026 for customers without strong tax positions or capital availability. Tax benefits accrue to the developer, who passes some of the value to the customer through a lower tariff.