Capex solar means the factory or commercial owner buys the plant. Opex or PPA solar means another party finances or owns the plant and the consumer pays under a contract. The right choice depends on cash flow, roof control, risk appetite, lender comfort and the quality of the contract.
Both models can work in India. Both can also disappoint if the proposal ignores demand charges, export limits, roof issues or future business changes. The decision is not only “pay now” versus “pay monthly”. It is a risk allocation decision.
What does capex solar give the owner?
Capex gives ownership. The owner pays for the system, claims the benefit of generation and carries operating responsibility through EPC warranties and maintenance contracts. This model suits businesses that have cash or financing capacity and want long-term control.
Capex can be attractive when:
- The roof is owned or securely controlled.
- The business expects to operate at the site for a long time.
- Internal finance is comfortable with the investment.
- The owner wants direct control over EPC quality and O&M.
- The bill has enough daytime load to absorb generation.
The risk is also direct. If generation is lower than expected, maintenance is weak, approvals are delayed or the plant is underused, the owner carries the impact.
What does an opex or PPA model change?
In an opex or PPA model, the provider usually invests in the plant and recovers money through a tariff or service payment. This can reduce upfront cash pressure. It also shifts some technical responsibility to the provider.
But it adds contract risk. The owner must understand:
- Tariff and escalation clauses.
- Minimum consumption or deemed generation terms.
- Tenure and termination conditions.
- Roof rights and access obligations.
- Insurance and damage responsibility.
- Metering and settlement process.
- What happens if the site shuts, shifts or changes load.
A low quoted solar tariff is not enough. The full contract decides whether the model is sensible.
Why do solar payback calculations mislead owners?
Solar savings are often shown against a simple unit rate. That shortcut can mislead. A factory bill includes demand charges, ToD treatment, PF or kVAh effects, duties, surcharges and sometimes export or banking rules. Solar may reduce imported daytime units but not every bill line.
Before choosing capex or PPA, test the assumptions:
| Assumption | Question |
|---|---|
| Daytime load | Will the site consume generation when the sun is available? |
| Demand charges | Which demand costs remain after solar? |
| Export treatment | How will surplus energy be credited or settled? |
| Tariff changes | Who carries future tariff movement risk? |
The article on solar payback mistakes in India is worth reading before any finance model is accepted.
How do lenders and accounts teams view the decision?
Accounts and lenders look at cash flow, obligations and evidence. Capex creates an asset and financing need. PPA creates a long-term payment commitment. Both affect how the business explains power expense.
Finance teams usually ask:
- What is the baseline electricity expense?
- What saving is assumed and how is it verified?
- What happens in low-production months?
- Who owns maintenance and downtime risk?
- Are roof rights and approvals clean?
- Is there any termination liability?
The article on CA and lender questions on power expense fits this discussion. A solar decision should survive finance review, not only engineering enthusiasm.
When does capex still win?
Capex can win when the owner has stable operations, secure roof rights, good daytime load and the ability to manage EPC selection. It also suits owners who dislike long-term tariff commitments to another party.
Capex may be weaker when cash is tight, the roof is leased, the site future is uncertain or internal maintenance discipline is poor. In those cases, a PPA may reduce execution burden, provided the contract is fair.
When does opex or PPA make more sense?
Opex can make sense when the business wants solar savings without upfront investment, or when a professional owner-operator can manage plant performance better. It may also help tenant factories if roof rights and landlord permissions are handled clearly.
Be careful where:
- The business may move.
- Roof access is contested.
- Future expansion may need the same roof.
- The contract has unclear escalation.
- The provider’s performance obligation is weak.
A PPA is a contract, not only a solar plant. Read it like a finance and operations document.
Tips from the field
- Compare capex and PPA on bill impact, cash flow and contract risk, not only quoted solar tariff.
- Ask who carries generation shortfall risk during poor maintenance, shading or inverter downtime.
- Check roof ownership, waterproofing access and future expansion before signing any long-term solar agreement.
- Model demand charges separately because rooftop solar may not remove the billing demand line.
- Ask lenders or CAs how the payment or asset will be treated before final approval.
- Keep a post-install proof plan using bills and generation reports so the saving remains visible.
How should the final choice be made?
Start with solar sizing from electricity bills, roof reality and load profile. Then compare capex and PPA using the same generation assumption, bill logic and risk notes. If the same assumption is not used, the comparison is unfair.
The better option is the one the business can live with through monsoon, maintenance, tariff changes and production changes. Solar is a long operating decision. Choose the model that matches the owner’s balance sheet and patience.