Understanding Solar ROI
Solar ROI estimates how the financial benefits of a solar project compare with its total cost over time. The result depends on system cost, electricity tariff, generation, financing, maintenance, applicable incentives and the billing framework.
Financial effects to model
Electricity Bill Savings
Solar can reduce electricity purchased from the grid, creating bill savings rather than investment income. The financial and tax treatment depends on the consumer and project structure; business users should obtain appropriate tax advice.
Long-term operating results
Solar projects can generate recurring electricity savings over a long operating life, but actual outcomes vary with generation, equipment performance, tariffs, maintenance, downtime and regulatory changes.
Tariff assumptions
If grid tariffs rise over time, the value of electricity offset by solar may also increase. Because future tariff changes are uncertain, tariff escalation should be treated as an assumption rather than a guaranteed source of higher returns.
Project-specific risks
Financing cost, equipment replacement, degradation, curtailment, credit treatment and changes to applicable rules can materially change the result.
Common evaluation metrics
Simple ROI
Cumulative net benefit divided by total cost. State the time period and whether values are nominal or discounted.
Net Present Value
Discounts future cash flows to today and subtracts initial cost. The selected discount rate materially affects the result.
Internal Rate of Return
The discount rate at which project NPV equals zero. It requires a complete, dated series of project cash flows.
Simplified residential example
Suppose a qualifying rooftop project has a net customer cost of ₹1,32,000 and first-year bill savings of ₹36,450. The simple first-year benefit-to-cost ratio is ₹36,450 ÷ ₹1,32,000, or about 27.6%. This is an educational one-year ratio, not an IRR or forecast. A full analysis must include later-year generation, tariffs, maintenance, financing, replacements and applicable credit rules.
For Lumifly's current planning assumptions, formulas and exclusions, see the Solar Calculator Methodology. Those calculator assumptions do not automatically govern every India-wide example on this page.
Commercial solar requires business-specific modelling
Commercial solar economics can differ significantly from residential systems because tariffs, load profiles, financing, depreciation treatment and project scale vary by business. Commercial users should model the project using their actual tariff, consumption profile, tax position and project quotation.
Managed or Managed Solar: Different Economics
Where a managed or managed-solar arrangement uses a subscription or participation fee rather than a conventional equipment purchase, traditional project IRR may not be the most useful measure. Instead, compare the total fees paid with the value of eligible electricity credits or bill savings over the same period.
Illustrative same-period cash flow
If a customer pays ₹1,500 in a month and receives ₹2,340 of eligible bill credits during that same month, the illustrative net benefit would be ₹840 for that billing period. Actual credits, fees and savings depend on project terms, generation and the applicable DISCOM and regulatory framework.
How Lumifly estimates solar economics
Lumifly's planning examples use explicit assumptions for generation, tariff, project cost, maintenance and subsidy treatment. Financial examples are educational and should not be treated as guaranteed outcomes.
See calculation methodology →