Model solar upfront cost, self-use savings, export credit, payback and NPV across three generation scenarios.
Each assumption moves 10% below and above your input. Ranked by the largest change from the expected result.
| Assumption | Lower case | Higher case | Largest movement |
|---|---|---|---|
| First-year solar generation | ₹2,35,634.61 | ₹3,66,525.38 | ₹65,445.39 |
| Starting grid tariff | ₹2,40,062.25 | ₹3,62,097.74 | ₹61,017.74 |
| Installed system cost | ₹3,31,079.99 | ₹2,71,079.99 | ₹30,000.00 |
Simple payback is undiscounted. ROI uses undiscounted lifetime net benefit divided by net upfront cost. Total cost of ownership is net CAPEX plus discounted operating cost, before energy benefits. NPV discounts annual net benefits. Financing, tax, downtime, component replacement and tariff-rule changes are excluded. Trust level: engineering estimate; verify site and equipment assumptions before purchase or installation.
| Scenario | First-year net benefit | Simple payback | NPV |
|---|---|---|---|
| Conservative | ₹35,320.00 | 7.79 years | ₹1,70,189.22 |
| Expected | ₹45,400.00 | 6.19 years | ₹3,01,079.99 |
| Optimistic | ₹55,480.00 | 5.14 years | ₹4,31,970.77 |
Method: annual benefit = self-used kWh × grid tariff + exported kWh × export tariff − annual operating cost
Inputs used: Year 1: 7200 kWh × (80% × 8 + 20% × 3) − 5000
Assumptions: Installed system cost Grant or subsidy Annual operating cost Generation used on site Starting avoided grid tariff Export credit Annual generation degradation Generation scenario spread Sensitivity range around each input
Scope and warnings: Simple payback is undiscounted. ROI uses undiscounted lifetime net benefit divided by net upfront cost. Total cost of ownership is net CAPEX plus discounted operating cost, before energy benefits. NPV discounts annual net benefits. Financing, tax, downtime, component replacement and tariff-rule changes are excluded.
National Renewable Energy Laboratory · PVWatts supported locations; use a location-specific model for a site estimate · effective PVWatts version 5 documentation · reviewed 2026-09-12
high confidence · Engineering estimate
Supports the transparent solar energy relationship and system-loss planning reference.
Exclusions: Not a structural, electrical or financing assessment. ToolMitra does not query PVWatts automatically.
Each year reduces generation by the entered degradation rate, escalates the avoided grid tariff, values self-used and exported energy separately, subtracts operating cost and discounts the resulting net benefit for NPV. Simple payback uses undiscounted cash flow.
A ₹3,00,000 system with 7,200 first-year kWh, 80% self-use, ₹8 avoided tariff, ₹3 export credit and ₹5,000 annual operating cost starts with about ₹45,400 net benefit before later escalation and degradation.
Simple payback answers when cumulative nominal benefits recover upfront cost. NPV also reflects timing and the selected discount rate. Either can change when tariff, self-use, export rules, maintenance or generation changes.
Calculations run on your device. Review your results before exporting or sharing them.
Self-used generation avoids the entered retail energy rate; exported generation earns only the export credit entered. Check bills and local rules before assuming those rates escalate together or remain available for the whole analysis period.
Payback ignores discounting while NPV includes it. Lifetime ROI uses undiscounted net benefit against net CAPEX, and total cost of ownership isolates upfront and discounted operating cost before energy benefits. Use the sensitivity table to see whether cost, production, tariff or operating cost moves NPV most; add financing, inverter replacement, tax and downtime externally when those amounts are material.
Published by ToolMitra — methods and editorial approach.