Solar Rooftop Savings & ROI Calculator India 2026
Rooftop solar turns an unused terrace into a power source that offsets domestic grid electricity. Under the central PM Surya Ghar: Muft Bijli Yojana, eligible Indian households receive direct bank subsidies up to ₹78,000 for installing grid-tied systems up to 3 kW. In most parts of India, 1 kW of solar capacity generates roughly 4.0 to 4.5 units (kWh) of electricity daily, producing 120 to 135 units every month. Because daytime electricity feeds household appliances directly while surplus exports through a bi-directional net meter, expensive high-tier consumption slabs drop significantly. Factoring in equipment costs, central subsidies, and local electricity board slab rates, a typical 3 kW residential setup recovers its initial investment within 3.5 to 4.5 years, generating free power for the remaining 20 years of its panel warranty.
Direct Benefit Transfer (DBT) into consumer bank accounts: ₹30,000 for 1 kW, ₹60,000 for 2 kW, and maximum ₹78,000 for ≥3 kW residential rooftop systems.
Need your exact state tariff with domestic slabs & duty?
Compare your solar rooftop generation directly against state DISCOM domestic telescopic slabs (TNEB, KSEB, BESCOM, MSEDCL, UPPCL, WBSEDCL, etc.).
How to Use the Solar Rooftop Savings Estimator
Choose Solar System Capacity
Select 1 kW for homes consuming under 120 units monthly, 2 kW for 2-bedroom homes using 200 to 250 units, or 3 kW to claim the maximum ₹78,000 central subsidy and cover high summer cooling loads.
Estimate Available Shadow-Free Roof Area
Verify unobstructed terrace space facing south. Modern 540W mono-PERC panels require roughly 80 to 100 square feet per kilowatt of installed capacity.
Verify Regional Daily Sun Hours
Most Indian states average 4.5 to 5.0 effective peak sunshine hours daily across the year, accounting for monsoon cloud cover and clear winter conditions.
Input State Slab Rate & Net Metering Rules
Enter your DISCOM per-unit tariff (average domestic rates range from ₹6.50 to ₹8.50 per unit) to calculate monthly generation, avoided slab charges, net subsidy support, and simple payback timeline.
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Solar Rooftop Generation Physics and ROI Formulas
Solar panel energy output depends on installed capacity, local solar irradiance, and system loss factors. A standard rooftop setup operates with a Performance Ratio (PR) of 75% to 80%, accounting for inverter conversion losses (3%), summer heat degradation (8% to 10%), dust accumulation (4%), and wiring resistance (2%).
Daily Solar Generation (kWh) = System Capacity (kW) × Peak Sun Hours (h/day) × Performance Ratio (0.78)
Monthly Units Generated = Daily Solar Generation × 30 Days
Monthly Bill Savings (₹) = Monthly Units Generated × Avoided Grid Tariff Slab Rate (₹/kWh)
Net Consumer Out-of-Pocket Cost (₹) = Total EPC Installation Cost − PM Surya Ghar Central Subsidy
Simple Payback Period (Years) = Net System Cost ÷ Annual Financial Savings
Residential Rooftop Solar Benchmark: Sizing, Subsidies & Payback (1 kW to 5 kW)
Calculations reflect average tier-1 mono-PERC installations, MNRE PM Surya Ghar subsidy rules, and ₹7.00 per unit grid tariff.
| Capacity | Roof Area | Daily Units | Monthly Units | Gross Cost | Govt Subsidy | Net Cost | Monthly Saving | Payback |
|---|---|---|---|---|---|---|---|---|
| 1 kW Plant | 80–100 sq ft | 4.2 kWh | 126 u | ₹65,000 | ₹30,000 | ₹35,000 | ₹882 | 3.3 Years |
| 2 kW Plant | 160–200 sq ft | 8.4 kWh | 252 u | ₹1,25,000 | ₹60,000 | ₹65,000 | ₹1,764 | 3.1 Years |
| 3 kW Plant | 240–300 sq ft | 12.6 kWh | 378 u | ₹1,80,000 | ₹78,000 | ₹1,02,000 | ₹2,646 | 3.2 Years |
| 4 kW Plant | 320–400 sq ft | 16.8 kWh | 504 u | ₹2,35,000 | ₹78,000 (Capped) | ₹1,57,000 | ₹3,528 | 3.7 Years |
| 5 kW Plant | 400–500 sq ft | 21.0 kWh | 630 u | ₹2,85,000 | ₹78,000 (Capped) | ₹2,07,000 | ₹4,410 | 3.9 Years |
Real-World Rooftop Solar Case Studies Across India
2 kW On-Grid System on Independent Terrace
• Prior Monthly Consumption: ~240 Units (₹1,750 bill)
• Solar Generation: 8.4 units/day (252 units/month)
• Net Bill: Fixed charges only (~₹180 to ₹220/month)
• Net Installation Cost after Subsidy: ₹65,000
• Annual Savings: ~₹18,360 | Payback in 3.5 Years
3 kW Plant Maximizing Free Power & Subsidy
• Summer Consumption: 480 Units/month (₹3,400 bill)
• Solar Generation: 378 units/month
• Net Grid Import: 102 units (Qualifies for Delhi 200u subsidy!)
• Net Energy Bill: ₹0 (Zero Bill achieved!)
• Annual Savings: ~₹31,000 | Payback in 3.3 Years
3 kW Plant Offsetting ₹11/Unit Slabs
• Prior Consumption: 400 Units (MSEDCL tariff ₹11.50/u top slab)
• Monthly Avoided Cost: 378 units × ₹9.20 weighted avg = ₹3,477
• Net System Cost: ₹1,02,000 after ₹78,000 subsidy
• Annual Savings: ~₹41,700 | Payback in 2.5 Years!
2 kW System with Partial Afternoon Shade
• Tree shade reduces PR to 70% (7.2 units/day avg)
• Monthly Solar Output: ~216 Units
• Bi-monthly TANGEDCO Offset: 432 units eliminated
• Annual Savings: ~₹15,100 | Payback in 4.3 Years
5 Practical Guidelines Before Installing Rooftop Solar
- 1. Match tilt angle to your city latitude: South-facing panels tilted between 12° and 25° maximize solar irradiance across both summer and winter solstices in India.
- 2. Wash panels twice a month in early morning: Ambient dust and pollution build-up causes a 5% to 12% drop in generation. Clean with plain water before panels heat up in the sun.
- 3. Verify your sanctioned load before applying: Most DISCOMs mandate that solar plant capacity cannot exceed 80% to 100% of your sanctioned connected load in kW. Upgrade your load if necessary before submitting the net-metering application.
- 4. Budget for inverter replacement at year 8 to 10: While solar panels carry 25-year performance warranties, central string inverters typically have a working lifespan of 8 to 10 years and cost 15% to 20% of the original plant cost to replace.
- 5. Verify vendor empanelment on the National Portal: Central PM Surya Ghar subsidies are only disbursed when installation is completed by an MNRE-empanelled vendor using ALMM-listed (Approved List of Models and Manufacturers) domestic modules.