Solar Calculator India: Sizing, Subsidy & 25-Year ROI
Calculate your exact rooftop solar panel requirement (kW), shadow-free terrace area (sq ft), PM Surya Ghar Central CFA subsidy (up to ₹78,000), state top-ups, net system investment, and SBI 7.00% green loan EMI.
To calculate solar capacity in India: System Size (kW) = Monthly Units (kWh) ÷ (30 days × Daily Sun Hours [4.8–5.5] × Performance Ratio 0.78). Each kilowatt requires ~90 sq ft of shadow-free RCC roof and generates ~120–140 units/month. For a standard home using 350 units/month (electricity bill ₹2,800–₹3,800), an optimal system is 3 kW, costing ₹2,00,000 gross − ₹78,000 subsidy = ₹1,22,000 net, yielding a 3.2-year capital payback.
Solar Calculator Sizing & Subsidy Ready-Reckoner Table (1kW to 10kW)
Turnkey benchmark costs, MNRE PM Surya Ghar DBT subsidies, monthly generation, bill savings, and SBI 7% green loan EMI for Indian households.
| System Size | Terrace Area | Monthly Generation | Gross Cost | Central Subsidy | Net Price | Monthly Savings | SBI 7% EMI | Payback |
|---|---|---|---|---|---|---|---|---|
| 1 kW | 100 sq ft | ~125 units | ₹75,000 | -₹30,000 | ₹45,000 | ~₹850 | ~₹680/mo | 4.4 Yrs |
| 2 kW | 180 sq ft | ~250 units | ₹1,40,000 | -₹60,000 | ₹80,000 | ~₹1,800 | ~₹1,208/mo | 3.7 Yrs |
| 3 kW | 280 sq ft | ~380 units | ₹2,00,000 | -₹78,000 | ₹1,22,000 | ~₹2,950 | ~₹1,842/mo | 3.2 Yrs |
| 5 kW | 450 sq ft | ~630 units | ₹3,20,000 | -₹78,000 | ₹2,42,000 | ~₹5,100 | ~₹3,654/mo | 3.7 Yrs |
| 7 kW | 650 sq ft | ~880 units | ₹4,40,000 | -₹78,000 | ₹3,62,000 | ~₹7,400 | ~₹5,466/mo | 3.9 Yrs |
| 10 kW | 900 sq ft | ~1260 units | ₹6,10,000 | -₹78,000 | ₹5,32,000 | ~₹10,800 | ~₹8,033/mo | 4 Yrs |
The Engineering & Financial Formula Behind SolarCalculator24
Capacity (kW) = Monthly Consumption (kWh) ÷ (30 × Sun_Hours × 0.78)Where Sun Hours ranges from 4.7 to 5.6 across Indian states, and 0.78 represents the standard balance-of-system Performance Ratio (accounting for inverter conversion losses, dust soiling, wiring drop, and temperature derating).
LCOE (₹/unit) = Total 25-Year Lifecycle Cost ÷ 25-Year GenerationRooftop solar electricity costs only ~₹1.80 per unit over 25 years. Compared to DISCOM grid tariffs of ₹7.00 to ₹17.80/unit, solar delivers an immediate 75% to 90% cost reduction on every kilowatt-hour generated.
Older polycrystalline panels degrade at 1.0%/year, and Mono PERC at 0.70%/year. SolarCalculator24 defaults to next-generation N-Type TOPCon panels with only 0.55% annual degradation and a guaranteed 87.4% output retention at year 25.
Payback (Years) = Net System Cost ÷ Annualized Bill SavingsNet System Cost equals Gross Turnkey Benchmark minus Central CFA Subsidy minus State Top-Up. The payback period factors in annual grid tariff inflation (3% conservative escalator).
Frequently Asked Questions: Solar Calculator & Sizing
How does the SolarCalculator24 algorithm calculate solar panel requirements?
The calculator takes your monthly electricity bill, isolates state-specific fixed charges and electricity duty, and calculates total monthly kilowatt-hours (kWh) consumed. It then applies the MNRE solar insolation factor (averaging 4.8 to 5.5 peak sun hours depending on your state) and a Performance Ratio (PR) of 0.78 to determine the exact system kilowatt (kW) capacity needed to offset up to 90% of your bill.
How much rooftop area is required for a 3kW solar panel system in India?
Modern high-efficiency N-Type TOPCon or Mono PERC solar panels (550W+ capacity) require approximately 80 to 90 square feet of shadow-free terrace area per kilowatt. Therefore, a 3 kW solar installation requires between 250 and 280 square feet of unshaded rooftop area.
How much electricity will a 3kW solar system generate per day and per month?
In India, a 3 kW rooftop solar system generates an average of 12 to 14 units (kWh) of electricity per day, which amounts to approximately 360 to 420 units per month, and over 4,400 to 4,800 units annually.
How does the PM Surya Ghar government subsidy apply in the calculator?
The calculator automatically deducts the official Ministry of New and Renewable Energy (MNRE) Direct Benefit Transfer (DBT) subsidy: ₹30,000 for 1kW, ₹60,000 for 2kW, and ₹78,000 for 3kW or higher. In states like Uttar Pradesh, it also includes the ₹30,000 UPNEDA top-up (total ₹1,08,000).
What is the typical payback period for a rooftop solar system?
In states with high residential electricity tariffs like Maharashtra, payback is reached in just 2.6 to 2.8 years. In states like Gujarat, Rajasthan, Karnataka, and Delhi, payback averages 3.1 to 3.4 years. After this payback period, your solar panels generate free electricity for the remainder of their 25-year guaranteed lifespan.
Ready to Simulate Your Home's 25-Year Solar Savings?
Enter your monthly bill amount or upload your power bill PDF/image to get an instant customized engineering audit with DCR TopCon panel pricing.