On-Grid Rooftop Solar Calculator for Indian Homes: System Size, Cost & Savings
Find out exactly how many kWp you need, your total cost after PM Surya Ghar subsidy, monthly bill savings, and your simple payback period — in seconds.
Free On-Grid Rooftop Solar Calculator — India 2025
Use the calculator below to get an instant estimate for your home. Enter your monthly electricity bill, your state, and available rooftop area — the tool does the rest.
The full interactive calculator is embedded below (or open the standalone tool for the best experience).
⚡ Open Full CalculatorHow to read the results: The calculator gives you a recommended system size in kWp (kilowatt-peak), the number of 400 Wp panels required, gross and net cost after subsidy, monthly savings in ₹, and a year-by-year payback visual across the 25-year panel life.
What Is an On-Grid Rooftop Solar System?
An on-grid solar system (also called a grid-tied solar system) is connected directly to your state electricity distribution company (DISCOM) network. Unlike off-grid systems that use batteries, on-grid systems feed surplus electricity back to the grid through a process called net metering.
How net metering works in India
When your panels generate more electricity than your home consumes, the excess units are exported to the grid and your DISCOM meter runs backwards (or records the export in a bidirectional smart meter). At the end of the billing cycle, you are billed only for the net units consumed — your import minus your export.
✅ Best suited for: Homes with a grid connection, a monthly electricity bill above ₹1,500, and at least 100 sq. ft of shadow-free south- or west-facing rooftop area.
On-grid vs off-grid: key differences
| Feature | On-Grid | Off-Grid |
|---|---|---|
| Batteries needed | No | Yes |
| Works during grid outage? | No (safety shutdown) | Yes |
| MNRE subsidy eligible | Yes | No |
| Cost per kWp (installed) | ₹45,000–₹65,000 | ₹80,000–₹1,20,000+ |
| Payback period | 4–7 years | 8–12 years |
| Ideal for | Urban homes with stable grid | Rural areas with frequent cuts |
How to Calculate Your Rooftop Solar System Size (kWp)
The most common mistake homeowners make is buying a system that is either too small (doesn't cover the bill) or too large (surplus that the DISCOM may not pay for under your net-metering policy). Here is the exact formula our calculator uses:
Step 1 — Find your monthly consumption in kWh
Divide your average monthly electricity bill by your per-unit tariff:
Monthly kWh = Monthly Bill (₹) ÷ Tariff (₹/kWh)
Example: ₹3,000 bill at ₹7/kWh → 428 kWh/month
Step 2 — Use peak sun hours (PSH) for your state
Peak sun hours represent the equivalent number of hours per day your location receives full 1,000 W/m² irradiance. This varies significantly across India — from 4.0 hrs in the Himalayas to 6.5 hrs in Rajasthan.
Step 3 — Account for system efficiency losses
No system is 100% efficient. Inverter conversion, wiring losses, soiling, and temperature de-rating typically bring effective system efficiency to around 75–82%. Our calculator uses a conservative 80%.
The system size formula
System Size (kWp) = Monthly kWh ÷ (PSH × 30 days × 0.80)
Example: 428 ÷ (5.5 × 30 × 0.80) = 3.24 kWp → round up to 3.5 kWp
⚠️ Rooftop area constraint: Each kWp of solar requires approximately 8–12 sq. ft of shadow-free area depending on panel efficiency. A 3.5 kWp system needs around 35–42 sq. ft minimum — but real installations need more space for gaps, walk-paths, and tilt frames. Plan for at least 100 sq. ft per kWp of total available rooftop.
How to Calculate Rooftop Solar Installation Cost in India (2025)
Solar prices in India have dropped dramatically over the last decade. As of 2025, the average all-inclusive installed cost for a quality on-grid system ranges from ₹45 to ₹65 per Watt-peak (Wp), depending on the brand, installer, inverter type, and roof structure.
What the installed cost includes
- Solar panels (monocrystalline PERC or TOPCon, 400–550 Wp each)
- String inverter or microinverters (MNRE-approved brands)
- Mounting structure (GI or aluminium, with wind load compliance)
- DC and AC wiring, cable trays, combiner boxes
- Net meter application, DISCOM approval fees
- Installation labour and commissioning
- 5-year AMC (Annual Maintenance Contract) — check with your installer
Indicative cost by system size (before subsidy)
| System Size | Panels (400Wp) | Budget (₹45/Wp) | Standard (₹55/Wp) | Premium (₹70/Wp) |
|---|---|---|---|---|
| 1 kWp | 3 | ₹45,000 | ₹55,000 | ₹70,000 |
| 2 kWp | 5 | ₹90,000 | ₹1,10,000 | ₹1,40,000 |
| 3 kWp | 8 | ₹1,35,000 | ₹1,65,000 | ₹2,10,000 |
| 5 kWp | 13 | ₹2,25,000 | ₹2,75,000 | ₹3,50,000 |
| 10 kWp | 25 | ₹4,50,000 | ₹5,50,000 | ₹7,00,000 |
💡 Pro tip: Get at least 3 quotes from MNRE-empanelled installers. Ask each for the make and model of panels and inverter — not just the wattage. Tier-1 panels (Waaree, Adani, Tata, Vikram) with Tier-1 inverters (Growatt, Solis, SMA) give the best long-term performance.
PM Surya Ghar Subsidy: How Much Will You Get in 2025?
The PM Surya Ghar Muft Bijli Yojana, launched in February 2024, is the Government of India's flagship rooftop solar subsidy scheme for residential consumers. It offers a direct central financial assistance (CFA) credited to your bank account after commissioning.
| System Size | Central Subsidy (CFA) |
|---|---|
| Up to 1 kWp | ₹30,000 |
| Above 1 kWp and up to 2 kWp | ₹60,000 |
| Above 2 kWp and up to 3 kWp | ₹78,000 |
| Above 3 kWp (residential) | ₹78,000 (capped) |
Some states offer an additional state-level subsidy on top of the central CFA. As of 2025, Kerala, Gujarat, and Maharashtra have additional incentives — check your state nodal agency (ANERT for Kerala, GEDA for Gujarat) for current rates.
How to apply: Visit pmsuryagarh.gov.in, register with your DISCOM consumer number, select an empanelled vendor, and apply online. The subsidy is released post-commissioning inspection, typically within 30 days.
Payback Period and 25-Year ROI for On-Grid Solar in India
The simple payback period is how many years of electricity bill savings it takes to recover your net investment. For on-grid residential solar in India in 2025, this typically ranges from 4 to 7 years depending on your tariff, system cost, and location.
Simple payback formula
Payback (years) = Net System Cost (₹) ÷ Annual Savings (₹)
Example: ₹1,50,000 net cost ÷ ₹36,000 annual savings = 4.2 years
Why 25-year ROI matters more
Solar panels are warranted for 25 years with a minimum 80% power output guarantee. Over that period, your annual savings compound because electricity tariffs typically rise 4–7% per year in India. A system with a 5-year payback will generate 4–6× its cost in savings over 25 years — making it one of the highest-return home investments available.
💡 Example: A 3 kWp system in Chennai costing ₹1,65,000 (after ₹78,000 subsidy net = ₹87,000), saving ₹2,500/month at current tariffs and 5% annual tariff rise, will generate approximately ₹14–16 lakhs in cumulative savings over 25 years.
State-Wise Solar Potential and Peak Sun Hours in India
Peak sun hours (PSH) is the single most important location variable when sizing a solar system. Here are average values for major Indian states:
| State | Average PSH (hrs/day) | Annual Solar Yield (kWh/kWp) | Potential Rating |
|---|---|---|---|
| Rajasthan | 6.0–6.5 | 1,700–1,800 | ⭐⭐⭐⭐⭐ Excellent |
| Gujarat | 5.8–6.2 | 1,650–1,750 | ⭐⭐⭐⭐⭐ Excellent |
| Tamil Nadu | 5.2–5.8 | 1,550–1,680 | ⭐⭐⭐⭐ Very Good |
| Andhra Pradesh | 5.4–5.8 | 1,580–1,680 | ⭐⭐⭐⭐ Very Good |
| Delhi / Haryana | 5.5–6.0 | 1,580–1,700 | ⭐⭐⭐⭐ Very Good |
| Maharashtra | 5.0–5.6 | 1,500–1,640 | ⭐⭐⭐⭐ Good |
| Karnataka | 4.9–5.5 | 1,470–1,620 | ⭐⭐⭐⭐ Good |
| Kerala | 4.2–5.0 | 1,350–1,500 | ⭐⭐⭐ Good |
| West Bengal | 4.5–5.0 | 1,400–1,500 | ⭐⭐⭐ Moderate |
| Himachal Pradesh | 3.8–4.5 | 1,200–1,380 | ⭐⭐ Low–Moderate |
⚠️ Kerala note: Kerala has relatively lower PSH due to cloud cover and monsoon duration — but the state's rising electricity tariffs (among the highest in India at ₹6–9/kWh) still make solar highly economical. A 3 kWp system in Thiruvananthapuram can still pay back in under 6 years.
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