Estimate basis: kW × sun hours × 0.85 system loss, subsidy-adjusted cost.
What does the solar savings calculator do?
Rooftop solar has become the most financially attractive upgrade in Indian homes — the PM Surya Ghar subsidy, falling panel prices, and state net-metering rules have made the payback period shrink to 3–5 years. But buying solar blindly is how families overpay by lakhs. This calculator turns your situation into a plan: enter your monthly electricity units, state, and average tariff, and it returns the right system size in kW, panel count, roof area needed, net cost after subsidy, monthly generation, and the % of your bill it offsets.
Size is everything in solar. An undersized system leaves you paying the DISCOM; an oversized one sells surplus at a poor rate. This tool sizes the system to your consumption and then shows you exactly what it will generate in your region, so the decision moves from guesswork to arithmetic.
How much electricity does a rooftop system generate?
Generation depends on sunshine, and India is blessed — most of the country gets 4–5.5 sunshine hours of usable irradiance daily. The rule of thumb used across the Indian solar industry: 1 kW of rooftop capacity generates 120–160 units per month, or roughly 3.5–4.5 units per kW per day, after dust, wiring, inverter and panel losses (the calculator applies a standard 15% system loss factor).
- 1 kW ≈ 130–150 units/month
- 2 kW ≈ 260–300 units/month
- 3 kW ≈ 390–450 units/month
- 5 kW ≈ 650–760 units/month
That India-average is why most households between 200 and 800 units/month land on a 2–5 kW system — enough to cover 80–90% of the bill without buying panels you don't need.
Solar size guide by monthly bill
| Monthly usage | System size | Panels (450W) | Rough cost* | Offset |
|---|---|---|---|---|
| 200–300 units | 2 kW | 5 | ~₹1.0–1.1 L | ~90% |
| 400–600 units | 3 kW | 7 | ~₹1.4–1.6 L | ~80% |
| 600–900 units | 5 kW | 11 | ~₹2.3–2.7 L | ~80% |
| 900+ units | 10 kW | 22 | ~₹4.4–5.0 L | ~90% |
*Cost after central subsidy estimate. Panels today are typically 450–550W, so a 3 kW system is 6–7 panels and fits easily on most Indian terraces.
PM Surya Ghar: the subsidy that changes the math
The PM Surya Ghar Muft Bijli Yojana gives a direct central subsidy that cancels the biggest objection to solar — the upfront cost:
- ₹30,000 for a 1–2 kW system
- ₹60,000 for a 3 kW system
- ₹78,000 for systems above 3 kW
Because the subsidy is paid directly to the DISCOM-registered vendor at install, it comes off the price you actually pay. A 3 kW system typically costs ₹1.6–1.8 L; with the ₹60,000 subsidy the outflow drops to ~₹1.0–1.2 L. At 400+ units/month that system can be cash-flow positive from day one, since its generation beats the bill it replaces.
Net metering: how your bill actually drops
Solar homes stay connected to the grid, and your meter runs backward-friendly. Net metering means: during sunny hours your home draws from the panels first, sends the surplus to the grid, and the meter nets generation against consumption over the billing cycle. You pay only for the net units imported. This is what makes "offset 80–90%" real. The caveats: net meter caps differ by state and a fixed monthly charge almost always survives even a zero-unit bill — which is why no calculator honestly promises a fully zero bill.
Battery or grid-tied?
For 95% of homes, no battery is required. A grid-tied (on-grid) system covers the bill and is the cheapest, most reliable setup — batteries (₹60,000–1,00,000+) add cost and maintenance for the rare benefit of riding out a power cut, and most DISCOMs pay poorly for storing your solar. Only off-grid or outage-prone homes should buy up. If you want power in cuts with solar, buy a small battery hybrid — not a full-storage package that doubles your payback.
Roof space & panel count
Each kW of rooftop needs roughly 100–110 sq ft (about one 450–550W panel per 90–100 sq ft). A 3 kW system therefore needs ~350 sq ft of usable, shade-free roof. South-facing and east/west pitches deliver best; a partially-shaded roof can cost you 20–30% of generation — worth fixing before you decide.
How payback works
Payback = (net system cost) ÷ (monthly saving). A ₹1.1 L, 3 kW system saving ₹1,800/month recovers its cost in ~61 months (~5 years), then generates free of charge for 20+ years. Panels lose about 0.5% output per year and are typically warrantied for 25 years — the "free years" are the entire point of this calculator.
Solar calculator FAQs
Will my electricity bill become zero with solar?
Only with net metering and generation ≥ usage — and you still pay the DISCOM's fixed charge. Drivers say 80–95% offset is realistic.
Do solar panels need battery?
No — grid-tied systems need no battery; batteries only help during outages and roughly double the usable cost.
How many panels do I need for 3 kW?
Mostly 6–7 panels of 450W. Roughly 20 sq ft of roof per panel.
Is solar worth it if I use 300 units/month?
Yes — a 2 kW system often covers 90% a 300-unit home and gets the full ₹30,000 subsidy, paying back in ~4 years.
Which state has the best solar payback?
Those with high tariffs and net-metering: Gujarat, Maharashtra, Delhi, Tamil Nadu, Karnataka. Your state value in this tool is applied automatically.
Can I sell excess solar power to the grid?
Only under net-meter/excess-export rules in your state, and usually at the DISCOM's lower export rate — a reason not to over-size.