Which Solar System Size Do You Need for Your Indian Home?
This is the most important decision when going solar — and getting it wrong costs you money either way. Too small and you miss out on savings. Too large and you overspend with no extra benefit (until DISCOM allows net metering credit carryforward).
Here's how to size your solar system correctly for India's conditions.
Solar System Sizes at a Glance (India 2026)
| System Size | Daily Generation | Annual Units | Monthly Bill Saving | Ideal Household |
|---|---|---|---|---|
| 1 kW | 3.5–4.5 units | 1,200–1,600 units | ₹800–1,400 | 1 BHK, small flat |
| 2 kW | 7–9 units | 2,400–3,200 units | ₹1,600–2,800 | 2 BHK, 3–4 people |
| 3 kW | 10.5–13.5 units | 3,600–4,800 units | ₹2,400–4,200 | 3 BHK, 4–5 people |
| 5 kW | 17.5–22.5 units | 6,000–8,000 units | ₹4,000–7,000 | 4 BHK, large home, light commercial |
| 10 kW | 35–45 units | 12,000–16,000 units | ₹8,000–14,000 | Bungalow, small business, villa |
Generation varies by city — Delhi and Rajasthan generate 15–20% more than Mumbai or Kolkata. Bill savings depend on your current per-unit tariff (₹4–12/unit depending on DISCOM and slab).
How to Calculate Your Ideal System Size
Step 1: Find Your Monthly Electricity Consumption
Look at your last 12 months' electricity bills. Find the average monthly units (kWh). Or just note the units on your latest bill.
Step 2: Calculate Daily Consumption
Monthly units ÷ 30 = daily units consumed
Example: 300 units/month ÷ 30 = 10 units/day
Step 3: Divide by Your City's "Peak Sun Hours"
| City | Peak Sun Hours | Daily generation per kW |
|---|---|---|
| Delhi, Jaipur | 5.0–5.5 hrs | 4.5–5.0 units/kW |
| Ahmedabad, Hyderabad | 5.0–5.5 hrs | 4.5–5.0 units/kW |
| Mumbai, Pune | 4.5–5.0 hrs | 4.0–4.5 units/kW |
| Bangalore, Chennai | 4.5–5.0 hrs | 4.0–4.5 units/kW |
| Kolkata, Lucknow | 4.0–4.5 hrs | 3.5–4.0 units/kW |
| Kerala, NE India | 3.5–4.5 hrs | 3.0–4.0 units/kW |
Formula: System size (kW) = Daily consumption ÷ peak sun hours
Example: 10 units/day ÷ 4.5 = 2.2 kW → round up to 3 kW system
Step 4: Apply the 80% Rule
Solar doesn't produce its rated output 100% of the time. Account for:
- Dust soiling: 10–15% loss
- Inverter efficiency: 3–5% loss
- Wiring losses: 2–3% loss
- Temperature derating: 5–10% loss in summer
So divide your formula result by 0.8 to get the installed kW needed.
Revised example: 2.2 kW ÷ 0.8 = 2.75 kW → install 3 kW system
1 kW Solar System — Details
- Generation: 3.5–4.5 units/day (1,200–1,600 units/year)
- Cost (2026): ₹65,000–85,000 installed
- After subsidy (PM Surya Ghar): ₹35,000–55,000
- Subsidy amount: ₹30,000 central + state subsidy
- Roof area needed: ~7–8 sq. metres
- Payback period: 5–7 years
- Ideal for: 1 BHK flat, 1–2 people, monthly bill of ₹500–1,000
- Covers: 2–3 fans, LED lights, TV, phone charging — basic loads
2 kW Solar System — Details
- Generation: 7–9 units/day (2,400–3,200 units/year)
- Cost (2026): ₹1.10–1.40 lakh installed
- After subsidy: ₹68,000–98,000
- Subsidy amount: ₹60,000 central + state
- Roof area needed: ~14–16 sq. metres
- Payback period: 5–6 years
- Ideal for: 2 BHK, 3–4 people, monthly bill of ₹1,000–2,000
- Covers: All above + 1 AC (1 ton, 8 hrs/day in summer)
3 kW Solar System — Details (Most Popular)
- Generation: 10.5–13.5 units/day (3,600–4,800 units/year)
- Cost (2026): ₹1.50–2.0 lakh installed (on-grid)
- After subsidy: ₹72,000–1.22 lakh
- Subsidy amount: ₹78,000 central (max for residential)
- Roof area needed: ~22–24 sq. metres
- Payback period: 4–6 years
- Ideal for: 3 BHK, 4–5 people, monthly bill of ₹2,000–4,000
- Covers: 2 ACs (1 ton each), refrigerator, washing machine, all basic loads
- Note: 3 kW is the maximum size eligible for PM Surya Ghar's ₹78,000 central subsidy
5 kW Solar System — Details
- Generation: 17.5–22.5 units/day (6,000–8,000 units/year)
- Cost (2026): ₹2.20–2.80 lakh installed
- After subsidy: ₹1.42–2.02 lakh (₹78,000 max central subsidy applies)
- Roof area needed: ~35–40 sq. metres
- Payback period: 5–7 years
- Ideal for: 4 BHK bungalow, 5–6 people, monthly bill of ₹4,000–6,000
- Covers: 3 ACs, all home appliances, electric vehicle charging
10 kW Solar System — Details
- Generation: 35–45 units/day (12,000–16,000 units/year)
- Cost (2026): ₹4.0–5.5 lakh installed
- Subsidy: Limited subsidy; primarily for commercial/institutional
- Roof area needed: ~65–80 sq. metres
- Payback period: 4–6 years for commercial
- Ideal for: Large bungalow, villa, small office, retail shop, small factory
Common Sizing Mistakes Indian Buyers Make
- Sizing for peak summer only: Your AC-heavy summer bill shouldn't be your only reference. Average across all 12 months.
- Ignoring future load growth: Adding an EV? Planning a new AC? Size 20% larger to future-proof.
- Installing too large for DISCOM's net metering limit: Some DISCOMs limit residential net metering to 1–10 kW. Check your DISCOM's policy before sizing above 5 kW.
- Ignoring roof shading: A tree that casts shade on 20% of your panels reduces your effective capacity proportionally. Always do a solar site survey.
- Not accounting for appliance upgrades: Planning to install more ACs or a water heater next year? Factor it in now.
Quick Reference: Which Size for Your Bill?
| Monthly Electricity Bill | Monthly Units (Approx) | Recommended System Size |
|---|---|---|
| ₹500–1,000 | 80–150 units | 1 kW |
| ₹1,000–2,000 | 150–300 units | 2 kW |
| ₹2,000–4,000 | 300–500 units | 3 kW |
| ₹4,000–6,000 | 500–700 units | 4–5 kW |
| ₹6,000–10,000 | 700–1,200 units | 5–8 kW |
| ₹10,000+ | 1,200+ units | 10 kW+ |
Note: These are rough guides. Actual sizing depends on your city's solar irradiance, tariff slab, and specific appliance usage patterns. Always get a detailed site survey from a certified installer.