Solar ROI Explained (with Simple Payback Examples for Indian Homes)
When people say “solar ROI”, they’re usually mixing three different ideas:
- Payback period (years): How long your bill savings take to recover the upfront cost.
- Simple ROI (%/year): Your yearly savings as a percentage of what you paid.
- IRR (advanced): A finance-style return that accounts for time value of money (useful, but not necessary for most homes).
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| Solar ROI made easy - see simple payback examples and estimate how fast rooftop solar can recover its cost. |
In this post, we’ll keep it practical and use simple payback with easy, realistic home examples.
What you actually need to calculate solar payback
You only need 3 things:
1) Net system cost (after subsidy, if applicable)
Residential rooftop solar under PM Surya Ghar: Muft Bijli Yojana provides a subsidy that can go up to ₹78,000 depending on system size and consumption category.
2) Annual generation (units per year)
A rough India-wide thumb rule:
- 1 kW = ~3.5 to 5 units/day
- That’s ~1,300 to 1,800 units/year (varies by city, roof direction, shading, and panel quality)
For simple examples, I’ll use 4 units/day per kW (a conservative middle).
3) Value of each unit (₹/unit)
This is where most ROI confusion happens:
- If your solar unit replaces a unit you would have bought, it’s worth your retail tariff (often ₹6–₹10/unit for many urban homes).
- If your solar unit is exported to the grid, the value depends on your state’s policy (net metering vs net billing) and DISCOM rules. Example: Rajasthan recently reported ~₹3.26/unit for surplus under net metering.
The simplest payback formula
Payback (years) = Net solar cost ÷ Yearly net savings
And:
Yearly net savings = (Self-used units × Retail tariff) + (Exported units × Export rate) − (Yearly maintenance)
For maintenance, a realistic assumption is ₹2,000–₹4,000/year for cleaning and minor upkeep.
Download: Solar ROI + Payback Excel Calculator
Example 1: 3 kW rooftop solar (typical middle-class home)
Assumptions
- System size: 3 kW
- Generation: 3 × 4 × 365 = 4,380 units/year
- Retail tariff: ₹7/unit
- Policy: Net metering-like scenario (most units offset your bill)
- Maintenance: ₹2,000/year
- Installed price (example): ₹1.9 lakh
- Subsidy (example cap for residential): ₹78,000
- Net cost: ₹1,90,000 − ₹78,000 = ₹1,12,000
Savings
- Bill offset value: 4,380 × ₹7 = ₹30,660/year
- Net savings after maintenance: ₹30,660 − ₹2,000 = ₹28,660/year
Payback
- ₹1,12,000 ÷ ₹28,660 = 3.9 years
Simple ROI (%/year)
- ₹28,660 ÷ ₹1,12,000 ≈ 25.6% per year (simple ROI)
Example 2: 5 kW rooftop solar (home with AC + higher bills)
Assumptions
- System size: 5 kW
- Generation: 5 × 4 × 365 = 7,300 units/year
- Retail tariff: ₹8.5/unit
- Maintenance: ₹3,000/year
- Installed price (example): ₹3.2 lakh
- Subsidy (still capped at ₹78,000 in many cases): ₹78,000
- Net cost: ₹3,20,000 − ₹78,000 = ₹2,42,000
Savings
- Bill offset value: 7,300 × ₹8.5 = ₹62,050/year
- Net savings after maintenance: ₹62,050 − ₹3,000 = ₹59,050/year
Payback
- ₹2,42,000 ÷ ₹59,050 = 4.1 years
Example 3 (most common mistake): Oversizing when export is paid low
Here’s the ROI killer: you install 5 kW, but your daytime usage is low, so a big chunk goes to the grid at a lower rate.
Assumptions
- Same 5 kW system: 7,300 units/year
- Self-consumed: 50% = 3,650 units
- Exported: 50% = 3,650 units
- Retail tariff: ₹8.5/unit
- Export credit: ₹3.25/unit (example reported in Rajasthan)
- Maintenance: ₹3,000/year
- Net cost: ₹2,42,000
Savings
- Self-use value: 3,650 × ₹8.5 = ₹31,025
- Export value: 3,650 × ₹3.25 = ₹11,863
- Total before maintenance: ₹42,888
- Net savings: ₹42,888 − ₹3,000 = ₹39,888/year
Payback
- ₹2,42,000 ÷ ₹39,888 = 6.1 years
Takeaway: If export is low, right-sizing + shifting loads to daytime beats “bigger plant = better ROI”.
What changes solar ROI the most in India
Tariff slabs (your bill rate)
If your marginal units are billed at a higher slab, solar saves more per unit.
Your daytime usage pattern
Solar is most valuable when you use power while the sun is producing:
- Run washing machine/dishwasher midday
- Pre-cool rooms before evening
- Schedule water pumping in daylight
Net metering vs net billing rules
State rules can decide whether exports offset at retail rate or a lower credit.
Shading + roof direction
A small shadow can disproportionately cut output. Even “one pipe shadow” matters.
Quality of inverter + installation workmanship
Cheap wiring, poor earthing, or bad layout can quietly reduce generation.
Subsidy note (don’t skip this)
Under PM Surya Ghar: Muft Bijli
Yojana, subsidy support is described up to ₹78,000 and is linked to
system size/consumption categories; the scheme is routed via the national
portal and includes consumer guidance tools.
(Always verify eligibility and DISCOM-specific conditions before assuming the
subsidy in your ROI.)
A quick 60-second “your home” payback method
- Take your last 12 months total units (kWh).
- Estimate usable rooftop size (installer will confirm).
- Choose system size so that annual solar generation is close to 70–110% of your annual use (depends on policy).
- Use:
- Generation ≈ System kW × 1,400–1,700 units/year
- Savings ≈ Self-use × your tariff + export × export rate
- Payback = Net cost ÷ yearly net savings
Download: Solar ROI + Payback Excel Calculator
FAQs
Does battery storage improve ROI?
It can improve self-consumption, but batteries add significant cost. For most grid-connected homes, batteries improve backup, not payback. Hybrid systems make sense if outages are frequent.
What if my inverter fails?
Plan for an inverter replacement fund around year 10–12 depending on usage and quality. This matters more for IRR than simple payback, but it’s real.
How accurate are these examples?
They’re “clean math” examples. Your exact result depends on:
- City sunlight + shading
- Your slab tariff
- Policy (net metering/net billing)
- Final quote and subsidy approval
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