Solar Payback After ₹1 Lakh Subsidy: Tamil Nadu 2026 Math
Short answer: with the full ₹1 lakh subsidy (₹78,000 PM Surya Ghar + ₹22,000 Tamil Nadu top-up), rooftop solar in Tamil Nadu pays back in about 2.5-3.5 years for homes with two-month bills above about ₹5,000, around 4-5 years for bills near ₹3,000-3,500, and 8+ years for small bills under ₹1,500. After that, the system keeps saving for 20+ more years.
We show the real slab-based math below, because many quotes promise "2-year payback" for everyone. That is not true for every home.
Payback by Bill Size (Tamil Nadu, 2026)
| Two-month units | Two-month bill (approx.) | Right system | Net cost after subsidy* | Yearly saving (approx.) | Payback |
|---|---|---|---|---|---|
| 450 | ₹1,300 | 2kW | ₹60,000 - ₹75,000 | ₹7,000 | 8 - 10 years |
| 650 | ₹3,300 | 3kW | ₹80,000 - ₹1,00,000 | ₹19,000 | 4 - 5 years |
| 900 | ₹5,650 | 3kW | ₹80,000 - ₹1,00,000 | ₹33,000 | 2.5 - 3 years |
| 1,200 | ₹8,850 | 5kW | ₹2,00,000 - ₹2,30,000 | ₹52,000 | 4 - 4.5 years |
| 1,500 | ₹12,150 | 5kW | ₹2,00,000 - ₹2,30,000 | ₹72,000 | 3 - 3.5 years |
*Market-average system prices minus ₹1 lakh subsidy (eligible Tamil Nadu homes). Bills use the approximate slab rates from our TNEB slab guide plus a fixed charge, averaged across seasons. Savings assume the system covers most of your use through the net meter under current rules. Your real numbers depend on your bill, roof and system price.
Why Bill Size Changes Everything
Tamil Nadu's tariff is telescopic and cheap at the bottom:
- Homes using 500 units or less (two months) get the first 200 units free and pay about ₹4.50-6.00 for the rest.
- Above 500 units, only 100 units are free, and the slabs climb to ₹8, ₹9, ₹10 and ₹11 per unit.
So each solar unit saves you ₹4.50 in a small home but ₹9-11 in a big AC home. The same 3kW system is worth almost twice as much to a home on the expensive slabs. This is why AC homes get the fastest payback. See average electricity bill by home size.
Worked Example: 3BHK With One AC, 900 Units per Two Months
- Bill without solar: about ₹5,650 every two months (about ₹2,825 a month).
- 3kW solar produces about 720-900 units per two months.
- Bill with solar: close to the fixed charge for most of the year.
- Yearly saving: about ₹33,000.
- Net cost: ₹1.8-2.0 lakh market price minus ₹1 lakh subsidy = ₹80,000-1,00,000.
- Payback: about 2.5-3 years.
- 25-year savings: roughly ₹7.5-8.5 lakh at today's tariffs, after allowing for panel ageing and one inverter replacement. If tariffs rise, savings rise too.
25-Year View of a 3kW System
| Item | Amount (approx.) |
|---|---|
| Net cost after ₹1 lakh subsidy | ₹80,000 - ₹1,00,000 |
| Inverter replacement around year 10-12 | ₹20,000 - ₹35,000 |
| Cleaning, minor maintenance (25 years) | ₹15,000 - ₹30,000 |
| Total cost of ownership | ₹1.15 - 1.65 lakh |
| Units produced over 25 years (with ageing) | about 1,05,000 - 1,15,000 |
| Cost per unit over 25 years | about ₹1.0 - 1.6 |
Compare that with ₹4.50-11 per unit from TNEB. Solar electricity is the cheapest power your home can buy. TOPCon panels age slowly (well under 1% a year), which keeps the numbers strong. Read mono vs bifacial panels.
What Makes Payback Faster or Slower
| Faster payback | Slower payback |
|---|---|
| High bill (500+ units per two months) | Small bill, mostly in the free slab |
| Full ₹1 lakh subsidy (registered from 5 Aug 2026) | Missed the Tamil Nadu top-up or the central subsidy |
| Shade-free, south-facing roof, raised structure | Shade from trees, tanks or walls |
| Daytime use (work from home, AC in afternoon) | Most use at night with no net meter benefit |
| Correct system size | Over-sized system for a small bill |
| Quality install (low losses, no downtime) | Cheap install with frequent faults |
The biggest lever is size. An over-sized system for a small bill wastes money. We size every system from your last six bills.
Without the Tamil Nadu Top-up
If you registered on PM Surya Ghar before 5 August 2026, or the state cap is used up, you get only the central ₹78,000. Your net cost rises by ₹22,000, and payback grows by roughly 4-12 months depending on your bill. For AC homes it still pays back in about 3-5 years. For small bills, consider waiting until your usage grows.
Solar vs Fixed Deposit
Putting ₹1 lakh into solar that saves ₹33,000 a year is like earning over 30% a year, tax-free, on that money (for the 900-unit example). Even the 650-unit home earns roughly 19-24% a year. Few safe investments come close. For EMI options, see solar EMI and loans in Tamil Nadu.
Before You Decide
- Total your last six bills (one year of units).
- Check if you are above 500 units per two months in summer; if yes, solar pays back fast.
- Confirm subsidy eligibility and act before the deadlines: PM Surya Ghar last date 2027.
- Get a correctly sized quote, not the biggest system possible.
Solar Savings Calculator Tamil Nadu
Enter your EB bill to see the system size, savings and payback.
Enter amount between ₹2,000 and ₹30,000 • We specialize in 2 kW+ systems
Frequently Asked Questions
How many years does solar take to pay back in Tamil Nadu?
Why is payback slower for small bills?
What happens after the payback period?
Does the payback include inverter replacement?
What if I do not get the ₹22,000 Tamil Nadu top-up?
Get Your Personal Payback Calculation
WhatsApp your last two TNEB bills to +91 7904369094. We will calculate your exact payback with your slab, your roof and your subsidy, and tell you honestly if solar is worth it for your home.
Get a Free Rooftop Assessment
Our engineers will visit your site, analyze shadow-free area, and provide a detailed solar report.
Book Free AssessmentTags
Ready to Switch to Solar?
Get a customized solar solution for your home. Save up to 90% on electricity bills!
- Free Site Visit
- Govt. Subsidy Support
- 25 Years Warranty