3 kW vs 5 kW Solar: Which Is Right for Your Home?
The two most popular home system sizes, compared side by side: price after subsidy, units generated, roof space, what each can run and how fast it pays back.
Rainbow Solar Energy Team
7 min read
Updated
In this article
Key takeaways
- A 3 kW system makes about 360 units a month in Tamil Nadu and suits bills of ₹2,500–₹4,000 a month.
- A 5 kW system makes about 600 units a month and suits bills of ₹4,000–₹6,000+, or homes with 2–3 ACs.
- Both get the same ₹78,000 + ₹22,000 subsidy, so 3 kW has the lower net cost and slightly faster payback.
- Choose based on your units, roof space and future plans (EV, more ACs), not just today's bill.
Most Tamil Nadu homeowners end up choosing between a 3 kW and a 5 kW system. One is cheaper and pays back faster; the other wipes out a much bigger bill. Here is how to decide in a few minutes.
3 kW vs 5 kW at a glance
3 kW system Best value
Ideal for a 2–3 BHK home with 1 AC and a monthly bill of ₹2,500–₹4,000.
- ~12 units a day
- ~300 sq ft shadow-free roof
- Net cost ~₹0.70–0.90 lakh
- Payback ~3–4 years
5 kW system Bigger savings
Ideal for larger homes with 2–3 ACs, a monthly bill of ₹4,000–₹6,000+ or an EV.
- ~20 units a day
- ~500 sq ft shadow-free roof
- Net cost ~₹1.75–2.10 lakh
- Payback ~4–5 years
| 3 kW | 5 kW | |
|---|---|---|
| Units per day (Tamil Nadu avg.) | ~12 | ~20 |
| Units per month | ~360 | ~600 |
| Roof space needed | ~300 sq ft | ~500 sq ft |
| Panels (at ~550 Wp) | 5 – 6 | 9 – 10 |
| Price before subsidy | ₹1.70 – ₹1.90 lakh | ₹2.75 – ₹3.10 lakh |
| PM Surya Ghar subsidy | ₹78,000 + ₹22,000 | ₹78,000 + ₹22,000 |
| Net cost | ₹0.70 – ₹0.90 lakh | ₹1.75 – ₹2.10 lakh |
| Est. yearly savings | ₹28,000 – ₹36,000 | ₹45,000 – ₹58,000 |
| Payback | 3 – 4 years | 4 – 5 years |
| 25-year savings (approx.) | ₹8 – 10 lakh | ₹13 – 16 lakh |
Indicative figures for on-grid systems at ₹7–8 per unit. 25-year savings allow for normal panel ageing and modest tariff increases.
Which size matches your electricity bill?
The simplest way to size solar is from your units, not your rupees. Look at the units on your last few TNPDCL bills, add them up for a year and divide by 12.
| Average monthly units | Typical monthly bill | Recommended size |
|---|---|---|
| Up to 250 | Up to ₹2,500 | 2 kW |
| 250 – 400 | ₹2,500 – ₹4,000 | 3 kW |
| 400 – 500 | ₹3,500 – ₹5,000 | 4 kW |
| 500 – 700 | ₹4,000 – ₹6,000 | 5 kW |
| 700+ | ₹6,000+ | 6 – 10 kW |
TNPDCL bills every two months: halve your bimonthly units and amount first.
Skip the maths: our solar calculator recommends the right size from your PIN code and bill, with cost, subsidy and payback.
What can each system run?
On-grid solar doesn't power appliances directly at night; net metering credits your daytime surplus against night-time use. Over a day, this is roughly what each size can offset:
| Appliance | Daily use | 3 kW (~12 units) | 5 kW (~20 units) |
|---|---|---|---|
| 1.5-ton inverter AC | ~1.2 units/hour | ~8 hours | ~8 hours + 2nd AC ~5 hours |
| Refrigerator | ~1.5 units/day | ✓ | ✓ |
| Fans, lights, TV, Wi-Fi | ~3 units/day | ✓ | ✓ |
| Washing machine, mixer, iron | ~1.5 units/day | ✓ | ✓ |
| Electric vehicle (scooter / car) | 2 – 8 units/day | Scooter only | ✓ Scooter or part of a car |
When 3 kW is the smarter choice
- Your bill is under ₹4,000 a month and you don't expect big changes.
- Your terrace has only about 300 sq ft of shadow-free space.
- You want the fastest payback: the ₹78,000 + ₹22,000 subsidy covers more than half the price.
- You want to use the concessional PM Surya Ghar loan, which covers systems up to 3 kW.
When 5 kW is worth it
- You run 2–3 ACs through Tamil Nadu's long summer, or your bill is over ₹4,500 a month.
- You plan to buy an electric car, add a floor, or install more ACs in the next few years.
- You are in a higher tariff slab, where each unit saved is worth more.
- You want to add a battery later: a bigger array charges the battery and still covers daytime use. See solar + battery for power cuts.
Still not sure? Ask an engineer.
We check your bills and roof for free and recommend the size that saves you the most.
Our verdict
For a typical Tamil Nadu family with one AC, 3 kW gives the best return for every rupee spent. If your home already uses 500+ units a month, or will soon, 5 kW saves far more over 25 years, even though the payback is a year longer. Size for the next five years, not just this month's bill.
See detailed prices for every size in our Tamil Nadu solar price guide, or explore rooftop solar for homes.
Written by our solar engineers and subsidy specialists, who design and install rooftop systems for homes, societies and businesses across Tamil Nadu. Figures are indicative and reviewed regularly; your free site survey gives exact numbers for your roof.
