When switching to solar, the most common question homeowners in Tamil Nadu and Puducherry ask is: "Should I install a 3kW or a 5kW system?"

These two sizes are the most popular for residential rooftops in districts like Cuddalore and Panruti. With electricity bills rising to ₹1,500 – ₹3,500 monthly, choosing the right capacity is critical to eliminating your bill completely. A system that is too small won't cover your bills, and one that is too big might be an unnecessary expense if you don't have the load for it.

The decision depends on your monthly usage, roof space, and budget. With the PM Surya Ghar Subsidy changing the payback dynamics, a 5kW system might offer better value than you think. At Surya’s Solar, we analyze your specific needs to recommend the perfect size. This guide compares both options in detail to help you decide.

Quick Summary Table (3kW vs 5kW)

Here is a side-by-side comparison to help you decide quickly.

Expected Solar Generation (TN & Puducherry)

Solar output varies slightly based on location and climate. Tamil Nadu is blessed with high solar irradiation, meaning panels here perform better than in many other states.

Tamil Nadu (Cuddalore, Panruti, Neyveli)

• 3kW: Generates 12–14 units/day.
• 5kW: Generates 20–22 units/day.
• Reason: High solar irradiation in these districts ensures maximum output. The dry heat of Panruti and Neyveli is excellent for solar generation.

Puducherry (Coastal)

• 3kW: Generates 11–13 units/day.
• 5kW: Generates 19–21 units/day.
• Reason: Coastal humidity and cloud cover can slightly reduce peak output. A 5kW system is often recommended here to compensate for this and ensure your ACs run smoothly even on humid days.

Cost Comparison (With Subsidy)

Thanks to the subsidy, the cost difference is less than you might expect.

3kW Cost (After Subsidy)

• Approx: ₹90,000 – ₹1,20,000
• Subsidy Benefit: Receives the maximum subsidy of ₹78,000.
• Verdict: Extremely affordable. The subsidy covers nearly 40% of the cost.

5kW Cost (After Subsidy)

• Approx: ₹1,40,000 – ₹1,90,000
• Subsidy Benefit: The subsidy is capped at ₹78,000 (same as 3kW).
• Verdict: You pay the full difference for the extra 2kW. However, the cost per watt is lower for larger systems due to economies of scale.

Insight: While a 5kW system costs more upfront, it generates almost double the power, offering a better long-term ROI for larger families.

Which System Fits Your Home?

Let's break it down by usage profile.

Choose 3kW If:

1. Bill Range: Your monthly bill is consistently between ₹1,500 – ₹2,500.
2. AC Usage: You use 1 AC occasionally (mostly at night for 6-8 hours).
3. Family Size: You have a small family of 2–4 people.
4. Roof Space: Your roof is small or has shadow issues.
5. Budget: You want to minimize upfront investment and maximize subsidy benefit.

Choose 5kW If:

1. Bill Range: Your monthly bill is between ₹2,500 – ₹4,000.
2. AC Usage: You run 1.5–2 ton ACs daily or during the day (e.g., for a home office or elderly parents).
3. Family Size: You have a larger family of 4–6 people or a joint family.
4. Heavy Appliances: You use a washing machine, fridge, and RO daily.
5. Future Proofing: You plan to buy an Electric Vehicle (EV) or add another AC soon.

Local Recommendations

• Puducherry: Coastal homes benefit from 5kW systems to offset the slight efficiency loss from humidity and to power ACs longer.
• Cuddalore / Panruti: With high sunlight, a 5kW system gives the best ROI by exporting maximum units to the grid, building up a credit for the monsoon season.

Calculate Whether 3kW or 5kW Is Better for Your Home

Use our Solar Calculator to estimate savings, units generated, and ROI for 3kW vs 5kW systems.

Roof Space Requirements

Before you decide, check your roof. You need shadow-free space facing South for maximum generation.

• 3kW Solar Needs: Approx 240–300 sq ft. (6–8 panels of 550W each).
• 5kW Solar Needs: Approx 380–450 sq ft. (10–12 panels of 550W each).

Note: If you choose a rail-less or elevated structure, the area requirements might change slightly. An elevated structure allows you to use the space underneath, effectively "saving" your roof space.

Inverter Size Difference

The inverter is the heart of your system.

• 3kW System: Comes with a 3kW inverter. Good for standard loads.
• 5kW System: Comes with a 5kW inverter.
  • Advantage: Runs more appliances simultaneously.
  • Performance: Handles heavy daytime loads (like a water pump or AC) much better.
  • Hybrid Option: If you choose a Hybrid Inverter, a 5kW unit can charge batteries faster, providing better backup during power cuts.

➡ Read More: Solar Inverter Guide for Tamil Nadu

ROI Comparison

Which one pays back faster?

• 3kW ROI: 4.5 – 5 years.
• 5kW ROI: 3.5 – 4.5 years.

Why? A 5kW system generates significantly more "excess" units that are exported to the grid. This builds up a larger credit in your net-metering account, potentially wiping out your bill entirely even in peak summer months when your AC usage spikes.

➡ Read More: Residential Solar ROI in Tamil Nadu

Future Expansion Importance

Think ahead before you buy. Solar is a 25-year investment.

• EV Charging: If you plan to buy an electric scooter or car, definitely go for 5kW. An EV consumes a lot of power (approx 3-4 units per charge for a scooter, 20-30 units for a car).
• AC Upgrade: Adding another AC next year? A 3kW system might fall short, forcing you to pay electricity bills again.
• Roof Constraints: If your roof is small, stick to 3kW with high-efficiency N-Type TOPCon panels to maximize generation per square foot.

Common Mistakes Homeowners Make

1. Choosing too small: Installing 3kW when the bill is ₹4,000+ leads to disappointment because you still get a bill.
2. Ignoring Shade: A 5kW system in the shade will perform worse than a 3kW system in the sun. Always do a shadow analysis.
3. Wrong Inverter: Undersizing the inverter limits your peak generation.
4. Expecting "Zero Bill": A 3kW system might not give a zero bill if your consumption is high. Be realistic about your usage.

Frequently Asked Questions (FAQs)

Need Help Choosing Between 3kW & 5kW?

Surya’s Solar offers free home assessment to suggest the right system size based on your electricity bill, usage, and roof space. We serve Cuddalore, Panruti, Neyveli, and Puducherry.