Choosing the wrong solar system size is the most expensive mistake Indian homeowners make. Install too small and your electricity bill stays stubbornly high; install too large and you’ve paid lakhs for capacity that sits unused on your roof.
This guide gives you a concrete formula to calculate the right size for your home, then walks through the exact costs, subsidies, output, and payback for 3 kW, 5 kW, and 10 kW systems in 2026, so you can make the decision with actual numbers rather than a salesperson’s guess.
The short answer: A 3 kW system suits most 2 to 3 BHK homes with a monthly electricity bill of ₹1,500–₹2,500. A 5 kW system fits 3 to 4 BHK homes with 2 ACs and bills up to ₹4,500/month. A 10 kW system is right for large bungalows or bills above ₹5,000/month. PM Suryaghar subsidy is capped at ₹78,000 for systems 3 kW and above, so picking 5 kW over 3 kW gives you more capacity with zero additional subsidy.
The Real Bill-to-Solar Sizing Rule
Most installers size your system with rough guesses. Heaven Green Energy uses a formula built from actual generation data across our 10,000+ installations.
The formula:
kW required = Average monthly kWh consumed ÷ 120 (Gujarat/Rajasthan) or ÷ 105 (UP/Delhi/cloudy regions)
The divisors come from real-world generation:
- 120 = average monthly kWh output per 1 kW installed in Gujarat (5.0 peak sun hours/day × 30 days × system efficiency factor of ~80%)
- 105 = equivalent figure for cloudier regions with fewer peak sun hours
Examples:
- Gujarat household consuming 300 kWh/month → 300 ÷ 120 = 2.5 kW → round up to 3 kW
- Delhi household consuming 600 kWh/month → 600 ÷ 105 = 5.7 kW → 6 kW system
- Gujarat bungalow consuming 1,200 kWh/month → 1,200 ÷ 120 = 10 kW → 10 kW system
To find your monthly kWh consumption: look at the “units consumed” line on any recent electricity bill. It’s usually printed near the billing period summary.
💡 Fast tip
Your bill shows "units", that's kWh. If your summer bills show 450 units and winter bills show 200 units, average them. Use 6 to 8 months of bills for accuracy, not just one. Most homes are highest in May–June (AC season) and lowest in December–January.
System Costs and Subsidies in 2026
The PM Suryaghar Muft Bijli Yojana subsidy structure has one critical detail most homeowners miss: the subsidy is capped at ₹78,000 for 3 kW and above. Installing a 5 kW system instead of a 3 kW system adds roughly ₹1.2–₹1.5 lakh in cost with zero additional central subsidy.
| System | Monthly Output (Gujarat) | Full Cost (Before Subsidy) | PM Suryaghar Subsidy | Net Cost |
|---|---|---|---|---|
| 1 kW | 110 to 130 kWh | ₹60,000–₹75,000 | ₹30,000 | ₹30,000–₹45,000 |
| 2 kW | 220 to 260 kWh | ₹1,20,000–₹1,50,000 | ₹60,000 | ₹60,000–₹90,000 |
| 3 kW | 330 to 390 kWh | ₹1,80,000–₹2,25,000 | ₹78,000 | ₹1,02,000–₹1,47,000 |
| 5 kW | 550 to 650 kWh | ₹3,00,000–₹3,75,000 | ₹78,000 | ₹2,22,000–₹2,97,000 |
| 10 kW | 1,100 to 1,300 kWh | ₹6,00,000–₹7,50,000 | ₹78,000 (capped) | ₹5,22,000–₹6,72,000 |
Subsidy source: MNRE PM Surya Ghar operational guidelines (no extra Gujarat state top-up). Costs are indicative for Gujarat; actual prices vary by panel brand and installer. Full subsidy details at mnre.gov.in.
💰 Real numbers
A 3 kW system in Gujarat at ₹1,47,000 net (after subsidy) generating 360 kWh/month saves roughly ₹2,160–₹2,700/month at ₹6 to 7.50/unit domestic tariff. That's a payback of 54 to 68 months, under 6 years, followed by 19+ years of near-free electricity worth ₹5 to 7 lakh over the system's life.
For a detailed breakdown of what’s inside the cost figure, see our solar panel cost breakdown guide.
Rooftop Space Required
Shade-free rooftop area is often the binding constraint. Modern 550 to 580 W panels are physically larger than older 250 W panels, but fewer of them are needed.
| System | Number of Panels (550 W) | Rooftop Area Needed |
|---|---|---|
| 1 kW | 2 panels | 80 to 100 sq ft |
| 2 kW | 4 panels | 160 to 200 sq ft |
| 3 kW | 6 panels | 240 to 300 sq ft |
| 5 kW | 10 panels | 400 to 500 sq ft |
| 10 kW | 18 to 19 panels | 800 to 1,000 sq ft |
These figures assume standard portrait mounting on a flat or pitched roof with minimal inter-row shading. If your roof has water tanks, AC compressor units, or parapet walls that cast shadows, effective usable area will be lower. An on-site shadow analysis is essential before finalising system size.
⚠️ Watch out
[Sanctioned load](/glossary/sanctioned-load) limits apply in many states. Most Indian residential connections are sanctioned for 2 to 5 kW, and many DISCOMs will not approve a solar system larger than your sanctioned load without a load enhancement first. Gujarat is an exception: under GERC's net metering regulations (3rd amendment, 2022), residential rooftop solar is allowed irrespective of sanctioned load. Outside Gujarat, check your state's rule before finalising a 10 kW system. Your electricity bill states the sanctioned load in kW.
Who Each System Size Is For
1 to 2 kW: The Apartment Option
A 1 to 2 kW system is appropriate for compact 1 to 2 BHK apartments with limited rooftop access and monthly bills under ₹1,500. These homes typically run ceiling fans, LED lights, a refrigerator, and a television, but no AC or only a small window unit. The subsidy at this size (₹30,000–₹60,000) is proportionally the highest relative to system cost, making it an attractive entry point.
One note: many apartment buildings have shared rooftop rights that complicate installation. Check your society’s bylaws and get written permission from the RWA before proceeding, our guide to solar for housing societies covers the group net metering angle in detail.
3 kW: The Sweet Spot for Most Indian Homes
The 3 kW system is one of India’s most popular rooftop solar sizes. At 3 kW, you hit the maximum PM Suryaghar central subsidy (₹78,000) without paying for excess capacity. The system generates 330 to 390 kWh/month in Gujarat, enough to offset most of a typical household’s consumption including one AC.
A 3 kW system is the right choice if:
- Your monthly bill is ₹1,500–₹2,500
- You have one inverter AC or one 1.5-ton split AC
- You have 240 to 300 sq ft of shade-free rooftop
See our detailed 3 kW solar system guide for a full component-by-component breakdown, or our walkthrough on how to design solar for a 3BHK home if that’s your exact house type.
5 kW: For Two-AC Homes and Future-Proofing
A 5 kW system suits families where two ACs run simultaneously during summer months, pushing monthly consumption to 500 to 600 kWh. It also makes sense for anyone planning to add an EV charger in the next 2 to 3 years, sizing up now avoids the cost of a future system upgrade.
The critical financial consideration: upgrading from 3 kW to 5 kW adds roughly ₹1.2–₹1.5 lakh in system cost with no additional PM Suryaghar central subsidy. You’re paying full market rate for those extra 2 kW. This is still worthwhile if your consumption genuinely requires 5 kW, but don’t oversize “just in case.”
10 kW: Large Homes and High Consumption
A 10 kW system is appropriate for large independent bungalows with 4+ ACs, significant water heating, and monthly bills consistently above ₹5,000. At this scale, net metering becomes a meaningful revenue stream, excess generation during the day earns credits that offset night-time grid consumption.
For homes in this category, the on-grid vs off-grid vs hybrid comparison is essential reading before deciding on system type. Most high-consumption homes choose on-grid systems with net metering rather than battery-backed systems, simply because the economics are better.
Payback Period by System Size
Payback depends on your local electricity tariff, how much of the solar generation you consume directly (self-consumption ratio), and whether excess units earn net metering credit.
| System | Net Cost (After Subsidy) | Monthly Savings (Gujarat, ₹6/unit) | Payback Period |
|---|---|---|---|
| 1 kW | ₹37,500 | ₹720/month | ~52 months (4.3 yr) |
| 2 kW | ₹75,000 | ₹1,440/month | ~52 months (4.3 yr) |
| 3 kW | ₹1,24,500 | ₹2,160/month | ~58 months (4.8 yr) |
| 5 kW | ₹2,59,500 | ₹3,600/month | ~72 months (6 yr) |
| 10 kW | ₹5,97,000 | ₹7,200/month | ~83 months (6.9 yr) |
Assumes mid-range cost and savings figures. Payback improves if local tariff is higher (₹7–₹7.50/unit in UGVCL domestic slabs) or if significant excess generation earns net metering credit. Detailed methodology in our solar payback period guide.
The 1 to 2 kW range shows the shortest payback because the subsidy covers a larger percentage of system cost. The 5 to 10 kW range has longer payback partly because the subsidy percentage is lower and partly because larger systems may export more than they self-consume at off-peak times.
Key Decisions Before You Finalise System Size
1. Check Your Sanctioned Load
Your electricity bill states your sanctioned load in kW. Gujarat is an exception: under GERC’s net metering regulations (3rd amendment, 2022), residential rooftop solar is allowed irrespective of sanctioned load, so UGVCL, DGVCL, PGVCL, MGVCL and Torrent Power customers do not need a load upgrade just to fit a bigger system. Many other states cap solar at the sanctioned load, and there a household with a 3 kW sanctioned connection cannot install a 10 kW system without first upgrading the load. If your PM Suryaghar application already got flagged over this, see our sanctioned load mismatch fix guide.
Check before you sign a contract.
2. Future AC or EV Plans
If you’re planning to add a 1.5-ton AC in the next 12 to 18 months, that adds roughly 120 to 150 kWh/month to your consumption in Gujarat summer conditions. If you’re planning to add an EV charger to your solar system, account for 200 to 300 kWh/month of additional load.
Solar installations typically last 25 years. It’s worth sizing for what you expect to consume in 3 to 5 years, not just your consumption today.
3. Roof Orientation and Shade
South-facing roofs in Gujarat get the best output. West-facing roofs get roughly 10 to 15% less. East-facing roofs get similar to west-facing. North-facing roofs are generally not viable for solar in India.
If your rooftop has significant shade from adjacent buildings or trees between 9 am and 3 pm, your actual output will be meaningfully lower than the figures in this guide. Ask your installer to model the shade losses using tools like PVsyst or Helioscope before finalising system size.
💡 Fast tip
Don't know your monthly kWh consumption? Use this quick estimate: each 1.5-ton split AC running 8 hours/day in summer uses roughly 120 to 135 kWh/month. A refrigerator adds about 35 to 40 kWh. Lights and fans add 30 to 50 kWh. Add them up for a working estimate if your electricity bill is hard to read.
Net Metering: How Excess Generation Earns You Credits
All three system sizes qualify for net metering in Gujarat under GERC’s net metering regulations. Net metering means that when your solar system produces more power than you’re consuming at that moment, during midday when everyone is at work, for example, the excess flows to the grid and your meter runs backward. Exported units are set off against your consumption within the billing cycle, so they cover your night-time use.
This is what makes on-grid solar financially compelling even if your household isn’t home during peak generation hours. You don’t need to store the energy in batteries; the grid does that for you, in effect.
For net metering to work:
- Your installer must apply for net metering on your behalf with the DISCOM
- A bi-directional meter must be installed (cost typically included in installation)
- Your system must be DISCOM-approved and connected by the DISCOM-approved contractor
Heaven Green Energy handles the entire net metering application process as part of every residential installation.
Pros and Cons by System Size
- Highest subsidy-to-cost ratio (₹78,000 on ~₹1.25 lakh net)
- Fits most residential sanctioned loads
- Fastest payback among subsidy-eligible sizes
- Needs only 240 to 300 sq ft rooftop
- Won't fully offset high-consumption homes (2+ ACs)
- May be undersized if EV added later
- Limited future-proofing room
- Fully offsets high-consumption households
- Significant net metering credits possible
- Future-proof for AC / EV additions
- Higher absolute annual savings (₹70,000–₹1,00,000+)
- No additional PM Suryaghar subsidy vs 3 kW
- Higher upfront cost (₹2.2 lakh–₹6.7 lakh net)
- Longer [payback period](/glossary/payback-period) (6 to 7 years)
- Requires larger roof area (and, outside Gujarat, often a higher sanctioned load)
Step-by-Step: How to Right-Size Your Solar System
- Pull 6 to 12 months of electricity bills. Note the “units consumed” (kWh) for each month. Identify the average, peak (summer), and lowest (winter) months.
- Apply the sizing formula. Divide average monthly kWh by 120 (Gujarat) or 105 (North India). Round up to the nearest standard size (1, 2, 3, 5, 6, 8, 10 kW).
- Check your sanctioned load. Your bill shows this. Outside Gujarat, many states cap solar at the sanctioned load; Gujarat allows residential rooftop solar irrespective of it.
- Measure usable rooftop area. Exclude area shaded by water tanks, parapets, or adjacent structures between 9 am–3 pm.
- Factor in future loads. Adding AC in 2 years? Add 120 to 150 kWh/month. Adding EV charging? Add 200 to 300 kWh/month. Size for 3-year projected consumption.
- Verify subsidy eligibility. Confirm your DISCOM is on the pmsuryaghar.gov.in portal and that your installer is a vendor registered on that national portal.
- Get itemised quotes from 2 to 3 installers. Compare panel brand/model, inverter specification, and scope (does it include net metering application?).
- Review the performance guarantee. Ask for a written kWh/year generation commitment in the contract.
Curious what solar would cost for your home? Use our free solar calculator, subsidy + savings in 60 seconds.
How Heaven Green Energy Helps with System Sizing
Heaven Green Energy has completed 10,000+ solar installations across 25+ cities in India. Our engineering team uses generation data from this portfolio to calibrate sizing recommendations, not generic software defaults.
Every residential inquiry starts with a free site visit by a salaried engineer (not a commission-based salesperson). The engineer:
- Analyses 6 to 12 months of your electricity bills
- Measures usable rooftop area with a shade analysis
- Checks your DISCOM sanctioned load
- Proposes a system size with a written annual generation commitment (kWh/year)
- Handles the complete PM Suryaghar subsidy application and net metering process
We’re empanelled with UGVCL, DGVCL, PGVCL, and MGVCL for PM Suryaghar in Gujarat, and GEDA-empanelled for PM KUSUM agricultural solar.
Explore our residential solar service or read the complete Gujarat installation guide for the full process.
Get a free site visit. Our engineer visits in 24 hours, sends a custom proposal in 48 hours. Get your free quote →
Frequently Asked Questions
What is the right solar system size for a 2 BHK flat in Gujarat?
Most 2 BHK apartments in Gujarat consume 150 to 250 kWh/month, placing them in the 1 to 2 kW range. Use the formula: monthly kWh ÷ 120. A 150 kWh/month flat needs 1.25 kW, a 1.5 kW or 2 kW system is appropriate. If you have one AC, move to 2 to 3 kW.
Is 3 kW enough for one air conditioner?
Yes, in most cases. A 1.5-ton inverter AC in Gujarat summer conditions uses roughly 3 to 4 units/day (90 to 120 kWh/month). A 3 kW solar system generates 330 to 390 kWh/month. If the AC is your primary load alongside normal lights/fans/refrigerator, a 3 kW system typically covers 70 to 90% of total consumption.
Why does PM Suryaghar subsidy stay at ₹78,000 for both 3 kW and 5 kW?
The PM Suryaghar Muft Bijli Yojana central subsidy is structured as follows: ₹30,000/kW for the first 2 kW, and ₹18,000/kW for the 3rd kW, capped at ₹78,000 for 3 kW and above. This cap is a policy decision to make the subsidy accessible to more households rather than concentrating benefit in larger systems. State top-up subsidies (where available; Gujarat has none) may partially offset this gap.
Can I install a 10 kW system on a residential connection?
Yes in Gujarat: GERC’s net metering regulations allow residential rooftop solar irrespective of sanctioned load, and systems up to 10 kW are deemed technically feasible without a DISCOM study. Many other states cap solar at the sanctioned load, and most standard residential connections are 3 to 5 kW, so there you would need a load enhancement first.
How much rooftop space does a 5 kW system need?
A 5 kW system using modern 550 W panels requires approximately 10 panels, needing 400 to 500 sq ft of shade-free, structurally sound rooftop. This is the usable area, not the total roof area, space occupied by water tanks, AC units, or parapet walls doesn’t count.
What happens if my solar system generates more than I consume?
Excess generation flows to the DISCOM grid via your net meter. You receive credits (in units or ₹) that offset your future bills. Under Gujarat’s net metering regulations, exported units are set off within each billing cycle, and any surplus left at the end of the cycle is bought by the DISCOM at ₹2.25 per unit for the first five years on self-owned systems. See our net metering guide for full details.
Should I install 3 kW now and expand to 5 kW later?
Expansion is possible but adds cost. You’d need to add panels, potentially upgrade the inverter, and re-apply for DISCOM approval. The total cost of two installations is typically 15 to 25% higher than a single 5 kW installation. If you’re confident you’ll need 5 kW within 3 years, install 5 kW now. If you’re uncertain, 3 kW now is the lower-risk choice.
How accurate is the “kWh ÷ 120” sizing formula for Gujarat?
It’s designed as a starting estimate, not a final engineering calculation. Actual output depends on roof orientation, tilt angle, shade, panel brand, and inverter efficiency. In our portfolio of 10,000+ installations, actual annual generation is within 8 to 12% of the formula estimate in 90% of cases. A proper PVSyst simulation by your installer is the next step after applying this formula.
What is the PM Suryaghar application process timeline?
From application to subsidy credit: 45 to 90 days is typical in Gujarat. The steps are: you (or your vendor on your behalf) apply on pmsuryaghar.gov.in → DISCOM feasibility → a portal-registered vendor installs → DISCOM inspects and installs the net meter → commissioning is approved on the portal → the subsidy is processed within 15 days of DISCOM approval and credited to your bank account. Heaven Green Energy manages this entire process on your behalf.
Is solar financing available if I can’t pay the full net cost upfront?
Yes. Public sector banks offer collateral-free PM Surya Ghar loans: SBI charges 5.75% up to ₹2 lakh and 7.90% from ₹2 lakh to ₹6 lakh, over up to 120 months, with nil processing fee. If the system is financed, the subsidy goes to the loan account first. Our solar financing options guide covers the loan routes in detail, and our solar loan EMI comparison for 3 kW, 5 kW, and 10 kW systems breaks down monthly payments by size.