A 3BHK apartment is the most common urban home in India — typically 750–1,200 sqft of built-up area, three bedrooms with three air-conditioners (AC), a family of four, and a monthly electricity bill of ₹2,500–₹5,000. For this exact household, the PM Suryaghar: Muft Bijli Yojana subsidy of ₹78,000 lands on the 3 kW system size, but the right sizing for most 3BHK flats sits at 5 kW (kilowatt) — bigger than the subsidy sweet spot, smaller than wasteful, and enough to cover three ACs running through summer. This guide walks through how to design a solar system for a 3BHK flat in 2026 using a 6-input method we’ve refined across hundreds of apartment installations.
Apartment solar is not the same as a bungalow rooftop. Roof access is shared, society NOC (No Objection Certificate) is mandatory, the net meter (NMM — Net Metering Module) sits on the individual flat connection while the RWA (Resident Welfare Association) controls common-area billing, and the sanctioned load on the flat meter may be the binding constraint instead of roof area. Get any one of these wrong and the system either fails commissioning or under-generates for the rest of its 25-year life.
Direct answer. A 3BHK apartment in India typically consumes 350–600 kWh/month and is best served by a 5 kW rooftop solar system — generates ~700 kWh/month, costs ₹2.60 lakh all-in, claims the maximum ₹78,000 PM Suryaghar subsidy, and pays back in 36 months. The 3 kW option (₹78,000 subsidy, 28-month payback) is the max-subsidy pick for bills under ₹3,500. Society NOC and flat-level NMM are both mandatory.
If you’ve been told a 3 kW system “is enough because of the subsidy cap,” that advice ignores three air-conditioners and a 25-year horizon. We’ll size on consumption first, then optimise for subsidy — not the other way around.
Typical Energy Profile of a 3BHK Apartment
A 3BHK flat’s load is dominated by three categories: cooling (3 ACs, 1 fridge, 1 deep freezer if present), lighting and small appliances (≈10% of total), and seasonal kitchen load (induction, microwave, water heater). The Bureau of Energy Efficiency (BEE) star ratings on these appliances drive the consumption envelope more than the city tariff does.
| City | Avg 3BHK monthly consumption | Avg monthly bill | Peak summer (May–June) | PSH (Peak Sun Hours) |
|---|---|---|---|---|
| Jaipur | 480 kWh | ₹3,400 | 650 kWh | 5.7 |
| Mumbai | 520 kWh | ₹4,100 | 720 kWh | 4.8 |
| Delhi-NCR | 540 kWh | ₹4,300 | 780 kWh | 5.2 |
| Bengaluru | 380 kWh | ₹2,900 | 460 kWh | 5.0 |
| Hyderabad | 460 kWh | ₹3,300 | 620 kWh | 5.3 |
| Chennai | 500 kWh | ₹3,700 | 640 kWh | 4.9 |
| Pune | 420 kWh | ₹3,200 | 540 kWh | 5.1 |
Source: Heaven Green residential installation data 2024–25, cross-checked with MNRE Solar Atlas PSH figures. A flat in Mumbai needs a larger kW system than the same flat in Jaipur to generate the same kWh, because every installed kilowatt produces fewer units per day. This is the city-correction step most installers skip — and it’s why a quote built off “1 kW = 4 units/day” never matches what your roof actually delivers in Bandra or Andheri.
The seasonality within these averages matters as much as the average itself. A Delhi 3BHK that draws 540 kWh on the 12-month mean is closer to 320 kWh in November–February and 780 kWh in May–June. Design to the summer peak; the surplus monsoon-and-winter generation banks to your DISCOM credit and offsets the peak-month deficit, which is exactly what the net metering framework is built for.
The 3BHK Solar Design Method — 6 Inputs
This is the named framework we use for every 3BHK design call. Six inputs, in this exact order. Skip the order and you’ll size on the wrong constraint.
Input 1: Average Monthly Bill (₹)
Pull the last 12 months of bills, not just the latest one. Take the average. A bill of ₹3,200 in October and ₹5,400 in May tells you the AC load is the design driver — you size for the May peak, not the October average. For most 3BHK flats this lands at ₹2,500–₹5,000.
Input 2: Number of ACs and Run-Hours
Three 1.5-ton inverter ACs at 5-star BEE rating draw ≈1.4 kW each when running. Three units, 8 hours a day in May–June, equals 33 kWh/day from cooling alone — that’s 1,000 kWh/month before lights, fridge, or kitchen. Two-star ACs draw 1.8 kW each; same math gives 1,300 kWh/month. AC star rating drives the system size more than any other single input.
Input 3: Family Size and Routine
Family of four with daytime occupancy (work-from-home, kids, retired parents) consumes 30–40% more daytime kWh than a family that’s empty 9–6. Daytime consumption matters because solar self-consumption is worth full retail tariff (~₹7/kWh) while exported surplus is credited at the Average Power Purchase Cost (APPC, ₹2.50–₹3.50/kWh). Sizing should match daytime load profile.
Input 4: Roof Share / Allocated Area
In a mid-rise apartment, the roof is common property. The RWA allocates a share — typically 150–300 sqft per 3BHK flat in a 12-flat building. A 5 kW system needs ≈300 sqft of clear, shadow-free roof. Check your allocation before committing to capacity. If roof share is the binding constraint, scale down system size or negotiate a larger share through the society NOC process.
Input 5: Sanctioned Load on Flat Meter (kW)
The flat-level DISCOM connection has a sanctioned load — typically 4–7 kW for a 3BHK in 2026. Your rooftop solar capacity cannot exceed this without a load enhancement. A flat with 4 kW sanctioned load cannot install a 5 kW system without filing a load enhancement application first (15–25 days, separate process).
Input 6: Future EV and Expansion Plans
If you’re planning to buy an electric vehicle (EV) within 3 years, add 15 kWh/day to your load estimate (a 30 kWh battery EV doing 50 km/day on home charging). That bumps a 5 kW design to a 7 kW design — and the marginal kilowatts beyond 3 kW don’t get extra subsidy but do get full net-metering credit. Plan capacity for where you’ll be in 5 years, not where you are today. See home solar system size guide for the EV-add math.
Sizing Options — 3kW vs 5kW vs 7kW for 3BHK
Once you’ve run the 6 inputs, three sizing options remain on the table for almost every 3BHK. Here’s the head-to-head.
| Spec | 3 kW | 5 kW | 7 kW |
|---|---|---|---|
| All-in cost (Heaven Green) | ₹1.65 lakh | ₹2.60 lakh | ₹3.85 lakh |
| PM Suryaghar subsidy | ₹78,000 | ₹78,000 | ₹78,000 |
| Out-of-pocket | ₹87,000 | ₹1.82 lakh | ₹3.07 lakh |
| Monthly generation | ~450 kWh | ~700 kWh | ~1,000 kWh |
| Bill coverage (₹3,500 bill) | ~95% | 100% + export | 100% + heavy export |
| Roof area required | ~180 sqft | ~300 sqft | ~420 sqft |
| Payback | 28 months | 36 months | 48 months |
| Best for | Bill ₹2,500–₹3,500 | Bill ₹3,500–₹5,000 | Bill ₹5,000+ or EV planned |
The 5 kW option is the sweet spot for a typical 3BHK because it matches summer peak generation to peak consumption while still claiming the full ₹78,000 subsidy. For a deeper comparison, read the 3 kW vs 5 kW vs 10 kW home solar 2026 breakdown.
A flat running three ACs continuously through Indian summer is a 5 kW use case — see our Suryaghar for 3-AC home deep-dive for the cooling-load math.
Why the 7 kW option exists at all
The 7 kW design isn’t for every 3BHK — it’s specifically for households planning an electric vehicle within three years, or those with a sanctioned load of 7 kW and a monthly bill consistently above ₹5,000. The marginal cost from 5 kW to 7 kW is ₹1.25 lakh for an extra 300 kWh/month of generation, which translates to roughly ₹2,200/month in additional savings. The 48-month payback on that incremental capacity is still excellent on its own, but only if you’ll actually use the extra units. Surplus exported to the grid is credited at the APPC rate (₹2.50–₹3.50/kWh), well below the retail tariff you save with self-consumption — so oversizing without daytime load to absorb the generation pushes payback into the 5+ year range.
What about 4 kW or 6 kW sizes
PM Suryaghar pays the same ₹78,000 for 3 kW, 4 kW, 5 kW, 6 kW, and 7 kW systems. Custom sizes between the standard tiers exist, but the panel-count math (most ALMM modules are 540–580 W) means real systems land on round-kW figures because the inverter MPPT (Maximum Power Point Tracker) channels are designed around 3, 5, 7.5, and 10 kW string sizes. Going off-grid-tier costs more per kW than going to the next standard size.
Roof Space and Society NOC for 3BHK Apartments
Apartment rooftops are governed by the registered society or RWA. Even if you own your flat, you don’t own a slice of the terrace by default — terrace is “common area” under most cooperative housing society bye-laws. The society NOC is the legal instrument that allocates a roof share to your flat for solar.
| Roof allocation scenario | Typical area per 3BHK | System size possible |
|---|---|---|
| Low-rise (G+3, 6–8 flats) | 250–400 sqft | Up to 7 kW |
| Mid-rise (G+7, 12–24 flats) | 150–250 sqft | 3–5 kW |
| High-rise (G+15, 50+ flats) | 80–150 sqft | 2–3 kW or RWA-stack model |
| Penthouse / top-floor private terrace | Full terrace | Limited only by sanctioned load |
For mid-rise and high-rise buildings, the RWA-stack model (where the society installs a single larger system and credits common-area meter savings to flat owners proportionally) often beats individual flat installations on per-kW economics. See our Suryaghar society and flat-owner guide for the full RWA pathway.
The roof allocation negotiation usually goes more smoothly when one early-mover flat owner has done the legwork. The first 3BHK installation in any society sets a precedent — site survey done, society NOC template signed off, conduit route walked and approved, net meter installed on the riser. Subsequent flat owners ride that template, and per-application timelines drop from 90 days to 60 days. Heaven Green’s apartment-solar team explicitly tracks “first installation” and “follow-on installation” as separate workstreams because the rejection rate and timeline differ that much.
Society NOC checklist
A valid NOC must be on society letterhead, signed by the secretary, mention the registration number, specify the roof area allocated to your flat in sqft, and confirm no objection to mounting, wiring conduit through risers, and a separate net meter installation. Generic "no objection" letters routinely fail JVVNL, BSES, MSEDCL, and BESCOM feasibility checks.
Get a free 3BHK solar feasibility check. Our team reviews your roof share, society NOC format, and sanctioned load before you spend a rupee. Get your free quote →
Cost, Subsidy, and Payback Math for 3BHK
The ₹78,000 PM Suryaghar subsidy is fixed for any system 3 kW or larger. The economics shift when you account for actual generation and city-specific tariff slabs.
| City | 5 kW all-in | After subsidy | Annual generation | Annual savings | Payback |
|---|---|---|---|---|---|
| Jaipur | ₹2.60 lakh | ₹1.82 lakh | 8,250 kWh | ₹61,000 | 36 months |
| Mumbai | ₹2.65 lakh | ₹1.87 lakh | 7,200 kWh | ₹64,000 | 35 months |
| Delhi-NCR | ₹2.60 lakh | ₹1.82 lakh | 7,800 kWh | ₹58,000 | 38 months |
| Bengaluru | ₹2.58 lakh | ₹1.80 lakh | 7,500 kWh | ₹52,000 | 41 months |
| Hyderabad | ₹2.60 lakh | ₹1.82 lakh | 7,950 kWh | ₹55,000 | 40 months |
| Chennai | ₹2.62 lakh | ₹1.84 lakh | 7,350 kWh | ₹53,000 | 42 months |
Assumptions: 75% performance ratio (PR), city-specific PSH, blended tariff after slab mix, 0.5% annual degradation per IS-IEC 61215. The Mumbai payback comes in shorter than Jaipur despite lower PSH because BEST and Tata Power retail tariffs are higher. For a per-bill payback calculation, use the Heaven Green solar calculator.
For the deeper subsidy breakdown including state-level adders where applicable, see the PM Suryaghar complete guide.
25-year cumulative savings on a 5 kW 3BHK system
The 36-month payback headline understates the lifetime case. A 5 kW apartment solar system generates roughly 1.85 lakh kWh over 25 years after accounting for the standard 0.5%/year degradation curve. At a blended ₹7.20/kWh tariff that’s ₹13.3 lakh of gross savings, against ₹1.82 lakh out-of-pocket — a 7.3x return on capital, tax-free, and inflation-hedged because retail electricity tariffs in India have risen 4–6%/year for the last decade. The economics aren’t close. The only question is whether your specific flat clears the sanctioned-load and society-NOC gates, which is what the 6-input design method is built to answer in the first half-hour of a feasibility call.
Design Considerations Unique to Apartment Living
A bungalow design copies poorly to an apartment. Five factors change.
Shared roof access. Wiring runs from the rooftop array to your flat’s electrical panel pass through common risers. The society must agree to the conduit route in writing — typically as part of the NOC. Heaven Green’s installers carry RWA-format route diagrams to make this approval painless.
Common-area meter vs flat meter. The common-area meter (lifts, lights, pumps) is the RWA’s connection; your flat’s individual meter is yours. PM Suryaghar can subsidise either — but only one at a time per registered consumer ID. Choose based on whose bill the solar should offset.
NMM at flat connection. The net meter must be installed at the flat-level DISCOM connection point, not at the rooftop junction. This adds wiring length and conduit cost compared with a bungalow setup. Budget ₹8,000–₹15,000 extra for vertical run material on a G+7 to G+12 building.
Sanctioned load is usually the constraint, not roof. Most 3BHK flats have 4–6 kW sanctioned load and 200–300 sqft of roof share. The sanctioned load caps system size first. File a load enhancement before applying for solar if your design needs more.
Earthing per IS 3043. Common-area earthing in apartments is often shared and may not meet IS 3043 requirements for solar systems. A dedicated earth pit (or two) for the solar inverter and DC array is mandatory for safe commissioning.
Lightning protection on shared roofs. A rooftop solar array in an apartment is one of the tallest points on the building once mounted. If the building already has a lightning arrester, the new array must tie into it; if not, the installation must include a Type-1 surge protection device (SPD) at the inverter input. DISCOM inspectors specifically check this on apartment installations because the consequence of a strike on shared roof equipment is more serious than on an individual bungalow.
Common 3BHK Sizing Mistakes
Across the 3BHK installations we’ve delivered, six mistakes show up repeatedly. Each one costs subsidy, generation, or both — and every one is preventable with the 6-input method. The pattern is so consistent that we now run a pre-quote audit specifically to catch these issues before the customer signs anything. Most of these mistakes originate from installers quoting on bill amount alone, without asking for the seasonal profile, the sanctioned load print, the society NOC format, or the EV plan.
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1
Sizing on January bill instead of annual average. Winter bills under-represent AC load. Use 12-month average and add a 20% summer cushion.
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2
Capping at 3 kW just to "max the subsidy." The subsidy is fixed at ₹78,000 for any size 3 kW and above — extra kilowatts above 3 kW still earn full net-metering returns. Don't undersize to chase a number.
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3
Ignoring sanctioned load. A 5 kW system on a 4 kW sanctioned load triggers feasibility rejection. File for load enhancement first; it adds 15–25 days but saves the application.
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4
No EV planning. Buying an EV within 3 years adds 400+ kWh/month to your load. A 5 kW design suddenly under-generates. Plan for the EV upfront.
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5
Generic society NOC. A typed "no objection" without society letterhead and secretary signature fails DISCOM feasibility every time. Use the format checklist above.
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6
Off-ALMM panels to cut cost. Panels not on the MNRE ALMM (Approved List of Models and Manufacturers) list fail inspection and forfeit the ₹78,000 subsidy. Verify the model before signing.
A seventh, subtler mistake worth flagging — sizing on bill amount without checking the slab structure. A ₹3,200 bill at ₹6/kWh blended is 530 kWh; the same ₹3,200 bill in a high-tariff Mumbai building is 380 kWh. Two different sizing answers from the same bill rupee figure. Always work from kWh, not rupees, and pull the slab consumption print from the bill itself rather than back-calculating from the total.
3kW Max-Subsidy vs 5kW Better-Coverage
This is the single design decision most 3BHK owners debate. Both qualify for the full ₹78,000 PM Suryaghar subsidy. Here is the head-to-head.
- + Lowest out-of-pocket: ₹87,000
- + Fastest payback: 28 months
- + Fits 180 sqft roof share — easier RWA approval
- − Under-generates in May–June for 3-AC homes
- − No EV expansion headroom
- + Covers full summer 3-AC load
- + Same ₹78,000 subsidy applied
- + Headroom for one EV within 3 years
- − Higher out-of-pocket: ₹1.82 lakh
- − Needs 300 sqft roof share + 5 kW sanctioned load
Verdict. For a 3BHK with 3 ACs and a monthly bill above ₹3,500, the 5 kW system wins — same ₹78,000 subsidy, materially better summer coverage, and 36-month payback that still beats most fixed-deposit returns. The 3 kW option is right only when the monthly bill is consistently under ₹3,500 or the roof share is capped at 200 sqft. Don’t undersize a 25-year asset to chase a one-time subsidy ratio.
The subsidy-to-system-cost ratio looks better at 3 kW (47%) than at 5 kW (30%), and that headline number is what most installer quotes anchor on. But absolute rupee savings — not subsidy percentage — is what your bank account experiences. A 5 kW system saves ₹61,000/year against a 3 kW system’s ₹40,000/year; the extra ₹21,000/year compounds over 25 years to ₹5.2 lakh of additional lifetime savings, against an incremental investment of only ₹95,000. That’s the math that should drive the decision, not the subsidy ratio.
How Heaven Green Energy Designs 3BHK Solar Systems
Heaven Green Energy is MNRE-empanelled across all major DISCOMs and we run a dedicated apartment-solar workflow. For 3BHK flat owners, the process is end-to-end:
- 6-input sizing call with last 12 months of bills, AC inventory, and society NOC pre-check.
- RWA liaison — we draft the NOC in the format your DISCOM accepts, attend the society meeting if needed, and handle the roof-share negotiation.
- ALMM-listed tier-1 panels (Adani, Waaree, Tata) — never off-list imports — and BIS-certified inverters.
- Sanctioned-load enhancement application filed in parallel with the PM Suryaghar portal submission.
- Dedicated earth pit per IS 3043 for safe commissioning.
- Net meter coordination with DISCOM field engineers for first-pass inspection clearance.
- 25-year performance support backed by O&M contracts.
Explore the services that match your project:
- Residential Solar — 1–10 kW rooftop systems with PM Suryaghar subsidy handled end-to-end.
- Solar Calculator — see your 3BHK subsidy, payback, and savings in 60 seconds.
- Contact us — book a 3BHK feasibility call with the Heaven Green design team.
For step-by-step subsidy application, see the PM Suryaghar complete guide.
We’ve handled apartment installations across mid-rise housing societies in Jaipur, Mumbai, Delhi-NCR, Hyderabad, and Bengaluru — every project starts with the 6-input feasibility, ends with DBT subsidy credited to the flat owner’s account, and is backed by our 25-year performance guarantee. The team specifically knows how to navigate the soft politics of getting a society resolution passed, which is the single biggest cause of dropped apartment-solar projects across the industry.
If you’re at the stage of “I think my flat can do solar but I’m not sure about the NOC,” book a 30-minute call. We’ll review the last 12 months of your bills, check your sanctioned load and roof share, draft the society NOC in your DISCOM’s preferred format, and give you a firm 3 vs 5 vs 7 kW recommendation with a per-month savings number. No pressure, no marketing fluff — just the design output the 6-input method produces.
Frequently Asked Questions
What size solar system is best for a 3BHK apartment in India?
A 5 kW rooftop solar system is the best fit for a typical 3BHK apartment with three air-conditioners, a family of four, and a monthly bill of ₹3,500–₹5,000. It generates around 700 kWh/month, covers full summer load including peak AC use, and qualifies for the maximum ₹78,000 PM Suryaghar subsidy. For lower bills under ₹3,500/month or constrained roof share, the 3 kW option (28-month payback) is the better pick.
Can I install solar on my 3BHK flat without society approval?
No — a society NOC on RWA letterhead is mandatory for any rooftop solar installation in a registered cooperative housing society. The terrace is common property, and DISCOMs (JVVNL, BSES, MSEDCL, BESCOM, TPDDL) all require a valid society NOC during PM Suryaghar feasibility approval. The NOC must specify roof area allocated, conduit route permission, and net meter placement. Generic typed letters fail inspection.
How much does a 5 kW solar system cost for a 3BHK apartment in 2026?
A 5 kW rooftop solar system for a 3BHK apartment costs ₹2.55–₹2.70 lakh all-in across most Indian cities in 2026. After the fixed PM Suryaghar central subsidy of ₹78,000, the out-of-pocket lands at ₹1.77–₹1.92 lakh. This includes tier-1 ALMM panels, BIS-certified inverter, mounting structure for apartment roof, AC and DC cabling, dedicated earth pit, and net meter coordination. Vertical conduit runs in mid-rise buildings can add ₹8,000–₹15,000.
How much roof area does a 3BHK apartment need for 5 kW solar?
A 5 kW rooftop solar system needs approximately 300 sqft of shadow-free roof area. In a mid-rise apartment (G+7, 12–24 flats), the per-flat roof allocation is typically 150–250 sqft — which may cap your system at 3 kW unless you negotiate a larger share with the RWA. Penthouse and top-floor flats with private terraces are not limited by allocation. Always confirm the allocated area in writing as part of the society NOC.
Is my flat’s sanctioned load enough for a 5 kW solar system?
Most 3BHK flats in India have a sanctioned load of 4–7 kW on the DISCOM connection. Your rooftop solar capacity cannot exceed the sanctioned load without filing a separate load enhancement application — typically 15–25 working days. Check the “Sanctioned Load” or “स्वीकृत भार” figure on your monthly bill before sizing. A 4 kW sanctioned load flat needs enhancement to install 5 kW solar; this can be filed in parallel with the PM Suryaghar application.
Does the ₹78,000 PM Suryaghar subsidy apply to apartment flats?
Yes — the ₹78,000 PM Suryaghar central subsidy applies to any individual residential connection with a 3 kW or larger solar system, whether the home is an independent bungalow or a flat in a cooperative housing society. The subsidy is released via Direct Benefit Transfer (DBT) to the Aadhaar-linked bank account within 30 days of DISCOM commissioning. Society NOC and individual flat metering are required for apartment applications.
How long does the PM Suryaghar process take for a 3BHK flat owner?
A typical 3BHK PM Suryaghar application takes 60–90 days end-to-end: portal registration and document submission (3–5 days), DISCOM feasibility approval (10–18 days), society NOC and load enhancement if needed (15–25 days, often parallel), installation (3–5 days), net meter inspection (7–14 days), and subsidy DBT credit (up to 30 days). Apartment applications take 10–15 days longer than bungalow applications on average due to NOC processing.
Should a 3BHK flat owner install solar individually or through an RWA group system?
It depends on building size and consumption profile. For low-rise buildings (G+3, 6–8 flats) with adequate roof share, individual flat installations work well. For mid-rise and high-rise buildings (G+7 and above), the RWA-stack model — where the society installs a single larger system with the ₹18,000/kW group housing subsidy and credits common-area savings proportionally — usually beats individual installations on per-kW economics. Heaven Green offers both pathways; the right one depends on a 6-input feasibility review.
