Solar System for Home: Size, Cost and the 3 kW Cliff
The right solar system for home use is the one that matches your actual consumption, and you can calculate it from your electricity bill in one line: divide your monthly units by 120. A house consuming 360 units a month needs roughly 3 kW. That figure, worked out before you speak to a single installer, is the most useful thing you can bring to a quote, because it stops you being sold a system sized to the seller's margin rather than your load.
This guide gives you the arithmetic, the appliance numbers behind it, and the two places where the economics break in ways nobody quotes.
At a glance
Question | Answer |
|---|---|
Sizing shortcut | System kW is roughly monthly units divided by 120 |
Generation planning figure | 4 units per kW per day |
Roof area | About 100 sq ft per kW installed |
On-grid installed cost | ₹50,000 to ₹75,000 per kW |
Hybrid installed cost | ₹80,000 to ₹1,00,000 per kW with tubular batteries |
Off-grid installed cost | ₹90,000 to ₹1,25,000 per kW |
Maximum central subsidy | ₹78,000, reached at 3 kW |
Backup during outage | On-grid no, hybrid and off-grid yes |
Realistic payback, on-grid | 4 to 6 years post-subsidy |
Annual maintenance | ₹6,000 to ₹9,000 for 3 to 5 kW |
Panel degradation | 0.5% to 0.7% a year |
All figures September 2026 and time-sensitive. Verify at publish.
The sizing calculation
Two steps, and you can do them on your last twelve electricity bills.
Daily consumption (units) = Monthly units ÷ 30System size (kW) = Daily consumption ÷ Daily generation per kW
At the national planning figure of 4 units per kW per day, this collapses to:
System size (kW) ≈ Monthly units ÷ 120
Use a twelve-month average, never a summer bill. This is the single most common sizing error in India. Peak air-conditioning months overstate annual load by 40% to 60%, and a system sized on a May bill will spend eight months of the year exporting surplus at a settlement rate well below what you pay for imports.
Worked examples:
System | Monthly units covered | Daily generation | Annual generation | Bill band it suits |
|---|---|---|---|---|
1 kW | ~120 | 4 units | 1,450 to 1,550 | ₹800 to ₹1,200 |
2 kW | ~240 | 8 units | 2,900 to 3,100 | ₹1,500 to ₹2,500 |
3 kW | ~360 | 12 units | 4,400 to 4,650 | ₹2,500 to ₹4,500 |
5 kW | ~600 | 20 units | 7,300 to 7,700 | ₹4,500 to ₹7,500 |
10 kW | ~1,200 | 40 units | 14,500 to 15,500 | ₹7,500 to ₹15,000 |
A cross-check some installers use: system kW is roughly your monthly bill in rupees divided by 1,800. If the two methods disagree by more than about 20%, your tariff slab is unusual and the unit-based calculation is the one to trust.
Regional adjustment. The 4 units per kW per day figure is a national average. Jodhpur and Ahmedabad achieve 5.5 to 6.2 units in good conditions; Mumbai and Delhi sit at 4.8 to 5.2 before losses; the North East is lowest. Those higher city figures are pre-loss theoretical yields. Once you subtract soiling at 8% to 18%, partial shading at 5% to 25%, inverter losses at 3% to 8%, cable losses and summer temperature derating, real-world output lands close to the conservative 4. Size on 4 and be pleasantly surprised.
What your appliances actually draw
Sizing from the bill is more reliable than sizing from an appliance list, because bills capture behaviour and lists capture intentions. But the appliance numbers matter for a different reason: inverter sizing.
Appliance | Running watts | Typical daily units |
|---|---|---|
LED bulb | 9 to 12 W | 0.05 to 0.10 |
Ceiling fan, conventional | 70 to 80 W | 0.6 to 0.8 |
Ceiling fan, BLDC | 28 to 35 W | 0.25 to 0.35 |
LED TV, 32 to 43 inch | 60 to 120 W | 0.3 to 0.6 |
Refrigerator, single door | 100 to 250 W | 1.0 to 1.8 |
Refrigerator, double door | 150 to 400 W | 1.5 to 3.0 |
Washing machine | 400 to 800 W | 0.5 to 1.5 |
Water pump, 0.5 to 1 HP | 450 to 900 W | 0.5 to 1.5 |
Microwave | 1,000 to 1,500 W | 0.3 to 0.7 |
Geyser | 2,000 to 3,000 W | 0.6 to 2.0 |
AC 1.5 ton, 3 star | 1,400 to 1,800 W | 9 to 14 |
AC 1.5 ton, 5 star inverter | 900 to 1,500 W | 6 to 10 |
The detail competitors omit: startup surge. Motor-driven appliances draw three to six times their running wattage for a moment at start. A 900W water pump can demand 2,700W to 5,400W for a second, and a 1.5 ton air conditioner can spike to 4,000W or more. On-grid systems ride this out on the grid. Off-grid and hybrid inverters must be sized to the surge, not the steady state, or they will trip every time the compressor kicks in.
Home solar system types: on-grid, off-grid and hybrid
On-grid | Hybrid | Off-grid | |
|---|---|---|---|
Battery | None | Yes | Yes |
Grid connection | Yes | Yes | No |
Cost per kW | ₹50,000 to ₹75,000 | ₹80,000 to ₹1,00,000 | ₹90,000 to ₹1,25,000 |
Works in a power cut | No | Yes | Yes |
Exports surplus for credit | Yes | Yes | No |
Central subsidy | Yes | Yes, solar portion only | No |
Payback | 4 to 6 years | Longer | Rarely on economics alone |
Best for | Stable-grid urban homes | Homes with frequent outages | Genuinely unelectrified sites |
The on-grid limitation surprises people, so state it plainly: a grid-tied inverter shuts down when the grid fails. That is anti-islanding protection, required so that a system does not energise a line a technician is working on. A plain on-grid system gives you cheaper electricity, not backup.
The subsidy position matters just as much. Off-grid systems get nothing under PM Surya Ghar because the guidelines exclude off-grid installations from central financial assistance. Battery-hybrid systems can qualify, but only where they remain grid connected, carry reverse power relay protection and have State Electricity Regulatory Commission approval, and the battery attracts no additional subsidy. So a household spending ₹2.7 lakh on a 3 kW hybrid receives the same ₹78,000 as one spending ₹1.8 lakh on 3 kW on-grid. The people who most want backup are buying the least-subsidised configuration.
Will a solar panel system for home use run an air conditioner
Yes, with an important qualification that consumer pages skip.
A 1.5 ton air conditioner running eight hours consumes roughly 9 to 14 units a day. A 3 kW system generates around 12 units a day. So a 3 kW system is the standard answer for one 1.5 ton AC, and the arithmetic works out over the billing cycle.
But the AC mostly runs at night, when the panels produce nothing. On-grid, the grid carries the night load and net metering settles the difference. On-grid solar does not run your air conditioner in real time. It cancels its bill.
To genuinely run a 1.5 ton AC overnight from stored energy, you need roughly 8 to 12 kWh of usable battery, which at lithium prices of ₹25,000 to ₹40,000 per nominal kWh is ₹2.5 lakh to ₹5 lakh on top of the panels. That is the honest answer to the most-asked question in this category, and it is why hybrid quotes look so different from on-grid quotes.
Rough guidance: one inverter AC points to 3 kW; two ACs running six to eight hours points to 5 kW; three or more points to 10 kW.
Residential solar system costs by type
Published per-kW figures vary by more than two to one across sources, which usually reflects module tier, whether DCR-compliant panels are used, and whether structure, net-metering liaison and protection equipment are bundled.
Worked 5 kW example, with the component split:
Component | Share of cost | 5 kW indicative |
|---|---|---|
Solar modules | 45% to 60% | ₹1,10,000 to ₹1,60,000 |
Inverter | 10% to 30% | ₹30,000 to ₹1,40,000 |
Mounting structure | 8% to 15% | ₹18,000 to ₹30,000 |
Wiring and protection | n/a | ₹15,000 to ₹30,000 |
Labour | n/a | ₹12,000 to ₹20,000 |
On-grid total | ₹2,30,000 to ₹2,70,000 |
Battery costs, where they apply, are where the largest source disagreements sit. Retail listings support the lower end: a 150Ah 12V tubular battery is 1.8 kWh nominal at ₹12,000 to ₹18,000, which is ₹6,700 to ₹10,000 per kWh. Honest bands are lead-acid at ₹7,000 to ₹12,000 per nominal kWh and lithium at ₹25,000 to ₹40,000.
Lithium LiFePO4 | Lead-acid tubular | |
|---|---|---|
Cost per nominal kWh | ₹25,000 to ₹40,000 | ₹7,000 to ₹12,000 |
Usable depth of discharge | 80% to 100% | 50% |
Cycle life | 4,000 to 6,000 | 500 to 1,500 |
Round-trip efficiency | 95% to 98% | 80% to 85% |
Service life | 10 to 15 years | 4 to 6 years |
Maintenance | None | Distilled water every 2 to 3 months |
Lead-acid looks cheaper and is not, once you account for 50% usable depth and a replacement at year five. Budget ₹60,000 to ₹80,000 every three to five years for a 3 kW off-grid lead-acid bank. Our comparison of lithium and lead-acid battery economics works through this in more detail.
Solar system cost: what the payback claims leave out
Claims in this market run from 1.5 years to 7. The spread is not dishonesty in every case, it is different assumptions left unstated.
Variable | Effect on payback |
|---|---|
Tariff | The biggest single factor. Gujarat at ₹5.50 to ₹6.50 per unit repays far faster than Delhi at ₹4.50 to ₹5.50 on identical hardware |
Daytime consumption | Self-consumption typically covers only 60% to 80% of the bill; the rest exports at ₹2 to ₹4 rather than offsetting at retail |
Tariff escalation | 8% to 10% a year improves returns over time |
Degradation | 0.5% to 0.7% a year erodes them slightly |
Maintenance | ₹6,000 to ₹9,000 a year for 3 to 5 kW, almost never counted |
Inverter replacement | Five to ten year warranty against 25 on panels; years four to seven are the failure window |
Add maintenance and one inverter replacement and realistic payback moves out by eight to fourteen months. Four to six years post-subsidy for on-grid in most states is the defensible figure. Three to four years happens only in high-tariff states with a state top-up and heavy daytime use.
What people get wrong when sizing
Oversizing errors, in order of frequency:
- Sizing on the summer bill. Use the twelve-month average.
- Choosing 4 kW over 3 kW. There is zero additional subsidy above 3 kW, so the fourth kilowatt costs full retail. If you need it, buy it. If it is headroom, expand later.
- Exceeding sanctioned load. Solar capacity must not exceed your sanctioned load for net metering approval. Exceeding it gets the application rejected or the excess disconnected, and a load enhancement application then takes two to four weeks.
- Going above 10 kW residential. Many DISCOMs drop net-metering eligibility above that, at which point exports settle near ₹3.35 per unit instead of offsetting ₹7 to ₹8 of consumption. That destroys roughly 60% of the value of every exported unit.
- Pre-building for a future electric vehicle. Install to current load.
Undersizing errors:
- Inverter sized to running watts, not surge. Causes clipping losses of 3% to 8% and nuisance trips on AC and pump startup.
- Skipping the shadow study. Water tanks and parapets cut output 15% to 25%, and partial shading is the largest single loss factor.
- Battery bank sized to average use with no autonomy factor. Discharging lead-acid past 50% repeatedly kills it in two years instead of five.
Honest pros and cons
What works. The subsidy is real and substantial at up to ₹78,000. Panels carry 25-year performance warranties and degrade slowly. Tariff escalation makes the investment better each year. A correctly sized 3 kW on-grid system on a decent tariff genuinely repays in four to six years and then runs for two decades more.
What the quotes hide. The subsidy stops dead at 3 kW, so large systems have far worse economics per rupee than the headline suggests. On-grid gives no backup at all. Battery backup for an air conditioner costs more than the entire solar array. Monsoon output drops 40% to 60% and winter fog can halve it in North India. Maintenance runs ₹6,000 to ₹9,000 a year and is worse per kW on small systems because labour is a fixed cost. The inverter will need replacing well before the panels do. Off-grid gets no subsidy whatsoever. And exports are settled below the rate you pay for imports, so a house empty all day earns less from the same system than one occupied.
Decision framework
Strong fit for on-grid at 3 kW. You consume 300 to 400 units a month, have 300 sq ft of shadow-free roof, are on a tariff above ₹6, own the property, and have someone home during the day. This is the configuration the scheme is designed around and it is where the economics are strongest.
Strong fit for hybrid. You have two or more outages daily, need specific loads to ride through them, and accept a longer payback in exchange for reliability. Buy it for the reliability, not the return.
Marginal fit. Consumption under 150 units a month, where even 1 kW repays slowly. Partial roof shading. A rented property, where roof consent and the connection holder's identity complicate the application. Consumption that genuinely needs 6 to 10 kW, where the subsidy covers a small fraction and a proposed net-metering charge on systems above 5 kW may apply from late 2026.
Not a fit. You want backup only, in which case an inverter and battery costs far less than a hybrid solar system. You cannot fund the full cost upfront and wait for reimbursement after commissioning. You have no allocated roof rights, though a housing society can apply collectively.
Frequently asked questions
How do I calculate what size solar system for home use I need?
Divide your average monthly units by 120. That gives system size in kW at the planning figure of 4 units per kW per day. A house using 360 units a month needs about 3 kW. Always use a twelve-month average rather than a summer bill, because peak air-conditioning months overstate annual load by 40% to 60%.
What is the cost of a home solar system in India?
On-grid costs ₹50,000 to ₹75,000 per kW installed, hybrid ₹80,000 to ₹1,00,000 per kW and off-grid ₹90,000 to ₹1,25,000 per kW. A 3 kW on-grid system is therefore ₹1.5 to ₹2.25 lakh before subsidy and roughly ₹72,000 to ₹1.47 lakh after the ₹78,000 central assistance.
Can a solar panel system for home use run a 1.5 ton AC?
A 3 kW system generates about 12 units a day and a 1.5 ton AC running eight hours uses 9 to 14 units, so the bill nets out. But the AC runs at night when panels produce nothing, so on-grid solar cancels the AC's bill rather than powering it live. Running one overnight from batteries needs 8 to 12 kWh of storage, which is ₹2.5 to ₹5 lakh of lithium.
What is the best size residential solar system for most Indian homes?
3 kW, for two reasons. It covers roughly 360 units a month, which matches typical urban consumption, and it is exactly where the central subsidy maxes out at ₹78,000. Every kilowatt above 3 receives no additional subsidy and is paid at full retail.
How much roof space does a home solar system need?
About 100 sq ft per kW of shadow-free roof, so 300 sq ft for 3 kW. The bare panel footprint with 540W modules is nearer 60 to 80 sq ft per kW; the extra allows for walkways, tilt spacing and shadow clearance. Older official guidance quoting 130 sq ft per kW was based on obsolete 250 to 330W panels.
What is the real solar system cost after maintenance and repairs?
Add an annual maintenance contract of ₹6,000 to ₹9,000 for a 3 to 5 kW system, plus at least one inverter replacement between years five and ten. Together these push realistic payback out by eight to fourteen months compared with claims that count only the purchase price.
Do I need a battery with a home solar system?
Only if you want power during outages. On-grid systems have no battery, cost the least and repay fastest, but shut down completely during a power cut. Batteries add 60% or more to the cost, receive no additional central subsidy, and in the case of lead-acid need replacing every four to six years.
How long does a solar system last?
Panels carry 25-year performance warranties and typically retain around 85% of rated output at year 25, degrading 0.5% to 0.7% a year. Inverters last five to ten years and will need replacing at least once. Lead-acid batteries last four to six years and lithium ten to fifteen.
Does a bigger solar system get a bigger subsidy?
No, and this is the most expensive misunderstanding in the category. Central assistance is ₹30,000 per kWp for the first 2 kW and ₹18,000 for the third, capped at ₹78,000 total. A 10 kW system receives exactly the same ₹78,000 as a 3 kW system.
What happens if my solar system is bigger than my sanctioned load?
The net-metering application is normally rejected, or the excess capacity is disconnected, and penalties or higher fixed charges can follow. You need a load enhancement application with your DISCOM first, which adds two to four weeks. Check your sanctioned load on your electricity bill before finalising system size.
.jpeg)
.jpeg)
.jpeg)
.jpeg)
