3 kW is the most searched solar size in India, and for a good reason. It suits a normal family home, and it is exactly the point where central subsidy stops paying. Understanding both facts together tells you almost everything about sizing a system.
What it costs
| System type | Price range | What you get |
|---|---|---|
| On-grid, no battery | Rs 1,35,000 – 1,80,000 | Runs when the grid is up. Most common choice. |
| Hybrid, with battery | Rs 2,40,000 – 3,30,000 | Also gives backup during cuts. |
| Off-grid | Rs 2,70,000 – 3,60,000 | No grid connection at all. Rarely worth it in a city. |
Most homes should be looking at the first row. The other two roughly double the cost and give you backup, not savings — a distinction we come back to below.
What is inside that price
| Component | Share |
|---|---|
| Solar panels | 45 – 50% |
| Inverter | 15 – 20% |
| Mounting structure | 10 – 12% |
| Cables, protection, earthing | 8 – 10% |
| Installation labour | 8 – 10% |
| Net meter and paperwork | 3 – 5% |
What you actually pay after subsidy
Under PM Surya Ghar, a 3 kW system earns the maximum central subsidy:
So on a Rs 1,60,000 system:
| System cost | Rs 1,60,000 |
| Central subsidy | – Rs 78,000 |
| State subsidy, where it exists | varies |
| Your net cost | Rs 82,000 |
Why 3 kW and not more
This is the part installers do not lead with:
| System size | Subsidy | Subsidy per kW |
|---|---|---|
| 2 kW | Rs 60,000 | Rs 30,000 |
| 3 kW | Rs 78,000 | Rs 26,000 |
| 5 kW | Rs 78,000 | Rs 15,600 |
| 8 kW | Rs 78,000 | Rs 9,750 |
| 10 kW | Rs 78,000 | Rs 7,800 |
Look at the last column. Every kilowatt above the third is paid for entirely by you. A 10 kW system receives exactly the same Rs 78,000 as a 3 kW one.
That does not automatically make bigger systems wrong. It makes them a different decision:
- Go bigger only if you genuinely use more than about 400 units a month and your state gives proper net metering
- Do not go bigger if your state does net billing — your surplus is bought back at a much lower rate than you pay, so the extra panels earn very little
How many units will 3 kW make?
The working is straightforward:
That is roughly 350 units a month, or 11 to 12 units a day. By region:
| Region | Sun hours | Units per year |
|---|---|---|
| Rajasthan, Gujarat | 5.5 | ~4,600 |
| Maharashtra, MP, Telangana | 5.0 | ~4,200 |
| Delhi, UP, Punjab, Haryana | 4.6 | ~3,900 |
| Kerala, North East, hills | 4.2 | ~3,500 |
These are yearly averages. Monsoon months run well below, clear winter months well above. That swing is exactly why net metering matters — it lets you bank the surplus.
Is 3 kW right for your home?
Match it to your consumption, not to your house size:
| Monthly units | Suggested size |
|---|---|
| Up to 150 | 1 – 1.5 kW |
| 150 – 250 | 2 kW |
| 250 – 400 | 3 kW |
| 400 – 600 | 4 – 5 kW |
Find your units on the electricity bill — look for "units consumed" or kWh. Do not go by how big your house is. A large house with two people uses less than a small flat running two ACs.
Roof space needed
| Panel type | Area for 3 kW |
|---|---|
| Polycrystalline | 330 – 360 sq ft |
| Mono PERC | 270 – 300 sq ft |
| High efficiency | 225 – 255 sq ft |
Remember only about 80% of a roof is usable once you allow for the water tank, stairs, parapet shadow and walking space. So for 3 kW on mono PERC you want a roof of roughly 350 to 375 sq ft in total.
What it saves you
At Rs 8 per unit and 4,200 units a year:
In practice, payback for most homes lands between 3 and 5 years, because you rarely use every unit at the moment it is generated and tariffs vary by slab. After that you get around twenty more years of nearly free electricity.
One thing that projection leaves out: the inverter usually needs replacing once, somewhere around year 12 to 15. Budget Rs 25,000 to Rs 50,000 for it and subtract that from your lifetime figure.
Before you sign anything
- Use a vendor listed on the national portal. A cheaper quote from an unregistered vendor means no subsidy at all — and that is a Rs 78,000 mistake.
- Check for shading across the whole day, and think about whether a neighbour might build up.
- Confirm your state's metering rule before deciding size.
- Get the warranty in writing — panels, inverter and workmanship are three separate warranties.
- Verify current subsidy amounts on the official portal. They change, and nothing on this site is a substitute for the portal.
3 kW against the other common sizes
| Size | Cost | Subsidy | Net | Net per kW |
|---|---|---|---|---|
| 1 kW | Rs 60,000 | Rs 30,000 | Rs 30,000 | Rs 30,000 |
| 2 kW | Rs 1,12,000 | Rs 60,000 | Rs 52,000 | Rs 26,000 |
| 3 kW | Rs 1,60,000 | Rs 78,000 | Rs 82,000 | Rs 27,300 |
| 5 kW | Rs 2,55,000 | Rs 78,000 | Rs 1,77,000 | Rs 35,400 |
| 8 kW | Rs 3,92,000 | Rs 78,000 | Rs 3,14,000 | Rs 39,250 |
Look at the last column. Net cost per kW is lowest around 2 to 3 kW and climbs steadily after that. An 8 kW system costs 44% more per kilowatt than a 3 kW one, entirely because the subsidy stopped.
What a 3 kW system runs
At about 350 units a month, a 3 kW system covers the normal consumption of a family home:
| Appliance | Watts | Units per month |
|---|---|---|
| Fridge | 150 | ~36 |
| 4 fans, 10 hours | 300 | ~90 |
| LED lighting | 100 | ~18 |
| TV, 5 hours | 100 | ~15 |
| Washing machine | 500 | ~15 |
| Geyser, winter | 2,000 | ~60 |
| 1.5 ton AC, 6 hours | 1,500 | ~270 |
Everything except the AC comes to roughly 234 units. Add one AC running six hours a day and you are past 500. Air conditioning is the single item that decides your system size — a home with no AC rarely needs more than 2 kW.
What can go wrong, and what it costs
| Problem | Effect | Avoidable? |
|---|---|---|
| Unregistered vendor | No subsidy — Rs 78,000 | Yes, check the portal |
| Shading discovered later | 10 – 40% less output | Yes, survey properly |
| Sanctioned load too low | Application rejected | Yes, check before applying |
| Name mismatch on documents | Subsidy not transferred | Yes, fix first |
| Cheap inverter | Failure in 3 – 5 years | Yes, insist on brand |
| Neighbour builds up | Permanent output loss | Partly — ask around first |
Questions people ask
How much does 3 kW save per month?
About 350 units. At Rs 8 that is roughly Rs 2,800 a month, though the exact figure depends on your tariff slab and how much you use during daylight.
Will my bill become zero?
Close, but not exactly. Fixed charges, meter rent and electricity duty stay on the bill regardless of generation. Most people with a well-sized system see their bill drop to a few hundred rupees.
How long does installation take?
The physical work is two to five days. The whole process from application to a working net meter is three to five months, and almost all of that wait is with the DISCOM.
What maintenance does it need?
Cleaning, monthly in most places and fortnightly in dusty areas. Beyond that, an annual check of connections and mounting. There are no moving parts.
Can I add panels later?
Sometimes, if the inverter has headroom and the DISCOM approves the higher capacity. It is cheaper to size correctly at the start — the second installation pays no subsidy and repeats the fixed costs.
Is 3 kW enough if I have one AC?
Usually yes if the AC runs a few hours a day, and it will be tight if it runs all night through summer. Look at your May and June bills rather than your annual average — those are the months that decide the size.
What if my sanctioned load is only 2 kW?
Many DISCOMs cap the system at your sanctioned load, so you would need to raise it before installing 3 kW. That is a separate application with its own fee and its own waiting period, so start it early rather than discovering it at the feasibility stage.
Do I need permission from my housing society?
For an independent house, no. In an apartment or a gated society the terrace is usually common property, and you will need a written no-objection. Get this before applying — DISCOMs ask for it and it is the step most likely to take months.