How Much Solar for 300 Units a Month? 3 kW Explained
300 units a month needs about 2.4 kW of solar; most homes fit 3 kW. Roof area, 2026 cost, ₹78,000 subsidy and real savings, city by city.
Short answer: 300 units a month is 3,600 units a year. At a typical Indian rooftop yield of 1,400–1,650 units per kW per year, you need about 2.2 to 2.6 kW. Most homes install 3 kW, which also collects the maximum PM Surya Ghar subsidy of ₹78,000 (check current notification). Plan for about 250–300 sq ft of shadow-free roof.
The calculation
- Yearly use = 300 × 12 = 3,600 kWh
- Size = 3,600 ÷ city yield
| City | Yield (kWh/kWp/yr) | Exact size | Typical install |
|---|---|---|---|
| Pune | 1,513 | 2.38 kWp | 3 kW |
| Nagpur | 1,490 | 2.42 kWp | 3 kW |
| Surat | 1,553 | 2.32 kWp | 2.5–3 kW |
| Jodhpur | 1,659 | 2.17 kWp | 2.5 kW |
| Lucknow | 1,390 | 2.59 kWp | 3 kW |
| Hyderabad | 1,510 | 2.38 kWp | 3 kW |
| Coimbatore | 1,513 | 2.38 kWp | 3 kW |
| Bhopal | 1,518 | 2.37 kWp | 3 kW |
Long-term Global Solar Atlas yields, derated 5% for rooftop losses (Sunlectric Studio data, Oct 2026).
Why 3 kW is the sweet spot
- Subsidy cap. The central subsidy maxes out at 3 kW. For a 3 kW system it is ₹30,000 + ₹30,000 + ₹18,000 = ₹78,000.
- Equipment fits neatly. Five or six modules of 540–590 Wp give 2.7–3.5 kWp on a standard 3 kW single-phase inverter.
- Headroom. The extra output covers panel ageing, dusty weeks and the next appliance you add.
The CFA is counted on the lower of the module (DC) and inverter (AC) capacity, so a 3.3 kWp array on a 3 kW inverter is treated as 3 kW.
How much roof do you need?
Six modules of about 2.3 m × 1.1 m cover roughly 15–16 m² (160–170 sq ft). On a flat RCC roof, add space for walkways, setbacks and row gaps. Budget 250–300 sq ft of roof that stays shadow-free from about 9 am to 3 pm.
In Maharashtra and Karnataka, many residential structures are raised about 1 m above the slab so the terrace stays usable for drying clothes and storage. That costs a little more steel but keeps your roof useful.
What does it cost in 2026?
| Item | 3 kW on-grid, DCR modules |
|---|---|
| Installed price before subsidy | about ₹1.5–2.1 lakh |
| Central subsidy (PM Surya Ghar) | ₹78,000 (check current notification) |
| State top-up | only in some states (UP, Rajasthan for small systems, Chhattisgarh, AP for some groups) |
| Net cost to you | about ₹70,000–1.3 lakh |
| Yearly generation | about 4,100–4,900 kWh |
The GST on solar modules and solar power devices fell from 12% to 5% from 22 September 2025, which brought system prices down. When an installer bills one composite supply-and-install contract, the effective GST is about 8.9% under the 70:30 valuation rule (check with your CA). See solar cost per kW in 2026.
How much will you save?
Savings depend on what each unit costs you at the margin, the "top slab". For a home using 300 units:
- Maharashtra (MSEDCL): units between 101 and 300 cost ₹10.80 energy + ₹1.60 wheeling, plus 16% electricity duty, about ₹14.4 per unit. If solar covers all 300 units, the energy, wheeling and duty part of the bill (about ₹42,000 a year) goes, plus a small surplus payment (check your bill, as rates were revised several times).
- Gujarat: the slab rate is about ₹4.15–5.20, but the fuel surcharge (FPPAS) adds roughly ₹2.5–3 per unit. Real value is about ₹7–8 per unit.
- Karnataka: a flat ₹5.80 plus tax and surcharge, but Gruha Jyothi free units may already cover part of your use.
Use the payback simulator to see your own case:
Monthly reality: monsoon vs summer
A 3 kW system in Pune makes about 470 units in March but only about 240 in July, when clouds roll in. Net metering smooths this out: surplus from sunny months is banked and used in cloudy months, then settled at the end of the year in most states. Read solar in the monsoon for what to expect.
Common mistakes at 300 units
- Oversizing to "make money". In most states surplus units at the year-end are paid at ₹2–3.9, while you spent about ₹55,000–70,000 per kW to make them.
- Ignoring sanctioned load. If the bill says 2 kW sanctioned, ask the installer to apply for enhancement along with the solar application.
- Buying non-DCR panels and expecting subsidy. Only DCR modules qualify. From 1 June 2026 new net-metered systems also need modules with ALMM List-II (approved) cells. See DCR vs non-DCR.
- Choosing on price per watt alone. The structure, earthing and cabling decide whether the system lasts 25 years. Use our installer checklist.
When 300 units means a bigger system
If your bill is 300 units in winter but 450 in summer because of AC use, size for the yearly average, not the winter month. Add up 12 bills and divide by 12. If the average is closer to 400–500, read solar for 500 units. If it is nearer 200, see solar for 200 units.
Talk to Sunlectric
Not sure if your roof fits 3 kW? WhatsApp a photo of your bill and roof to +91 89567 89307 (wa.me/918956789307). Our Solar Desk will check the size, and our network of registered installers can quote with modules, inverter and structure dispatched from our Pune hub the same day. Installers can design the job in Sunlectric Studio.
Sources
- PM Surya Ghar CFA (₹30,000/kW up to 2 kW, ₹18,000 for the third kW, max ₹78,000): pmsuryaghar.gov.in; PIB guidelines document, Aug 2024; Mercom on revised CFA norms (accessed Oct 2026)
- GST cut on solar devices to 5% from 22 Sep 2025 and 70:30 composite rate: Reslink, 2025
- ALMM List-II for cells from 1 Jun 2026: SolarQuarter, 29 Jul 2025; Angel One, 26 May 2026
- MSEDCL tariff FY 2026-27: MSEDCL tariff details (rates medium confidence; verify on bill)
- City yields: Global Solar Atlas, fetched 19 Oct 2026
Questions people ask
Is 3 kW solar enough for 300 units per month?
Yes. A 3 kW on-grid system makes about 4,100–4,900 units a year, or 340–410 a month on average. That covers 300 units with margin in most cities, though monsoon months will fall short and winter months will run ahead.
Why does 3 kW get the maximum subsidy?
PM Surya Ghar pays ₹30,000 per kW for the first 2 kW and ₹18,000 for the third kW, capped at ₹78,000. Anything above 3 kW gets no extra central subsidy (check current notification).
Can a 3 kW system run my AC?
An on-grid system does not run any appliance directly; it feeds your home and the grid together. Over a year, 3 kW produces enough units to offset roughly one 1.5-ton inverter AC used a few hours a day plus normal household loads.
Do I need three-phase supply for 3 kW?
No. A 3 kW system works on a normal single-phase connection. Your sanctioned load should be at least 3 kW in most states.