How Many Units Does 1 kW Solar Generate?
The most asked solar question, answered with real numbers: daily, monthly and yearly generation by system size and city, and what quietly reduces your output.
Rainbow Solar Energy Team
6 min read
Updated
In this article
Key takeaways
- In Tamil Nadu, 1 kW of solar makes about 4 units a day, roughly 120 units a month and 1,450 units a year.
- Output varies by place: about 3.6 units/kW/day in the Nilgiris and up to 4.5 in Tirunelveli and Thoothukudi.
- Summer months produce more and monsoon months less, but net metering balances it over the year.
- Shade, dust, heat and poor tilt can cut output by 10–25%, so design and maintenance matter.
Every solar quote starts from one number: how many units (kWh) each kilowatt of panels will produce on your roof. Get it right and you size the system correctly; get it wrong and you either overpay or still get an electricity bill.
Units generated by system size (Tamil Nadu)
| System size | Units per day | Units per month | Units per year | Suits monthly use of |
|---|---|---|---|---|
| 1 kW | ~4 | ~120 | ~1,450 | Up to 130 units |
| 2 kW | ~8 | ~240 | ~2,900 | 130 – 250 units |
| 3 kW | ~12 | ~360 | ~4,350 | 250 – 400 units |
| 5 kW | ~20 | ~600 | ~7,300 | 500 – 650 units |
| 10 kW | ~40 | ~1,200 | ~14,600 | 1,100+ units |
Yearly averages for a south-facing, shadow-free roof. Your engineer confirms the figure for your roof after a site survey.
How location changes generation
Sunshine (solar irradiance) differs across Tamil Nadu and India. Our calculator uses your PIN code to pick the right figure:
| Location | Units per kW per day | Units per kW per year |
|---|---|---|
| Chennai | ~4.0 | ~1,460 |
| Coimbatore | ~4.2 | ~1,530 |
| Trichy, Salem | ~4.3 | ~1,570 |
| Madurai | ~4.4 | ~1,600 |
| Tirunelveli, Thoothukudi | ~4.5 | ~1,640 |
| Nilgiris (Ooty) | ~3.6 | ~1,310 |
| Rajasthan | ~4.8 | ~1,750 |
| Kerala, West Bengal | ~3.8 – 3.9 | ~1,400 |
Indicative yearly averages after normal system losses.
Enter your PIN code and bill or EB units in our solar savings calculator: it uses the sunshine for your area to size your system.
The simple formula
Daily units = system size (kW) × peak sun hours × performance ratio
Tamil Nadu gets about 5–5.5 peak sun hours a day on average. A well-installed system turns about 75–80% of that into usable AC power after losses in wiring, heat and the inverter. So 1 kW × 5.2 hours × 0.78 ≈ 4 units a day.
Month-by-month: summer vs monsoon
Tamil Nadu's generation peaks from March to May, when 1 kW can make 4.5–5 units a day. During the northeast monsoon (October to December), cloudy spells can drop it to 2.5–3.5 units. Net metering carries your summer surplus forward, so the annual average is what counts. Read more in do solar panels work on rainy and cloudy days.
5 things that reduce your units
- Shade from water tanks, parapets, trees or neighbouring buildings. Even partial shade on one panel can pull down a whole string.
- Dust and bird droppings, which can cost 5–15% if panels aren't cleaned. See our cleaning and maintenance guide.
- Heat. Panels lose about 0.3–0.4% output for every °C above 25°C, so good airflow under raised structures helps.
- Wrong tilt or direction. In Tamil Nadu, panels should face south at a tilt of about 10–15°.
- Ageing. Panels lose roughly 0.5% a year, still giving 80%+ after 25 years.
Find out how many units your roof can make
Our engineer checks shade, tilt and space, then gives you a generation estimate in writing.
Using this to size your system
Add up the units on your last six TNPDCL bills, divide by 12 to get monthly units (TNPDCL bills every two months), then divide by 120. A home using 360 units a month needs about 3 kW. Compare the two most popular sizes in 3 kW vs 5 kW solar.
Written by our solar engineers and subsidy specialists, who design and install rooftop systems for homes, societies and businesses across Tamil Nadu. Figures are indicative and reviewed regularly; your free site survey gives exact numbers for your roof.
