On This Page
Quick answer: A well-installed 1 kW rooftop system in Tamil Nadu generates about 4 units (kWh) a day on average across the year — roughly 120–130 units a month and 1,450–1,550 units a year. That means a 3 kW system makes about 12–13 units a day, a 5 kW system about 20–21, and a 10 kW system about 40–42. Output peaks in February–April (close to 5 units/kW/day) and dips in November during the northeast monsoon (around 3.2–3.6 units/kW/day).
These are the numbers our solar calculator uses (4.2 units/kW/day), and they are the numbers you should hold an installer to.
Daily and Monthly Generation by System Size
Annual average, south-facing or flat-tilted panels, no significant shading:
| System size | Units per day | Units per month | Units per 2-month TANGEDCO cycle | Units per year |
|---|---|---|---|---|
| 1 kW | 4.0–4.3 | 120–130 | 240–260 | 1,450–1,550 |
| 2 kW | 8.0–8.5 | 240–260 | 480–520 | 2,900–3,100 |
| 3 kW | 12–13 | 360–390 | 720–780 | 4,350–4,650 |
| 5 kW | 20–21 | 600–650 | 1,200–1,300 | 7,250–7,750 |
| 10 kW | 40–42 | 1,200–1,300 | 2,400–2,600 | 14,500–15,500 |
The bi-monthly column matters most, because TANGEDCO bills you every two months. Compare it directly against the "units consumed" line on your EB bill.
Month-by-Month: Chennai, Coimbatore and Madurai
Units per kW per day. These are modelled estimates built from long-term solar irradiance data for each city, with a system performance ratio of about 77% (which accounts for heat, inverter losses, wiring and normal dust).
| Month | Chennai | Coimbatore | Madurai |
|---|---|---|---|
| January | 4.2 | 4.6 | 4.5 |
| February | 4.8 | 5.0 | 5.0 |
| March | 5.0 | 5.1 | 5.1 |
| April | 4.9 | 4.9 | 5.0 |
| May | 4.6 | 4.4 | 4.6 |
| June | 4.1 | 3.7 | 4.3 |
| July | 3.9 | 3.6 | 4.2 |
| August | 4.0 | 3.8 | 4.2 |
| September | 4.0 | 4.0 | 4.1 |
| October | 3.7 | 3.8 | 3.8 |
| November | 3.2 | 3.6 | 3.5 |
| December | 3.5 | 4.0 | 3.9 |
| Annual average | ~4.2 | ~4.2 | ~4.4 |
Three patterns stand out:
- Chennai loses most in October–December. The northeast monsoon brings the city most of its rain, so heavy cloud cover cuts output. See solar during the northeast monsoon.
- Coimbatore dips in June–August. The southwest monsoon pushes cloud through the Palakkad Gap, but the northeast monsoon is gentler there. See our Coimbatore installation guide.
- Madurai is the most even. It sits in a rain shadow for much of the southwest monsoon and gets less northeast monsoon rain than the coast.
May isn't the best month, even though it's the sunniest. Panels lose roughly 0.3–0.4% of output for every degree above 25°C, and rooftop panels in May often run at 60–65°C. Clear, cooler February and March days usually beat May. More on this in why generation drops in summer heat.
Why Your System Might Make Less
If your inverter app shows numbers well below the table, check these, roughly in order of how often they're the cause:
- Shading. A water tank, staircase head-room or neighbour's wall that shades even one panel for two hours can cut a string inverter's output by far more than one panel's share. Micro-inverters or optimisers limit the damage.
- Dust. In Tamil Nadu's dry months, uncleaned panels lose 5–15% within a few weeks. Hard-water cleaning leaves scale that's worse than dust; see cleaning with hard water.
- Orientation. North-facing tilt can cost 10–15% a year. Flat-mounted panels lose a little and collect more dust.
- Undersized or tripping inverter. If the inverter clips at noon or trips on high grid voltage, you lose your best hours. Your app's daily curve should look like a smooth hill, not a hill with a flat top or a gap. See how to read your inverter display.
- Grid outages. An on-grid inverter produces nothing while the grid is down. Here's why.
Panels also degrade by about 0.4–0.7% a year (most Tier-1 panels warrant at least 80% output at year 25), so expect year-10 numbers to be about 5% below year-1.
Using This to Size Your System
- Take the units consumed on your last six bi-monthly EB bills and average them.
- Divide by 250 (units one kW makes in a two-month cycle).
- Round up to the nearest whole kW.
A household using 750 units every two months needs 750 ÷ 250 = 3 kW. One using 1,200 units needs 5 kW. Sizing a little high is usually fine under net metering, since surplus units bank against later months. Sizing low leaves you in the expensive upper slabs. Our 3 kW vs 5 kW vs 10 kW cost comparison shows what each size costs after subsidy, and choosing the right capacity covers roof-space and sanctioned-load limits.
FAQ
How many units does a 1 kW solar system generate per day in Tamil Nadu?
About 4 units a day on average, ranging from roughly 3.2 units on cloudy northeast-monsoon days in November to around 5 units in February–March. That's roughly 120–130 units a month and 1,450–1,550 units a year.
How many units does a 3 kW solar system produce per month?
A 3 kW system in Tamil Nadu produces about 360–390 units a month, or 720–780 units per two-month TANGEDCO billing cycle. That's enough to bring most households using up to about 750 units bi-monthly close to a zero energy charge.
How many units does a 5 kW solar system generate per day?
About 20–21 units a day on average — 600–650 units a month or 1,200–1,300 units per bi-monthly cycle.
Which month gives the highest solar generation in Tamil Nadu?
February and March usually give the highest daily output: strong sun, clear skies and lower panel temperatures than April–May. November is usually the lowest, especially in Chennai and coastal districts.
Does solar work on cloudy or rainy days?
Yes, at reduced output. A heavily overcast day may produce 30–50% of a clear day's generation. Over a full monsoon month the average drop is much smaller, which is why November still averages around 3.2–3.6 units/kW/day. See does solar work in the rainy season.
Why is my solar generating less than 4 units per kW?
The most common causes are shading, dust or hard-water scale on the panels, north-facing tilt, and inverter clipping or tripping. Check one week of daily curves in your inverter app first. A dent at the same time every day points to shading; a flat top points to an undersized inverter.
Sources & Updates
- Tristar estimate (not measured data): the month-by-month table is our modelled estimate. It assumes typical long-term solar irradiance for each city and a 77% system performance ratio. It isn't the output of a specific installation. The 4.2 units/kW/day annual average is the figure our solar calculator uses.
- PVGIS: Photovoltaic Geographical Information System (European Commission Joint Research Centre): free satellite-based irradiance and PV yield modelling with Indian coverage. Use it to model your own roof's tilt and orientation.
- NREL PVWatts Calculator: an independent free yield estimator to cross-check monthly figures.
- Temperature loss of 0.3–0.4% per °C and degradation of 0.4–0.7% a year are typical datasheet values for mono-PERC and TOPCon panels. Check the datasheet and warranty for your own panel.
Real output varies by year, by roof and by how often panels are cleaned. Treat the table as a benchmark, not a guarantee.
Last verified: 5 November 2026.
Ready to Go Solar?
Get a personalized solar quote based on your electricity consumption and roof area.
Related Articles
Why Solar Output Drops in Summer: Heat Degradation
More sunlight doesn't always mean more power. Learn how extreme summer heat in Tamil Nadu causes 15–20% generation loss, what temperature coefficient means for your panels, and practical tips to minimize heat degradation.
Solar Panel Cleaning: Can You Use Hard Water in Coimbatore/Chennai?
Using bore water to clean your solar panels in Coimbatore or Chennai? The mineral deposits could be cutting your generation by 5–15%. Learn proper cleaning methods for hard water areas and maintain peak performance.
LPG vs Induction Cooking on Solar: Real Savings in Tamil Nadu
At ₹957.50 a cylinder in Chennai, does switching to induction cooking on rooftop solar pay off? The unit math per cylinder, why induction on grid power can cost more than LPG under TANGEDCO's slabs, and when adding solar for cooking makes sense.