"How many units will it make?" is the first thing almost everyone asks us. It deserves a straight answer rather than the best-case figure that ends up in a lot of brochures.
The short answer
A well-designed, shadow-free plant on the plains of Bengal makes about 3.4 to 4 units per kW per day, averaged over a full year. That's roughly 1,240 to 1,460 units per kW per year. Sites further south, around Kolkata, often do a little better.
You will see 4.5 or even 5 units per kW quoted. We don't use those figures, because satellite weather data for Siliguri doesn't support them. When we modelled a site near Fulbari using PVGIS, the European Commission's solar database, a south-facing roof at a gentle 10° tilt came out at 3.43 units per kW per day. Even at the ideal tilt for this latitude it was 3.65. An east-west roof was 3.19.
By plant size
| Plant size | Units a day | Units a month | Units a year |
|---|---|---|---|
| 1 kW | 3.4 – 4 | 102 – 120 | 1,240 – 1,460 |
| 2 kW | 6.8 – 8 | 204 – 240 | 2,480 – 2,920 |
| 3 kW | 10.2 – 12 | 306 – 360 | 3,720 – 4,380 |
| 5 kW | 17 – 20 | 510 – 600 | 6,210 – 7,300 |
| 10 kW | 34 – 40 | 1,020 – 1,200 | 12,410 – 14,600 |
| 50 kW | 170 – 200 | 5,100 – 6,000 | 62,050 – 73,000 |
| 100 kW | 340 – 400 | 10,200 – 12,000 | 1,24,100 – 1,46,000 |
It isn't the same every month
Generation follows the weather and the length of the day. March to May are usually the strongest months here: clear skies and long days. The weakest are December and January, when days are short and winter haze sits over the plains. July to September dip too, on cloudy, rainy days.
That's why we quote a yearly figure and show the monthly pattern alongside it. If someone shows you a single number built on a sunny April, ask them what happens in December.
Under net metering the swings mostly even out. Extra units in a good month are credited and used against what you draw in a poor one, as long as it all balances before the bank resets on 1 April.
What lowers output on a real roof
- Shade. Water tanks, parapets, stair rooms, trees and taller buildings next door. Shade on one panel can drag down a whole string, so the layout matters as much as the size.
- Direction. South-facing is best here. East-west layouts lose around 7%, which is often a fair trade on a shed roof.
- Dust. In dry months panels can lose a noticeable share of output within a couple of weeks. A rinse with plain water every fortnight in the dusty season keeps generation up.
- Heat. Panels make slightly less when they're very hot. Airflow underneath helps, which is one reason elevated structures do well.
- Hills. Darjeeling, Kalimpong and Sikkim are a different story. Slope, aspect and morning cloud change from one site to the next, so we always simulate hill sites individually.
Over 25 years and more
Panels slowly lose output with age. Waaree's N-Type TOPCon modules carry a linear warranty: at least 99% of rated output in the first year, then no more than 0.4% loss a year, which still leaves 87.4% in year 30. A plant keeps doing most of its job for a very long time.
A number for your roof
Every Solarverse proposal includes a 3D model of your actual roof with month-by-month generation, so the figure is for your building rather than an average. For a quick first estimate, try the estimator. If you're still working out the size, start with how many kW your home needs.
Quick answers
How many units does a 5 kW solar plant generate per day?
In Bengal, about 17 to 20 units a day averaged over the year, or roughly 510 to 600 units a month.
Does solar work in the monsoon?
Yes, but output drops on cloudy, rainy days. The monsoon months make less than spring, though December and January are usually lower still. Net metering credits extra units from sunnier months against them.
How much does a 1 kW solar plant produce in a month?
About 102 to 120 units a month on average on the plains of Bengal.