NCR solar generation: monsoon, dust, winter

A rooftop system in Delhi NCR does not make the same electricity every month. It generates the most in the long, clear days from March to June, dips through the monsoon cloud of July to September, recovers in the clear weeks of early October before the smog settles, and touches its lowest in the fog and short days of December and January. Averaged across a year, this site plans on Verde Solaire's published yield of 1,500 units per kW a year in Noida and 1,450 in Delhi , less a 10% derate for dust and season, which puts a 3 kW system at about 338 units a month in Noida and about 326 units a month in Delhi.

This page describes the pattern without inventing monthly percentages, explains why one month's reading misleads, and covers the two things an owner can do about the seasons: wash the glass after dust, and watch the numbers.

The year on a Delhi NCR roof

March to June. The days are longest and the sky clearest, so these are the months of highest generation. Two things take the edge off. A silicon panel makes slightly less electricity as its cells heat up, so a scorching May afternoon gives a little less than the same sunlight would at a cooler temperature; and from April the hot westerly wind brings dust storms that leave a film on the glass. A clean panel on a clear day in April is close to the best the roof will ever do.

Late June to September. The monsoon brings cloud, humidity and rain. Generation falls on overcast days and rises on the clear days between showers, and it never stops: panels produce from diffuse light as well as direct sun, so a grey day in August still puts units on the meter, just fewer of them. The rain washes off the summer's dust, though not bird droppings or the streaks it leaves as it dries. After the first heavy rain, check the DC and AC boxes for water and the sealant where the structure meets the roof; an earth-fault warning on a wet morning is the installer's job, and the common problems page explains those messages.

October and November. The rain stops, the air goes still, and the smog settles on every surface, including the glass. Early October can be as clear as spring; by November the haze cuts the light before it reaches the roof, and dust that is not washed off adds to the loss every day.

December and January. The lowest months. The days are short, the sun sits low, and fog can hide it until mid-morning. Nothing on the roof needs changing: the panels sit at the tilt that gives the best annual total. February starts the climb back.

None of this is a fault. It is the sky the whole of Delhi NCR sits under, and it is why every projection on this site works in years, not months.

What a 3 kW system produces, on average

The company's June 2025 guide to a 3 kW system in Delhi gives 360 to 400 units a month from 300 to 350 square feet of shadow-free roof. The calculator on this site plans lower on purpose. It starts from the yield Verde Solaire published on its 2023 savings pages, 1,500 units per kW a year in Noida and 1,450 in Delhi, and takes 10% off for soiling and season. That gives about 338 units a month in Noida and about 326 units a month in Delhi for 3 kW. The derate is a planning assumption, not a measurement of any roof, and the calculator prints it under every result.

The gap between the two figures is the seasons. A May reading will sit above the company's higher figure; a foggy January will sit below the calculator's lower one. Neither month tells you whether the system is performing. The year does. Three consequences follow for anyone checking payback:

1. Judge the system on twelve months. The payback years on the worth-it page come from the annual figure. A system commissioned in November looks weak for three months; one commissioned in March looks better than it is.
2. Net metering carries the surplus across the seasons. In Delhi, credits roll over month to month, and any surplus left at the end of the financial year is paid at the DISCOM's average power purchase cost. Summer export offsets winter import on the same connection, so the bill settles on the year's balance. In Uttar Pradesh, under the UPERC rooftop solar regulations of 2019, residential users may choose net or gross metering, and the DISCOM allows capacity within transformer limits.
3. Size on the year's consumption, not the summer bill. The sizing guide matches annual consumption to annual generation. A system sized to cover June's air-conditioning exports heavily for the other nine months, and export earns less than the units it would have replaced.

Dust: the loss you control

Cloud and fog are weather. Dust is a chore, and the one seasonal loss an owner can keep small. A film of dust scatters the light before it reaches the cells, so the loss grows every dry day after the last wash and disappears with the next. In Delhi NCR the two stretches that matter are the dust storms of April to June and the still, smoggy weeks of October and November.

The routine is short: rinse with plain water every two to three weeks in the dry months, always within the week after a dust storm, and once at the end of the monsoon to take off the streaks. Wipe bird droppings the same week, because a dropping shades one cell and that cell heats up. Clean early in the morning from the walkway, with a soft brush and no detergent, and never stand on the panels. The maintenance and cleaning guide has the safe method in full and the annual check, which is best done in September or October, after the monsoon and before the dust. The routine is this site's recommendation, not a rule from a manufacturer or a policy document.

How to monitor

Every inverter records the day's generation, on its display or in its app, and that record is the only way to tell weather from a fault.

• Note a clear-day figure in each season. One good day in April, August, November and January. Those four numbers are your roof's own pattern, and next year's readings can be judged against them.
• Keep a monthly tally. Compare the twelve-month sum with the calculator's annual figure for your size and city.
• Test dust with a wash. Note a clear day's reading, wash, and compare the next clear day. A noticeable recovery means you waited too long.
• Call the installer for zero, not for low. Low on a foggy day is the season. Zero on a clear day, a missing string, or a fault code that survives a restart is a fault.