Solar Panel Generation in Delhi: Summer vs Winter Output per kW (2026)

If you size a Delhi rooftop system on summer numbers, you''ll oversize and overpay. If you size on winter numbers, you''ll undersize and import grid power exactly when bills hit peak slabs. The honest answer requires both numbers, plus what happens in the fog week.

This is the actual seasonal generation curve for solar in Delhi — measured across BSES Rajdhani, BSES Yamuna, and TPDDL territory homes — and how to size your system so the math works in January, not just May.

The Real Seasonal Curve (per kW)

Delhi sits at ~28.6° N. Peak sun-hours vary by month:

Numbers are field-corrected for Delhi-specific losses: soiling (8–12%), inverter clipping (2%), and ambient-temperature derating (the per-kW number is lower in May than peak sun-hours suggest because panels above 45°C lose 8–10% efficiency).

Why Winter is Worse Than the Tilt Math Predicts

Winter in Delhi isn''t just shorter days. Three compounding factors hit generation:

1. Sun angle. Even with a 28° fixed tilt, December''s low azimuth means a third of the array shadows the other two-thirds for 90 minutes around solar noon on heavily-built independent floors.
2. Fog and PM2.5. Late December through mid-January routinely sees 7–14 consecutive days of <2 units/day per kW across south Delhi. Not a fault — the irradiance just isn''t there.
3. Cold-start inverter behaviour. Below 8°C ambient, string inverters wait an extra 20–35 minutes for the array to clear morning dew. You lose the cleanest hour of winter generation.

Anyone quoting you a flat "4 units per kW per day all year" hasn''t looked at a Delhi inverter logbook.

How to Size Your System Using Both Numbers

Take a typical south Delhi 3-BHK independent floor consuming 450 units/month.

The wrong way (summer-only sizing):

• 450 units ÷ 30 days ÷ 5.0 (summer per-kW) = 3 kW system
• Result: full offset in May, 40% grid import in January, ₹1,400/month winter bill survives.

The right way (annual average + winter floor):

• 450 units ÷ 30 ÷ 4.2 (annual avg per-kW) = 3.6 kW → round up to 4 kW
• Result: ~600 unit/month surplus banked in summer, drawn back in winter via net metering, bill drops to ₹0–200 even in January.

This is why we routinely recommend Delhi homes size 15–20% above their average monthly consumption divided by 4.2 — and why ignoring the winter floor is the #1 reason "subsidy customers" feel disappointed three months after install.

The Fog Week — and Why It''s Not a Bug

Every year, somewhere between December 20 and January 10, Delhi gets 4–7 consecutive days where per-kW generation drops to 1.5 units/day. Heavy fog, weak winter sun, near-zero diffuse irradiance.

This is normal. It''s why net metering exists — the surplus units you exported in May, June, and October sit as bill credits and get consumed during fog week. A correctly-sized system shouldn''t need any cash bill payment even through fog week.

If your installer hasn''t walked you through net-metering carry-forward rules (especially the BSES quarterly settlement and the TPDDL annual reset), they haven''t finished selling you the system.

What This Means for 3 kW, 5 kW, and 10 kW Systems in Delhi

For the cost side of these system sizes in Delhi, see our Delhi NCR solar pricing guide. For comparable numbers in other NCR cities, see Faridabad, Gurugram, and Noida.

FAQ

How many units does 1 kW of solar generate per day in Delhi? 4.0–4.5 units/day on an annual average. Summer peak is 5.0–5.4; winter floor is 3.0–3.5. Late-December fog week can drop to 1.5–2.0 units/day for 4–7 days.

Why does my solar generate less in winter even though it''s sunny? Three reasons: shorter days (~10 hours of useful sun vs 13 in May), lower sun angle (worse incidence on a fixed-tilt array), and morning fog delaying inverter cold-start. Even on a "clear" December day, a Delhi rooftop sees 30–40% lower irradiance than a clear May day.

Should I size my system for summer or winter? Neither alone. Size for the annual average (~4.2 units/day per kW) plus a 15–20% buffer for the winter floor. Then rely on net-metering carry-forward to smooth out fog week.

Is generation worse in BSES Rajdhani vs TPDDL areas? Generation is identical — same sun, same irradiance. The difference is net-metering settlement: TPDDL allows annual carry-forward, BSES Rajdhani settles quarterly. This matters for fog-week economics.

What''s the worst real-world day a Delhi rooftop has logged? We''ve seen 0.8 units/day per kW on a heavily-foggy December 28 in Rohini. Once a year, this happens. It''s why oversizing by 15% beats undersizing by 15%.

Does panel cleaning actually move winter numbers? Yes. Delhi PM2.5 plus November dew creates a sticky film that costs 8–15% generation by mid-December. A pre-winter cleaning (mid-November) is the highest-ROI maintenance call of the year. See our Gurugram cleaning pricing — the same costs apply across Delhi.

Get a Site-Specific Generation Estimate

The numbers here are the Delhi average. Your roof, your shading from a neighbour''s water tank, and the orientation of your independent floor''s terrace can all shift these numbers ±20%. We''ll measure your roof, run a shading analysis, and give you a month-by-month generation forecast before you commit. Free, no obligation.