Winter solar output in Lahore — realistic numbers

Why winter output drops in Lahore

Three things conspire against a solar panel in a Lahore winter. The sun is lower in the sky, so the angle of incidence on a flat-tilted panel is poorer. The day is shorter, with daylight hours falling to around 10 hours 15 minutes at the December solstice versus 13 hours 50 minutes in late June. And then there is fog, which is the big one.

Lahore winter fog runs from late November into early February, with the heaviest concentration in late December and through January. On a heavy fog morning the visible irradiance on the panels can drop to 200 to 400 watts per square metre between 8 am and 11 am, sometimes lasting until early afternoon. Lahore foggy winter days are why annual generation in this city is a few percentage points lower than the latitude would suggest.

Realistic winter generation — 5 kW system in Lahore

Month	Avg daily kWh	Monthly kWh	vs May peak
November	19 – 22	580 – 660	72%
December	15 – 18	460 – 550	58%
January	14 – 17	440 – 520	55%
February	17 – 20	500 – 570	65%
March	23 – 26	700 – 800	92%
April	26 – 29	790 – 870	100%
May (peak)	27 – 30	830 – 900	100%

The January numbers are roughly 55 percent of the May peak. December is similar. This is the worst-case for the year. A 5 kW system that produced 27 kWh on a sunny day in April will produce 14 to 17 kWh on a sunny winter day with low fog, and as little as 5 to 8 kWh on a heavy-fog day where the sun does not show until after lunch.

Fog days versus clear winter days

A clear winter day in Lahore, with the sky free of fog by 9 am, is a surprisingly good day for solar. The cooler ambient temperature helps panel efficiency. The lower sun angle reduces output by 25 to 30 percent versus a peak summer day, but a clear-sky December day in Lahore can still deliver 20 to 22 kWh from a 5 kW system, which is more than enough for most household daytime loads.

A heavy-fog day is a different animal. If the fog does not lift until 12 noon, the morning generation is essentially zero, and the post-noon recovery only gives 4 to 6 hours of usable production at maybe 60 to 75 percent of the clear-day rate. Daily generation lands at 7 to 11 kWh.

Across a typical Lahore winter (December plus January, 62 days total), the breakdown is roughly: 20 to 25 heavy-fog days, 18 to 24 partial-fog days that clear by mid-morning, and 18 to 22 clear days. The monthly average lands in the 440 to 550 kWh band for a 5 kW system because the heavy-fog days drag the mean down.

Panel tilt — fixed versus seasonal

Lahore sits at 31.5 degrees north latitude. The optimal panel tilt for year-round generation is 27 to 29 degrees, facing south. Most installations use a fixed tilt around 23 to 25 degrees because the structure costs are lower and the roof slopes accommodate it.

A few installations use adjustable mounting that allows the tilt to be changed twice a year: roughly 15 degrees for the summer six months and 45 degrees for the winter six months. The adjustable mount adds PKR 15,000 to PKR 35,000 to the structure cost on a 5 kW system. The winter generation gain is about 8 to 14 percent on December and January production, or roughly 35 to 65 kWh per month. At PKR 27 per kWh net-billing buy-back, the seasonal-tilt upgrade saves around PKR 950 to PKR 1,750 per month during the winter and recovers its cost in 4 to 7 years.

For most Lahore homeowners the seasonal-tilt option is not worth the trouble. The mount needs to be physically adjusted twice a year, which means somebody climbing on the roof and re-clamping each panel. The PKR 15,000 added to structure cost is better spent on a slightly larger panel array, which gives more output across all months and needs no manual intervention.

Winter cleaning — actually matters more than summer

Lahore winter brings dry, dusty air and a thick layer of suspended particulate from brick kilns, vehicle exhaust and stubble burning in surrounding agricultural areas. There is no rain to wash the panels between November and late February. By mid-December a panel that was clean on November 1 will have lost 8 to 14 percent of its output to grime.

A single winter cleaning, properly done in mid-December or early January, recovers that lost output for the rest of the winter. The cleaning should be done with mains water and a soft cloth or a low-pressure washer rated for solar panels. Avoid hard scrubbing and avoid pressure washing.

For households with net metering on a 5 kW system, a missed winter cleaning costs roughly 60 to 100 kWh of generation across December and January, worth PKR 1,600 to PKR 2,700. A professional cleaning in Lahore costs PKR 1,200 to PKR 2,500 for a 5 kW array. The maths is straightforward.

Battery behaviour in winter

Lithium batteries operate fine in Lahore winters. The city's coldest mornings are around 2 to 5 degrees Celsius, which is well within the operating range of a LiFePO4 battery. There is no performance penalty for cold below freezing because Lahore essentially does not freeze.

What does change is the battery's role. In summer the battery is mostly there for evening AC and outage backup. In winter, with shorter daylight and lower solar output, the battery becomes more about extending the household's self-consumption window after sunset. The morning solar peak is delayed by the fog, so a household running heaters early morning often draws from the battery rather than the panels.

This means winter battery cycling is more frequent than summer, even though the household load is lower. A 10 kWh battery in a Lahore winter typically sees one full cycle every 1 to 2 days. The cycle counter on the battery's BMS goes up faster than most owners expect.

What to actually do in winter

Clean the panels once in mid-December and once in mid-February if dust has accumulated. Check the monitoring app weekly for any day where generation is far below the expected band — a fallen branch or animal nest on the panels is easier to spot in winter when bird activity is high. Otherwise leave the system alone.

One last thing. Winter is the season when LESCO bills look the most dramatic for solar households because the household consumption is also lower (no AC, lower fan use, lower fridge load). On a 5 kW system in Lahore, December and January bills often show negative balances even with the lower solar production, because the household is consuming less than the panels generate.

The summer months are when solar shines (literally) on the bill, but the winter months are when the household sees what 5 kW of panels can do when they are not fighting against three air conditioners. Both seasons are needed for the annual payback maths to work.