Solar Panels in Winter and Smog in Pakistan: How Much Output Drops and How to Plan

Seeing lower numbers in your inverter app? That's normal from November to January. This guide explains why output drops in winter, smog and fog, how big the drop usually is, and what you can do about it. To size a new system, use the solar calculator.

Every November the same questions start: "sardiyon mein solar kitni bijli banata hai?", "smog mein solar kaam karta hai?", "dhund mein solar panel kyun kam chal rahe hain?" People who were proud of their summer readings open the inverter app on a grey Lahore afternoon and see half the units. Some start to worry their panels are fake.

Usually nothing is broken. Winter in Punjab and Khyber Pakhtunkhwa brings shorter days, a low sun, smog, fog and dusty glass all at once. This guide explains each cause, gives real numbers from NASA satellite data for five cities, and covers what it means for your bill, battery and cleaning routine.

The short answer

Yes, solar works in winter, smog and fog. Panels make electricity from daylight, not heat, and they still produce under a hazy or overcast sky. They just produce less.

Over the year, 1 kW of panels in Pakistan makes about 3.6 units a day on average, the figure our calculator and system pages use. In December and January, across the north and centre of the country, expect clearly less than that. A clear winter day can come close to it. A day of thick fog may give only a small fraction.

Why output drops from November to January

Shorter days and a low sun. In December the sun rises later, sets earlier and stays low in the southern sky. Fewer daylight hours means fewer generating hours, and low-angle light passes through more atmosphere and strikes flat or gently tilted panels at a glancing angle. This part of the drop happens every winter, smog or not.

Smog and haze. Punjab's smog season, from late October into winter, fills the air with fine particles from crop burning, traffic, brick kilns and industry. They absorb and scatter sunlight. Some scattered light still reaches the panels as diffuse light, which is why they keep working under a grey sky, but the total is lower. There is no honest single "smog loss" percentage for every rooftop, so be wary of anyone who quotes one.

Fog (dhund). Dense fog in the Punjab plains, often in December and January, hurts more than haze. Fog that lifts at 11 am costs you half of an already short day. Fog that sits all day keeps output very low.

Dust and soot on the glass. This is the part you can control. Smog particles settle on the panels, winter brings little rain to wash them off, and morning dew turns the dust into a film that dries hard. Flatter panels collect more.

A LUMS study in Lahore (Ullah et al., Renewable Energy, 2019) found that after 100 days without cleaning, a horizontal panel lost 26.2% of its energy compared with a clean one, and a vertical panel 13.5%. Their model put losses at up to about 10% for lightly soiled panels and up to about 40% for heavily soiled ones. A global study in Nature Sustainability (Li, Mauzerall and Bergin, 2020) found that in heavily polluted and desert regions, airborne particles and dirt together can cut generation by more than half if panels are never cleaned, with dirt on the panels making up more than two-thirds of that loss.

In smog season, dirty glass can cost you as much as the smog in the sky, and unlike the sky, you can clean it.

How much less sunlight do panels get in winter?

NASA's POWER project publishes long-term monthly averages of sunlight reaching the ground, from 25 years of satellite data (2001–2025). We pulled the figures for five cities. They're averages over a wide area, not a measurement of your roof, and individual smoggy or foggy weeks can be much worse, but they show the size of the seasonal swing.

For panels at a fairly typical low tilt of about 15–20 degrees, average December sunlight compared with the yearly average is roughly:

• Lahore: about 69%, and about half of May.
• Islamabad and Rawalpindi: about 71%.
• Multan: about 71%.
• Peshawar: about 71%.
• Karachi: more than 80%, because Karachi's winters are sunny.

NASA also publishes a "clear-sky" figure, the sunlight you would get with no cloud. In Lahore the real average is about 12% below it in December and about 20% below it in January. That gap is mostly cloud and fog, which is why January often feels worse than December in Punjab even as the days lengthen.

In units: if your system averages 3.6 units per kW a day over the year, an average December day in Lahore, Islamabad, Multan or Peshawar is more likely to give roughly two-thirds to three-quarters of that, with foggy days far lower. A 5 kW system averaging about 540 units a month across the year will make clearly fewer in December and January.

The best check is your own data. In your inverter app, compare this December with last December, not with June.

Tilt angle: does it help in winter?

Yes. A steeper panel faces the low winter sun more squarely and sheds dust better. NASA's data for Lahore shows the best monthly tilt moving from nearly flat in May to July to about 50 degrees in December, with a best fixed all-year tilt of about 25 degrees. Panels tilted near the city's latitude (around 30 degrees in Lahore) get about three-quarters of their yearly average sunlight in December, against about two-thirds at a 15–20 degree tilt. The LUMS study found that changing the tilt four times a year in Lahore could raise yearly generation by about 6.6%.

What to do with that:

• Face south. East-west layouts lose more in winter, when the sun is low in the south.
• Ask about tilt on new installs. Many rooftop frames are set quite flat to save steel or reduce wind load. A moderate tilt of roughly 20–30 degrees is a reasonable all-year compromise in Punjab and KP, subject to the structure's wind design.
• Only adjust frames built to move. Seasonal tilt changes are worth it only if the frame was designed for them. Never loosen bolts on a fixed structure.
• Watch for winter shade. The low sun makes water tanks, parapet walls and neighbouring buildings cast much longer shadows than in June. If you need to get above shade, see elevated solar structure cost.

Cleaning panels in smog season, safely

1. Clean early morning or late afternoon, when the glass is cool. Dew has already softened the dirt, and you avoid cold water on hot glass.
2. Use plain water and a soft brush, sponge or panel mop. No detergent, acid, kerosene or abrasive pads, which can damage the anti-reflective coating and may void the warranty.
3. No close-range pressure washers. High pressure can force water into frames and junction boxes.
4. Never stand, walk or lean ladders on panels. That can crack cells without visible damage.
5. Mind the roof. Fog and dew make it slippery. On a high frame, use a long-handled mop from a safe spot or ask the installer.
6. Keep water off wiring, especially cable joints, the DC isolator and connectors lying on the roof.

How often? There's no fixed rule. Note your units on the first clear day after cleaning, then compare with later clear days. If clear-day output keeps sliding while the weather hasn't changed, clean again. In heavy smog weeks that may be weekly.

What winter means for your bill and net metering

Winter output is lowest, but in most homes so is use, because the ACs are off. Lower generation often still covers daytime use. The exceptions are homes that switch to electric heaters or geysers because of gas shortages, and homes with heavy evening use. Electric heating takes a lot of units, so a winter bill can rise even with solar.

How your green meter treats summer and winter depends on your agreement:

• Old net-metering agreements (signed before 9 February 2026) keep the old one-for-one swap of exported and imported units until they expire. Leftover credit is carried forward or settled under your agreement.
• New connections are on net billing. Imports are billed at your normal slab or time-of-use rate, and exports are bought at a much lower rate, currently Rs 8.13 per unit. Credit carries to your next bill or is paid quarterly, as our net metering vs net billing guide explains.

Under net billing, summer exports don't "bank" winter units at full value. A unit exported in June earns Rs 8.13, while a unit imported on a December evening costs your full slab rate, which at 300 units a month is Rs 33.10 before fixed charges, adjustments and taxes. Oversizing just to cover winter means exporting a lot in summer at the low rate, which rarely pays.

To see your winter units in rupees, use the LESCO bill calculator, the IESCO bill calculator or the electricity bill calculator.

Sizing for winter

• Size from your bills across the year. Our guide on sizing solar from your electricity bill works from your summer peak, which usually covers winter daytime use in a home without electric heating.
• Add up any winter heating separately. A heater draws a lot of power for hours, exactly when panels are weakest. Gas or more efficient heating may make more sense than a bigger system.
• Leave room to grow. Pick an inverter with spare PV input so you can add panels later. Compare the 3 kW, 5 kW and 10 kW system price pages.

Panels currently sell at Rs 37.5–42.1 per watt, so adding a few panels can be a cheaper fix for a winter shortfall than a new system, if your inverter and sanctioned load allow it. With an old net-metering agreement, check with your DISCO first, because expanding can move you onto net billing terms.

Batteries and load-shedding in winter

Winter load-shedding is usually lighter than in summer, but short grey days make battery planning harder.

• Less solar for charging. On a foggy day the panels may barely cover daytime use, so the battery may not be full by evening. Many hybrid inverters can allow grid charging in off-peak hours. Check your settings and tariff first.
• Know what one battery gives. A 5 kWh lithium (LiFePO4) battery gives about 4.6 kWh of usable storage and currently lists at Rs 217,000 – 260,000. That runs lights, a fridge, router, TV and a few fans for several hours. It won't run an electric heater through the night.
• Cold areas. In the plains, winter temperatures aren't usually a problem for lithium batteries kept indoors. In cold northern areas, check the datasheet: lithium batteries generally shouldn't be charged below freezing, and lead-acid batteries lose usable capacity in the cold.
• Tubular batteries need regular full charges. Weeks of weak winter charging can leave them undercharged. See lithium vs tubular battery.

For backup setups, see hybrid vs on-grid inverter. Live battery prices are on the lithium battery price page.

Don't blame "fake panels" too quickly

Low winter output is the most common reason people suspect fake panels. Rule out the normal causes first:

1. Compare like with like: this December with last December, or one clear winter day with another.
2. Check for export limits. With no green meter and a full battery, many inverters only produce what the house uses, which looks like low output.
3. Check the strings. If two similar strings face the same way and one reads far lower, look for shade, a loose connector or a faulty panel.
4. Clean the panels, then check on the next clear day.
5. Look for new winter shade from tanks, walls and trees.

If output is still well below reasonable, check the panels themselves with our guide on how to check original solar panels. Live prices by brand are on the panel price page, for example Longi and Jinko.

Common questions

Sardiyon mein solar kitni bijli banata hai? Less than in summer. In Lahore, Islamabad, Multan and Peshawar, December sunlight on typical low-tilt panels is about two-thirds to three-quarters of the yearly average, and in Lahore about half of May. Karachi drops much less. Check monthly totals in your inverter app.

Smog mein solar kaam karta hai? Yes. Panels still produce under haze from diffuse light, just less. The bigger problem is smog dust on the glass, so clean more often in smog season.

Dhund mein solar panel bijli banate hain? Yes, but thick fog cuts output sharply until it lifts. A foggy morning means a short generation day.

Kya sardi mein solar panel zyada efficient hote hain? Panels work slightly more efficiently when cool, so a clear cold day can be strong for the hours of sun available. Shorter days and a low sun usually outweigh that.

Winter mein panel kitni dafa saaf karein? When clear-day output slides without a change in weather. In heavy smog weeks that may be weekly. Use plain water and a soft brush, morning or evening.

Kya winter ke liye bara system lagana chahiye? Usually not. Under net billing, extra summer exports earn only Rs 8.13 per unit. Size for your yearly use and plan winter backup with your battery and settings.

Before you buy or upgrade

When you get quotes this winter, ask installers about tilt, facing, shade and cleaning access, not just brand and price. Run itemised quotes through Check my quote, which compares each line with today's market prices, and find installers in our installer directory. Our quotation checklist lists what each line should name.

اس گائیڈ کی قیمتیں ہماری ٹریک کردہ ڈیلر لسٹنگز سے خود اپڈیٹ ہوتی ہیں (آخری تازگی 4 نومبر 2026)۔ اشارہ جاتی مارکیٹ رینجز ہیں، کوٹ نہیں۔Prices update automatically from dealer listings we track (last refreshed 4 November 2026). Indicative ranges, not quotes.

Sources

• NASA POWER climatology (CERES SYN1deg, monthly averages January 2001 – December 2025): all-sky, clear-sky and tilted-surface solar irradiance for Lahore, Islamabad, Multan, Peshawar and Karachi, accessed 4 November 2026 through the POWER Climatology API: power.larc.nasa.gov. Percentages are our own rounded ratios of NASA's monthly and annual averages.
• Ullah, Imran, Maqsood and Butt, "Investigation of optimal tilt angles and effects of soiling on PV energy production in Pakistan", Renewable Energy 139 (2019) 830–843: abstract, DOI.
• Li, Mauzerall and Bergin, "Global reduction of solar power generation efficiency due to aerosols and panel soiling", Nature Sustainability (2020): nature.com.

Satellite averages describe a wide area over many years. Your roof, the week's smog and how clean your panels are all change the result, so treat these as a guide and trust your own inverter readings.