If you installed a rooftop solar system in Lucknow or Kanpur in the last couple of years, you have probably already noticed that your inverter's daily generation reading drops noticeably from late November through February. Your monitoring app shows 8 to 10 kWh on a clear October day and then 3 to 5 kWh on a foggy December morning. That difference is real, it is expected, and it matters far less to your annual savings than most homeowners assume.
This guide explains exactly how UP's dense fog season affects your solar panels, what generation numbers to actually expect between November and February, how the annual picture balances out through net metering, and the practical steps that protect your system and maximise output during the foggy months.
Why Dense Fog Hits UP's Solar Output Harder Than Clouds
Uttar Pradesh sits in the Indo-Gangetic Plain, a geography that traps moisture in winter. From late November to mid-February, low-pressure cold air from the Himalayas meets the moist plains air and creates a dense fog layer that can sit below 50 metres for entire days at a time. Lucknow, Kanpur, Barabanki, Raebareli, Sitapur, and Ayodhya are all in the core fog belt. This is different from the monsoon cloud cover that passes across the sky. Winter fog sits at ground level, directly between your panels and the sun, and it scatters incoming solar radiation much more completely than high-altitude clouds.
Peak Sunshine Hours in UP by Season
The key number for solar generation is peak sunshine hours (PSH), which measures the equivalent hours of full 1000 W/m2 irradiance received in a day. In Lucknow, PSH varies dramatically across the year:
- March to May (pre-summer): 6.0 to 6.8 PSH - highest generation of the year
- June (early monsoon): 5.0 to 5.5 PSH
- July to September (monsoon): 3.5 to 4.5 PSH
- October to November: 5.5 to 6.2 PSH - excellent generation, clear skies
- December to January (peak fog): 2.8 to 3.8 PSH - lowest generation of the year
- February (improving): 4.0 to 5.0 PSH
A 5 kW system in Lucknow that generates 28 to 32 kWh per day in April will produce 14 to 19 kWh per day in December and January. On the worst fog days, when visibility is under 50 metres by 10am, output can drop to 6 to 9 kWh for the entire day.
How Fog Scatters Sunlight
Unlike rain clouds, which block direct and diffuse light heavily, dense fog scatters incoming solar radiation in many directions. Some of that scattered diffuse light still reaches your panels. Modern monocrystalline panels are reasonably efficient at converting diffuse light, but they cannot compensate for the near-complete reduction in direct beam irradiance during dense fog. The practical result is that a foggy day in January generates about 40 to 55 percent of what a clear winter day produces, and a dense fog day produces 25 to 35 percent of a clear day.
The Annual Numbers: Why Winter Fog Does Not Ruin Your Economics
The critical thing most homeowners miss when they see low December and January generation is that UPPCL net metering operates on an annual banking cycle, not a monthly one. Credits you generate in excess of consumption from March through June roll forward and are applied to bills through the foggy winter months. The two seasons balance each other much better than the monthly numbers suggest.
Annual Generation for a 5 kW System in Lucknow
A correctly installed 5 kW rooftop solar system in Lucknow generates approximately 6,500 to 7,200 kWh per year across all seasons. That annual average works out to roughly 540 to 600 kWh per month, or 18 to 20 kWh per day. The winter deficit is real but it is fully covered by the spring and summer surplus through net metering credits.
A household consuming 400 units per month that installs a 5 kW system will typically see near-zero UPPCL bills from March through August and bills of Rs 500 to Rs 1,500 in December and January after credits are applied. At Rs 7 to Rs 9 per unit, annual savings still comfortably exceed Rs 50,000 per year for a 5 kW system in Lucknow.
The Net Metering Credit Banking System in UPPCL
Under current UPPCL net metering regulations, surplus units exported to the grid are credited at the same rate you are charged for consumption. Credits accumulate monthly and can be carried forward for up to twelve months before the billing cycle resets. In practice, most solar homeowners in Lucknow, Kanpur, and Barabanki who install a correctly sized system build up a credit surplus from March to September that fully covers their winter shortfall without any additional payment to UPPCL.
At Sunwize, we size systems specifically to cover the annual consumption including winter months, not just the peak summer generation, so our customers rarely see a bill in the Rs 3,000 to Rs 5,000 range that undersized systems produce in January.
Protecting Your System and Maximising Output During Fog Season
While you cannot change the weather, there are several practical steps that meaningfully improve your system's performance through the November to February window and protect the hardware from seasonal hazards.
Panel Cleaning During the Fog Season
Fog in UP carries particulate matter, agricultural dust, and crop residue from post-harvest stubble burning across Punjab and Haryana. As fog condenses and evaporates on panel surfaces, it deposits a thin layer of this particulate matter. This soiling effect compounds the fog's direct generation impact: panels that are dirty during fog season lose an additional 8 to 15 percent of whatever light does reach them.
Clean your panels every two to three weeks from November through February. The cleaning does not need to be elaborate. A soft microfibre mop or cloth with plain water on a clear morning before 9am is sufficient. Avoid cleaning during active fog because the panels will re-soil before the fog lifts. Never use hard-bristle brushes or abrasive materials, which scratch the anti-reflective coating and cause permanent output loss.
Homeowners in Barabanki and Sitapur, where paddy residue burning is heavier in October and November, should clean once a week through that specific window to prevent the black carbon buildup that can be harder to remove once it bonds to the glass surface.
Checking Your Inverter During Winter Months
Inverters perform reliably through UP winters, but there are two checks worth making in November. First, verify that your inverter's DC input voltage is within normal range on a clear morning. Cold temperatures temporarily increase panel output voltage, and in systems where the inverter's MPPT input ceiling is marginal, cold-weather over-voltage can cause the inverter to shut down at the moment panels should be generating their most. Second, check that your inverter's ventilation is not blocked by leaves, dust, or nesting material. A clogged inverter runs hot even in cold weather and reduces efficiency.
Earthing and Hardware Checks Before December
October and November are the ideal time for a thorough inspection of mounting hardware, wire connectors, and earthing. Cold and moisture from fog season can accelerate corrosion in mounting bolts and MC4 connectors that were already slightly compromised during the monsoon. A loose mount that rattles in December winds can cause panel displacement, micro-cracks, and generation loss that is not visible from the ground. Check all visible fasteners and ask your installer to test earthing continuity if you have not had a check in more than two years.
What to Do on Zero-Generation Fog Days
On days when dense fog keeps output below 2 kWh for the entire day, there is nothing practical to do except wait. Do not attempt to redirect panels, add reflectors, or make system adjustments based on a single bad day. These events are accounted for in the annual generation figure your installer used when sizing your system.
If you notice that your system's generation is significantly below what you expected even on clear winter days between fog events, that is worth investigating. December and January clear days in Lucknow should still produce 15 to 22 kWh from a 5 kW system. Consistently lower clear-day output usually indicates panel soiling, shading from new obstructions, or a fault in one string.
Setting Realistic Expectations for Your First Winter with Solar
If you installed your solar system in 2026 and are heading into your first fog season, the most important thing to know is that the lower generation numbers on your app are normal and expected. Homeowners in Kanpur, Ayodhya, Raebareli, and Lucknow who panic during January and conclude that their system is faulty almost always find that it is working exactly as it should when they check the annual figures in April.
A useful benchmark: if your system generates at least 2 to 3 kWh per kW of installed capacity on an average December day, it is performing normally for UP winter conditions. A 5 kW system generating 10 to 15 kWh on a typical December day, and 5 to 8 kWh on a dense fog day, is healthy. If it falls significantly below these numbers on a day that your neighbours report as reasonably clear, check for panel soiling first, then contact your installer.
The months from November to February account for roughly 18 to 22 percent of your annual solar generation in UP. The months from March to August account for 55 to 60 percent. The annual picture is overwhelmingly positive. Dense fog is an inconvenience, not a threat to the economics of going solar in Uttar Pradesh.
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