Why your solar output dropped in Lahore

First, know what normal looks like

Most low output complaints are not faults. They are a homeowner comparing June against October, or a 2026 winter against a 2025 winter, without knowing what the system should do in each month. Lahore has a wide seasonal swing and a smog season that no brochure mentions.

Here is the honest baseline for a well-installed 5kW array on a Lahore roof, tilted around 20 to 25 degrees and facing south.

Month	Good day (units)	Monthly total (units)	What limits it
March to April	25 to 27	720 to 800	Nothing much, the best months
May to June	21 to 24	650 to 720	Heat derating, dust, haze
July to August	13 to 21	480 to 620	Monsoon cloud, humidity
September to October	23 to 26	690 to 760	Second best window of the year
November to January	9 to 17	330 to 480	Smog, short days, low sun angle
February	17 to 21	500 to 570	Recovering light, occasional fog

Compare like for like. December against December. If this December is 15 percent under last December, something changed. If December is simply lower than October, that is physics, and the detail is in winter solar output in Lahore and monsoon output.

Cause 1: dust, and it is bigger than people think

Lahore air deposits a mix of construction dust, vehicle soot, and in winter an oily particulate film that does not blow off. On roofs near ongoing construction, and there is always construction somewhere in Bahria Town and DHA phases, a month without cleaning is measurable in the app.

Typical measured losses on Lahore arrays: 8 to 15 percent after four to six weeks in dry season, and 20 to 30 percent through peak smog if the array has not been washed since October. Bird droppings are worse per square centimetre because they create a hard shaded spot that drags a whole string down.

Rain is not a cleaner here. A monsoon shower moves dust around and leaves streaks, and the first dry day bakes it on. Proper cleaning with soft brushes and low pressure water, early morning before the glass is hot, is what recovers the output. Costs are laid out in solar cleaning cost in Lahore, and the schedule is handled by the cleaning service.

Cause 2: shading that was not there at install

Shade is the most under-diagnosed cause in Lahore because it arrives slowly. Things that grow, get built, or get installed:

• The neighbour's second storey, extremely common in Johar Town and Garden Town where plots are tight and vertical extensions are constant.
• A new water tank on a raised stand, often placed by a plumber without a thought for the array.
• A dish antenna or a new mobile tower guy wire cutting a thin shadow across a row.
• Trees. Jamun and neem grow fast and shade the eastern edge of a roof by year three.

Series-wired panels behave badly under partial shade. Shading 10 percent of one panel can cost far more than 10 percent of that panel's output, because the shaded cell throttles current for the entire string. If output falls off a cliff at a specific hour, say every day from 3:40 pm onward, that is a shadow arriving, not a component failing.

Cause 3: a dead string

Open the app and look at the per-MPPT figures rather than total power. On a two-string 5kW build, both strings should read within a few percent of each other at midday. If MPPT1 is at 2,400W and MPPT2 is at 40W, one string is down.

Causes in order of frequency on Lahore roofs: a blown gPV fuse in the combiner, a corroded or water-filled MC4 connector, a rodent-chewed DC cable, and a cracked panel. Rat damage is common where the roof adjoins trees or an open plot. A blown fuse costs PKR 900. Finding it costs the visit.

Cause 4: MPPT or tracker failure inside the inverter

An MPPT channel can fail on its own while the rest of the inverter works fine. The tell is a string with correct open circuit voltage at the terminals, correct fuse, healthy panels, and still no current once connected. Swap the two string inputs at the inverter. If the fault follows the input rather than the string, the tracker is the problem.

This is a board-level repair, PKR 18,000 to 45,000 depending on brand and parts availability. On a unit older than six years the sensible move is often a replacement instead. A 5kW hybrid is PKR 165,000 and a 6kW is PKR 158,000, so the arithmetic goes quickly against repairing an old unit. Brand-specific notes are in the pages for Solis, Inverex and Growatt.

Cause 5: heat derating in Lahore summer

Panels lose roughly 0.35 percent of output for every degree the cell rises above 25C. A Lahore roof in June puts cell temperature near 65C, which is a 12 to 14 percent loss before anything else goes wrong. That is normal and unavoidable, and it is why June often produces less than April despite longer days.

What is not normal is the inverter itself throttling because it is cooking. If afternoon output flattens into a straight line at, say, 3,800W on a 5kW system while irradiance is still rising, the unit is derating on temperature. That is a placement and ventilation problem covered in inverter overheating in Lahore summer.

Cause 6: panel degradation and the LID myth

Panels do age. Tier-1 modules lose about 0.4 to 0.55 percent a year after an initial first-year settling of around 1 to 2 percent. A five year old array should still be above 97 percent of its day one figure. Anyone blaming a 25 percent drop on degradation is dodging the real diagnosis.

Genuine panel faults do exist. Hairline cracks from someone walking on modules during a water tank repair, hot spots from long term bird dropping shade, and delamination on the cheapest imported stock. A thermal camera scan finds these in twenty minutes. Current panel pricing for replacements sits at PKR 19,500 for a Tier-1 585W, PKR 21,000 for a 645W bifacial, and PKR 25,450 for an Astronergy 585W N-type. More on module choice in 585W panels in Lahore and today's panel prices.

Cause 7: your load changed, not your production

Half the "my solar is weak" calls in summer are actually load calls. A new 2-ton AC in the drawing room, a tenant upstairs, or a growing family shifts consumption faster than most people notice. The array is producing exactly what it always did. The LESCO bill went up because the house is drawing more.

Separate the two numbers before assuming a fault. Production is what the inverter reports. Consumption is what the LESCO meter reports. If production is flat year on year and the bill still rose, read what your LESCO bill looks like after solar and summer AC load on solar.

Cause 8: net metering and export settings

On some builds the installer sets an export limit in the inverter to satisfy a LESCO requirement, then never removes it. The system clips at a fixed ceiling on good days. You see a flat top on the power curve at exactly the same wattage every clear day, which is a giveaway. Nothing is broken. A setting needs changing, and that is a five minute job for whoever manages your net metering. The 2026 rule changes that affect this are covered in net metering changes for 2026.

How to read the app data properly

Three views tell you nearly everything, whatever brand of dongle is fitted.

1. Today's power curve. A healthy Lahore day is a smooth bell shape peaking between 12:30 and 1:30 pm. A notch at a fixed hour means shade. A flat top means clipping or derating. A jagged curve on a clear day means a connection problem or grid instability.
2. Per-MPPT voltage and current. Voltage tells you the panel count in the string is intact. Current tells you the string is actually delivering. Low voltage on one string means an open circuit somewhere in it.
3. Monthly comparison against the same month last year. The only fair comparison. Anything else invites false alarms.

One honest caveat about app numbers. Cheap WiFi dongles in Lahore drop connection constantly, especially when the router sits two concrete walls away from a metal-cased inverter in the car porch. Missing data in the app is very often just a dead dongle, not lost generation. Check the inverter's own lifetime energy counter on its screen before panicking.

What a diagnostic visit actually involves

A proper low-output call is not a guess. String voltage and current measured at the combiner under load, a thermal scan of every MC4 and lug, insulation resistance on the DC side, an irradiance reading to compare against actual output, and a check of the inverter's stored fault history. That takes two to three hours on a 10kW build and produces a number you can act on.

Survey and diagnosis is PKR 3,000 across Lahore, adjusted into the final bill if work follows. Cleaning, fuse replacement, and reconnection work is usually done on the same visit. Larger jobs get quoted properly, and repair pricing is published in solar repair costs. If the conclusion is that the array is simply too small for the house now, the honest answer is expansion rather than repair, and the calculator or the installation team can size that.