Fault-finding
Solar output has dropped and nothing obvious changed
Check the pattern first. Every string down proportionally is almost always dust or seasonal angle. One string down while others are normal is electrical — a connector, a fuse or an isolator. A cliff-edge drop overnight points at the inverter or a tripped protective device rather than the panels.
Last reviewed
Read the inverter before touching anything
Modern inverters log per-string voltage and current and record why they curtailed or stopped. Compare today's string figures against the commissioning sheet from installation. If one string reads low and the others read normal, the fault is located to that run and there is no reason to inspect the whole array.
Rule out dust and season
A proportional drop across every string is dirt or sun angle, not a fault. Dust accumulates fast here and a fine post-monsoon film shades more than people expect. Winter output is legitimately well below summer at this latitude. Compare against the same month last year rather than against last month, or you will chase a fault that is just December.
Check protection and connectors
A tripped DC isolator, a blown string fuse or a corroded MC4 connector takes one string out cleanly and looks dramatic on the graph. Connectors are the commonest single culprit on systems more than a couple of years old, because heat cycling and UV work on them continuously. They are also cheap and quick to replace.
Only then go on the roof
If the logs point at a specific string, inspect that run: connector condition, cable ties perished in the sun, any panel with visible damage or a hot spot on the back sheet. Doing this last rather than first is the difference between a one-hour visit and a day of looking.
Why has my solar output suddenly dropped?
How much output should dust cost me?
Enough to notice, and more than most people expect. It is why we compare a before-and-after figure on every cleaning visit rather than asserting the wash helped. If a clean does not move the number, the problem was never dirt and you have just ruled out the cheapest explanation for the price of a wash.
My generation is down but the inverter shows no fault. Why?
Because most causes are not faults from the inverter's point of view. Dust, shading from something newly built, a slowly failing connector raising resistance, or panels degrading all reduce output without tripping anything. The inverter reports what it received; it cannot tell you why that was less than yesterday.
Should I have a commissioning sheet?
Yes, and if you do not have one, that is the first thing to fix. String voltages and first-day output from installation are what turn 'seems lower' into a measurement. Without a baseline, a slow decline is invisible until it is severe. We record fresh figures at the end of any visit for exactly this reason.
Rather have it done?
When a solar system stops producing, the fault is usually the inverter, a string connector or a tripped protection device rather than the panels themselves. Diagnosis in Islamabad or Rawalpindi starts at PKR 5,000, taken off the bill if you go ahead with the repair.
Solar inverter and panel repair in Islamabad — prices and scope