First question: is generation actually abnormal?
Solar output changes every day. Clouds, haze, seasonal sun angle, module temperature and grid availability all affect energy production. A single low day is therefore weak evidence of a fault.
Start by comparing like with like. Compare the same month with the previous year if reliable records exist, or compare several clear days with recent clear days. Look at total daily energy as well as the shape of the power curve if your monitoring portal provides it.
If the plant shows a sustained change that cannot be explained by weather or seasonal conditions, move through the following checks.
1. Check whether the inverter was actually online
A plant can have perfectly healthy modules and still produce very little if the inverter is repeatedly disconnecting.
Review the inverter app or display for:
- periods when the inverter was offline during daylight hours;
- recurring grid-voltage or grid-frequency alarms;
- insulation, earth or leakage warnings;
- temperature-related derating or shutdown;
- DC input or string-related alarms;
- communication gaps that might be a monitoring problem rather than a generation problem.
Do not assume a missing graph automatically means zero generation. Sometimes the datalogger or internet connection fails while the inverter continues operating. Cross-check with the inverter’s local energy reading or electricity-meter data where possible.
2. Look for new shading
Shading can appear months after installation. A growing tree, water tank, telecom structure, neighbouring construction, parapet modification or even an object temporarily stored near the array can change the plant’s production pattern.
Partial shading does not always reduce every module equally. Depending on the array design and inverter MPPT configuration, one shaded section can affect a string differently from the rest of the plant.
Photograph the array at different times of day if shading is suspected. Compare the current roof environment with old installation photographs if available.
3. Assess soiling before ordering repeated cleaning
Dust, bird droppings, leaves and other deposits can reduce the light reaching the cells, but the effect varies widely with site conditions and rainfall. Heavy non-uniform soiling can be more problematic than a thin uniform layer.
If the modules are visibly dirty and the performance pattern supports soiling as a likely cause, cleaning is reasonable. If generation does not recover after safe cleaning, do not continue assuming dirt is the only problem.
4. Consider temperature and seasonal effects
Solar modules are rated under standard test conditions, not at the higher temperatures commonly seen on real roofs. Module power typically falls as cell temperature rises, while winter irradiance, fog and seasonal sun angle can reduce energy in other periods.
This means the hottest sunny day is not automatically the highest-energy day. Compare production over meaningful periods instead of expecting a fixed daily number throughout the year.
5. Check grid behaviour
A grid-connected inverter must operate within permitted grid conditions. If local voltage moves outside the inverter’s operating limits, the inverter may disconnect and reconnect repeatedly even though the solar array itself is healthy.
This can create a distinctive pattern: good generation earlier in the day, repeated trips around peak solar hours, and normal operation again later. In such a case, replacing panels would not address the root cause.
Record the exact alarm code and time of occurrence before contacting the installer, service provider or electricity utility.
6. Investigate string or DC-side faults
When one string or MPPT input is underperforming, total generation can drop without a complete plant shutdown. Possible causes include damaged connectors, cable faults, loose terminations, water ingress, animal damage, a disconnected string or a module-level problem.
These checks involve live DC circuits and should be handled by competent personnel using appropriate test equipment and safe isolation procedures.
7. Review AC-side protection and wiring
Loose connections, damaged protection devices, repeated breaker trips or other AC-side issues can also interrupt generation. Any sign of overheating, burning smell or damaged electrical equipment should be treated as a safety issue, not merely a performance issue.
A practical diagnostic sequence
Use this order to avoid unnecessary replacement:
- confirm that the low generation is persistent;
- compare weather and season;
- review inverter uptime and alarm history;
- inspect for shading and visible soiling;
- check whether cleaning changes the result;
- review grid-related alarms;
- escalate to string, DC and AC electrical testing where required.
The goal is not to guess the most common cause. It is to remove possible causes one by one until the evidence points to the root problem.
What information helps a technician diagnose faster?
Before requesting support, keep these details ready: system capacity, location, inverter make and model, recent daily generation, screenshots of alarms, date the problem started, whether the plant was recently cleaned and any visible roof changes.
Solar Service India can use this information to decide whether the next step is remote review, cleaning, grid investigation or a technical site inspection.