If your solar plant output is falling month by month—or you feel like “it used to generate more earlier”—there’s usually a clear reason behind it. The good news is: many issues can be found early with simple checks before they turn into bigger losses.
This blog explains the most common causes of low solar plant generation in a way that’s easy to understand, along with what to check first.
First, how do you know your solar plant is underperforming?
You may be underperforming if you notice:
- Your monthly units (kWh) are lower than the same month last year
- Inverters show frequent trips or long downtime
- You see mismatch between inverters/strings
- Your O&M team keeps “fixing small issues” but output doesn’t improve
Before jumping to conclusions, compare:
This month vs same month last year
Sunny days output vs earlier sunny days output
Inverter-wise generation (which inverter is lagging)
12 Common Causes of Underperformance (Simple Explanation + Checks)
1) Panels are dirty (dust, bird droppings, leaves)
Even a small layer of dust can reduce output.
What to check:
- Are panels visibly dusty or patchy dirty?
- Is cleaning happening regularly and properly?
Quick fix: Better cleaning schedule + correct method (avoid hard water marks).
2) Shadow falling on panels
A small shadow from a tree, pipe, wall, or nearby structure can reduce generation.
What to check:
- Any new construction near the plant?
- Morning/evening shadows on rows?
Quick fix: Trim trees, shift objects (if possible), redesign strings (if required).
3) Hotspots or damaged panels
Hotspots happen when one part of a panel heats more due to cell damage.
What to check:
- Panels with burnt marks, cracks, yellowing
- Use thermal camera (if available) to find hotspots
Fix: Replace damaged modules (and check why it happened).
4) Loose DC connectors or joints (common hidden loss)
Loose connectors create resistance and heating, reducing power.
What to check:
- Burnt MC4 connectors
- Smell of burning near DC junction points
- Hot connectors (touch carefully only by trained person)
Fix: Replace connectors, tighten joints, use proper crimping tools.
5) DC cable damage (sunlight/rat bite/aging)
DC cables exposed to harsh sun or rodent bites create power loss and safety risk.
What to check:
- Cracked insulation
- Rat bite marks
- Cable bends and exposed copper
Fix: Replace damaged sections, improve cable routing and protection.
6) String mismatch (one weak string reduces overall output)
If one string produces less current, it impacts the inverter MPPT performance.
What to check:
- Compare string current readings
- One MPPT always lower than others
Fix: Identify weak string, check modules, connectors, fuses, polarity.
7) Inverter faults or frequent tripping
Inverters stop generation when they trip.
What to check:
- Alarm history / event logs
- Grid error, over-voltage, over-temperature, insulation fault, DC low/high
Fix: Root cause analysis (grid issue, ventilation, component aging).
8) Grid problem or voltage fluctuations
If grid voltage is unstable, the inverter will trip or limit output.
What to check:
- Frequency/voltage alarms
- More trips during peak load time
Fix: Coordination with utility, protective settings review (as per standards).
9) Soiling loss is high due to location
Some sites need more frequent cleaning (cement dust, highways, coastal salt).
What to check:
- Output improves immediately after cleaning but drops fast again
Fix: Optimize cleaning frequency; consider anti-soiling methods (site-based).
10) Combiner box / fuse / SPD issues
A blown fuse can stop an entire string.
A failed SPD can increase damage risk.
What to check:
- DC fuse status
- SPD indicator (green/red)
- Water ingress inside combiner box
Fix: Replace faulty fuses/SPDs, improve sealing and inspection routine.
11) Earthing or insulation resistance (IR) problems
Poor earthing or low insulation triggers inverter shutdown and safety risk.
What to check:
- Insulation fault alarms
- IR test trend reports
- Earth continuity checks
Fix: Correct earthing points, replace damaged cables, improve bonding.
12) Weak monitoring / no proper data
Without proper monitoring, problems stay hidden and losses grow.
What to check:
- Do you get inverter-wise and string-wise data?
- Are alarms being noticed and responded quickly?
Fix: Upgrade monitoring and set alert response process.
What to Check First
If output is low, start with these steps:
- Compare generation with last year (same month)
- Check inverter alarms and downtime hours
- Inspect cleaning and shadow issues
- Check for hotspots / burnt connectors
- Verify combiner box fuses and SPD health
- Check IR and earthing health (trained technician)
This gives fast clarity on whether the issue is:
- cleaning/shading
- electrical faults
- inverter/grid issues
- aging equipment needing upgrades
When is it time to think beyond repairs?
If the same problems keep coming back and generation continues to drop even after maintenance, it may be time to consider:
- inverter upgrade
- module replacement
- DC redesign / string balancing
- monitoring upgrade
(These are often part of a repowering plan, but the first step is always diagnosis.)
FAQs
Why is my solar plant generating less electricity?
Most common reasons are dust, shading, inverter trips, loose connectors, and DC losses.
How can I increase my solar plant output?
Start with cleaning, shading removal, checking inverter downtime, fixing DC connector issues, and improving monitoring.
What causes inverter tripping in solar plants?
Common reasons include grid voltage problems, insulation faults, overheating, DC imbalance, and component aging.
How do I know if my solar panels are damaged?
Visible cracks/burn marks and hotspots found in thermal scanning are strong indicators.