solar troubleshooting
PV array underproducing vs. estimate
Common symptoms: solar producing less than expected; low solar output; panels underperforming; production below estimate; kwh lower than quoted
Stop and call a pro if:
- PV modules are energized whenever exposed to daylight — never disconnect DC conductors under load (arc-flash)
- do not open combiner boxes or touch damaged/hot conductors
- batteries store lethal energy even when the system reads 'off'
Step-by-step diagnostic flow
Step 1
Do you see or smell any arcing, burning, scorched or melted connectors, hot/damaged conductors, or a swollen battery?
PV arrays are live in daylight and can sustain a DC arc. Any of these signs is an emergency.
Step 2
How are you comparing production — against a daily/seasonal estimate, or against a specific clear-sky day?
Production naturally drops with shorter days, low winter sun, clouds, and high panel temperatures. Estimates are annual averages.
Step 3
On a sunny day around midday, is any part of the array shaded (trees, vent pipes, a new structure) or visibly soiled with dust, pollen, leaves, or snow?
Even partial shade on one panel can drag down a whole string on string inverters.
Step 4
In your monitoring app, is production low across the whole system or only on one string / a few panels?
Per-panel (microinverter / optimizer) systems show individual modules. String inverters show per-string totals.
Step 5
Around solar noon on a clear day, does the power curve flatten at a hard ceiling (a plateau) rather than peaking?
A flat-topped curve at the inverter's rated AC power is 'clipping' — normal when an array is oversized to the inverter, and not a fault.
Possible outcomes
Stop — possible DC arc or battery hazard
high confidenceArcing, burning smells, scorched connectors, hot conductors, or a swollen battery indicate an active electrical fire risk on an energized system.
- Activate the rapid-shutdown switch if you can reach it safely
- Keep clear of the array and equipment
- Call your installer and, if there is smoke or heat, call the fire department
Likely normal seasonal/weather variation
high confidenceCloudy skies and short, low-sun winter days reduce output well below the annual-average estimate; this is expected, not a fault.
- Compare output on a few clear days against the same season last year if available
- Track production over a full month before concluding there's a problem
Shading or soiling is limiting output
high confidenceNew shade or a layer of dust, pollen, leaves, or snow reduces irradiance on the modules and can disproportionately cut string output.
- Rinse accessible soiling from the ground with water — never climb the roof or use harsh cleaners
- Trim vegetation that has grown to shade the array
- Re-check production after the array is clean and unshaded
- Photos of the shading source and time of day it occurs
- Which panels/strings the monitoring app shows as low
Possible string or module/optimizer fault — call your installer
medium confidenceOne string or a handful of panels reading low (while the rest are fine) points to a failed module, optimizer/microinverter, or string connection — diagnosis requires opening live DC equipment.
- Do not open combiner boxes or disconnect DC connectors yourself
- Note exactly which panels/strings are affected in the app
- Schedule your installer for a service visit
- Screenshot of per-panel/per-string production showing the low units
- Module and inverter/optimizer make and model
- How long the underperformance has persisted
Need per-panel data to localize the loss
low confidenceWithout per-string or per-panel monitoring it isn't possible to tell normal variation from a hardware fault.
- Ask your installer to confirm whether your inverter/optimizers report per-unit data
- Record daily kWh for a week alongside weather to build a baseline
- Daily kWh log with weather notes
- Inverter make and model
- Original production estimate from your contract
Likely inverter clipping — usually normal
medium confidenceA flat plateau at the inverter's AC rating means the array is producing more DC than the inverter can convert; this is by design on oversized arrays and only trims a small amount of annual energy.
- Confirm the plateau sits at your inverter's rated AC kW
- If clipping is heavy and persistent, ask your installer whether the array/inverter sizing matches your contract
- Inverter AC rating and array DC size
- Screenshot of the clipped midday curve
Even system-wide shortfall — have your installer review
low confidenceA uniform shortfall with no shading, soiling, or clipping can come from an undersized install, an inverter running derated, or an optimistic original estimate — all need professional review.
- Gather a month of daily production data
- Compare actual output to the contracted estimate
- Ask your installer to verify inverter settings and array configuration
- Monthly production vs. contracted estimate
- Inverter and module models
- Any inverter event or warning logs
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