Solar · Updated 2026-04-25
What should I do if my solar panels are underperforming?
Check the monitoring app first, compare actual kWh to your design's PVWatts estimate, look for new shading or soiling, then verify the inverter and PSEG Long Island net-meter readings.
Healthy residential PV in Suffolk County typically produces 1,150–1,300 kWh per kW of installed DC capacity per year. If your monitoring (Tesla, Enphase Enlighten, SolarEdge mySolarEdge) is 15%+ under that — and not just for one cloudy month — work through shading, soiling, inverter faults, and meter readings before assuming a failed module.
Step-by-step
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1
Pull a 12-month production report from your monitoring app
Open Tesla, Enphase Enlighten, or SolarEdge and export the last 12 months of monthly kWh. Sum to a yearly total.
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2
Run NREL PVWatts for your address
Visit pvwatts.nrel.gov, enter your DC size (kW), tilt, azimuth, and module type, accept defaults, and note the annual kWh.
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3
Compare and quantify the gap
Calculate (PVWatts - actual) / PVWatts. If the gap is < 10%, the system is healthy. 10–20% likely soiling/shading. >20% needs a technician.
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4
Inspect for new shading and soiling
Walk the property at 10am, noon, and 3pm noting shadows. Photograph each module from the ground for visible dirt, pollen, or stains.
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5
Check inverter and module-level faults
Look for active alarms in the monitoring dashboard. On microinverter systems, sort modules by yield to spot a single underperformer.
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6
Compare to your PSEG LI net-meter bill
Confirm the monitoring number matches kWh delivered to PSEG LI on your bill. A monitoring/billing mismatch points at a meter or interconnection issue, not the array.
Common follow-up questions
How do I know what 'normal' production should be?
Run your address through NREL's free PVWatts Calculator with your system's DC size, tilt, and azimuth. PVWatts gives a month-by-month kWh expectation for a typical year using NSRDB irradiance data. Compare your monitoring app's actuals to PVWatts' P50 estimate, not to last year (which had its own weather).
What's the difference between shading and soiling?
Shading is new obstruction (a tree that grew, a neighbor's addition, a chimney shadow at low sun angles). Soiling is dirt — pollen in spring, salt spray in shore towns, bird droppings, wildfire smoke residue. Soiling losses on Long Island typically run 2–5% per year, mostly in late summer; shading losses can be 20%+ on a single string.
What are common inverter faults to look for?
Most string inverters log fault codes that bubble up into the monitoring app: Riso (insulation resistance), GFDI (ground-fault), or arc-fault detection. Microinverter systems (Enphase) flag individual modules in the Enlighten dashboard. A single module showing 30% less than its neighbors usually means a bypass diode, MLPE, or module failure.
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Need help with this on Long Island?
NovaLee Solutions is a licensed roofing, solar, and electrical contractor serving Suffolk County and all of Long Island. Our crew is GAF-certified, Tesla-Powerwall-certified, and Suffolk County master-electrician licensed.