How to Check Solar Panel Performance: A Complete Guide

Your SolarEdge or Enphase app tells you how many kilowatt-hours your panels produced today. But is that number good or bad? How do you know if your system is performing as expected?

Most homeowners have no way to answer this question. Their monitoring app shows data without context. It's like getting a blood pressure reading without knowing whether those numbers are healthy. This guide teaches you how to properly evaluate your system's performance.

Step 1: Manual Visual Inspection

Before diving into data analysis, do a basic visual check of your system:

• Check for shading. Stand in your yard at different times of day and look at your roof. Any tree shadows, chimney shadows, or roof edges blocking panels?
• Look for visible damage. Use binoculars if your panels are on the roof. Cracks, discoloration, or bird droppings are obvious red flags.
• Check the inverter. If you have a string inverter, verify it has power, is showing a green status light, and is not displaying error codes on its front panel.

If everything looks normal visually, move to the data analysis step.

Step 2: Check Your Monitoring App for Errors

Open your SolarEdge or Enphase app and look for:

• Alert notifications. Red or yellow warnings indicate your system isn't operating at full capacity.
• Inverter status. It should show "producing" or "operating" on sunny days. "Night mode" is normal at night. "Offline" or "faulty" is a problem.
• Individual optimizer/inverter status. If any power optimizers (SolarEdge) or microinverters (Enphase) show offline or low voltage, that's a clue to the problem.

Error codes usually indicate a real issue — don't ignore them. However, absence of errors doesn't mean your system is performing optimally.

Step 3: Use PVWatts to Calculate Expected Production

PVWatts is a free tool from NREL (National Renewable Energy Laboratory) that estimates solar production based on your system specifications and location.

To use PVWatts:

1. Go to pvwatts.nrel.gov
2. Enter your address
3. Enter your system size in kW (e.g., a 6.5 kW system)
4. PVWatts will estimate monthly production for your location

Now compare PVWatts estimates to your actual production from your monitoring app. How do they compare?

If your actual production is 85-115% of PVWatts estimate, your system is performing well. Below 85% suggests underperformance that needs investigation. Above 115% is unlikely unless you have optimally positioned panels with minimal shading.

Step 4: Analyze Production Trends Over Time

A single month's production doesn't tell you much — weather varies. Instead, look at trends across multiple months:

• Seasonal patterns are normal. Summer production should be 2-3x higher than winter production in most US locations.
• Watch for unexpected drops. If production this August is 30% lower than last August, something has changed (shading, soiling, or equipment failure).
• Look for gradual decline. Slow degradation (0.7-1% per year) is normal. Faster decline suggests panel or equipment problems.

Most monitoring apps let you export historical data or show charts. Graph your monthly production over 2-3 years and look for anomalies.

Step 5: Calculate Your System's Performance Ratio

Performance ratio (PR) is a standard metric that accounts for all system losses — inverter efficiency, wiring losses, soiling, and temperature effects.

Performance Ratio = (Actual Production / Theoretical Production) × 100

Healthy systems typically have a PR of 75-85%. Below 70% indicates significant problems.

To calculate this accurately, you need:

• Your system's actual production (from monitoring app)
• Solar irradiance data for your location and time period
• Panel specifications (efficiency, temperature coefficient)

This gets complex quickly — which is why the next step is easier.

Step 6: Use SolarDoctor for Instant Performance Analysis

SolarDoctor automates steps 3-5. Connect your SolarEdge account and we instantly calculate what your system should produce based on NREL's latest weather data for your location. We then compare your actual production and give you a health score from 0-100.

A score of 90+ means your system is performing excellently. 75-90 is good but watch for trends. Below 75 means investigate — something needs attention.

SolarDoctor also tracks your performance ratio automatically, alerts you when production drops unexpectedly, and identifies which panels or optimizers might be underperforming.

What to Do If You Find Problems

If your performance check reveals underperformance, here's the next step:

• Check for obvious causes first — shading, soiling, or error codes
• Try simple fixes — clean panels if visibly dirty, trim tree branches if shading is the issue
• Call a professional if needed — a solar technician can do infrared scans, test panel output, and diagnose equipment failures

The key is catching problems early. A 10% production loss today becomes a 1.2 MW·year loss over a month — and that's money lost forever.