How to Identify an Underperforming Solar System
By Team Faseeh Lall
Your solar panels do not need to stop working completely for your system to start losing value.
An underperforming solar system may continue producing electricity every day while generating less energy than it reasonably should. Because the system still appears active in the monitoring app, the problem can remain unnoticed for weeks or even months.
For a homeowner, that can mean lower electricity savings. In markets where solar production generates Solar Renewable Energy Credits, reduced production can also mean fewer credits available for sale.
The difficult part is knowing whether lower production represents a real system problem or normal variation caused by weather, seasons, temperature, or other operating conditions.
The National Renewable Energy Laboratory's PVWatts calculator estimates photovoltaic energy production using system characteristics and local solar-resource data, while also warning that actual production varies because of weather and site-specific conditions. For that reason, identifying underperformance requires more than looking at one low-production day.
This guide explains the warning signs of an underperforming solar system, how to compare actual and expected production, what commonly causes performance loss, and when professional help may be appropriate.
What Is an Underperforming Solar System?
A solar system is underperforming when its actual electricity production remains materially below what would reasonably be expected for its design, location, weather conditions, season, and operating condition.
That does not necessarily mean the entire system has failed.
Underperformance may affect:
The entire solar array
One inverter
One string of panels
Individual panels or microinverters
Monitoring or communications equipment
The production meter
A shaded section of the array
A system can therefore show production in an app while still having a performance problem.
This is one reason structured performance monitoring matters. SAMSMD's monitoring process compares actual production with expected performance and reviews production drops, inverter conditions, and communications issues rather than relying only on whether the system is technically online.
1. Check Whether Your Solar Production Has Dropped
The first place to look is your solar monitoring platform.
Most modern solar systems provide an inverter portal, mobile application, or online dashboard that shows daily, monthly, and lifetime energy production.
Look for changes such as:
A sudden drop in daily production
Several days of unexpectedly low output
Production falling to zero during daylight hours
One section producing noticeably less than the others
A significant difference from the same season in previous years
Production remaining low despite clear weather
Missing or incomplete production data
Do not judge performance from a single day.
Cloud cover, storms, seasonal daylight changes, temperature, and other environmental conditions can create significant short-term variation. NREL's PVWatts documentation specifically notes that photovoltaic performance estimates contain uncertainties and that energy production can vary from year to year because of weather.
Instead, look for a pattern.
A sustained unexplained decline is much more meaningful than one disappointing Tuesday.
2. Compare Actual Production With Expected Production
Knowing that your system produced 600 kilowatt-hours last month does not tell you whether 600 kilowatt-hours was good or bad.
You need something to compare it with.
Useful benchmarks include:
Your original solar proposal or production estimate
Previous-year production for the same month
Similar months under comparable weather conditions
Installer performance estimates
A photovoltaic production model such as NREL PVWatts
NREL's PVWatts calculator estimates energy production for grid-connected photovoltaic systems based on location and system information. It can provide homeowners with a useful reference point for expected performance, although its results remain estimates rather than guarantees.
SAMSMD also uses production verification as part of its management services, comparing actual system production against estimated production to help determine whether a system is performing as expected.
Do Not Expect Actual Production to Match an Estimate Exactly
Production estimates are not promises.
Actual output can vary because of:
Weather
Temperature
Shading
Snow
Soiling
Equipment availability
System orientation
System age
Site-specific conditions
The goal is not to panic whenever actual production differs slightly from a model.
The goal is to identify persistent differences that cannot reasonably be explained by normal operating conditions.
3. Look for Sudden Changes Instead of Normal Seasonal Changes
Solar production naturally changes throughout the year.
A Washington, D.C. rooftop system will not normally produce the same amount of electricity in December that it produces during longer, sunnier summer days.
That variation alone does not indicate failure.
More concerning patterns include:
Sudden Production Drop
If output falls sharply from one day or week to the next without a clear weather explanation, investigate the system.
Possible causes may include:
Inverter shutdown
Electrical fault
Breaker issue
Communications failure
Damaged equipment
New shading
Meter problem
Gradual Production Decline
A gradual decline may be less obvious.
Possible factors include:
Increasing soiling
Growing vegetation
New shading
Equipment deterioration
Developing inverter problems
Wiring or connector issues
Gradual changes in system condition
Repeated Intermittent Drops
If production repeatedly disappears and returns, that may indicate an intermittent inverter, communications, electrical, or equipment problem.
The pattern itself can provide useful information when a technician later investigates the system.
4. Check Your Inverter for Errors or Warnings
The inverter is one of the most important components in a solar photovoltaic system.
It converts the direct-current electricity generated by solar panels into alternating-current electricity that can be used by the property or delivered to the grid.
If an inverter or microinverter develops a fault, production may fall substantially even though the panels themselves appear completely normal.
Watch for:
Error messages
Warning lights
Offline status
Repeated fault codes
Unexpected shutdowns
One inverter producing less than others
Missing inverter data in your monitoring portal
NREL's photovoltaic operations and maintenance guidance emphasizes structured maintenance and performance management to reduce performance risk and improve the effectiveness of operating photovoltaic systems.
Do not open an inverter or electrical enclosure yourself unless you are properly qualified to perform that work.
Record the error message or fault code and contact an appropriate professional.
5. Make Sure a Monitoring Failure Is Not Being Mistaken for a Production Failure
Sometimes the solar system is producing electricity correctly, but the monitoring system has stopped reporting it.
This can happen because of:
Lost Wi-Fi connection
Failed communications gateway
Monitoring-platform outage
Inverter communications problem
Changed internet equipment
Meter communications failure
Account or portal configuration problem
That creates an important distinction:
No monitoring data does not automatically mean no solar production.
Compare your inverter status, utility information, meter readings, and monitoring dashboard before assuming the entire solar system has stopped working.
SAMSMD specifically monitors both production and communications because a connectivity problem can hide system performance from the homeowner even when parts of the equipment remain operational.
6. Look for New Shading
A solar system that performed well when installed may develop shading problems later.
Trees grow.
New buildings appear.
Satellite dishes, roof equipment, antennas, or neighboring structures can change the amount of sunlight reaching the array.
Look from a safe location for:
Tree branches crossing the array
New nearby construction
Chimney shadows
Roof equipment
Satellite dishes
Vegetation growth
Objects casting shadows during peak sunlight hours
Shading can affect one section of an array more strongly than another, which is why panel-level or inverter-level monitoring can be useful when available.
If one section consistently produces less than similar unshaded sections, shading should be investigated as a possible cause.
7. Check Whether the Panels Are Heavily Soiled
Dust, pollen, bird droppings, leaves, and other debris can reduce the amount of sunlight reaching the solar cells.
The effect varies significantly depending on the site, weather, panel angle, surrounding environment, and amount of buildup.
NREL's current PVWatts model includes soiling as one of the system-loss categories that can affect modeled photovoltaic production.
Look for:
Heavy dust buildup
Bird droppings
Leaves
Pollen
Construction dust
Persistent staining
Debris collecting around panels
Cleaning may help when soiling is actually responsible for reduced output.
However, repeatedly cleaning panels without checking performance can waste time if the real problem is an inverter fault, wiring issue, shading problem, or equipment failure.
SAMSMD offers solar cleaning as part of its broader management approach, alongside monitoring, inspections, production verification, and issue-resolution support.
8. Compare Different Sections of the System
If your monitoring platform provides panel-level, string-level, or inverter-level information, compare similar parts of the array.
Suppose two roof sections have similar orientation and sunlight exposure.
If one consistently produces substantially less than the other, the difference may help narrow the problem.
Possible causes could include:
A failed microinverter
String fault
Damaged panel
Localized shading
Wiring issue
Connector problem
Heavy localized soiling
Equipment communications problem
This type of comparison is often more useful than looking only at total system production because total output can hide a partial failure.
9. Review Your Electricity Bills
Your utility bill should not be your only solar-monitoring tool, but it can provide another warning sign.
If your electricity purchases from the grid suddenly increase without a corresponding change in household electricity use, lower solar production may be one possible explanation.
Compare:
Current utility consumption
Previous months
The same season last year
Solar production during the same period
Major changes in household electricity use
Be careful with this comparison.
A higher electricity bill can also result from:
Increased energy use
New appliances
Electric-vehicle charging
Heating or cooling demand
Electricity-rate changes
Billing-cycle differences
Use the utility bill as supporting evidence, not proof by itself.
10. Check Your Solar Renewable Energy Credit Production
For eligible solar owners, another clue may appear in Solar Renewable Energy Credit generation.
SAMSMD states that one Solar Renewable Energy Credit is created for each 1,000 kilowatt-hours of qualifying solar production. If the physical system produces less electricity, the number of credits it can generate may also decline.
If Solar Renewable Energy Credits appear to be arriving more slowly than expected, investigate two separate possibilities:
Physical Underperformance
The solar system may actually be generating less electricity.
Possible causes include equipment faults, shading, soiling, or downtime.
Reporting or Administrative Problem
The system may be producing normally, but production data may not be reported or processed correctly.
That distinction matters.
A missing Solar Renewable Energy Credit does not automatically prove that the panels are underperforming.
SAMSMD combines Solar Renewable Energy Credit brokerage with production tracking, monitoring, and solar asset management, allowing system performance and certificate activity to be reviewed together.
Common Signs of an Underperforming Solar System
Production suddenly drops close to zero it could be the inverter, electrical, grid, or system fault
Production falls only on one section the issue may be raiseed because of shading, microinverter, string, panel, or wiring issue
Production gradually declines the issue can be soiling, growing shade, equipment condition, or other long-term changes
Monitoring data disappears may be caused because of communications or monitoring failure
Inverter displays repeated errors there be a possibilty of inverter or electrical problem
Production remains low after cleaning problem may not be caused by dirt
Utility purchases rise unexpectedly? Possible solar production loss or increased household usage
Solar Renewable Energy Credit generation slows your solar panel production is became lower or reporting issue
Output remains materially below expected production system investigation may be appropriate
These signs help identify where to start. They are not a substitute for professional diagnosis.
What Does Not Automatically Mean Your Solar System Is Underperforming?
Homeowners sometimes interpret any lower production as a problem.
That can lead to unnecessary service calls.
Lower output may be completely normal during:
Cloudy weather
Winter months
Shorter daylight periods
Snow coverage
Very hot conditions
Grid curtailment or utility events
Temporary shading
Different weather from the comparison period
NREL's PVWatts methodology accounts for environmental and system-loss factors and specifically cautions that predicted production includes assumptions and uncertainties.
A meaningful diagnosis therefore compares similar conditions rather than treating every production dip as equipment failure.
A Simple Homeowner Solar Performance Check
If you think your solar system is underperforming, follow this sequence:
Open your monitoring application.
Check whether the system is online and producing.Review recent production history.
Look for sudden or sustained changes.Compare similar periods.
Compare this month with the same season or previous year rather than an unrelated month.Check inverter status.
Record warnings or error codes.Look for visible shading or debris.
Inspect only from a safe location.Compare actual production with expected production.
Use your original estimate, installer documentation, or an appropriate modeling resource such as NREL PVWatts.Review your utility information.
Check whether grid electricity consumption has unexpectedly increased.Review Solar Renewable Energy Credit activity if applicable.
Determine whether slower certificate creation reflects lower production or a reporting problem.Document what you find.
Save screenshots, dates, error codes, production readings, and photographs.Get professional help when the pattern remains unexplained.
This process helps separate normal production variation from a problem that actually deserves attention.
Why Early Detection Matters
A solar system can underperform without creating an obvious emergency.
That is precisely what makes underperformance expensive.
If a complete system shuts down, the homeowner is more likely to notice.
If the system simply produces less than expected while remaining online, the loss can continue quietly.
Structured operations and maintenance practices are intended to improve photovoltaic performance, reduce performance risk, and make system management more effective over the operating life of the asset.
For solar owners, earlier detection can help protect:
Electricity production
Utility savings
Solar Renewable Energy Credit generation
Equipment condition
Warranty documentation
Long-term system value
How SAMSMD Helps Identify Solar Underperformance
Finding a production problem is only the first step.
Someone still has to determine whether the issue is related to monitoring, equipment, cleaning, maintenance, an installer, or a warranty provider.
SAMSMD combines Solar Renewable Energy Credit brokerage with solar asset management for Washington, D.C. solar owners. Its current management services include proactive monitoring, production verification, system cleaning, system inspections, and issue-resolution support.
SAMSMD can help by:
Reviewing system production data
Comparing actual and expected production
Identifying unusual output changes
Monitoring inverter and communication issues
Verifying production
Coordinating cleaning where appropriate
Coordinating system inspections
Supporting maintenance requests
Communicating with installers
Helping coordinate warranty-related issues
Tracking Solar Renewable Energy Credit production and brokerage
The objective is not merely to determine whether your solar panels are online.
It is to understand whether the system is producing at a reasonable level and help move unexplained performance problems toward resolution.
When Should You Call a Solar Professional?
Professional support may be appropriate when:
Production unexpectedly falls to zero
Output remains unusually low despite normal weather
The inverter repeatedly shows warnings
One part of the system consistently underperforms
Monitoring remains offline
Visible panel or wiring damage appears
Production does not recover after appropriate cleaning
A storm may have damaged the system
Solar Renewable Energy Credit generation appears inconsistent with reported production
You cannot determine why actual production differs significantly from expected performance
Do not climb onto a roof or open electrical equipment simply to investigate production loss.
Roof access and electrical work can create serious safety risks and should be handled by appropriately qualified professionals.
Final Thoughts
An underperforming solar system does not always look broken.
The panels may appear clean.
The inverter may still be running.
The monitoring application may still display production.
But if actual energy generation remains below reasonable expectations, your system may be losing electricity production and financial value without an obvious warning.
The best way to identify underperformance is to combine several pieces of evidence:
Production history
Expected production
Comparable seasonal performance
Inverter status
Monitoring data
Shading and soiling conditions
Utility information
Solar Renewable Energy Credit activity
Do not focus on one number or one cloudy day.
Look for patterns.
When a production gap continues without a reasonable environmental explanation, investigate it before months of lost output accumulate.
Frequently Asked Questions
How do I know if my solar system is underperforming?
Compare actual production with expected production, previous comparable periods, inverter status, and current weather conditions. A persistent unexplained production gap may indicate system underperformance.
Why are my solar panels producing less electricity than before?
Possible causes include shading, soiling, inverter problems, wiring or connector issues, communications failures, equipment problems, weather differences, or normal system aging. The production pattern and system data can help narrow the cause.
How much solar production loss is considered underperformance?
There is no single percentage that applies to every solar system. Expected production depends on system design, location, weather, season, shading, temperature, and equipment condition. Persistent deviation from an appropriate performance baseline should be investigated.
Can my solar system underperform even if the monitoring app says it is working?
Yes. A system can remain online while one inverter, string, panel group, or other component performs below expectations. Total system production may hide a partial failure.
Can dirty solar panels cause underperformance?
Soiling can reduce photovoltaic production, but the impact varies by site and environmental conditions. If production remains low after appropriate cleaning, another technical or environmental issue may be responsible.
Can an underperforming solar system reduce Solar Renewable Energy Credit income?
Yes. Solar Renewable Energy Credits depend on qualifying solar electricity production. Lower system output may result in fewer credits being generated, although reporting problems can also delay certificate creation.
What should I do if my solar system is producing less than expected?
Review your monitoring data, compare production with similar periods and expected output, check inverter warnings, look for visible shading or debris from a safe location, document the problem, and contact a qualified professional if the unexplained performance gap continues.