When I worked as a solar system designer, one of the most common issues we faced as a company was the customer coming back a few months after installation because the solar panel system we installed in their house or business did not produce the amount of electricity as promised.
In this post, I will explain the process I followed to troubleshoot and the common causes that caused these issues.
Here is the scenario that can happen to you. You did the math. You sized your system, reviewed the installer’s production estimates, and signed the contract, expecting to generate a certain number of kilowatt-hours every month. So why is your solar system producing less than expected?
The frustrating truth is that underperformance is one of the most common complaints among solar owners, and in most cases, it is fixable.
Why Is My Solar System Producing Less Than Expected?
The causes range from simple (dirt on the panels) to more serious (equipment defects or poor installation).
Either way, understanding what is happening is the first step toward getting the output you paid for.
This guide breaks down the ten most likely reasons your solar system is falling short, how to identify each one, and what action to take.
Shading: The Number One Culprit
Shading is responsible for more solar underperformance than any other single factor. Even partial shade on a small section of one panel can drag down the output of an entire string in traditionally wired systems.
What catches homeowners off guard is that shading sources change over time. A tree that was short at installation may now tower over the roofline.
A neighbor’s new addition, a satellite dish, or even a chimney casting a longer shadow in winter can all reduce production significantly.
What to do
Use your monitoring app to identify which panels are underperforming at which hours of the day. If a specific panel drops during morning hours and recovers by midday, directional shading is likely the cause.
Consider trimming vegetation, or ask your installer about adding power optimizers or microinverters to limit the impact of shade on individual panels.
Soiling and Dirty Panels
Solar panels are exposed to the outdoor environment every day. Dust, pollen, bird droppings, and air pollution accumulate on the glass surface and block sunlight from reaching the photovoltaic cells.
In dry climates or areas with high dust levels common across much of Latin America, soiling losses can reduce output by 5 to 25 percent if panels go uncleaned for months.
Rain does help, but it is not always sufficient, especially in arid regions where rain is infrequent and dust is heavy.
What to do
Visually inspect your panels every few months. For most systems, cleaning two to four times per year with water and a soft brush is enough. Avoid cleaning during peak sun hours to prevent thermal shock to the glass.
Incorrect Panel Orientation or Tilt Angle
The angle and direction your panels face have a direct impact on how much sunlight they capture. In the northern hemisphere, panels should face true south at an optimal tilt angle that corresponds to your latitude. In the southern hemisphere, they should face true north.
If your installer oriented the panels to face east or west, sometimes unavoidable due to roof geometry, you should expect lower production than the theoretical maximum.
The problem becomes serious when the orientation is miscalculated, and the original production estimate did not account for it accurately.
What to do
Cross-reference your actual production data against a solar irradiance simulation tool for your specific location and roof orientation.
If the original estimate was based on an ideal south-facing orientation but your panels face southeast, the shortfall may simply reflect reality, and the estimate may have been overstated.
High Ambient Temperatures
This surprises most new solar owners; solar panels produce less electricity when they get too hot. Photovoltaic cells are rated at a standard test condition temperature of 25°C (77°F).
When the panel surface temperature exceeds this, which it routinely does on a hot afternoon in summer, output decreases.
Most crystalline silicon panels lose roughly 0.3 to 0.5 percent of their rated output for every degree Celsius above 25°C.
On a rooftop where surface temperatures reach 60–70°C, that can add up to a 15 to 20 percent reduction compared to nameplate capacity.
What to do
This is largely unavoidable in hot climates, but make sure your panels have adequate airflow underneath them.
Flush-mounted panels with no gap between the panel and the roof trap heat more than racked panels with ventilation.
If your installer did not factor temperature coefficients into the production estimate for your climate, the projection may have been unrealistic from the start.
Inverter Issues or Undersized Inverter
The inverter is the brain of your solar system. It converts the direct current (DC) produced by your panels into the alternating current (AC) used by your home.
When the inverter is malfunctioning, operating outside its optimal range, or undersized relative to the panel array, production suffers.
Common inverter problems include:
- Fault codes that cause partial or complete shutdowns
- Clipping: when the panels produce more DC power than the inverter is rated to handle, the excess energy is simply discarded
- Aging inverter efficiency losses are more common in older string inverters
What to do
Check your inverter’s display or monitoring portal for fault codes or error messages. Compare your inverter’s rated capacity to your panel array’s total wattage.
If your 6 kW array is connected to a 5 kW inverter, you are losing output every time production peaks. Contact your installer or the inverter manufacturer for remote diagnostics.
How to Choose the Right Solar Inverter for Your Home or Business
Panel Degradation
All solar panels degrade over time. This is normal. The industry standard degradation rate is approximately 0.5 to 0.8 percent per year for quality panels.
After ten years, you might expect output to be roughly 5 to 8 percent lower than when the system was new.
However, some panels experience accelerated degradation due to manufacturing defects, extreme weather, or poor quality control.
Potential-induced degradation (PID), light-induced degradation (LID), and microcracks from hail or improper installation can all cause panels to underperform well ahead of schedule.
What to do
If your system is relatively new and already underperforming significantly, request an on-site inspection or electroluminescence (EL) imaging test to detect microcracks or cell defects invisible to the naked eye.
Most quality panels come with a 25-year performance warranty, guaranteeing at least 80 percent of rated output.
Wiring Losses and Connection Problems
Electricity is lost as heat as it travels through wiring; this is known as resistive loss. If your system was installed with undersized cables, long wire runs, or loose connections, those losses add up across every hour of operation.
Corroded connectors, particularly MC4 connectors exposed to moisture, can also introduce resistance over time and degrade performance gradually. In severe cases, they become fire hazards.
What to do
Ask your installer about the wire gauges used in your system and whether the cable runs were kept as short as possible.
If your system is several years old, have an electrician inspect the DC connectors and junction boxes for signs of corrosion or heat damage.
Software Configuration or Monitoring Errors
Sometimes the panels are performing exactly as they should, but the monitoring software is providing inaccurate readings.
Meter calibration issues, gateway communication failures, and software misconfigurations can all lead to production data that does not reflect reality.
Similarly, some systems have production offsets built into the monitoring software that need to be calibrated after installation. If the baseline was never set correctly, the reported output will always appear off.
What to do
Cross-check your monitoring data against your actual utility meter readings. Your electricity bill tells you exactly how much solar energy was credited to your account each month.
If the utility credits match your monitoring data, the system is likely performing as reported. If they diverge significantly, contact your monitoring provider for recalibration.
Overestimated Production Projections
Not all underperformance is a technical problem; sometimes the issue is the estimate itself. Solar installers use simulation software that makes assumptions about local irradiance, weather variability, soiling, and system losses.
If those assumptions were overly optimistic, the original projection will be higher than what your system can realistically achieve.
Common examples of inflated estimates include.
- Using irradiance data from a nearby location with better sun exposure
- Applying zero or minimal loss factors for soiling, wiring, and temperature
- Ignoring seasonal variation and presenting only the best-case annual averages
What to do
Request the detailed simulation file (typically a PVsyst or SAM report) that underpinned the original production estimate.
Review the assumptions used. If the installer used unrealistic loss factors, you may have grounds to dispute the estimate, or at a minimum, you will understand the true expected range.
Grid Curtailment or Export Limits
In some regions, utilities impose limits on how much solar energy a residential system can export to the grid.
If your system produces more than the allowed export limit at certain times, the inverter is instructed to throttle output, and that production is simply lost.
This is increasingly common as solar penetration rises and grid operators struggle to manage midday surges.
Depending on your utility contract and local regulations, export curtailment may account for a meaningful portion of the production gap.
What to do
Check your interconnection agreement with your utility for any export limits. If curtailment is occurring, your inverter monitoring system may log it as a separate event.
Adding battery storage can help by absorbing excess production instead of sending it to a grid that won’t accept it.
How to Diagnose Your Own System
Before calling your installer or filing a warranty claim, run through this simple diagnostic process:
- Check your monitoring app for error messages, offline panels, or inverter fault codes.
- Compare your monthly production to the installer’s original year-one estimate, broken down by month.
- Look at your utility bill to confirm how much solar energy was actually credited.
- Inspect your panels visually from the ground for debris, shading, or visible damage.
- Review your production by time of day; consistent drops at specific hours often point to shading.
If you find no obvious cause and the shortfall is significant (more than 20 percent below projections), it is worth requesting a formal performance inspection. Many installers offer this as part of their warranty service.
Frequently Asked Questions
How much should a solar system produce?
A well-designed residential system in a location with good sun exposure typically produces 4 to 5 kWh per day per kilowatt of installed capacity. A 5 kW system in a sunny region might generate 20–25 kWh on a typical day.
Is it normal for solar production to vary by season?
Yes, significantly. Production in winter months can be 30 to 50 percent lower than in summer due to shorter days and lower sun angles. Year-over-year comparisons are more meaningful than month-to-month comparisons.
What is a normal degradation rate for solar panels?
Reputable tier-1 panels degrade at roughly 0.5 percent per year. Some budget panels degrade faster. After 25 years, a quality panel should still produce at least 80 percent of its original rated capacity.
Can I fix underperformance myself?
Cleaning the panels and trimming shading vegetation are safe DIY tasks. Any work involving the inverter, wiring, or electrical connections should be handled by a licensed solar technician.
Final Thoughts
If your solar system is producing less than expected, the answer is rarely “that’s just how it is.” In most cases, there is an identifiable cause and an actionable fix.
Start with the simplest possibilities (shading, soiling, inverter errors) before assuming a deeper technical problem.
Document your system’s production data carefully, compare it against your original projections, and hold your installer accountable for the performance they promised.
A solar system is a long-term asset, and keeping it running at peak output is well worth the attention.
