How Well Is My PV System Doing?
Your inverter tells you that your solar panels are producing electricity. But is your PV system performing as well as it should?
That is a surprisingly difficult question to answer from a single number on an inverter display.
A better approach is to understand what your system was doing when it was known to be operating normally, establish a practical reference, and then look for meaningful changes over time.
The day your solar system doesn't look quite right
Imagine that your PV system has been working for several years. You regularly see electricity being generated and, most of the time, you do not think about it.
Then one day you look at the inverter app and notice that the production seems lower than you remember.
Is something wrong?
Perhaps.
But perhaps the weather is different. The sun is at a different angle. A part of the array is shaded. The modules are dirty. The temperature is higher. Your household consumption has changed. Or the inverter is operating under conditions that are different from the previous occasion.
Why the inverter kWh figure is only part of the story
The inverter is an essential source of information because it records or reports the electrical energy produced by the PV system.
However, the energy produced during a particular period depends on much more than the condition of the solar modules.
Solar irradiance, temperature, shading, orientation, time of day, weather and system operating conditions can all affect the result.
Therefore, comparing today's production directly with yesterday's production is not necessarily a meaningful performance test.
Three things to consider when checking PV performance
Sunlight
How much solar irradiance was reaching the PV modules at the time of the measurement?
PV system condition
Are the modules, wiring, connectors, inverter and other system components operating as expected?
Measurement conditions
Was the measurement made in a sufficiently comparable way to the previous reference?
Establishing a baseline can make future checking easier
One useful concept in PV maintenance is a baseline.
A baseline is a record of the system's condition under a defined set of circumstances when the system is considered to be operating normally.
It does not have to be a complicated engineering report. For a homeowner, it could simply mean recording measurements under repeatable conditions and keeping the information for future comparison.
The value comes later, when you can compare a new measurement against the earlier reference.
What should you record?
The more consistently you record your observations, the more useful your future comparisons are likely to be.
A practical PV checking record might include:
- Date and approximate time of measurement
- PV string or test area being checked
- Module orientation
- Irradiance measurement or reference
- Inverter reading or relevant electrical information
- Weather and sunlight conditions
- Any visible shading or obstruction
- Unusual observations such as soiling, damage or installation changes
Why irradiance matters when investigating a PV system
Solar irradiance is the sunlight power received on a surface and is normally expressed in watts per square metre (W/m²).
Because PV modules depend on sunlight to generate electricity, irradiance provides important context for understanding an electrical measurement.
Consider two measurements:
- Measurement A is taken under bright, stable sunlight.
- Measurement B is taken while clouds are rapidly passing across the array.
Even if the PV system itself has not changed, the two measurements may be very different.
This is why a useful PV checking method needs to consider both the system result and the sunlight conditions.
Stable sunlight makes comparison more useful
For comparative field checking, try to avoid rapidly changing sunlight whenever practical.
Passing clouds, partial shading and rapidly changing atmospheric conditions can make it difficult to determine whether a difference is caused by the PV system or simply by changing sunlight.
The closer your test conditions are to your established reference conditions, the more meaningful the comparison is likely to be.
Why looking at individual strings can be useful
A PV installation may contain several strings of modules. Depending on the system design, these strings may not all have exactly the same orientation, shading conditions or operating characteristics.
Consequently, treating the entire roof as though every module receives exactly the same sunlight can sometimes hide useful information.
A practical investigation can instead begin with a selected string or test area and establish an appropriate reference for that area.
Strings with the same orientation can be considered together where appropriate. For strings with different orientations, separate references may be more meaningful.
What if you find a deviation?
A deviation does not automatically mean that a solar module has failed.
It is better regarded as a reason to investigate further.
Possible things to investigate include:
- New or seasonal shading
- Dirt or soiling on the modules
- Physical damage
- Connector or wiring problems
- Changes in inverter operation
- Module degradation or mismatch
- Changes to the surrounding environment
- Measurement or test-condition differences
Further electrical testing or professional inspection may be appropriate depending on the size and nature of the deviation.
Where PVBuddy can help
PVBuddy is designed around the idea of repeatable, comparative PV field checking.
The PVS01 sensor measures irradiance and works with the PVBuddy App. The sensor can be set up for a particular test area and a practical reference can then be established.
Flexi-Cal™
PVBuddy provides flexible reference setting.
Where a suitable laboratory-calibrated irradiance meter is available, PVS01 can be tuned against that reference. Alternatively, it can be tuned using the inverter kWh reading of a representative string or strings having the same orientation.
Once the reference is established, subsequent measurements can be compared against it under suitable, stable sunlight conditions.
The objective is not to claim that a single measurement proves the condition of a PV module. Instead, a change from an established reference can provide useful information and indicate when further investigation may be worthwhile.
A typical PVBuddy checking flow
- Step 1 — Select the test area. Place the PVS01 sensor in the same orientation as the module or string being assessed.
- Step 2 — Set the reference. Check the inverter kWh reading and tune the sensor using the PVBuddy App for that string, or for strings having the same orientation.
- Step 3 — Test and compare. Repeat the test under comparable, stable sunlight conditions and compare the result with the established reference.
How often should you check your PV system?
There is no single frequency that is appropriate for every PV installation.
A homeowner may choose to establish a reference when the system is known to be operating normally and then repeat checks periodically or when there is a reason to investigate a change.
Additional checks may also make sense after events that could affect the system, such as nearby construction, new shading, severe weather, physical work on the roof or changes to the electrical installation.
The objective is not to create unnecessary work. It is to make changes easier to notice before they become difficult to understand.
A simple PV owner checklist
- Know which strings or areas make up your PV system.
- Understand the normal inverter readings for your system.
- Record a useful baseline when conditions are suitable.
- Keep sensor orientation consistent when making comparative measurements.
- Prefer reasonably stable sunlight for repeat testing.
- Record unusual conditions such as shading or soiling.
- Investigate persistent or significant deviations rather than assuming the cause.
The real value is knowing what has changed
A PV system can continue producing electricity even when something has changed.
That makes it difficult for a homeowner to recognise a gradual deterioration simply by looking at whether the inverter is producing power.
A reference gives you something more useful to compare against.
It turns the question from:
into:
That distinction can make routine PV checking more practical and more informative.
Continue your PV checking journey
If you are new to irradiance measurement, start with our guide to Types of Solar Irradiance Meters .
You can also learn more about regular solar PV health checks and practical solar panel testing .
Want to establish your own PV reference?
Explore PVBuddy PVS01 and see how irradiance measurement and Flexi-Cal™ reference setting can be used for comparative PV field checking.
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