A solar system can look perfectly normal from the ground while quietly producing far less electricity than it should. If you are asking, why are solar panels underperforming, the answer is not always the panels themselves. Output can be limited by shading, inverter faults, damaged wiring, ageing components, grid behaviour or a system that has simply not been checked since it was installed.

For Canberra and ACT solar owners, lower production often becomes noticeable after a high bill, an app alert, a hailstorm or a notification that inverter testing is due. The practical question is not whether one cloudy day reduced generation. It is whether your system is consistently falling short of what it should produce for the season and its design.

Start by separating normal variation from a real fault

Solar output changes throughout the year. Shorter winter days, low sun angles, smoke haze, extended cloud and summer heat can all reduce daily generation. Panels work best in clear sunlight, but their output drops as panel temperature rises. A hot, windless afternoon can therefore produce less power than a cooler, sunny morning.

Electricity use also affects what you see on a bill. A system may be generating normally, while household consumption has increased because of heating, cooling, an electric vehicle, a pool pump or more people at home. Comparing one power bill with another is useful, but it is not enough to diagnose a system fault.

A better comparison is the same month year-on-year, allowing for weather and any changes to your home. Monitoring data is even more useful. Look for a sustained reduction in production, unusually low peak output on clear days, gaps in generation during daylight hours, or one inverter performing differently from another.

Why solar panels underperform: the most common causes

Shade that has gradually changed

Shade is one of the most common and underestimated causes of poor solar production. A tree that was small at installation may now cast a shadow across part of the array. New construction, a neighbour’s extension, a television aerial, vent pipe or accumulated leaf litter can have the same effect.

Even partial shade can reduce output well beyond the covered area, particularly on older string inverter systems where panels are connected in series. The effect depends on the array layout, bypass diodes and whether the system has optimisers or microinverters. That is why a site inspection matters more than guessing from a photo.

Dirt, debris and surface damage

A layer of dust is not usually enough to explain a dramatic loss of generation, especially after normal rain. However, persistent grime, bird droppings, leaves and pollen can create localised shading. Panels installed at a low angle may be more prone to build-up.

Hail damage needs more careful attention. Some damage is obvious, but hairline cracks, broken cells and damaged junction boxes may not be visible from the ground. Water can then enter through compromised areas and create a fault that worsens over time. Cleaning alone will not fix physical damage, and walking on a roof or attempting DIY panel repairs can create further risk.

Inverter faults and poor inverter performance

The inverter is the working heart of most rooftop solar systems. It converts the DC electricity from panels into AC electricity your home and the grid can use. When it is not operating correctly, panel output may be reduced or stopped altogether.

A failed inverter may show an error code or a red fault light, but not every problem is that obvious. It may be intermittently disconnecting, limiting output, overheating, losing communication with monitoring, or restarting during the day. An inverter can also appear online in an app while a fault is affecting one string or one of several connected units.

Inverters have a finite service life. If your system is older, a decline in performance may be linked to an inverter issue rather than panel degradation. A qualified electrician can check operating data, fault history, connections and compliance settings before recommending repair or replacement.

Grid voltage and export limits

Your system must disconnect from the grid if grid supply fails. This anti-islanding protection is a safety requirement that protects electrical workers and the network. During testing, an electrician verifies that the inverter responds correctly under specified conditions.

High local grid voltage can also cause an inverter to reduce generation or disconnect temporarily. This is more likely in areas with substantial rooftop solar generation, particularly around the middle of a sunny day. The inverter may record grid overvoltage events, which can be mistaken for a panel problem.

Export limits are another consideration. A system may be producing power, but the inverter may be configured to limit how much is sent to the grid. Battery settings, consumption control equipment and recent electrical changes can also affect the result. These issues need to be assessed against the installation design and current network requirements, not adjusted blindly.

Isolators, cables and connections

Solar systems operate outdoors in heat, cold, wind and rain. Over time, isolators, cable entries, conduits and rooftop connections can deteriorate. Water ingress, brittle cable insulation, loose terminals and corrosion can cause intermittent faults, voltage loss or a complete shutdown.

These are not issues to leave until the system stops completely. DC solar wiring can remain energised whenever panels are exposed to light. A licensed electrician should inspect and test the relevant components using the correct procedures and equipment.

Ageing panels and module mismatch

Solar panels slowly lose output as they age. Some decline is expected, but sudden or uneven loss is not simply normal ageing. Individual panel faults, failed bypass diodes, delamination, moisture ingress and potential-induced degradation can affect a portion of an array.

A common issue on expanded systems is mismatch. If newer, more powerful panels have been added to an existing string, or panels face different directions on the same input, the system may not operate at its best. The weakest-performing panel or string can limit the group. The right remedy depends on the original design, not just the panel wattage printed on the label.

What a proper solar health check should establish

A useful inspection should move beyond a quick look at the inverter screen. The goal is to identify whether the loss is caused by the panels, the inverter, the electrical connection, the grid, shading or monitoring data that is being misread.

A qualified solar inspection can assess physical condition, electrical performance and safety. Depending on the system and service scope, this may include visual checks of panels and mounting equipment, inspection of isolators and cabling, inverter fault-history review, output assessment, testing of electrical connections and confirmation of required anti-islanding operation.

The findings should be clear enough to support a sensible decision. You should know whether the system is safe to keep operating, what is likely affecting performance, what repair work is recommended, and whether an issue needs to be documented for insurance or warranty purposes.

Solar Testing and Maintenance provides electrician-led testing and diagnostics for existing systems, including full health checks and anti-islanding inverter testing. For owners who have received an Evoenergy notification, completing the required testing also helps confirm that the system remains compliant with grid safety requirements.

Avoid the common quick fixes

It is tempting to reset the inverter, clean the panels and assume the problem is solved. A restart can clear a temporary communication issue, but repeated faults need investigation. Similarly, panel cleaning may improve a heavily soiled array, but it will not correct shading, a failing inverter or water ingress.

Do not open isolators, remove inverter covers or access rooftop equipment unless you are qualified and authorised to do so. The risk is not limited to electric shock. Incorrect work can damage equipment, affect warranties, create compliance problems and leave a fault hidden until the next period of bad weather.

If your monitoring shows a clear change in output, take screenshots before any reset. Note the date, weather conditions, error messages and whether the issue is continuous or intermittent. This gives the electrician a stronger starting point and can make fault finding more efficient.

A solar system is an investment that earns its keep one day at a time. When its output no longer looks right, timely testing is usually cheaper than allowing a minor electrical, weather-related or compliance issue to become a long period of lost generation.