There’s a version of this story that plays out every week somewhere in Australia. A family goes solar. The first few bills look okay. Six months later a neighbour mentions their system paid itself off in four years, and suddenly the maths on your own place doesn’t add up. The panels are working. The monitoring app says so. The inverter is on. But something is off.
Most of the time, the problem isn’t the panels.
It’s the design. A shade issue visible from the street that nobody mapped. An inverter undersized to keep the quote low. Panels facing the wrong direction for when the household actually uses power.
None of this surfaces in a maintenance check. A sparky can inspect a system, call it fault-free, and walk away from something that was never going to perform properly. This post is about that problem specifically the design and commissioning failures that stay invisible until you’re comparing bills with someone who got it right. In this blog will explain Why some solar systems underperform and how to tell if yours is one of them
What “underperforming” actually means
This is worth pinning down first, because “my solar isn’t saving me money” can mean a dozen different things.
An underperforming system is one that produces measurably less than it should given its size, location, and panel orientation. Not less than some marketing promise less than what a properly designed, correctly installed system of the same capacity would produce at your address.
In Pakenham and south-east Melbourne, a well-designed 6.6kW system typically generates between 24 and 28 kWh on a good summer day and around 14 to 18 kWh on a typical winter day. If your 6.6kW system is consistently producing well below these figures on clear days and your monitoring app confirms the panels aren’t faulted something in the design or installation is probably wrong.
The gap matters. A 6.6kW system that runs at 80% of its potential output costs you roughly $300–$500 per year in lost generation. Over a 10-year system life, that’s real money —and it compounds, because you’re exporting less and buying more grid power than you should be.
The main reasons solar systems underperform and how to spot each one
1. Shading that wasn’t properly assessed
This is the most common culprit and the most avoidable.
Solar panels are more sensitive to shade than most people realise. A shadow covering 10% of a panel’s surface can reduce that panel’s output by 50% or more and depending on how the system is wired, one shaded panel can drag down the entire string.
The problem is that shade changes. A tree that casts no shadow on your roof in January will drop a clean stripe across your panels in June when the sun angle drops. Neighbouring houses go up. Trees grow. A shade analysis done in the middle of a summer site visit which is when most installers come out can miss winter shading entirely.
How to tell if shading is your problem:
Open your monitoring app and look at your generation data for winter mornings and late afternoons. If output drops sharply at the edges of the day more than you’d expect from the sun angle alone a nearby obstruction is probably the cause. Some monitoring systems (Fronius Solar.web, SolarEdge monitoring, Enphase Enlighten) show panel-level or string-level data that makes this obvious. If you only have inverter-level monitoring, you won’t see where the shade is hitting.
A good shade analysis uses software like PVSyst or similar tools to model your roof’s shading across all seasons before a panel is placed. If the installer who quoted your system never asked about trees, neighbouring roofs, or chimneys or if they did the site visit in summer this step probably didn’t happen properly.
2. Panels facing the wrong direction for your usage pattern
North-facing panels produce the most total energy per day in Australia. That’s not in dispute. But “most total energy” isn’t the same as “best financial return,” and they’re not always the same thing.
If your household uses most of its power in the morning you’re up early, running the kettle, dishwasher, dryer before 8am east-facing panels might actually save you more money than north-facing ones, even though they produce less total generation. That’s because east panels peak earlier in the day, which means more of their output matches your consumption directly, rather than going to the grid at a low feed-in rate.
The reverse is true for households that shift consumption to the afternoon. West-facing panels extend generation into the 3–6pm window, which is when time-of-use tariffs often charge the most, and when self-consumption can displace the most expensive grid power.
A competent system design accounts for your usage profile, not just your roof orientation. If the installer put all your panels north because “that’s where they produce most” without asking when you use power that’s a design gap.
How to tell if orientation is your problem:
Pull your electricity bills from before and after solar. If your grid import hasn’t dropped as much as expected in the morning or evening — but your total solar generation looks normal your panels are generating at the wrong time for your household.
3. The inverter was undersized (or overclipped)
Inverter sizing is one of those things that looks fine on paper and causes real problems in practice.
In Australia, the Clean Energy Council allows installers to “overclip” a solar array meaning install more panel capacity than the inverter can actually handle at its rated output. For example, a 5kW inverter with a 6.6kW array of panels is legal and extremely common. The logic is that panels rarely hit their theoretical maximum, so a bit of oversizing is fine.
That’s true. Up to a point.
Where it goes wrong is when an installer pairs a 5kW inverter with a 10kW array to cut the cost of the quote, or installs a cheap inverter with a low maximum input voltage that clips the system’s output on bright, cool mornings which is exactly when solar production is highest in Melbourne.
Inverter clipping happens when the array tries to produce more power than the inverter can convert. The inverter caps its output and the excess is wasted. On a mild, bright spring morning which Pakenham gets plenty of this is where you lose the most generation.
How to tell if clipping is your problem:
On your monitoring app, look at your system’s output on a clear spring or autumn day. If the output graph has a flat top it rises in the morning, hits a plateau, and stays there for several hours before dropping again in the afternoon that flat top is clipping. A naturally producing solar system should trace a smooth bell curve across a clear day. A clipped system has its peak cut off.
4. The system wasn’t commissioned properly
“Commissioned” means the system was configured correctly after installation the inverter parameters set for the local grid, the panels checked for proper string connections, the monitoring system linked and tested.
Bad commissioning is surprisingly common. It doesn’t mean the system won’t turn on. It means settings that affect performance like the inverter’s voltage response settings, the maximum power point tracking behaviour, or in battery-connected systems, the charge/discharge thresholds were left at factory defaults or set incorrectly.
Here’s a concrete one: inverters ship with conservative grid protection settings designed for the European grid. In Victoria, the grid voltage runs a bit higher than in some other regions. An inverter not properly set for local grid conditions will regularly trip offline during peak production hours usually around midday and you’ll miss the best generation window of the day.
How to tell if commissioning is your problem:
Look for gaps in your generation data periods where the inverter shows zero or near-zero output during what should be peak production hours, followed by a return to normal. These are inverter trips. If they happen on hot, bright days especially, grid voltage settings are the likely culprit. Your installer should be able to pull the inverter’s event log remotely or on-site and tell you what’s causing it.
5. String wiring mismatches
Solar panels in a standard string inverter system are wired in series like batteries in a torch. The voltage of each panel adds up. If one panel is a different type, older, or more degraded than the others or if panels in the same string face different directions the weakest panel limits the entire string.
This happens when installers add panels to an existing system without properly accounting for the original string configuration, or when panels of slightly different specs are mixed because a particular model was out of stock. It also happens on split roofs where a north-facing string and a west-facing string are mixed producing panels and coasting panels in the same circuit, pulling each other down.
How to tell if string mismatch is your problem:
This one usually requires an installer to check. But a tell is output that’s consistently lower than expected even on clear days with no obvious shading, and a clipping-free generation curve. If the system looks normal but produces less than similar systems in the area, string-level checks are worth doing.
Benchmarking your system against what it should produce
Before you call anyone, it helps to know whether your system is actually underperforming or whether your expectations were just set too high.
Pakenham sits at roughly the same solar resource level as Melbourne about 4.2 peak sun hours per day on average. For a 6.6kW system in Pakenham, a reasonable annual output target is around 9,000 to 10,000 kWh depending on orientation and shading.
Solar output benchmarks for Pakenham
| System size | Expected annual output | Summer clear day | Winter clear day |
| 5kW | 7,000 – 7,800 kWh | 20 – 23 kWh | 12 – 15 kWh |
| 6.6kW | 9,000 – 10,000 kWh | 24 – 28 kWh | 14 – 18 kWh |
| 10kW | 13,500 – 15,000 kWh | 36 – 42 kWh | 21 – 27 kWh |
| 13kW | 17,000 – 19,500 kWh | 46 – 54 kWh | 27 – 34 kWh |
Based on north-facing install, 15° tilt, minimal shading. West or east-facing systems will produce 15–20% less total energy.
What to do if you think your system was badly designed
Step 1: Download 12 months of output from your monitoring system. Most inverters Fronius, SolarEdge, Sungrow, Enphase have online portals where you can export this.
Step 2: If you’re more than 15–20% below the expected range consistently not just in a cloudy month you have a real underperformance issue.
Step 3: Look for the patterns described above. Clipping (flat-topped curve), inverter trips (generation gaps on bright days), morning or afternoon shading dips. These are different problems with different fixes.
Step 4: Get a second opinion from a CEC-accredited installer who wasn’t involved in your original install. Your original installer has an incentive to tell you everything is fine. A new one doesn’t.
Step 5: If the underperformance is significant and the installer is unresponsive, the Clean Energy Regulator accepts complaints about STCs. The Victorian Managed Insurance Authority also covers some consumer protection claims.
A note on getting it right the first time solar panel installers in Pakenham
Most of the problems described in this article share a common cause: the installer prioritised a low quote over a good design.
Proper shade analysis takes time. Modelling a household’s usage pattern takes a conversation. Sizing an inverter correctly sometimes means recommending a more expensive one. These are things a good installer does automatically. They’re also the first things to go when an installer is competing purely on price.
The solar panel installers in Pakenham who’ve been in the area long enough to see what good and bad installs produce over time not just at commissioning are the ones with the clearest view of what actually works here.
Three quotes is still sensible. But the quotes worth comparing are the ones that come with a shade assessment, a system design document, and an installer who can explain why they sized the inverter the way they did — without needing to check with someone in an office two states away.
You can also read our guide on how to spot a dodgy solar quote in Pakenham before you start talking to anyone.
The underperformance checklist
| Problem | Key symptom | How to confirm |
| Shading | Output drops at edges of day, worse in winter | Panel/string-level monitoring; winter vs summer comparison |
| Wrong orientation | Generation doesn’t match consumption timing | Compare generation curve vs household usage profile |
| Inverter clipping | Flat-topped output curve on clear days | Monitoring app — look for cut-off bell curve |
| Poor commissioning | Inverter trips midday on hot/bright days | Inverter event log — check for grid protection trips |
| String mismatch | Consistently below benchmark, no obvious cause | On-site string voltage check by a qualified installer |
| Undersized system | Great design, just not enough panels | Output is proportionally correct but total is low — needs upgrade |
“Working” just means the inverter is on and converting power. It doesn’t mean the system is producing what it should. A clipped system “works.” A shaded system “works.” A poorly oriented system “works.” The monitoring app tells you what’s happening; a proper system assessment tells you whether what’s happening is what should be happening.
An inspection checks safety and basic compliance correct wiring, weatherproofing, labelling, earthing. It doesn’t assess whether the system was well-designed for your roof, your shading profile, or your usage pattern. You can pass every inspection standard and still have a poorly performing system.
Sometimes. If the shading comes from a tree you can trim, that’s straightforward. One solution is adding microinverters or DC optimisers (like SolarEdge power optimisers) to panels that get shaded these allow each panel to operate independently rather than dragging the whole string down. A redesign of string configuration can also help.
Get a written assessment from an independent CEC-accredited installer. That gives you something concrete to put in front of the original company. If that goes nowhere, lodge a complaint with the Clean Energy Regulator (for STCs-related issues) or Consumer Affairs Victoria. If the installer is CEC-accredited, the CEC also has a complaints process.
Depends on the cause. If the problem is a clipping inverter, swapping to a correctly sized one is usually worth it the generation improvement pays it back. If the system is more than 10 years old and was a cheap install to begin with, a full replacement with a properly designed new system often makes better financial sense.
For a household with typical daytime usage in Pakenham, a well-designed 6.6kW system installed in 2024–2025 should pay back in around 4 to 6 years. If you’re beyond year 7 and the bills still haven’t shifted materially, the system either wasn’t designed well or there’s an ongoing performance issue.
Not directly. The issues described in this article shading, orientation, clipping, commissioning happen with premium panels and budget panels alike. Better panels tend to come with better monitoring systems, which makes it easier to detect and act on underperformance problems.
Start with your system size in kilowatts and your location. Pakenham averages about 4.2 peak sun hours per day, so a 6.6kW system should produce roughly 27.7 kWh on an average good day, accounting for inverter losses and temperature (80–85% system efficiency is realistic). Annual output should land in the 9,000–10,000 kWh range for a north-facing 6.6kW system. Consistently below that range on a system that looks healthy? Worth investigating.