Solar system fault finding guide + solutions Leave a comment

Solar panels are a great investment for most homes and businesses but a surprising number of owners do not know if their solar panels are working correctly or if the system is performing as expected. When buying a solar system the solar retailer or installer should provide you with a basic operating manual that includes a system performance estimate, this will indicate how much solar energy you would expect to generate throughout the year (month by month averages). Remember, depending on your location, the summer months can often produce up to 3 or 4 times more energy compared to the winter months due to the longer days and sunnier weather. In this article, we will guide you through the most common solar system faults and help you determine if your solar system is operating correctly, plus offer several solutions to some of the more common problems.

Before we get into too much detail you will need a basic understanding of the terminology and how solar systems work. Also, when comparing your solar output it is important to know the difference between Kilowatts (kW) and Kilowatt-hours (kWh).

  • kW – Kilowatt = the amount of power being generated at a certain point in time.
  • KWh – Kilowatt-hour = the total amount of energy generated over time. Such as over a day.

High electricity bills?

If you have solar and you receive an unusually high electricity bill, this is generally not an indication that your solar system is not working correctly. There are many reasons for your electricity consumption to increase which may not be obvious at first. Electricity bills are often much higher in winter due to electric heating or hot water systems unless your house is very efficient. Most people often don’t realise that small portable electric heaters use a huge amount of electricity (generally 2000 Watts) and can even consume the equivalent of an entire homes energy use if left on overnight, which can more than double your electricity bill. Also, solar feed-in tariffs (credits) around Australia and have decreased by almost 50% over the last few years which means you will receive far less credit for the excess energy you sell to the grid. This is where increasing your self-consumption of solar by using simple timers and running appliances like dishwashers and dryers during the day can make a huge difference.

Small electric heaters are convenient but very inefficient and consume a lot of electricity – often up to 20kWh per day

Additionally, it is not uncommon for people with solar installed to be misled by a salesman or solar installer and told that their bills will be reduced to zero. Unless a detailed energy analysis has been undertaken and the solar system is adequately oversized to meet the household demand, reducing a bill to zero using solar alone is generally very difficult. On average, most households with solar installed will see a bill reduction of 40% to 70%, depending on how much electricity is used during the day and if you make the most of the free solar generation.

The amount of savings also depends on the feed-in tariff (credits) you receive from your electricity retailer which can vary greatly depending on your state and rates provided. Due to misleading information from the solar company, your solar system may actually be working fine and you have been given the wrong expectations. However, it may also be the case that your solar system is NOT working properly or has been installed incorrectly.

Does your solar system have a problem?

The LCD display of a SMA solar inverter shows the current power being generated and the daily generation in kWh.

If you believe your solar system is not operating correctly or the performance has noticeably decreased there are several ways you may be able to diagnose a problem. The first and easiest method, for those with solar system monitoring installed, is to compare the daily solar generation, measured in kWh, with previous days, weeks and months. Most modern solar inverters come with built-in Wifi communication and a system monitoring app or website portal, although, many older systems do not have any monitoring installed. Fortunately, most older solar inverters do have a digital LCD display that can provide valuable information to help diagnose any problems (explained in detail in the solar inverter section below).

The solar inverter display or Wifi App can provide you with some basic information about how much your system is generating at a point in time (kW) and how much it has generated over recent days or weeks (kWh). If your system is not generating any power then you obviously have a serious problem, but if the system is just under performing it can be difficult to tell without some idea of how much you should expect for the time of year! For example, the solar performance chart below highlights the large difference between summer and winter generation.

Factors that reduce solar system performance

Solar panel power ratings are measured in Watts (W) and determined under standard test conditions (STC) at 25°C in a controlled lab environment. However, a solar panel will generally not produce at 100% of its rated power in real-world conditions due to one or more of the issues and loss factors listed below. On average, a solar panel will generate around 80% of its rated power depending on the orientation, season and air temperature. It is common for a 5kW solar array (group of panels) to produce only 4kW of power during the middle of the day in summer; this is why most modern solar arrays in Australia are oversized to 6.5kW and coupled with a 5kW solar inverter.

Main solar system loss factors

  • Build up of dirt, dust, mould, leaves or bird droppings
  • Solar panel orientation and tilt angle
  • Shading issues, even partial shading can have a big impact
  • Solar inverter problems or faults
  • High grid voltage issues
  • The local climate, seasons and weather conditions
  • Solar panel degradation or faults

Dirty panels

Build up of dirt, dust and mould is a common reason for poor system performance and can reduce the power output by 5 to 10% on average. A build-up of bird droppings on one or more panels can have an even greater effect and even cause hot spots if one or more solar cells are even partially covered causing a reverse current. Mould and lichen growth, especially in colder climates can also severely reduce performance if the lichen grows over a portion of one of the cells resulting in reverse current. As highlighted in the image below, this can potentially lead to hot spot formation and permanent cell damage. Any mould or lichen growth should be removed using water and a brush.

Solution – To reduce the effect of dirty panels, it is recommended that solar panels should be cleaned at least once a year or more frequently in dusty environments. Cleaning solar panels should be done using only water and a soft broom. Solvents and detergents should NOT be used to wash the surface of solar panels as this can lead to water ingress and may void the manufacturer’s warranty. Note, cleaning solar panels on a roof can be very dangerous so using a certified solar professional is advised.

Panel orientation

Solar panel orientation and tilt greatly influence solar performance depending on your distance from the equator. In the southern hemisphere, the ideal orientation is North facing (South in the northern hemisphere) at a tilt angle roughly equal to your latitude. For example, in Sydney, Australia, the ideal orientation is North facing at 30 degrees. However, installing the solar array at the optimum orientation and tilt is often impossible or impractical, as the roof layout and angle determine the orientation of most rooftop solar systems. It is not uncommon for solar panels to be facing East and West due to the building orientation, but this does not mean the system will not perform well. In practice, a split East and West solar array will generate more energy in summer than a north-facing array. Although, it’s important to note the winter performance will be much lower, which is often when the power is needed most for heating, particularly in colder climates. determine how much solar you should be generating based on your location, panel orientation, and tilt angle.

Example: Annual solar performance in Victoria, Australia from a 6.6kW solar system facing North at an average roof angle of 20 degrees. As shown in the chart below, the solar generation in the summer months is more than double the winter months.

A basic solar performance estimate will give you a good guide to determine if your system is performing as expected at certain times of the year.
A solar performance estimate for Victoria, Australia – This will give you a good guide to determine if your system is performing as expected at certain times of the year.

Expected amount of generation in southern Australia from an average 6.6kW solar system.

  • Summer = 37 kWh/day
  • Winter = 16 kWh/day
  • Average = 27 kWh/day

Solar panel shading

Solar array where the installation of a rooftop air-conditioner caused a serious shading issue.
Solar array where the installation of a rooftop air-conditioner caused a serious shading issue.

The performance of a solar system is affected by a number of important factors of which many people are unaware, the most significant of these is solar panel shading. Even partial shading of one or two solar panels can cause a serious reduction in system performance so check that no trees or branches have grown significantly and are now causing shading on one or more panels. Note, this may not be obvious during the middle of the day when the sun is higher in the sky.

To explain why partial shading is such a problem, you first need to have a basic understanding of how solar systems work – Solar panels are generally connected together in strings of 4 to 14 panels unless you have micro inverters installed on each solar panel. The reason for this is because strings of panels generate a higher voltage which is more efficient for your solar inverter to convert to AC electricity and power your home or business. However, if one or more panels in a string are shaded it also affects the performance of all the other panels in the same string due to a phenomenon known as reverse voltage bias.

Solution – If regular shading on a few panels is an obvious problem, it can be overcome by adding power optimisers. Power optimisers are small add-on devices that are attached directly to each solar panel and effectively enable each panel to operate independently to minimise the impact of shading. Additionally, some solar inverters, such as those from Fronius, SMA and Goodwe, have inbuilt shade functions to help lower losses in the case of partial shading. These functions can generally be enabled via the display or setup app.

Solar inverter problems

The first step is to check if the solar inverter has any warnings, alerts or red lights showing? If all operating lights are green, this is generally a sign that everything is ok. If any red lights are showing, then it’s very likely that you have an inverter or grid fault. You may also see an error code, if so the solar inverter manual should be able to give you some idea of what the fault code means. If your inverter has an LCD display, you can check the amount of solar generation per day (kWh) and the instantaneous generation in watts or kilowatts. The kWh figure per day is generally the most reliable as the instantaneous figure can be misleading depending on the time of day and orientation of the solar panels.

Solar inverter not working due to a relay fault detected
Solar inverter not working due to a relay fault detected

When comparing kWh figures, as explained above, remember to take into account the often large seasonal variations. For example, in most locations, summer generation is far greater than winter and the difference becomes greater the further you are from the equator. If the system has been installed for several years you can often refer back to the previous year’s data for a much clearer comparison to see if the performance has noticeably dropped. However, be sure to check no trees have grown and now causing shading.

For those with micro-inverters such as Enphase, or a SolarEdge system with DC optimisers then diagnosing a problem is typically much easier as you can get access to individual panel performance and generation data. Also, those with advanced third party monitoring systems installed such as Solar Analytics will find it very easy to find out if there is a defect or performance problem as this system will automatically notify you.

High grid voltage issues

Most solar inverters will detect grid-related faults, such as high grid voltage which can significantly reduce your solar system performance. For a solar inverter to feed energy to the electricity grid, it must push out power at a slightly higher voltage than the grid. This is typically not a problem, but as more solar systems are connected to the electricity grid, especially in Australia with almost one in four homes now with rooftop solar, the grid voltage can slowly increase to a point where it can no longer accept any more locally generated solar energy.

In Australia, high grid voltage issues generally start occurring at 253V and will become very problematic above 260V. Due to the Australian standard AS 4777.2 and regulatory requirements of the local grid operators (known as the Electricity Distribution Network Service Providers or DNSP), all solar inverters must derate or switch off if the grid voltage goes above the local limit which is typically 255V, for a short amount of time. Once the inverter has stopped generating, it cannot reconnect for 60 seconds, after which it can begin exporting again. Unfortunately, this often results in the local grid voltage rising to the upper limit again and tripping off the inverter. This cycle can continue throughout the day resulting in the spiked generation profile shown below and a notable reduction in performance.

High grid voltage issues will cause a ‘spike’ pattern in the daily solar generation profile due to the on and off cycling of the solar inverter.

For those that are a little more tech-savvy and have a solar inverter with a display, you can often press a button and cycle through different information screens on the display. Check the grid (AC) voltage is not going above 255V, if so this could be part of the problem as most inverters will reduce generation above 255V or instantly shut off if the grid voltage goes above 260V.


Option 1 – Transformer retap – If you experience high grid voltage issues, the first step is to contact your local DNSP and inform them of the problem. Unfortunately, if you are not an electrician or solar installer, this can be somewhat difficult, so it’s best to ask your solar company to make a formal request and provide proof of the high voltage issue which can be obtained from your inverters datalogger or online monitoring portal. Once the request is received, the DNSP should retap the local transformer in your area to lower the network voltage. In some cases, a relatively simple transformer retap may not be possible for numerous reasons. If this is the case, other measures can be taken to reduce the local voltage explained in the next section.

Option 2 – Export limiting – The amount of voltage rise in your home due to exporting excess solar energy is generally dependent on two main factors, the distance from your home to the local transformer (large utility pole-mounted steel box) and the amount of solar being exported. While you cannot move your house closer to the transformer, you can limit the amount of energy being exported using an export limiting device such as an energy meter (CT). The amount of grid voltage rise is directly proportional to the amount of solar being exported, so limiting the export amount, say from 5kW to 3kW, can in some cases solve the problem. Some solar systems, especially those with a battery, will already have a CT meter installed as these are required to monitor household consumption and control the battery discharging.

Option 3 – Increase self-consumption – The easiest and most economical way for a homeowner to reduce high grid voltage issues is to self-consume as much solar energy as possible. Increasing self-consumption will reduce the amount solar being exported and thus reduce the grid voltage; it will also help save money by using less energy from the grid. Running energy-intensive appliances like washing machines, dryers, heaters, air-conditioning and pool pumps during the middle of the day can be achieved using simple inbuilt timers or smart home controls.

Solar panel degradation and faults

If you do not have solar system monitoring installed, then the first step is to check for any obvious issues with the solar panels such as a build-up of dirt, dust, mould, or leaves. Maybe a good wash with a soft broom and water is all that they need. Also, check no nearby trees have grown significantly and are shading the panels. Solar panels can suffer from a range of faults and degradation over time which we explain in much more detail in this article – Solar panel degradation and faults explained.

Five common reasons for solar panel degradation or failure

  1. LID – Light-Induced Degradation – Slow performance loss of around 0.5% per year (Normal)
  2. PID – Potential Induced Degradation – Long term losses due to voltage leakage (Serious)
  3. General Degradation – Failure due to water ingress or de lamination (Serious)
  4. LeTID – Light and elevated Temperature Induced Degradation (Serious)
  5. Micro-cracks and hot spots – Potential long term failure due to broken or hot cells (Serious)

Earth leakage is a common problem with older solar panels that is often caused by either water ingress or PID or potential induced degradation. Strings of solar panels operate at high voltages up to 600V and operating at these elevated voltages over many years can in some cases develop a current or earth leak through the cells to the aluminum frames of the solar panels, resulting in a significant loss of performance. Unfortunately, it is very difficult to detect an earth leakage without specialized equipment and often even a trained solar professional can have trouble diagnosing an earth fault.

Six Basic steps to solar panel fault finding

  1. Check the solar system performance data on the app and website, if available
  2. Check the solar panels for any obvious dirt, leaves, mould, or shade issues
  3. Check the solar inverter for any warnings or faults
  4. Check the isolators are all on, and the circuit breakers have not tripped off
  5. Check the grid voltage on the inverter display or app for over-voltage issues
  6. Hire a solar professional or electrician to inspect the solar system

Advanced guide to diagnosing a problem

Micro-cracks may not cause any noticable performance issues at first but over time they can develop into more serious problems and result in system failure.
Micro-cracks may not cause any noticable performance issues at first but over time they can develop into more serious problems and result in system failure.

For those much more tech-savvy people, you can compare the solar panel string voltages via the inverter display or WiFi app. Solar panels are typically linked together in strings of between 4 and 14 panels and most residential solar inverters have two independent string inputs (often called MPPTs). Most common panels have an operating voltage between 28V and 37V, depending on the air temperature and amount of sunlight. Looking at a typical rooftop solar array, you should see rows of panels which are typically the strings. If you have a simple roof profile, you may have two equal rows of panels which lets you easily compare the string voltages using the solar inverter display or monitoring app.

For example, two strings of 10 panels will have a string voltage of around 300V on a sunny day and using the solar inverter you should be able to display the string voltages. If one string is 275V and the other is 300V and there are no shading issues, then you know you have a problem with one of the strings. Also, if the current (Amps) on one string is significantly different from the other then this may also indicate a problem. Note, if the strings are different lengths, then you will have to divide the total string voltage by the number of panels in that string, then multiply this by the number of panels in the other string. If you think you have a problem with string voltages then you should contact your solar retailer, a solar installer or a solar professional to inspect the system.

A simple method using the string (MPPT) readings from a solar inverter to determine if two strings with the same number of solar panels are operating correctly. Note, the panel voltage can vary significantly depending on the type and size panel, temperature and amount of sunlight
A simple method using the string (MPPT) readings from a solar inverter to determine if two strings with the same number of solar panels are operating correctly. Note, the panel voltage can vary significantly depending on the type and size panel, temperature and amount of sunlight

IMPORTANT – Solar inverters and panels generally operate at dangerous voltages and can cause serious harm, injury or even death. Never disconnect any cables or plugs from the solar inverter or panels! All inspections should be carried out by trained solar professionals or electrical qualified tradespeople only.

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