The 5 Most Common Issues With Solar String Inverters

Solar Inverter Troubles? Here Are the 5 Most Frequent String Inverter Failures

Your inverter: The hardworking heart of your solar investment

Thinking about your solar system, the panels often get the most attention. But the inverter is the real unsung hero – and often the component most likely to encounter issues during the system’s lifespan. It’s a sophisticated piece of power electronics operating continuously, often in challenging environmental conditions like the Australian heat. String inverters, where panels are linked in series (‘strings’) feeding into the inverter, are a popular choice due to their balance of cost and performance.

However, understanding their potential weaknesses is key to making informed choices and ensuring long-term value. Let’s explore the five most common issues in more detail.

1. Internal component failure: When the electronics give way

What it really means: Inside your inverter are complex circuit boards populated with components like capacitors, transistors (IGBTs), relays, and sometimes cooling fans. Failure of these critical parts can stop the inverter dead in its tracks, significantly reduce its power output, or drastically shorten its operational life.

Digging deeper into the ‘why’

• Capacitor Ageing: Electrolytic capacitors, crucial for smoothing power flow, are often the first components to degrade. They contain a liquid electrolyte that can dry out over time, especially when exposed to high temperatures. This degradation accelerates significantly with heat.
• Thermal Stress & Cycling: The constant heating up during daytime operation and cooling down at night (thermal cycling) puts physical stress on solder joints and components. Australia’s wide temperature swings can exacerbate this.
• Component Quality Variance: There’s a tangible difference between budget and premium inverters. Higher-quality units generally use components rated for higher temperatures and longer lifespans, undergo more rigorous testing, and may feature better internal heat management design.
• Wear and Tear: Like any machine, parts wear out. Relays that connect/disconnect the inverter from the grid perform thousands of cycles, and fans (if present) have a finite lifespan.

Signs and consequences

Complete shutdown is obvious. More subtle signs include intermittent error codes, reduced peak power output even on clear, cool days, or unusual noises (buzzing, clicking). Failure often occurs outside the typical 5-year warranty offered by many budget brands, leading to unexpected replacement costs. While premium brands often offer 10-year warranties (sometimes extendable), it’s crucial to check if labour costs for replacement are included. Remember, your panels might last 25+ years, but you’ll likely replace a string inverter at least once or twice during that period.

2. Overheating: Performance drain in the Aussie heat

What it really means: Inverters aren’t 100% efficient; they lose some energy as heat during the DC-to-AC conversion. If this heat builds up faster than it can dissipate, the internal temperature rises, triggering protective measures.

Digging deeper into the ‘why’

• Installation Location is Key: This is critical. Mounting an inverter in direct, harsh afternoon sun (especially on a dark-coloured wall) drastically increases its operating temperature. Enclosed, unventilated spaces like meter boxes, small cupboards, or even hot roof cavities are common but poor choices. Garages are often better, but still need airflow.
• Inadequate Clearance: Manufacturers specify minimum clearances around the inverter for airflow – usually 15-30cm above, below, and to the sides. Ignoring these traps heat around the unit’s heatsink fins.
• Ambient Temperature: On a 40°C day, an inverter sitting in the sun can easily reach internal temperatures well over 60-70°C, pushing its operational limits.
• Dust and Debris: Accumulating dust on heatsinks or blocking ventilation slots acts like insulation, preventing effective cooling. Inverters with fans can suck in dust, requiring occasional cleaning if accessible.

Signs and consequences:

The most common symptom is ‘derating’. As the inverter heats up, it automatically limits the amount of power it converts to protect its internal components. You’ll see your system’s output flatten or drop off during the hottest part of the day, even when it’s perfectly sunny. In severe cases, the inverter will shut down completely with an over-temperature fault, restarting only when it cools. Chronic overheating significantly accelerates the degradation of internal components (like capacitors), shortening the inverter’s lifespan.

3. Communication failures: Losing sight of performance

This covers issues with the inverter’s built-in display screen or its ability to connect and transmit data to monitoring platforms (usually via Wi-Fi, Ethernet, or sometimes older serial connections).

Digging deeper into the ‘why’:

• Screen Degradation: LCD screens are susceptible to UV damage and heat, leading to fading, pixelation, becoming unreadable, or failing entirely over the years of exposure.
• Wi-Fi Woes: Home Wi-Fi networks can be temperamental. Routers get changed, passwords updated, signals can be weak in garages or near meter boxes, or interference from other devices can disrupt the connection. The inverter’s own Wi-Fi module can also fail.
• Firmware/Software Glitches: Occasionally, bugs in the inverter’s firmware or the monitoring platform’s software can cause communication dropouts or display errors. Updates often resolve these.
• Cabling Issues: For hardwired Ethernet or RS-485 connections, damaged cables or loose connections can interrupt data flow.

Signs and consequences:

A blank or garbled screen prevents quick status checks at the unit. More significantly, losing connection to your monitoring app or web portal means you lose visibility of your system’s performance. You won’t know if it’s working optimally, underperforming due to other issues (like shading or a fault), or has stopped working entirely. This is crucial for tracking energy savings, diagnosing problems, and potentially for warranty claims. Some newer inverters are omitting screens altogether, making reliable cloud connectivity even more vital. Basic troubleshooting like rebooting the inverter and router, or checking Wi-Fi signal strength, can sometimes help.

4. Fault codes and tripping: When safety systems activate

The inverter is detecting a condition – either internally, from the solar array, or from the electricity grid – that falls outside safe operating parameters, causing it to display an error code and/or disconnect from the grid (trip).

Digging deeper into the ‘why’

• Grid Disturbances (Voltage Rise): A very common issue in Australia, especially in areas with lots of rooftop solar. When many systems export power simultaneously, the voltage on the local grid can rise. AS/NZS 4777.2 mandates that inverters must trip if the voltage exceeds set limits (typically averaged over 10 minutes). This protects the grid and appliances but halts your solar export and potentially self-consumption. This is often a grid network issue (managed by your DNSP), not necessarily an inverter fault, though correct inverter grid profile settings by the installer are crucial.
• Insulation Resistance Faults: Moisture ingress is a prime suspect here. Rainwater finding its way into DC isolators (a known weak point), panel junction boxes, or damaged DC cabling can create a small leakage current to earth. The inverter’s sensitive safety systems detect this potentially hazardous situation and trip, often displaying an “Isolation Fault”, “ISO Fault”, or “RCD Fault”. This is more common after rain or in humid conditions.
• Installation/Wiring Errors: Incorrect AC or DC wiring, loose terminals, or improperly configured settings (like the grid connection profile) during installation can lead to various fault codes and tripping.
• Internal Inverter Faults: Persistent, specific error codes that remain after resetting the system often do indicate a genuine hardware problem within the inverter itself.

Signs and consequences:

You’ll see specific error codes on the display or app (e.g., “Grid Voltage High”, “Isolation Fault”). The inverter might repeatedly trip off and attempt to restart during daylight hours. Ignoring these can mask serious safety issues (like potential shock hazards from insulation faults) or underlying grid problems that might need reporting to your DNSP. Always note the code and conditions when it occurs before contacting your installer or a qualified solar electrician.

5. Shade impact: The Achilles’ heel of string systems

While not an inverter malfunction, this performance limitation is inherent to how basic string inverters work with series-connected panels. Shade on even a small part of one panel acts like a bottleneck, reducing the electrical current flow for the entire string connected to that inverter input (MPPT).

Digging deeper into the ‘why’

• Series Circuit Physics: Panels in a string are like links in a chain; the current must flow through all of them. A shaded panel generates much less current. The string inverter’s MPPT (Maximum Power Point Tracker) tries to find the best voltage/current combination for the string, but it can’t force more current through the shaded panel than it’s capable of producing. It usually has to lower the current for the whole string to match the weakest link, drastically reducing power.
• Sources of Shade: Trees (even distant ones casting morning/afternoon shade), vent pipes, chimneys, antennas, neighbouring structures, or even heavy bird droppings can cause significant losses.
• Mismatch Effects: Over many years, panels degrade slightly differently. A significantly degraded panel or an improperly matched replacement panel can also act like a partially shaded panel, limiting the string’s output. Uneven soiling can have a similar effect.

Signs and consequences:

You’ll observe a noticeable drop in your system’s overall energy production that correlates with known shading patterns across your roof. Monitoring systems might show the string’s current (Amps) dropping significantly when shade hits, even if the voltage stays relatively high. This can lead to substantial energy losses over the year, meaning lower savings and a longer payback period, especially if shade affects panels during peak sunshine hours.

Your informed decisions matter

Your string inverter is a critical component working tirelessly behind the scenes. By understanding its common potential failure points – component wear, overheating, communication glitches, fault conditions, and sensitivity to shade – you’re better equipped to choose the right equipment, ensure a quality installation, and keep an eye on its performance. This knowledge helps protect your significant solar investment and ensures you maximise the clean energy generated on your rooftop for years to come.

If you’re concerned about your current inverter’s performance, or need guidance selecting the best technology for your home, Your Energy Answers is here to help.