There is no simple answer to this question as it depends on a number of factors.

A number of the early inverters that were installed over seven years ago are starting to fail in a big way. Some of these were the early Chinese models but even some of the European makes are experiencing issues in the 5 to 10-year age bracket.

Inverter warranties vary from 5 to 15 years (e.g., SolarEdge offers a 12-year warranty). The technology associated with central inverters is improving, but they are still the most likely components to experience failures in solar PV systems. Micro-inverters generally have longer warranties than central inverters, ranging from 10 to 25 years. This is due to higher reliability associated with micro-inverters because their switches and energy storage parts generally have lower power processing requirements (e.g., whereas central inverters are typically rated to handle 5 kW or higher, each micro-inverter is generally rated to handle 200–250W. ABB Group offers a 10-year product warranty for their micro-inverter systems and Enphase Energy offers a 25-year warranty for their micro-inverters

A major issue with inverter failure can be attributed to where the inverter is located.

By installing a solar inverter in an unvented location with high temperatures the unit can be exposed to unhealthy levels of heat. Most inverters have a maximum heat tolerance of 60 degrees which can be easily achieved in many Australian States in peak summer conditions and in unventilated locations (On a hot wall or in a garage with poor insulation)

Some inverters have onboard fans to aid in the cooling process.  These fans can become stressed as they are overworked and again fail prematurely as a result, this has the cascading effect of shutting down or de-rating the inverter.

Blocking air circulation to the inverter or its cooling channels can have the same results as above. Whilst most inverters can cope with high temperatures, what they can’t cope with is their cooling mechanisms being impaired.  Solar inverters require a free flow of air around the units to keep them cool and operating within their design parameters.  Blocking these channels of air can have a significant effect on both yield and service life due to the inverter shutting down or reducing its output by dropping into a de-rate mode.

Water and Dust Ingress. 

If your inverter is located outside, in a dirty dusty environment or worse a moist and humid area of a building then it should be rated for that location.  Humidity has been shown to contribute to around 20% of electronic failures.  Most manufacturers cater for such locations by producing an inverter which is capable of dealing with these harsh environments.  If an inverter designed for dry clean environments has been installed in an environment described above, then expect problems.  Not only may the inverter fail early it may contribute towards a dangerous situation from fire or shock risk.  Water damage can also create corrosion.  Where electronics are exposed to both hot and humid conditions 70% premature failure rates can be expected.

Overvoltage – A/C

It is quite common in Australia to see high grid voltages way in excess of the perceived 240V line voltage we have historically transmitted.  This is mainly due to weak networks with settings on substation transformers turned up to maximum to hold voltages within the grid defined limits at the far end of a long cable run.  This means that supplies nearer to the sub station transformer can expect high grid voltages, in particular at times of low local usage as the voltage rises with low demand.  This can result in Solar inverters regularly dropping out on their over voltage settings which they must have ironically to stop the grid voltage rising above the grid upper limits.  This has two effects on the Solar Inverter, firstly there can be significant losses due to the inverter being off line until the grid voltage drops back into limits and secondly the inverter is being over stressed by high grid voltages.  This can show up as early failures of the over voltage relay on board the inverter.  Most inverters have an upper limit of 250 volts

Mechanical Damage

Mechanical damage can sometimes be quite obvious, especially where significant impact damage has taken place.  Sometimes though what can seem like a small none relevant indent can have pronounced effects on such items as seals designed to keep out moisture and gasses.  Where equipment is located in areas with increased risk from mechanical stresses such as where fork trucks and machinery is in operation then it is advised that regular inspection of these items is carried out.

Vibrations

Failure rates of electronics due to vibrations has been proven to be significantly greater than those which are not exposed to such conditions.  Surveys show that around 20% of failure rates of electronics is down to excessive vibrations.  Any surface where a Solar inverter is mounted should be free from vibrations.

So, to sum up – today’s new inverter models are of better quality and all now come with a minimum product warranty of 5 years with most offering extended warranties up to 10 years. At times the major brands run promotions where they offer the extra 5 years for no extra cost so always ask about any promotions if looking at a replacement or new system.

While quality has improved it still comes down to other factors as discussed above as to how long your solar inverter will last so use an accredited installer who will know best on placement.