How Long Do Solar Inverters Last: The Reliability of Enphase Micro Inverters
Enphase microinverters have completely revolutionised the solar industry in Australia. The key benefits of an Enphase System include back to base monitoring and panel level control, Enphase systems output more power, are battery ready and 1KOMMA5° is now able to offer 24/7 support to our customers. But one of the biggest advantages of Enphase systems isn’t often talked about, and that is the reliability and longevity of Enphase Micro Inverters compared to a standard inverter.
How Long Do Solar Inverters Last?
Previously, it was expected that system owners would need to replace their inverter every 10 years or so, and we have seen that a lot of the cheaper string inverters break just after their 5-year warranty expires. This is obviously less than ideal because solar panels are built to last for decades, in many cases over 30 years. Enphase Microinverters on the other hand, are built to last over 20 years.
The Enphase Micro-inverter has been designed for a service life of over 20 years, significantly longer than any other inverter on the market.
The Bathtub Effect
When electronic products are produced in large numbers, the characteristic failure rate over their life is known as The Bathtub Curve, due to the shape illustrated below. The curve can be divided into three parts: early failures (known as Infant Mortality Failures), Constant Failures and Wear Out. All solar inverters exhibit this typical failure curve:
Infant Mortality
Higher than normal failure rates typically occur at the start of a product’s life and relate to the quality of the manufacturing process. From analysing the data from Enphase systems around the world, Enphase microinverters have a typical infant mortality period of 2 to 3 weeks. 1KOMMA5° has had an incredible reliability rate with our Enphase systems with around 1 in 3,000 micro-inverters failing during this time. This failure rate is an order of magnitude better than any other brand on the market, including the top European-Made string inverters.
“In order to ensure that Infant Mortality is minimised, every Enphase Microinverter undergoes extensive testing during manufacturing including Visual Optical Inspections, Functional Test, and System Test. Rather than using generic test equipment, Enphase made the decision to develop custom test stations in order to subject every Micro-inverter to a rigorous manufacturing test standard.”
Enphase analyses every failure and applies corrective action to an already strictly-controlled manufacturing quality process. This way there is a continual improvement in the infant mortality rate. Enphase Micro-inverters come with a 10-year warranty and so in the unlikely event of a failure, 1KOMMA5° customers are covered by a full-service warranty – a full replacement at no cost (including labour). This is something that very few solar installers offer and one of the main reasons why 1KOMMA5° is ranked as one of the top solar power installers in Australia.
The Expected Life of an Enphase Micro Inverter
The life of an Enphase microinverter is illustrated in the graph above as the Wear Out mechanism. This measures the useful service life of Enphase Microinverters, which is when there is an increase in the rate of failure due to the microinverter wearing out. The Enphase Microinverter has been designed for a service life of over 20 years, significantly longer than any other inverter on the market. In contrast, we are now starting to see a significant number of string inverters fail after only 5 or 6 years, especially the cheaper models made in China. In most of these cases the warranty period is only 5 years and so system owners need to spend thousands of dollars getting their solar system back online. A good quality string inverter will cost at least $2000-$3000.
The Technical Details
Enphase uses a testing process known as Accelerated Lifecycle Testing (ALT), which simulates the entire service life of a product in a shorter period of time. The Micro inverters are subject to three tests in a row:
10 days where the product is cycled over a temperature range from -45C to 85C at 85% relative humidity. During the low-temperature part of the test cycle, the product is subject to a hard freeze.
50 days where the product is cycled over a temperature range from -45C to 85C.
50 days where the product is subject to a constant temperature of 85C.
The Results
Mean Time Between Failures (MTBF) is not an indication of the actual life of a product but is rather an indication of the statistical probability that a unit will fail under specific operating and environmental conditions during the period. More information is available in the PDF below.
The Enphase M-Series Micro Inverter scored an MTBF of over 300 years, and this was confirmed by independent testing from Relex, a respected reliability engineering company that performs reliability testing for organisations such as Boeing and the U.S. Military. This is an incredible improvement on the average string inverter, which has an MTBF score of only 10-15 years.
Why are Micro Inverters so much more reliable?
One of the advantages of an Enphase system is that each and every Micro-inverter is capable of transmitting its performance data back to Enphase. This means that Enphase can monitor performance and then use this information to continually improve. Enphase has been doing this for over a decade and is now manufacturing their 7th generation product.
Enphase is also able to reset and update firmware remotely, ensuring that the majority of failures are fixed without a service call required. This is a remarkable transformation to the idea of how a manufacturer is able to provide support and something that no other inverter manufacturer could hope to achieve with their product.
Conclusion
Considering the negative impact and the frustration of historically high inverter failure rates on installers and customers in the solar industry, Enphase knew that a successful new Microinverter technology must have unparalleled reliability. The result of this fixation on reliability is an inverter technology that exhibits an order of magnitude improvement in MTBF compared to existing inverter technology.
Enphase continues to focus on reliability improvements with each successive generation of the inverter, with the goal of reaching an MTBF of 600 years, comparable to PV modules.