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Inverter lifetime, performance and reliability

In recent years, solar power has become very popular in the renewable energy industry. Solar systems have two main components: solar panels and solar inverters.

While the solar panels capture solar energy, the main function of solar inverters is converting or “inverting” the captured energy from direct current (DC) to alternating current (AC), so that your business and utility grid can use it. If they do not work, then the solar energy cannot be used and the entire system must be turned off.

Its operation is therefore crucial and it is considered the weakest component of the solar system, causing 43% of system failures.

This article will explore the advantages and disadvantages of the diverse models offered in the market, as well as common faults during their installation and operation, as well as experts' advice to extend their lifecycle.


Lifespan, and warranty of the inverters


It is a difficult task to pinpoint the lifespan of one particular inverter. But what we can do is work out the probability of when a solar inverter will fail by looking at data from the millions of solar systems installed all around the world since the 1950s.

The lifespan and the reliability of inverters depend on many factors, such as manufacturer, model, ambient temperature, solar irradiance, and the site operating temperature. The below table shows the best inverters for different categories.

The best solar inverter manufacturers and models for different categories

Table 1 - The best solar inverter manufacturers and models for different categories


When considering the life expectancy of string solar inverters, the average lifetime is less than 15 years, 10 years less than the average lifecycle of solar panels. However, it is possible, with appropriate maintenance checkups, for inverters to last up to 20 years.


To prolong the life of a solar inverter, the first crucial step is its installation. Inverters need to be protected from the weather as much as possible. Its electrical components are heat sensitive. The failure rate will depend on its capacitance, operating voltage and temperature. Moreover, variable solar irradiance and ambient temperature have an adverse effect on lifespan and reliability of inverters. Therefore, a cool and well-ventilated location is most preferable for its installation. Inverters also need to be protected from moisture and water damage.


Micro solar inverters and DC optimisers have an average lifetime between 20 to 25 years and 20 to 25 years warranty. Although they are more expensive, their failure rate is lower.

Most manufacturers offer between 5 to 10 years of warranty for string inverters and some manufacturers provide up to 20 years of extended warranty.


Performance, common faults, and reliability of the inverters


Inverter failures can be categorised for three main categories according to the type of defect involved.

  • Manufacturing quality:

  • Loose terminals and screws

  • Broken wires

  • Loose connections

  • Cooling fan

  • Inadequate design:

  • Insufficient wire gauges

  • Inadequate cooling

  • Incorrect capacitor sizes

  • Defective electronic components:

  • Insulated-gate bipolar transistors (IGBT) or Intelligent power module (IPM)

  • Bus-link capacitors

  • Transformer

  • Control circuit board

  • Electrical contactor relays

There is not sufficient data to determine the most common reason for solar inverter failures. Residential and commercial string inverters use different classes of electronic components, which have different failure rates. The below table shows the frequency of failure tickets for each general failure.


Frequency of failure tickets for each general failure area

Table 2 - Frequency of failure tickets for each general failure area


Reliability predictions assume one of the electronics parts’ failure is the reason for the system failure due stress or incorrect manufacturing.

The failure rate can be defined as the number of units failing per unit time. And it is usually described through “The bathtub curve”, shown in Figure 1.

Bathtub curve

Figure 1 - Bathtub curve


According to the bathtub curve, there are three main sections over the lifespan of any product. There is a high failure rate during the early period due to the manufacturing errors.

The subsequent straight line of the curve shows the useful life period. Manufacturers try to increase this period as much as economically feasible. The last section is called “wear out failure”. In this section the solar inverters become old because of material degradation, oxidation, vibration, or temperature and chemical damage. In most cases, the manufacturer's warranty covers the early failure period and useful life period.

15 years ago, replacing PV string solar inverters after operating 5 years was a common situation. These devices usually include a 5 year manufacturer’s warranty at that time.

Currently, warranties have increased up to 12 years as a result of an extension on their useful life period. At present, the average life of string solar inverters is 14 years. This useful life average is applicable to string inverters that are developed, manufactured, and tested under demanding engineering processes and controls, and backed by a solid field history. The below graph shows that about 50% of the installed inverters have failed at the year 14 mark.


Curve of expected annual string inverter failures

Figure 2 - Curve of expected annual string inverter failures


Useful life expectancies are expected to further increase in the future as a result of additional analysis, testing, and field experience. Also, most manufacturers offer 10 years extended warranty or more now. Consequently, we can assume that we need to replace the inverter at least once during the system’s lifetime period.


The below comparison shows the pros and cons for different inverter replacement scenarios such as replacing the inverter at the end of the manufacturer's warranty period, replacing the inverter when it’s faulty, and replacing the inverter at the average useful life period, 14 years.


Comparison of different inverter replacement scenarios

Table 3 - Comparison of different inverter replacement scenarios


Hassle Free Solar Installations


Solar Power Purchase Agreements (SPPA) offered by companies like Energy Terrain release businesses from the hassle of managing issues that come together with solar systems and their operation. Through a SPPA, Energy Terrain owns the PV installation on the roof of businesses and sells the energy at competitive rates. It is in our best interest to operate the system efficiently to get value, no energy, no charge.


Therefore, our company monitors the operation of the entire system and can handle the replacement and final destination of solar inverters, letting businesses focus on their core activities, knowing they are part of a greater vision for a sustainable world.


References


DNV - GL, 2019. PV Inverter Useful Life Considerations. [online] Available at: <https://issuu.com/dnvgl/docs/190327185601-219133592a204331b393643c3f486a4f>


Formica, T. J., Khan, H. A. & Pecht, M. G. 2017. The Effect of Inverter Failures on the Return on Investment of Solar Photovoltaic Systems. IEEE Access, 5, 21336-21343.


Ilumen, 2018. What Is The Lifetime Of An Inverter?. [online] Ilumen. Available at: <https://www.ilumen.be/en/what-is-the-lifetime-of-an-inverter/#:~:text=The%20lifetime%20of%20inverters%20in,an%20adverse%20effect%20on%20lifetime> [Accessed 11 January 2021].


Obeidat, F. & Shuttleworth, R. 2017. PV Inverters Reliability Prediction. World Applied Sciences Journal, 35, 275-287.


Solargain, 2021. Timeline: The History of Solar Power | Solargain. [online] Available at: <https://www.solargain.com.au/timeline-history-solar-power#:~:text=1954%20%E2%80%93%20The%20Birth%20of%20Photovoltaics,converted%20sunlight%20into%20electrical%20power> [Accessed 4 February 2021].


Solar Market, 2019. The Life Span Of A Solar Inverter. [online] Solar Market. Available at: <https://www.solarmarket.com.au/blog/the-lifespan-of-a-solar-inverter/> [Accessed 11 January 2021].


Solar wise, 2020. What Is The Lifespan Of A Solar Power System?. [online] Solar wise. Available at: <https://solarwiseww.com.au/what-is-the-lifespan-of-a-solar-power-system/> [Accessed 11 January 2021].


Svarc, J., 2021. Best Solar Inverters 2020. [online] Clean Energy Reviews. Available at: <https://www.cleanenergyreviews.info/blog/best-grid-connect-solar-inverters-sma-fronius-solaredge-abb> [Accessed 11 January 2021].


Those Solar Guys, 2020. How Long Do Solar Inverters Last? ( 2020 Guide ). [Online] Available at: <https://thosesolarguys.com/how-long-do-solar-inverters-last/> [Accessed 11 January 2021].

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