Another solar instructor and I have a question about grid-tied inverter lifespan. I have read that an average lifespan is 11 to 14 years, and the warranties seem to reinforce this. My colleague believes that 20 to 25 years is more likely for modern inverters. I would tend to believe the latter due to more solid-state electronics in today’s ungrounded inverters, but I can find no data to support this.
Jeff Foster • St. Louis, Missouri
While the expected lifetime of a grid-tied inverter will vary depending on its design, component quality, and the environment it is operating in, lifetimes beyond 14 years are likely for most of the high-quality inverters now available.
For power electronics devices, the environment in which they are installed has a significant impact on their life. I’ve seen inverters fail in less than a year when poorly installed and exposed to insects and moisture, and I have friends with inverters that I sold them more than 20 years ago that are still working well.
The biggest influence on inverter life is temperature—high temperatures will mostly impact the capacitors, which are usually the lowest-lifetime-rated components used in an inverter. Transformers usually will have a much longer life expectancy depending on their construction and operating temperature, so the life expectancy of transformerless, ungrounded inverters will not necessarily be higher. Since grid-tied inverters are typically designed to operate at very high efficiency levels, the electronic components usually do not operate at the temperature levels that are common in other power electronic applications (such as motor drives or power supplies), where efficiency is not as critical. This allows the components in a grid-tied inverter to be longer-lived.
Typically, grid-tied inverters do not operate 24 hours a day; they usually are “live” only about 12 hours a day, and often operate at high power levels only for a few hours. This helps extend their life expectancy. Grid-tied inverters also do not need to “surge” to start motors, so they have a pretty easy life compared to off-grid inverters, which are used with batteries and operate 24 hours a day, and are frequently subjected to overload conditions.
Some of the newer inverters (such as small microinverters) use special capacitors made for solar applications, which extend the lifetime of the inverter to better match the life expectancy of the solar-electric modules they are connected to. How much longer the life will be extended is uncertain, and we won’t really know until they have been operating for a long time, but several companies are offering warranties of up to 25 years.
Christopher Freitas • SunEPI