In the first part of this series, pv magazine reviewed the productive lifespan of solar panels, which are quite resilient. In this part, we examine residential solar inverters in their various forms, how long they last, and how resilient they are.
The inverter, a device that converts the DC power produced by solar panels into usable AC power, can come in a few different configurations.
Image: Solar Reviews
The two main types of inverters in residential applications are string inverters and microinverters. In some applications, string inverters are equipped with module-level power electronics (MLPE) called DC optimizers. Microinverters and DC optimizers are generally used for roofs with shading conditions or sub-optimal orientation (not south-facing).
Image: Solar Reviews
The technology ensures that each panel produces its max capability real-time and isn’t limited to the weakest link in the chain or “string.” String inverters are subject to the “Christmas light” effect where if one panel is not performing or is shaded, the rest of the panels connected in series will be limited to that panel’s production level.
Some string inverters are equipped with a bypass diode, a technology that prevents the “Christmas light” effect from taking place altogether, shown here by Fronius.
In applications where the roof has a preferable azimuth (orientation to the sun) and little no shading issues, a string inverter can be a good solution.
In a string inverter, there is generally less complicated wiring and a centralized location for easier repairs by solar technicians. Typically they are less expensive, said Solar Reviews. It said that inverters can typically cost 10-20% of the total solar panel installation, so choosing the right one is important.
How long do they last?
While solar panels can last 25 to 30 years or more, inverters generally have a shorter life, due to more rapidly aging components. A common source of failure in inverters is the electro-mechanical wear on the capacitor in the inverter. The electrolyte capacitors have a shorter lifetime and age faster than dry components, said Solar Harmonics.
EnergySage said that a typical centralized residential string inverter will last about 10-15 years, and thus will need to be replaced at some point during the panels’ life.
String inverters generally have standard warranties ranging from 5-10 years, many with the option to extend to 20 years. Some solar contracts include free maintenance and monitoring through the term of the contract, so it is wise to evaluate this when selecting inverters.
Image: Enphase Energy
Microinverters have a longer life, EnergySage said they can often last 25 years, nearly as long as their panel counterparts. Usually, these inverters have a 20–25-year standard warranty included. It should be noted that while microinverters have a long warranty, they are still a relatively new technology from the past ten years or so, and it remains to be seen if the equipment will fulfill its 20+ year promise.
The same goes for DC optimizers, which are typically paired with a centralized string inverter. These components last for 20-25 years and have a warranty to match that time period.
Failures
A study by kWh Analytics found that 80% of solar array failures occur at the inverter level. There are numerous causes of this.
According to Fallon Solutions, one cause is grid faults. High or low voltage due to grid fault can cause the inverter to stop working, and circuit breakers or fuses can be activated to protect the inverter from high-voltage failure.
Sometimes failure can occur at the MLPE level, where the components of power optimizers are exposed to higher temperatures on the roof. If reduced production is being experienced, it could be a fault in the MLPE.
Installation must be done properly as well. As a rule of thumb, Fallon recommended that the solar panel capacity should be up to 133% of the inverter capacity. If the panels are not properly matched to a right-size inverter, they will not perform efficiently.
Maintenance
To keep an inverter running more efficiently for a longer period, Those Solar Guys recommended choosing a cool, dry place with lots of circulating fresh air. It also suggested avoiding installing in areas with direct sunlight, though specific brands of outdoor inverters are designed to withstand more sunlight than others. And, in multi-inverter installations, it is important to be sure there is proper clearance between each inverter, so that there isn’t heat transfer between inverters.
Image: Wikimedia Commons
Those Solar Guys said it is best practice to inspect the outside of the inverter (if it is accessible) quarterly, making sure there are no physical signs of damage, and all vents and cooling fins are free from dirt and dust.
It is also recommended to schedule an inspection through a licensed solar installer every five years. These standups typically cost $200-$300, though some solar contracts have free maintenance and monitoring for 20-25 years. During the checkup, the inspector should check inside the inverter for signs of corrosion, damage, or pests.
In the next installment of the series, pv magazine will examine the life of residential battery energy storage applications.
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Simple easy to understand information much appreciated.
I need to know more about solar energy products.
Here is a link to our collection of “solar 101” articles that offer a good introduction to residential solar. https://pv-magazine-usa.com/?s=solar+101
What caught my eye in the article was what appears to be a Sunny Island inverter photo. I use a pair of these, though I don’t leave them out in the weather. I hope they will last a good, long time. Your article really did not cover inverters that run from solar-charged batteries. Has the term Solar Inverter come to apply only to those that are directly connected to solar modules? Are we calling inverters that have batteries in the system something else?
You say that the string and microinverters are predominant. I can see that, but it is a shame. They are great where there is true net metering, but more and more power companies are stacking the deck against home solar. I see hybrid and Zero Export Grid Tie (ZEGT) as the only realistic options in many areas. Much of my home is on off-grid style power and the rest is on battery-buffered ZEGT. The power company does not get involved in any special metering, connection fees or complex accounting.
Any way, I was curious as to how long I should I expect MY Sunny Islands to last. I suspect the answer will be the same, which is, “as long as the electrolytics last.” Beyond that, the questions are how easy will the electrolytics be to change and how much havoc will be created when they fail. An inverter which just gets a little erratic and has bolt-on capacitors would be a great design. One that causes massive chain-reaction failure of all the Flame Emitting Transistors (FETs) and has capacitors soldered in an inaccessible location would probably be a write-off.
Electrolytic caps last longer when they don’t get hot, as you pointed out. My inverters are outdoors in a fan-cooled cabinet, which is probably better than the one in the photo with direct sunlight heating. My backup inverter is in my air conditioned control room, which is probably where the SMA units should have gone for maximum life. I can’t imagine that the caps in a microinverter behind a hot solar panel would last as long as a string inverter in the shade of the eaves.
Hi Neal, if you look closely, it is actually a SunnyBoy not Sunny Island, but failure mechanisms are the same. The SunnyIsland just adds more components as the inverter operates bi-directionally. Good job putting it in a fan-cooled location. Keep all of your fan grilles clean from dust as the author suggests.
Electrolytics are a lot cheaper than film capacitors, which are more popular in micro-inverters, as they are rated at lower voltage and capacitance, because they support only about 1/10th of the power per unit.
A lot of printed circuit boards fail because of temperature cycling, corrosion (e.g. high humidity – and freeze). Memory failure is another big problem as it controls the operation of output FETs (actually IGBTs in most), thousands of times per second. Those IGBTs fail most likely on a clear sunny cold winter day when the inverter is cold and the sun comes up quickly at full insolation and output power, leading to internal thermal expansion at different rates, cracking the chip substrates.
We just returned from life-cycle testing a bunch of vintage inverters at Sandia National Labs, most of them with over 50,000 hours on the clock. While one SunnyBoy failed the first time we pushed up ambient temperature beyond spec, another unit was playing possum many days in a row, tripping a dozens of times at cold temperatures (when capacitors cause for more noise due increased internal resistance), but came back the next day, for a whole week straight. It surprisingly survived even 95 deg C measured heatsink temperature at increasing power output beyond spec.
Inverter reliability depends on many factors under and outside of the control of the manufacturer, hence we are developing an “Energy Cardio Graph” solution predicting failure of big utility-scale inverters in the field while operating. Those who fail more frequency then string inverters, and cause a lot more damage (having a few Megawatts going sideways).
My family has two solar arrays, the first was built with 4 and then 2 more panels and micro inverters. The second has 24 panels and an SMA Sunny Boy 5000. The Sunny Boy has shrugged off 2 lightning power surges by blowing a small fuse inside. First time, my solar guy came out, fixed it and I paid him. Didn’t buy extra fuse(s). Second time, jumped on Amazon after taking a multi meter and finding the same fuse blown. Two days later, installed fuse and all is well. Little array original 4 inverters built like a tank. About 9 years, no issues. The 2 added micro inverters have a nifty little light that’s either red or green when the sun’s out. I have had a total of 5 replacements on those, and they were installed more than a year after the first 4. I don’t claim this will be anyone’s outcome but mine, but I know which ones have performed and which have a somewhat lower resiliency.
Has anyone had a problem w glare issue from panels ? Our neighbors across a small waterway find their walls lighting up. It happened April 3 rd, lasted a month and has come back 6 mos later. Obviously seasonal position of sun. The ‘glare’ starts at one side and in the course of an hour moves across the panels. Our solar company seems dumbfounded and we need to solve or our HOA may have us remove solar panels.
Either adjust the angle of the panels and or plant a shade bush between you and them. Can’t change the sun!
Given government mandates in green energy it is unlikely your HOA can force removal of your solar panels particularly since I presume you submitted your installation plans to the HOA prior to obtaining city permits. Check your local state laws and consult a knowledgeable attorney.
I would call companies that manufacture various anti-reflective coatings and test them out; some coatings may even have the potential to slightly increase absorbed light, improving panel efficiency. A quick google search led me to:
https://sinovoltaics.com/learning-center/solar-cells/anti-reflective-coating-for-solar-panels/
https://www.pveducation.org/pvcdrom/design-of-silicon-cells/anti-reflection-coatings
Some other sources suggested that anti-reflective coatings (AR) like this can improve panel efficiency roughly 1%.
Very useful information
Thanks
I have been living off-grid for 21 years, using a Trace 4024 inverter, which is in the cellar along with all the other components of the system other than the (unshaded, tilt adjustable) arrays. It is not clear to me what advantage micro- or string-inverters have for my application, and outside placement seems highly detrimental to lifetime. In the next year or so I intend to at least double my 2100W array (still performing very well) and replace the inverter with a 240 split-phase and higher-output inverter, still off-grid. I’d really be interested in an evaluation of these off-grid products, and I’d like to know if any of the current off-grid inverters will work for 20+ years with utter reliability like the Trace. Yes, grid-tie is common but some of us tough geezers are still alive (and so are our DIY systems!)
Interesting article, you can still add to it:
https://mysolarperks.com/hm-pow-sol-panel
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.
You can find an informative infogrphic about solar inverters here:
https://www.promoandprintco.com.au/print/