Solar micro-inverter addresses capacitor reliability issues

From an installer standpoint, our main problem with microinverters is after the warranty period. If the inverters start to go, one at a time, who pays for the labor of climbing up onto the roof, removing a panel (middle of a large array) and reinstalling. Then doing it say another 23-25 times for a 5 kw system. With one inverter, your in and out in 1-2 hours. With cost, if you have 24 inverters and they are $200 ea, you have $4800 worth of inverters. With an SMA 5000, your looking at between $2-$3000. If you get into larger systems than 5-10kw, what a nightmare. You would have some great service contracts though, just bad for the consumer. As for individual panel monitoring, we've never replaced a single panel. GE told us they have a 1% module failure rate, historically.

diode answer guy, Recently some one sent me some bypass diodes for analysis due to quality issues/concern. I know very little about PV industry(and was not interested in it until now) but do know a few things about diodes and manufacturing of diodes. I decided to go beyond the samples sent to me and collected bypass diode samples by two other "manufacturers". I analyze their quality by first opening them up and inspect how well they are put together. All three failed in my analysis in that they all have faulty die soldering. Specifically, I found cold soldering and/or rampant solder voids in all these diodes. Poor die soldering can cause so many different problems. The most critical yet often overlooked one is the heat dissipation problem as a result of poor die soldering. The heat generated by electrical current flowing through silicon die(and by reverse leakage) will have great difficulty to dissipate to the outside should it has poor die attachments, causing junction temp. to rise rapidly(in turn cause higher reverse leakages which causes junction temp. to go up even more). Eventually, the silicon die is forced to operate at a much higher junction temp. if it ever reaches steady state at all, or worse it creates a thermal runaway situation, causing the diode to short out. Faulty solder joints all have very weak mechanical strength which can often lead to separation of solder joints under mechanical impacts and/or thermal cycling, cause "open" failure mode. The reason I posted the question is because I wonder if the poor die soldering I discovered in these bypass diodes are acceptable to the PV industry for what the bypass diode is designed to do under harsh working environments? Maybe I am missing something here?

One of the reasons Europe went away from micro-inverters was when a large manufacturer went out of business because a single grid power surge took out over 10,000 units at once. Ouch. All of the string inverters intermixed in the same area survived. The manufacturers who have the experience with many units in the field for many years will tell you it's a harsh world out there and the larger components tend to survive surges and lightning much better than smaller ones. My 15+ years in various power industries agrees. My experience also see's capacitor failure as a relatively low probability. From my experience the most common failures are due to bad solder joints, bad batches of components which fail through many hot/cold cycles, and AC power surges.

Could any of you comment on bypass diode? Any of you experienced any quality or reliability issues? From what I can tell, many bypass diodes on market seem to have very poor quality.

How about instead of all the little inverters with the less efficient way of doing things, a variable switching system so that the sections that don't provide enough current get re-arranged into a parallel hookup and the whole mess is in series. Yes, now you may have 600 or so volts on the line to the main inverter, that is what safety procedures are all about. I have worked on large arrays of series gell-cells, where not only was there a "quite high" DC voltage present, but no way to shut it off without unbolting a connection or a few. Gell-cells don't switch off, you see. And please note that I never got killed, even once. REstructuring an array would have much fewer sources of loss, and the ability to disconnect failed sections completely. And note that switching relays are a bit cheaper than inverters.

Roger.. I believe your math is incomplete. 10,000 rating was based on the higher temp (105C) and it was explained the expected increase in life was based on operating in Palm Springs measured temp of 46C. Obviously .. you can dis-agree... but your math isn't making your point. also.. It has been stated in prior postings... large or small solar arrays ... both need regular cleaning... No getting around it... you will have to be on the roof on a regular basis. I would expect the micro inverters to be smart enough to report their status / performance. not quite the same thing as a redundant indicator light going out... ( no one noticing until all lights are out).

Andy T, you are definitely on to something there. Since the panels have current running through them and we are rotating the panels in the earth's magnetic field we should also be able to generate excess current in the panels.

I think the best Micro-Inverter on the market is at www.xetenergy.com/solar/solutions/

I find the one inverter per panel very intriguing. 1) You get redundancy, on panle/inverter fails you only loose 200W. 2) You do not have to go for the whole 3.5KW install all at once. You could start out with 3 or 4 panels/inverters and work your way up over the years to more panels/inverters.

I love it - direct-to-grid 3600 RPM solar panel spinners; much better than the color wheel as it keeps the cells cool which boosts conversion efficiency. We can also harvest additional power from the spinning panels with downstream wind turbines a la Wile E Coyote.

The math does work out (barely), but only if the reliability numbers can be trusted. The slightly lower inverter efficiency is outweighed by the increase in lifetime energy harvest with a per-panel approach. Enough even to counteract Enphase's (temporary, I hope) very high cost/unit. Many in the industry are very skeptical about the reliability claims though, not just because of the low temperature assumptions and the hopeful take on e-caps, but also because of the complexity of the design. To seacrow, it seems you might have been fooled by Andy T's joke about the rotating color wheel, but maybe not - your suggestion of spinning the whole panel is right up there!