Double the lifetime of an inverter?

[solarix]

I totally agree that heat is the enemy of electronic reliability - especially with the new regime of lead-free solder. I'd like to know how the microinverter folks substantiate their 25 year warranties when operating at much higher temperatures than standard string inverters. I know they know have designed out the weak-link of elec. caps but I still do not trust them.

By the way, electrolytic caps are really only suitable when used at lower frequencies. This is not something that capacitor specs identify very well - which the whole electronic industry found out the hard way when the big move to switching power supplies came through and power supply frequencies went from 120hz to 2kHz to 5kHz to 10kHz to 20kHz and on up as advances in transistor switching times improved. Great for reductions in the transformers - but the poor low cost electrolytic's dissipation factors suffered. Just google the subject "bad caps" sometime.

[DaveDE2]

You go Butch, keep pedaling SE and your stories. Ignorance is bliss.

Mod Note: Please avoid personal attacks on other members.

[ButchDeal]

The only place I find for the 10 year estimate is that enphase pushed that in their marketing. Seems silly with inverters with base 12 year warranties that are extendable to 25 years.

[ButchDeal]

It comes from the fact that semiconductor and capacitor lifetime decreases by a factor of two for every 10C increase in operating temperature. The fact that the inverter spends a small part of the day operating at peak temp is irrelevant.

The 10 year estimate comes from typical time to failure of an inverter, which is about 10 years. Those failures are caused by and large by the average temperatures that the components reach over that lifetime.

semiconductors do not care that much about temperature.
Peak temp doesn't really matter, it is over operating temperature range. solaredge inverters for example have a peak operating temperature of 140F, most people are not going to have a problem staying under that.
Other inverters are like Outback (mine) have lower temperatures (well outback cut performance above 104F)

Old school data center managers back in the 70s, 80s used to keep data centers around 60F too thinking it would keep the computer working better. Many tests have shown there is no reason for this so most data centers started ramping temperatures up in the 90's , now most are 80F and even 85F in the COLD rows.

[jflorey2]

It comes from the fact that semiconductor and capacitor lifetime decreases by a factor of two for every 10C increase in operating temperature. The fact that the inverter spends a small part of the day operating at peak temp is irrelevant.

No, it's not.

If the inverter is dissipating almost no power, then the difference between forced air cooling and no forced air cooling is zero. No extension of life.
If the inverter is dissipating a lot of power, then the difference between forced air cooling and no forced air cooling is large - and only then do you see an extension of life.

Thus the time operating at high power matters a lot.

Also, keep in mind that while some failure mechanisms do scale like that (specifically electrolytic capacitors) semiconductors do not. The thermal effects (increased diffusion for example) are very small compared to the other failure modes - and in modern semiconductors, those other non-temperature-dependent failure modes dominate.

[DaveDE2]

It comes from the fact that semiconductor and capacitor lifetime decreases by a factor of two for every 10C increase in operating temperature. The fact that the inverter spends a small part of the day operating at peak temp is irrelevant.

The 10 year estimate comes from typical time to failure of an inverter, which is about 10 years. Those failures are caused by and large by the average temperatures that the components reach over that lifetime.

[sensij]

I know now that the MOSFETs (mounted in the heatsink) should last at least 10 years longer with said airflow. My next en devour will be to place temperature sensors inside the box, on the electrolytic capacitors. They are not intimately mounted to the heatsink but are non the less running cooler with the fan. More data later...

Huh? The inverter obviously spends only a small part of the day operating at peak temperature. Where does the 10 years estimate come from?

[DaveDE2]

My system is fired up now, two each 6kw inverters, each putting out about 4kw just now. I put a small low volume fan (5x5", don't know the cfm, maybe 15cfm?) close under one without any ducting and blowing upward toward the heatsink. The heatsink temp (60C) dropped by 18C compared to the other one. The front face of the inverter dropped by 6C compared to the other one.

I know now that the MOSFETs (mounted in the heatsink) should last at least 10 years longer with said airflow. My next en devour will be to place temperature sensors inside the box, on the electrolytic capacitors. They are not intimately mounted to the heatsink but are non the less running cooler with the fan. More data later...

[J.P.M.]

IMHO, air flow is important but air temperature and loading of the inverter are major factors in inverter life. I have my inverters attached to a concrete wall in a below grade basement. On the hottest day in the summer the incoming air temp is no more than 60 deg F. I also try to oversize inverters slightly with the goal of keeping the output below the maximum rating of the unit (no clipping). I find that the various solar installers all tend to oversize their arrays for the inverter and rarely do I see a microinverter sized to match up with a panel rating. Enphase even came out with technical paper insisting that a microinverter should intentionally be undersized so that it clips as that is best economics. I prefer long term reliability and probably would not even install a microinverter due to the environment it is located but I sure wouldn't overpanel it.

Knock on wood I have a 14 year old Advanced Energy inverter that is still running. These units were an early grid tied only inverter and most installers over paneled them. They had lot of warranty failures and it drove the company out of business. At least one former employee blamed a lot of the issues on thermal issues. It is passively cooled (no fan).

I see PR shots of PV installations and see inverters mounted on exterior walls siting right in the sun. Might be good for a PR shot but lousy for the electronics. The best place is indoors preferably in air conditioned space or in a cool basement.

Air (or other coolant) flow is not only important, it's essential, and what makes heat exchangers work to haul the waste heat away.

Q = M* c*delta T. where, Q = heat removed. M = mass flow rate, in this case air. c = The specific heat of air. Delta T = (to a 1st approx. here) the temp. diff between the heat exchanger and the air.

An additional and complicating consideration for nat. convection devices, at least in a gravity field : The M is largely controlled by the delta T, with design considerations to minimize pressure drop, make maint. as easy as possible, and of course, safety and cost considerations.

A thought experiment: Put a nat. convection cooled inverter in a sealed, insulated box while its operating and imagine what will happen. Without (cooler) air flowing through the heat dissipation apparatus on the inverter (cooling fins, etc.), things will heat up quite quickly and (hopefully) the protective devices will shut the unit down. The unit needs a cool air source.

Devices dependent on nat. convection for cooling will run cooler in cooler environments. An inverter cooled via nat. convection in a 60 deg. F. environment will run cooler than in, say, an 80 deg. F. environment by probably something like 20 deg. F. That's probably part of the reason why you're inverters are still functional. If they were in an outside shed with a commonn air temp. of, say, 90 F., they'd often be running something like 30 deg. F. warmer.

Your 60 F. basement temp. has probably contributed to the inverters' longevity.

Adding forced convection (fan assist) to any nat. convection cooled inverter in the same environment will decrease an inverter's delta T and thus lower the inverter operating temp. How effective the scheme is, and how cost effective it will be in terms of efficiency improvements, longevity and operating/maint. costs are separate questions and considerations that will change with the application and goals of the user.

When planning inverter location during system design, a stable environment with somewhat controllable conditions is often deemed best. That's usually indoors in a controlled environment with reasonable access. Under a panel in the middle of an array where access is limited and an annual temp. swings of, say 100 F. are possible, if not likely, as in the case of microinverter location, does not seem to meet the stable, accessible requirements part as well as does a garage or basement location for a sting inverter. However, the design process is always a set of tradeoffs and priorities.

[Mike90250]

..........I see PR shots of PV installations and see inverters mounted on exterior walls siting right in the sun. Might be good for a PR shot but lousy for the electronics. The best place is indoors preferably in air conditioned space or in a cool basement.

But that's an extra 15 feet of conduit !!

[peakbagger]

IMHO, air flow is important but air temperature and loading of the inverter are major factors in inverter life. I have my inverters attached to a concrete wall in a below grade basement. On the hottest day in the summer the incoming air temp is no more than 60 deg F. I also try to oversize inverters slightly with the goal of keeping the output below the maximum rating of the unit (no clipping). I find that the various solar installers all tend to oversize their arrays for the inverter and rarely do I see a microinverter sized to match up with a panel rating. Enphase even came out with technical paper insisting that a microinverter should intentionally be undersized so that it clips as that is best economics. I prefer long term reliability and probably would not even install a microinverter due to the environment it is located but I sure wouldn't overpanel it.

Knock on wood I have a 14 year old Advanced Energy inverter that is still running. These units were an early grid tied only inverter and most installers over paneled them. They had lot of warranty failures and it drove the company out of business. At least one former employee blamed a lot of the issues on thermal issues. It is passively cooled (no fan).

I see PR shots of PV installations and see inverters mounted on exterior walls siting right in the sun. Might be good for a PR shot but lousy for the electronics. The best place is indoors preferably in air conditioned space or in a cool basement.

[Willaby]

All I care about is prolonging the life of my inverter electronics per Arrhenius etc. I'm going to install a few small ducted fans and measure the with and without fan temps of the heatsink (FETs) and inside ambient air temp (Caps) and report back. Thanks.

I think its a good idea. I have a SE5000 (no fan) and was going to run a small computer fan via a small 5w solar panel, but I never got around to it. I figured the solar output would automatically ramp up the fan speed in conjunction with inverter load on a hot day at noon. IIRC, the inverter has never exceeded 110F, so I kind of lost interest thinking it really doesn't get that hot, but I still eventually want to do it.

[J.P.M.]

All I care about is prolonging the life of my inverter electronics per Arrhenius etc. I'm going to install a few small ducted fans and measure the with and without fan temps of the heatsink (FETs) and inside ambient air temp (Caps) and report back. Thanks.

+1 on Mike's comment about vibration.

[DaveDE2]

All I care about is prolonging the life of my inverter electronics per Arrhenius etc. I'm going to install a few small ducted fans and measure the with and without fan temps of the heatsink (FETs) and inside ambient air temp (Caps) and report back. Thanks.

[J.P.M.]

If you look at the "cooling fan system" on the high end gaming computers they use some type of "closed fluid" system in conjunction with the fan to keep the main processor cooler allowing it to run very fast. I wonder if something similar couldn't be used on a solar inverter components.

Yea, that's probably a closed system not unlike how a fridge or an air conditioner works. Advantages include perhaps less dust/crap exposure to the electronics and probably lower pumping costs. Reliability is probably similar to that of a refrigerator. The circulating fluid may be a refrigerant or not. Bigger inverters may work that way. Probably pretty expensive for residential inverters both in $$ and space requirements. I'd guess the $$ curve is different for gambling machines where down time can cost real money.