Adding Solar Panels

[madbrain]

Now had I been off the grid most of the above reasoning doesn't matter any more and the important fact that it needs to work off the grid makes Outback come to the top.

Right. Enphase doesn't support off-grid use with their micro-inverters anyway, so they would not be in the running.
But for grid-tie, Enphase is great.

 

[AndyH]

This is EXACTLY my point! The error I see in your analysis is trying to make a connection between a marketing device (warranty) and an engineering/design device (MTTF/MTBF). Those are two completely different things managed by two completely different groups within a company. I agree with your view of how this might affect the end user's perception - that's exactly why it's touted (or ignored) by sales folk. Thank you - you've just validated that sales techniques work!

Sorry, but the fact that there are different groups involved for engineering and marketing is irrelevant.
Whatever the marketing group decides in terms of warranty length, the company has to consider the cost of honoring that warranty. Are you seriously suggesting that nobody in the company would consult with their engineering group to attempt to predict what those warranty costs might turn out to be ?

I didn't say that the company wouldn't consult with engineering. I'm simply trying to separate a couple of areas that many people think are the same.

It's not in the interest of the company to overpromise in terms of warranty, if they are not able to actually deliver on it. The company would soon be history if that happened. There are two sides of the coin. Any reasonably run business would do a cost-benefit analysis.

Of course they would do a cost-benefit analysis. But it doesn't always go the way we might think. Part of the analysis includes the life of the product in the specified application. Part of the analysis includes the terms of the warranty insurance policy (some are supported by insurance, not directly by the company). Part of the analysis includes the likely percentage of those with problems actually filing a claim. More time in service means a smaller return rate for many tech items. A longer stated warranty can often result in more sales. At the end of the number crunching, a company might find that they can risk a warranty longer than their 'average' life.

For my system, for example, I have some spares for some items that might not be available later in the system's life. If they fail, it may not be worth it to file a warranty claim - I'll simply toss the bad widget and replace it with a spare and go back to gardening. When I was doing research for my business to determine how I'd provide warranty for the devices I manufactured, the number I kept finding from similar electronics industries is a 20% average warranty claim rate (20% of devices that failed while under warranty were actually returned.) Enphase units are probably potted and that likely makes them disposable items. A central inverter is highly repairable - and one is much more likely to want to repair a $2K device rather than a $125 unit.

IMO, the fact than Enphase used to offer 15 years standard warranty and now 25 years on their newer micro-inverters speaks to the fact that they expect to be able to honor the warranty somehow. Maybe it's because they really expect their products to last that long. Maybe it's because their products cost more per watt than string inverters in general, so they have more reserves to cover warranty claims. I like to think that it's a little bit of both.

That's fine - but that's your perception. Time will tell if it's correct.

It seems to me that the string inverters manufacturers have determined that they can't afford to offer and honor any warranties greater than 10 years. Why do you think that is ? If their products are as reliable as you say, why aren't they also offering 15 or 25 year standard warranties on any product, or even 15 or 25 year extended warranties on current product, at any price point?

Sorry - bad logic again. Warranty is marketing. Warranty is marketing.

In the real world of off-grid service, even older tech inverters last beyond 20 years. The newer inverters - with similar designs as the new micros - should last longer. It's commonly expected that if an electronic device survives the first (24 hours, week, month) in service it'll go to end of life unless something like lightning or an installation error kills it. Folks buying central inverters have some history to go on. They don't need a warranty enticement.

Why only a 5 or 10 year warranty? Because that's the industry standard for central inverters - that's all they 'need' to provide to entice sales in their niche. They're not competing with microinverters so the warranty rate in that market is irrelevant.

Microintervers don't have a history. And to add insult to injury, they're going to be mounted under a solar panel - and it's a royal pain to uninstall a row or column of panels to get to the failed inverter in the middle of an array. (Though maybe you have better luck than I and the unit that fails will be on the edge of the array. :lol: ) New products will generally NEED a longer warranty - and devices intended to be buried under solar panels with a 25 year life should have a similar warranty. Otherwise, Outback, SMA, and other companies will keep selling central inverters to these customers.

You might enjoy reading this:
http://www.isixsigma.com/industries/retail/save-cost-set-product-warranties-based-quality/

 

[QueenBee]

This is EXACTLY my point! The error I see in your analysis is trying to make a connection between a marketing device (warranty) and an engineering/design device (MTTF/MTBF). Those are two completely different things managed by two completely different groups within a company. I agree with your view of how this might affect the end user's perception - that's exactly why it's touted (or ignored) by sales folk. Thank you - you've just validated that sales techniques work!

Sorry, but the fact that there are different groups involved for engineering and marketing is irrelevant.
Whatever the marketing group decides in terms of warranty length, the company has to consider the cost of honoring that warranty. Are you seriously suggesting that nobody in the company would consult with their engineering group to attempt to predict what those warranty costs might turn out to be ?

It's not in the interest of the company to overpromise in terms of warranty, if they are not able to actually deliver on it. The company would soon be history if that happened. There are two sides of the coin. Any reasonably run business would do a cost-benefit analysis.
IMO, the fact than Enphase used to offer 15 years standard warranty and now 25 years on their newer micro-inverters speaks to the fact that they expect to be able to honor the warranty somehow. Maybe it's because they really expect their products to last that long. Maybe it's because their products cost more per watt than string inverters in general, so they have more reserves to cover warranty claims. I like to think that it's a little bit of both.

It seems to me that the string inverters manufacturers have determined that they can't afford to offer and honor any warranties greater than 10 years. Why do you think that is ? If their products are as reliable as you say, why aren't they also offering 15 or 25 year standard warranties on any product, or even 15 or 25 year extended warranties on current product, at any price point?

I still don't feel like I have an answer to this question. Becuase the standard is 10 and so they don't have to offer longer warranties just doesn't make sense to me. If I was making a product I would offer a longer warranty than my competitors, assuming I could afford to do so.

Your link indicates 10 years was the magic number in 2002. I guess time will tell if transformerless central inverters of today will increase that.
http://www.solelprogrammet.se/Global/Projekteringsverktyg/PDF/herman%20laukamp%20fin_rep.pdf?epslanguage=sv" onclick="window.open(this.href);return false;

Inverters too, have matured remarkably. Experience from most recent projects shows troublefree operation for 10 years.

It's commonly expected that if an electronic device survives the first (24 hours, week, month) in service it'll go to end of life unless something like lightning or an installation error kills it.

Yes, the bathtub curve. The issue is how does one know how long until end of life is? As a consumer I see warranties as being a hint at what the bathtub curve will be.

Folks buying central inverters have some history to go on. They don't need a warranty enticement.

I would argue and assume that the vast majority of consumers installing solar systems in 2012 didn't own one previously.

Why only a 5 or 10 year warranty? Because that's the industry standard for central inverters - that's all they 'need' to provide to entice sales in their niche. They're not competing with microinverters so the warranty rate in that market is irrelevant.

So are central inverter manufacturers not competing with each other? If you gave me a choice between two inverters and all things being similar, I'm going to buy the one with 25 year warranty. If modern central inverters really do have a useful life of 32 years then all it takes is one company to realize that warranty periods impact purchasing decision and overnight everyone is going to have to up their game to 25 years.

In its latest report, The World Market for Microinverters & Power Optimizers – 2012, IMS Research indicated that shipments of microinverters and power optimizers grew by more than 180 percent in 2011and revenues increased by 160 percent, to more than $200 million.

IMS Research said it anticipates that combined shipments will grow by 70 percent in 2012, to about 900 MW, despite the weak state of the PV industry as a whole. They are expected to capture more than 10 percent of the PV inverter market in 2016, generating revenues of $1.5 billion.

So only a small chunk of the entire market, but I would expect the residential market share to be a whole lot greater.

Microintervers don't have a history. And to add insult to injury, they're going to be mounted under a solar panel - and it's a royal pain to uninstall a row or column of panels to get to the failed inverter in the middle of an array.

BTW: You realize that the Enphase warranty covers both lost production and pays the installer to replace the module?

Regarding: http://www.solelprogrammet.se/Global/Projekteringsverktyg/PDF/herman%20laukamp%20fin_rep.pdf?epslanguage=sv" onclick="window.open(this.href);return false;

 

[AndyH]

This is EXACTLY my point! The error I see in your analysis is trying to make a connection between a marketing device (warranty) and an engineering/design device (MTTF/MTBF). Those are two completely different things managed by two completely different groups within a company. I agree with your view of how this might affect the end user's perception - that's exactly why it's touted (or ignored) by sales folk. Thank you - you've just validated that sales techniques work!

Sorry, but the fact that there are different groups involved for engineering and marketing is irrelevant.
Whatever the marketing group decides in terms of warranty length, the company has to consider the cost of honoring that warranty. Are you seriously suggesting that nobody in the company would consult with their engineering group to attempt to predict what those warranty costs might turn out to be ?

It's not in the interest of the company to overpromise in terms of warranty, if they are not able to actually deliver on it. The company would soon be history if that happened. There are two sides of the coin. Any reasonably run business would do a cost-benefit analysis.
IMO, the fact than Enphase used to offer 15 years standard warranty and now 25 years on their newer micro-inverters speaks to the fact that they expect to be able to honor the warranty somehow. Maybe it's because they really expect their products to last that long. Maybe it's because their products cost more per watt than string inverters in general, so they have more reserves to cover warranty claims. I like to think that it's a little bit of both.

It seems to me that the string inverters manufacturers have determined that they can't afford to offer and honor any warranties greater than 10 years. Why do you think that is ? If their products are as reliable as you say, why aren't they also offering 15 or 25 year standard warranties on any product, or even 15 or 25 year extended warranties on current product, at any price point?

I still don't feel like I have an answer to this question. Becuase the standard is 10 and so they don't have to offer longer warranties just doesn't make sense to me. If I was making a product I would offer a longer warranty than my competitors, assuming I could afford to do so.

Apparently we have a significant inability to communicate. Look, I've give you information and results of the research and due diligence I performed when I started my own tech manufacturing business, and information from independent sources that reinforce my position. I truly don't care what you chose to use. I do get a bit annoyed when people with a clear agenda don't provide full disclosure when pushing one product over another, however.

Your link indicates 10 years was the magic number in 2002. I guess time will tell if transformerless central inverters of today will increase that.
http://www.solelprogrammet.se/Global/Projekteringsverktyg/PDF/herman%20laukamp%20fin_rep.pdf?epslanguage=sv" onclick="window.open(this.href);return false;

Inverters too, have matured remarkably. Experience from most recent projects shows troublefree operation for 10 years.

Seriously? Have you already forgotten the 32 year number from Exeltech? No, the 2002 paper did not say anything about a 10 year magic number. What it said was that more recent projects (more recent than the projects reviewed which were installed in the 1990s) were still operating 10 years after installation. They hadn't failed.

In addition, the study clearly states that many of the projects surveyed were demonstration or proof-of-concept projects and were thus expected to not necessarily provide the best long-term performance.

That's not the same as a 10 year lifespan for any equipment type.

According to (Wilk 1997) from 1995 to 1996 the failure rate indeed dropped
from 0.7 to 0.4 defect per inverter and year.
He believes that inverters were mostly damaged by surge voltages from
the grid.

- From the German “Sonne in der Schule” Program between 12 and 8
inverter failures per 100 inverters and year are reported for some 350
inverter-years. This relates to a mean failure rate of about 1 failure in 8
to 13 years. The reported failures include also various malfunctions,
which were probably caused by improper grid conditions.

- Switzerland data from EPFL covering mostly the demosite pavilions
show a distinct improvement over time from 11 to 4 failures per 100
inverter-years. This relates to a mean failure rate of about one failure
in 7 years for a total of 133 inverter-years from 1992 to 2001 and one
failure in 24 inverter-years for the period of 1996 to 2001.

- Data from UK cover installations, which had been commissioned
between February 1999 and May 2001, of about 90 kWp array
capacity employing some 140 inverters, including some 60 Module
Integrated Inverters.
So far no system failure has been noted.

Please note that ALL of these were grid-tied string inverter installations as current microinverters didn't hit the streets until 2008. I had a small grid-tied system operating in 2002 with OK4-U/Trace Microsine inverters but they were pretty horrible. Since they were released in 1995 and many of the systems studied were in service before that year, it's a good bet that none of these installations used microinverters.

It's commonly expected that if an electronic device survives the first (24 hours, week, month) in service it'll go to end of life unless something like lightning or an installation error kills it.

Yes, the bathtub curve. The issue is how does one know how long until end of life is? As a consumer I see warranties as being a hint at what the bathtub curve will be.

I've already provided one way to determine how long to expect the equipment to last. I've also provided independent sources for more information.

As for the warranty, how many times do we have to go over this? As a consumer, you're welcome to believe what you wish - and the sales/marketing folks hope you'll turn your brain off and assume until the cows come home - or at least until after you write your check. As a business owner with my own products and their long-term warranty tail, and as a sales rep for a company that manufactures a number of industrial products, I can assure you that your view is not accurate. Do with that what you will.

Folks buying central inverters have some history to go on. They don't need a warranty enticement.

I would argue and assume that the vast majority of consumers installing solar systems in 2012 didn't own one previously.

You would argue, certainly. But again - do you twist on purpose? Central inverters have been available a very long time. Enphase released their first product in 2008. One of these has a history and the other one doesn't. It doesn't take any twisting to understand that.

Why only a 5 or 10 year warranty? Because that's the industry standard for central inverters - that's all they 'need' to provide to entice sales in their niche. They're not competing with microinverters so the warranty rate in that market is irrelevant.

So are central inverter manufacturers not competing with each other?

Apparently they are - and it's pretty clear from their pricing and warranty terms that's the case as well.[/quote]

If you gave me a choice between two inverters and all things being similar, I'm going to buy the one with 25 year warranty. If modern central inverters really do have a useful life of 32 years then all it takes is one company to realize that warranty periods impact purchasing decision and overnight everyone is going to have to up their game to 25 years.

Too bad you don't have that option, then. Of course, to have that option manufacturers would have to change the purpose of the warranty and that's very unlikely to happen.

In its latest report, The World Market for Microinverters & Power Optimizers – 2012, IMS Research indicated that shipments of microinverters and power optimizers grew by more than 180 percent in 2011and revenues increased by 160 percent, to more than $200 million.

IMS Research said it anticipates that combined shipments will grow by 70 percent in 2012, to about 900 MW, despite the weak state of the PV industry as a whole. They are expected to capture more than 10 percent of the PV inverter market in 2016, generating revenues of $1.5 billion.

So only a small chunk of the entire market, but I would expect the residential market share to be a whole lot greater.

I guess we can assume that string inverters will have 90% of the market shortly before 2016 then?

Microintervers don't have a history. And to add insult to injury, they're going to be mounted under a solar panel - and it's a royal pain to uninstall a row or column of panels to get to the failed inverter in the middle of an array.

BTW: You realize that the Enphase warranty covers both lost production and pays the installer to replace the module?

I frankly don't care. I'm the system designer and installer. I am going to make sure that the only wiring and/or devices physically under the panels are the pigtails from the panels on the way to intermediate combiner boxes. I intend to perform regular system inspections and don't want anything hidden.

There's not a chance in the world that I'm going to put devices with a 4-year track record under panels. Not Going To Happen.

You, on the other hand, are absolutely free to make whatever choice you wish. Just be careful with your marketing efforts as this forum has rules for vendors.

Take care.

 

[QueenBee]

Do we both agree that MTBF is not at all an indicator of a products service life? I see lots of references to what appear to MTBF numbers but I've yet to see anyone say "Today's inverters are expected to have a service life of x years". You have a quote of a guy saying a long time or whatever it was but I think when put into context it was not that long ago when inverters might only last months. I might have missed links to someone who says when calculating your ROI you should plan on replacing your inverter after x years.

 

[AndyH]

Do we both agree that MTBF is not at all an indicator of a products service life? I see lots of references to what appear to MTBF numbers but I've yet to see anyone say "Today's inverters are expected to have a service life of x years". You have a quote of a guy saying a long time or whatever it was but I think when put into context it was not that long ago when inverters might only last months. I might have missed links to someone who says when calculating your ROI you should plan on replacing your inverter after x years.

Yup - we have a significant communication problem.

I am talking about Real-World Service Life In The Field In Actual Service while you are talking about MTBF. Apples and oranges.

As long as you are either unwilling or unable to understand the significance of 1. real-world experiences of people that have been off-grid for about 40 years and 2. information from inverter manufacturers that show a considerable lifespan for their inverters (the source of the 32-year service life statement) and 3. the black-and-white numbers about string inverters in Europe that show statistically valid lifespans from 18 to 24 years in grid-tied service then there is no point is continuing.

Enjoy your weekend.

 

[lipower]

Here is an interesting example of where you would question a limited warranty period. The following company proclaims having been in the inverter manufacturing business for over 60 years and still is only able to provide a 10 year warranty? I would expect that much experience in a field would provide a significant amount of research into the service length of your product. Which is why the warranty is still only 10 years. If they knew it would last 30 don't you think they would like to "market" that? It's like stories of a Ford that just hit 500,000 miles. How many Ford's do you know that have 500,000 miles on them? Crazy thing happen but they are not the norm.

http://www.kaco-newenergy.com/products/solar-inverters/00xi-series" onclick="window.open(this.href);return false;
http://www.kaco-newenergy.com/downloads/Product_spec_sheets/110705_KACO_00xispecsheet.pdf" onclick="window.open(this.href);return false;

 

[AndyH]

Here is an interesting example of where you would question a limited warranty period. The following company proclaims having been in the inverter manufacturing business for over 60 years and still is only able to provide a 10 year warranty? I would expect that much experience in a field would provide a significant amount of research into the service length of your product. Which is why the warranty is still only 10 years. If they knew it would last 30 don't you think they would like to "market" that? It's like stories of a Ford that just hit 500,000 miles. How many Ford's do you know that have 500,000 miles on them? Crazy thing happen but they are not the norm.

http://www.kaco-newenergy.com/products/solar-inverters/00xi-series" onclick="window.open(this.href);return false;
http://www.kaco-newenergy.com/downloads/Product_spec_sheets/110705_KACO_00xispecsheet.pdf" onclick="window.open(this.href);return false;

No. We've covered this. Multiple times.

A warranty is not required. If it is offered, however, there are legal requirements. The FTC has more info on that aspect.

For the rest of the factors, however, one interested in understanding the process can easily find that warranty length factors are about 1/3 engineering, 1/3 marketing, and 1/3 sales. While service life is a factor in a warranty length decision, the major factors are marketing/sales related - How many more units can we sell (and thus how much more profit can we make) if we change the length of the warranty? Companies with mature products set the length based on SALES and PROFIT. Since the central inverter market is composed primarily of mature players, it should be no surprise that they have similar warranty lengths.

Research and engineering studies can provide a guideline but cannot guarantee actual field service - things happen in the real world. That's precisely why the service life for off-grid inverters tends to be longer than grid-tied inverters. Off-grid units tend to 'live' in climate-controlled spaces, they tend to receive periodic inspection/maintenance (because off-gridders are more actively involved in their power system on average), and because they are not negatively affected by the very dirty power grid. Grid-tied systems generally don't enjoy those same benefits.

I offered a lifetime warranty on the products I manufactured because I used the warranty term as a marketing tool -- but only after evaluating similar vendors, the return statistics, and the use patters for the consumer base FIRST - before even factoring in the expected life of the electronics!

A company might set their warranty so they spend somewhere between 0 and 2% of profit on that program. They don't care which customers are the 2 out of 100 with failed devices, they're focused on their cash flow. My job as a consumer, on the other hand, is to design my system so I'm NOT one of the 2%. And those are two completely separate worlds with completely different goals.

 

[QueenBee]

Do we both agree that MTBF is not at all an indicator of a products service life? I see lots of references to what appear to MTBF numbers but I've yet to see anyone say "Today's inverters are expected to have a service life of x years". You have a quote of a guy saying a long time or whatever it was but I think when put into context it was not that long ago when inverters might only last months. I might have missed links to someone who says when calculating your ROI you should plan on replacing your inverter after x years.

Yup - we have a significant communication problem.

I am talking about Real-World Service Life In The Field In Actual Service while you are talking about MTBF. Apples and oranges.

As long as you are either unwilling or unable to understand the significance of 1. real-world experiences of people that have been off-grid for about 40 years and 2. information from inverter manufacturers that show a considerable lifespan for their inverters (the source of the 32-year service life statement) and 3. the black-and-white numbers about string inverters in Europe that show statistically valid lifespans from 18 to 24 years in grid-tied service then there is no point is continuing.

Enjoy your weekend.

1. Peoples experience with inverters is just anecdotal. I know people that still drive cars which are 60 years old but I think we can both agree that the usefull service life of an automobile new or old is not 60 years.

2. As I already stated I've yet to see any inverter manufacturer who states a useful service life value. If I missed this please point me to it.

3. When I skimmed these reports I think I must have missed where their study stated that the useful service life of inverters was 18 - 24 years. I did see the 10 year quote that I pulled out...

I asked the people at Exeltech, who keep track of this stuff, what is your mean time before failure?...How many units do you have out there, how long have they been out there, and how many come back DOA 'please fix this for me'? Thirty-two years.

You keep referencing 32 years yet when you look at that quote it's not clear what question 32 years is the answer too. I can only assume that 32 years is the the answer to the question "what is your mean time before failure?" So 32 years is not relevant in the discussion of useful lifespans. It's certainly not been how long have they been out there since they have only been in business for 23 years.

I'm really not trying to be close minded about this notation that central grid tie inverters have a lifespan of around 10 years I'm just not seeing the data..

From 2009 http://ecmweb.com/ops-amp-maintenance/module-behavior" onclick="window.open(this.href);return false;

In comparison to the decades-long warranty for the cells, mean time to first failure (MTFF) for inverters is estimated to be between five and 10 years

From 2006 http://www.nrel.gov/docs/fy06osti/38771.pdf" onclick="window.open(this.href);return false;

Inverter lifetimes greater than 15 years appear difficult to achieve.

Inverters generally need to be replaced every 5-10 years, whereas modules and other system components have a life of 25 years or more.

Investment in a new inverter is required 3-5 times over the life of a PV system.

So unless you are claiming that the long life central grid tie inverters were not invented until after 2006 (I'm not at all disagreeing that inverters made today are of higher quality than even just 6 years ago) or you are going to claim that NREL is not a valid place to go to for data then I think it's pretty clear to me that this 10 year lifespan thing is real....

 

[QueenBee]

Yup - we have a significant communication problem.

I am talking about Real-World Service Life In The Field In Actual Service while you are talking about MTBF. Apples and oranges.

I think problem with your communication is we are trying to talk about service life and all you do is
continually quote MTBf while at the same time saying you are talking about service life.

According to (Wilk 1997) from 1995 to 1996 the failure rate indeed dropped
from 0.7 to 0.4 defect per inverter and year.
He believes that inverters were mostly damaged by surge voltages from
the grid.

- From the German “Sonne in der Schule” Program between 12 and 8
inverter failures per 100 inverters and year are reported for some 350
inverter-years. This relates to a mean failure rate of about 1 failure in 8
to 13 years. The reported failures include also various malfunctions,
which were probably caused by improper grid conditions.

- Switzerland data from EPFL covering mostly the demosite pavilions
show a distinct improvement over time from 11 to 4 failures per 100
inverter-years. This relates to a mean failure rate of about one failure
in 7 years for a total of 133 inverter-years from 1992 to 2001 and one
failure in 24 inverter-years for the period of 1996 to 2001.

- Data from UK cover installations, which had been commissioned
between February 1999 and May 2001, of about 90 kWp array
capacity employing some 140 inverters, including some 60 Module
Integrated Inverters.
So far no system failure has been noted.

Every single stat in this quote of yours is a MTBF or related number and this has no bearing on the conversation about useful service life....

Please note that ALL of these were grid-tied string inverter installations as current microinverters didn't hit the streets until 2008

Another failure in communication is you say your stats are all about central inverters yet you provide a quote about a study that included nearly 50% "module integrated" inverters.

I've already provided one way to determine how long to expect the equipment to last. I've also provided independent sources for more information.

I apologize for not being able to find your independent sources for the useful service life of inverter.

A theoretical analysis shows that inverter should have a “Mean Time Between Failures” (MTBF) about 50 years as long as they are not exposed to excessive temperature. (For example, mounted directly at a module without any rear side ventilation.) (Wilk 1997).

Another place where you are bringing up MTBF.....

Encased in a ruggedized package, the inverter is designed to remain in full-power operation for more than 25 years.

Here's a quote that is at least talking about the proper subject. It doesnt mention which manufacturers are designing for a 25 yesr life and it provides no data on if that design goal is actually be achieved in the real world. It was written in 2012 so it might be based on designs since 2006 when NREL said 15 years was hard.

Did you even read some if the links you pasted???

•Xantrex, Managing Director: “Why make inverters with a longer life when the customer is better off replacing the inverter every 10 years or so anyway? The inverters available in 10 years will be better products with higher efficiency.”•SMA America, President: “Why focus on higher reliability? Our customers worry only about first-cost. In any case, it’s more cost-effective to just replace the inverter in 10 years.”•Sustainable Energy Technologies, Director of Operations: “A 20-year lifetime for PV inverters is at least10 years away.”•Mitsubishi: “A 20-plus-year life for inverters is impossible. Some parts of the inverters would need to be replaced over such an extended period.”•SMA, Head of Solar:“A 20-year lifetime is not possible.”•Fronius, Head of Sales (Germany):“Inverter MTBF may reach 12 years by 2015. A 20-year lifetime can’t be achieved.”•GE Energyindicated that 20-year life would not be practical without a significant impact oncost. A 15-year life is more reasonable, and that should be reviewed based on life-cycle costs impact.•Contrary to statements made in a recent Photon International article (April 2005), manufacturers and other industry experts we spoke to do not believe that capacitorimprovements alone will result in inverters that can “keep going for more than 20 years.”

Here is a quote from you where you appear to be using MTBF and service life interchangebly.

The good news about the central inverter is that the modern high-frequency units are expected to last 30 years on average. There's good engineering behind that MTBF. I've yet to see anything, or hear anything from either inverter manufacturers or those that have been watching the industry for more than 40 years, that suggests micros will outlast central inverters.

Based on my recap of your data and direct quotes I am not convinced you are aware that MTBF does not mean the same thing as a usable service life. You claim to have experience in the electronics industry but don't seem to understand the statistical difference between the three different parts of the bath tub curves. I would suggest that for us to communicate better you read the great site on MTBF. http://nomtbf.com/perils/" onclick="window.open(this.href);return false;

 

[madbrain]

I didn't say that the company wouldn't consult with engineering. I'm simply trying to separate a couple of areas that many people think are the same.

Nobody implied that they were the same.

Part of the analysis includes the life of the product in the specified application. Part of the analysis includes the terms of the warranty insurance policy (some are supported by insurance, not directly by the company). Part of the analysis includes the likely percentage of those with problems actually filing a claim. More time in service means a smaller return rate for many tech items. A longer stated warranty can often result in more sales. At the end of the number crunching, a company might find that they can risk a warranty longer than their 'average' life.

I'm well aware of that, but if the product really doesn't live beyond the warranty life, the point is that the manufacturer is covering the cost of repair or replacement. Of course I would prefer that neither repair nor replacement be needed, but if they are, I don't care how the cost is being covered, as long as it is actually covered if needed. It is not very important to me if the coverage is provided by the company directly or an insurance company. An insurance company is probably better, if anything, as they may be more likely to be around. But certainly the insurance has a cost, and the insurance company would also evaluate those costs when pricing the insurance policies. The point is that it is taken care of for me.
If I bought a string inverter, the warranty would be much shorter, and nobody currently offers an warranty of 15 to 25 years on them. I haven't seen insurance companies advertising direct-to-consumer string inverter policies either, but if they did, it would probably be overpriced, vs what pricing the manufacturer can get.

For my system, for example, I have some spares for some items that might not be available later in the system's life. If they fail, it may not be worth it to file a warranty claim - I'll simply toss the bad widget and replace it with a spare and go back to gardening.

This seems to me like a good argument for micro-inverters. Even with no warranty whatsover, having a few cheap $125 extra units as spare would be much lighter on the wallet than having buying one extra spare string inverter to avoid downtime.

A central inverter is highly repairable - and one is much more likely to want to repair a $2K device rather than a $125 unit.

It might be more repairable indeed, but at what cost ? If you live in a high cost area like California, labor costs are through the roof. The repair might or might not be economical. The string inverters are big and heavy and cost a lot to lug around or ship back. With the string inverter, the entire array will be down too.

Whereas with the micro-inverters, only a few panels will likely be down. So the downtime cost will be much less. I would much rather have a quick replacement under warranty and ship one or two micro inverters back in a small package. I do agree that the installation cost will be higher to replace things under the panels, but it still compares favorably with a string inverter repair IMO, and also the manufacturer is covering the cost in the warranty.

IMO, the fact than Enphase used to offer 15 years standard warranty and now 25 years on their newer micro-inverters speaks to the fact that they expect to be able to honor the warranty somehow. Maybe it's because they really expect their products to last that long. Maybe it's because their products cost more per watt than string inverters in general, so they have more reserves to cover warranty claims. I like to think that it's a little bit of both.

That's fine - but that's your perception. Time will tell if it's correct.

Indeed !

Sorry - bad logic again. Warranty is marketing. Warranty is marketing.

No, once again, warranty is not just marketing, it's also an expense generator for the manufacturer. There are 2 sides to it, not just 1.

In the real world of off-grid service, even older tech inverters last beyond 20 years. The newer inverters - with similar designs as the new micros - should last longer. It's commonly expected that if an electronic device survives the first (24 hours, week, month) in service it'll go to end of life unless something like lightning or an installation error kills it. Folks buying central inverters have some history to go on.

I agree string inverters have more history, but where is all the data to backup all your statements about longevity ?

Why only a 5 or 10 year warranty? Because that's the industry standard for central inverters - that's all they 'need' to provide to entice sales in their niche. They're not competing with microinverters so the warranty rate in that market is irrelevant.

They are most definitely competing with micro-inverters in grid-tie applications. So it's not irrelevant. Most homes are connected to the grid. Do they really want to give up on 99% of their potential customers ?

I was certainly faced with a choice for my 2 installs between micro and string inverters. Warranty was one reason for my choosing Enphase, but not the only one. Shading is another. It's really interesting when I look at my array how the shade moves around, usually covering one panel almost completely at different times of the day, but never the same panel. I have to wonder how the whole thing would perform with a string inverter. So far it outperformed the original installer predictions by about 20% for the last 2 years. The second array is almost never shaded, though, except by weather.

Microintervers don't have a history. And to add insult to injury, they're going to be mounted under a solar panel - and it's a royal pain to uninstall a row or column of panels to get to the failed inverter in the middle of an array. (Though maybe you have better luck than I and the unit that fails will be on the edge of the array. :lol: ) New products will generally NEED a longer warranty - and devices intended to be buried under solar panels with a 25 year life should have a similar warranty. Otherwise, Outback, SMA, and other companies will keep selling central inverters to these customers.

I don't dispute that the replacement might be a pain. But again this is something covered by the manufacturer warranty. What matters to me as a PV user is the total cost of ownership over the long term, and getting the most electricity production for the lowest possible cost. The micro inverters are among the most expensive per watt, and time will tell if the extra production and promised reliability are worth the cost. I am very happy so far over the last 27 months, having saved over $8000 in PG&E bills. The payback for my first 28 panel system will be a total of 7 years, for the second one with the 12 panels I just added only 4 years.

I will read the article you posted.

 

[AndyH]

Yup - we have a significant communication problem.

I am talking about Real-World Service Life In The Field In Actual Service while you are talking about MTBF. Apples and oranges.

I think problem with your communication is we are trying to talk about service life and all you do is
continually quote MTBf while at the same time saying you are talking about service life.

According to (Wilk 1997) from 1995 to 1996 the failure rate indeed dropped
from 0.7 to 0.4 defect per inverter and year.
He believes that inverters were mostly damaged by surge voltages from
the grid.

- From the German “Sonne in der Schule” Program between 12 and 8
inverter failures per 100 inverters and year are reported for some 350
inverter-years. This relates to a mean failure rate of about 1 failure in 8
to 13 years. The reported failures include also various malfunctions,
which were probably caused by improper grid conditions.

- Switzerland data from EPFL covering mostly the demosite pavilions
show a distinct improvement over time from 11 to 4 failures per 100
inverter-years. This relates to a mean failure rate of about one failure
in 7 years for a total of 133 inverter-years from 1992 to 2001 and one
failure in 24 inverter-years for the period of 1996 to 2001.

- Data from UK cover installations, which had been commissioned
between February 1999 and May 2001, of about 90 kWp array
capacity employing some 140 inverters, including some 60 Module
Integrated Inverters.
So far no system failure has been noted.

Every single stat in this quote of yours is a MTBF or related number and this has no bearing on the conversation about useful service life...

Yes, the data from the field were reported a couple of different ways and one was to 'relate them to' MTBF. No bearing? Regardless of how one prefers to label the chart, the data are from actual field service - not models or projections. How can you possibly suggest real world useful life info doesn't somehow relate to real world useful life?

Regardless, though, if I was preparing a paper on failure rate metrics it would likely be different than the point of this chat - which was about warranties for two different categories of inverters and your attempt to suggest that a 5 or 10 year warranty means a 5 or 10 year service life.

Please note that ALL of these were grid-tied string inverter installations as current microinverters didn't hit the streets until 2008

Another failure in communication is you say your stats are all about central inverters yet you provide a quote about a study that included nearly 50% "module integrated" inverters.

Not quite. I did err in that 60 of the 140 inverters from the UNITED KINGDOM portion of the study were integrated inverters. The rest were not. I don't know what microinverter was used. The UK systems were reportedly commissioned from Feb 99 through May 01. The only microinverters of which I'm aware from that period were the OK4 (Europe)/Trace Microsine(US) http://www.oke-services.nl/docs/index.htm. They were not current-tech micros as those didn't hit the streets until 2008.

I've already provided one way to determine how long to expect the equipment to last. I've also provided independent sources for more information.

I apologize for not being able to find your independent sources for the useful service life of inverter.

The European study is one. The information from Richard Perez is another. The final link was to Robin Gudgel. That's three sources of vendor-neutral information on actual field experience.

Once again - here's the 1999 talk from Perez: https://www.dropbox.com/s/fa3fqshepp04igp/INVERT.WAV Enjoy.

A theoretical analysis shows that inverter should have a “Mean Time Between Failures” (MTBF) about 50 years as long as they are not exposed to excessive temperature. (For example, mounted directly at a module without any rear side ventilation.) (Wilk 1997).

Another place where you are bringing up MTBF.....

Encased in a ruggedized package, the inverter is designed to remain in full-power operation for more than 25 years.

Here's a quote that is at least talking about the proper subject. It doesnt mention which manufacturers are designing for a 25 yesr life and it provides no data on if that design goal is actually be achieved in the real world. It was written in 2012 so it might be based on designs since 2006 when NREL said 15 years was hard.

Did you even read some if the links you pasted???

Yes I did. As stated at the time, those were included solely to show that there's been significant progress over the past 20 years.

I did that, again, simply to show that your 5-10 year service life suggestions were incorrect.

Here is a quote from you where you appear to be using MTBF and service life interchangebly.

The good news about the central inverter is that the modern high-frequency units are expected to last 30 years on average. There's good engineering behind that MTBF. I've yet to see anything, or hear anything from either inverter manufacturers or those that have been watching the industry for more than 40 years, that suggests micros will outlast central inverters.

Yes, that was sloppy. This and my subsequent posts were focused on actual life in the field, not calculated expectations. I tried to make that very, very clear.

 

[QueenBee]

Looks like even today NREL still hasn't gotten the memo that inverters last "32 years"/"you never need to replace them".

From January 2013 http://www.nrel.gov/docs/fy13osti/57251.pdf" onclick="window.open(this.href);return false;

Warranties typically run 10 and 25 years with 10 years being the current industry standard. On larger units, extended warranties up to 20 years are possible. Given that the expected life of the PV panels is 25–30 years, an operator can expect to replace a string inverter at least one time during the life of the PV system.

The inverters, which come standard with a 10-year warranty (extended warranties available), would be expected to last 10–15 years.

From March 2011 http://www.nrel.gov/docs/fy11osti/49237.pdf" onclick="window.open(this.href);return false;

The inverters, which come standard with a 5- or 10-year warranty (extended warranties available), would be expected to last 10–15 years.

From September 2010 http://www.nrel.gov/docs/fy10osti/48853.pdf" onclick="window.open(this.href);return false;

The inverters, which come standard with a 5- or 10-year warranty (extended warranties available), would be expected to last 10–15 years.

 

[AndyH]

I didn't say that the company wouldn't consult with engineering. I'm simply trying to separate a couple of areas that many people think are the same.

Nobody implied that they were the same.

I was having a conversation with QueenBee, who suggested that warranty length was directly related to service life, and that we could directly compare warranty lengths for devices in separate categories.

Part of the analysis includes the life of the product in the specified application. Part of the analysis includes the terms of the warranty insurance policy (some are supported by insurance, not directly by the company). Part of the analysis includes the likely percentage of those with problems actually filing a claim. More time in service means a smaller return rate for many tech items. A longer stated warranty can often result in more sales. At the end of the number crunching, a company might find that they can risk a warranty longer than their 'average' life.

I'm well aware of that, but if the product really doesn't live beyond the warranty life, the point is that the manufacturer is covering the cost of repair or replacement. Of course I would prefer that neither repair nor replacement be needed, but if they are, I don't care how the cost is being covered, as long as it is actually covered if needed. It is not very important to me if the coverage is provided by the company directly or an insurance company. An insurance company is probably better, if anything, as they may be more likely to be around. But certainly the insurance has a cost, and the insurance company would also evaluate those costs when pricing the insurance policies. The point is that it is taken care of for me.
If I bought a string inverter, the warranty would be much shorter, and nobody currently offers an warranty of 15 to 25 years on them. I haven't seen insurance companies advertising direct-to-consumer string inverter policies either, but if they did, it would probably be overpriced, vs what pricing the manufacturer can get.

Absolutely. I was trying to look at the 'other side' of the warranty. As an end user, we want to know we're covered. Warranty is one way, but so is the company's reputation for taking care of customers.

I know, for example, that Midnite Solar will refurb my charge controller when it reaches the end of warranty. But I also know they'll mail replacement boards or jump through other hoops to make sure their customers are taken care of. It appears that Outback has the same reputation. For both of those companies, I personally don't care how long or short the warranty is because I have a high level of confidence that I won't be left in the dark. If I find in 20 years that I've made a mistake, I still have my soldering iron as a back-up plan.

edit... A bit more searching today provided stories about Xantrex repairing inverters after the 5 year warranty expired (bad capacitors); ExelTech's policy to fix anything that can be fixed, after the warranty expires, for a flat $100; and SMA blind-shipping replacement inverters and paying remove/replace expenses. FWIW.

For my system, for example, I have some spares for some items that might not be available later in the system's life. If they fail, it may not be worth it to file a warranty claim - I'll simply toss the bad widget and replace it with a spare and go back to gardening.

This seems to me like a good argument for micro-inverters. Even with no warranty whatsover, having a few cheap $125 extra units as spare would be much lighter on the wallet than having buying one extra spare string inverter to avoid downtime.

I agree - and if I used micros I'd keep a couple of spares. There's no way I'll keep a spare VFX3524 in the attic though. But because I'll have a DC 'critical systems' bus, I'm OK if I have to swap a circuit board at some point down the road. The most likely problem as the inverter ages is the electrolytic capacitors - and I can swap all of them myself for about $200.

A central inverter is highly repairable - and one is much more likely to want to repair a $2K device rather than a $125 unit.

It might be more repairable indeed, but at what cost ? If you live in a high cost area like California, labor costs are through the roof. The repair might or might not be economical. The string inverters are big and heavy and cost a lot to lug around or ship back. With the string inverter, the entire array will be down too.

Sure, the system would be down for a grid-tied system, but the grid's there for backup. For my off-grid system, the panel-to-battery interface is the separate charge controller. I'll have AC and DC lights, and the water system is DC, so everything critical stays alive if the inverter dies. I can completely rebuild the inverter and the charge controller by swapping a couple of circuit boards, and both Midnight and Outback will overnight boards.

Whereas with the micro-inverters, only a few panels will likely be down. So the downtime cost will be much less. I would much rather have a quick replacement under warranty and ship one or two micro inverters back in a small package. I do agree that the installation cost will be higher to replace things under the panels, but it still compares favorably with a string inverter repair IMO, and also the manufacturer is covering the cost in the warranty.

IMO, the fact than Enphase used to offer 15 years standard warranty and now 25 years on their newer micro-inverters speaks to the fact that they expect to be able to honor the warranty somehow. Maybe it's because they really expect their products to last that long. Maybe it's because their products cost more per watt than string inverters in general, so they have more reserves to cover warranty claims. I like to think that it's a little bit of both.

That's fine - but that's your perception. Time will tell if it's correct.

Indeed !

Sorry - bad logic again. Warranty is marketing. Warranty is marketing.

No, once again, warranty is not just marketing, it's also an expense generator for the manufacturer. There are 2 sides to it, not just 1.

Yes, fair enough. Or is it three sides - engineering, sales, and marketing?

edit... Of course you're right that it's an expense generator for the company - and since that cuts into profit, why does a company provide one? So they can sell more widgets and make more profit. While it does require input from engineering, it's a sales/marketing-driven tool. Sorry to beat on this, but that was the whole point of what's become a tangent.

In the real world of off-grid service, even older tech inverters last beyond 20 years. The newer inverters - with similar designs as the new micros - should last longer. It's commonly expected that if an electronic device survives the first (24 hours, week, month) in service it'll go to end of life unless something like lightning or an installation error kills it. Folks buying central inverters have some history to go on.

I agree string inverters have more history, but where is all the data to backup all your statements about longevity ?

For the thread, I only wanted to show a real-world life beyond the 5-10 year assertion from QueenBee - I wanted to disconnect service life and warranty.

For my own decision, the best I could do was talk with the manufacturers to find out how their earlier equipment is performing in off-grid service, and then adjust for improvements since that equipment was fielded. I started with docs from places like NREL, but most of the 'finished' papers and their service estimates were based on 1980s and 1990s tech, and most was grid-tied, so not very useful.

edit... I still think the paper based on European field studies is 'proof enough' that inverters live beyond their 10 year warranty since it shows inverters doing just that. Since all we really have for the latest batch of microinverters are MTBF and service life projections, why not include info along the same lines from a top-tier grid-tied string inverter company? SMA advertises a 100,000 hour MTBF and greater than 20 year service life - they're projecting a longer actual service life than their warranty. Yes, it's marketing info - but so are the numbers from Enphase. http://files.sma.de/dl/1371/SB-Info_2001-04_en.pdf

Why only a 5 or 10 year warranty? Because that's the industry standard for central inverters - that's all they 'need' to provide to entice sales in their niche. They're not competing with microinverters so the warranty rate in that market is irrelevant.

They are most definitely competing with micro-inverters in grid-tie applications. So it's not irrelevant. Most homes are connected to the grid. Do they really want to give up on 99% of their potential customers ?

Yes, they are both options, but from a warranty perspective they are in two different categories. It's similar to the way there are square wave, modified sinewave, and sinewave string inverters - they're in different categories as well.

I was certainly faced with a choice for my 2 installs between micro and string inverters. Warranty was one reason for my choosing Enphase, but not the only one. Shading is another. It's really interesting when I look at my array how the shade moves around, usually covering one panel almost completely at different times of the day, but never the same panel. I have to wonder how the whole thing would perform with a string inverter. So far it outperformed the original installer predictions by about 20% for the last 2 years. The second array is almost never shaded, though, except by weather.

Absolutely! That's where microinverters or per-panel MPPT units shine - that's the problem they're here to fix.

My application is a passive solar house - shade will be eliminated from the start.

Microintervers don't have a history. And to add insult to injury, they're going to be mounted under a solar panel - and it's a royal pain to uninstall a row or column of panels to get to the failed inverter in the middle of an array. (Though maybe you have better luck than I and the unit that fails will be on the edge of the array. :lol: ) New products will generally NEED a longer warranty - and devices intended to be buried under solar panels with a 25 year life should have a similar warranty. Otherwise, Outback, SMA, and other companies will keep selling central inverters to these customers.

I don't dispute that the replacement might be a pain. But again this is something covered by the manufacturer warranty. What matters to me as a PV user is the total cost of ownership over the long term, and getting the most electricity production for the lowest possible cost. The micro inverters are among the most expensive per watt, and time will tell if the extra production and promised reliability are worth the cost. I am very happy so far over the last 27 months, having saved over $8000 in PG&E bills. The payback for my first 28 panel system will be a total of 7 years, for the second one with the 12 panels I just added only 4 years.

I will read the article you posted.

No worries about the article, it was warranty related. The piece from Yale is probably more relevant but it has nothing to do with PV either.
http://www.econ.yale.edu/seminars/apmicro/am09/ishii-091001.pdf

edit... You might enjoy this thesis from 2011 - it's a small SMA string/Enphase side-by-side: http://libres.uncg.edu/ir/asu/f/Lee, David_2011_Thesis.pdf

I'm not against micros in any way and hope that I didn't come across that way. I just bristle a bit when one of our resident salesfolk starts throwing mud at the old-skool equipment. :lol:

I hope your system serves you well for a very long time!

Yet...another...edit...

Beware - inverter guts!

Swapping circuit boards in an Outback FX inverter - two parts:
http://www.youtube.com/watch?v=cb2PpRs9Bss
http://www.youtube.com/watch?v=fVwpHCsoKJA

Ditto for a Midnite Classic 150 charge controler:
http://www.youtube.com/watch?v=mkzYfSy75No

 

[AndyH]

Looks like even today NREL still hasn't gotten the memo that inverters last "32 years"/"you never need to replace them".

From January 2013 http://www.nrel.gov/docs/fy13osti/57251.pdf" onclick="window.open(this.href);return false;

Warranties typically run 10 and 25 years with 10 years being the current industry standard. On larger units, extended warranties up to 20 years are possible. Given that the expected life of the PV panels is 25–30 years, an operator can expect to replace a string inverter at least one time during the life of the PV system.

The inverters, which come standard with a 10-year warranty (extended warranties available), would be expected to last 10–15 years.

From March 2011 http://www.nrel.gov/docs/fy11osti/49237.pdf" onclick="window.open(this.href);return false;

The inverters, which come standard with a 5- or 10-year warranty (extended warranties available), would be expected to last 10–15 years.

From September 2010 http://www.nrel.gov/docs/fy10osti/48853.pdf" onclick="window.open(this.href);return false;

The inverters, which come standard with a 5- or 10-year warranty (extended warranties available), would be expected to last 10–15 years.

Yes of course - when one restates warranty terms they get, oddly enough, phrases that look like warranty terms.

Did you listen to Perez yet?

You can stop selling now - I've already bought my inverter. :lol:

 

[QueenBee]

I just bristle a bit when one of our resident salesfolk starts throwing mud at the old-skool equipment....You can stop selling now - I've already bought my inverter.

When you can't properly communicate your point the first thing you need to do is insult the other person.

I am talking about Real-World Service Life In The Field In Actual Service while you are talking about MTBF. Apples and oranges....

Again, your inability to properly communicate your point of view baffles me. It's almost like you can't talk about service life without bringing up data about MTBF.

The European study is one. The information from Richard Perez is another. The final link was to Robin Gudgel. That's three sources of vendor-neutral information on actual field experience.

I finally listened to the audio. It's hard for me to understand how his experience of using a sin wave inverter for only 6 years means that he has enough real world experience. But regardless after listening to it I've answered my own question about what he meant by 32 years. Again he was referring to 32 years MTBF which has no relevancy in this conversation about service life. He does state you can buy an inverter and it will last forever. If you believe that I've got a bridge for you.

How can you possibly suggest real world useful life info doesn't somehow relate to real world useful life?.....I still think the paper based on European field studies is 'proof enough' that inverters live beyond their 10 year warranty since it shows inverters doing just that.

That is if you ignore the fact that all the stats you quoted from the those studies was failures per year/etc which is just a MTBF. They did mention that after 10 years the inverters were functioning. Note they said after 10 years not 20 years.

I'm not knowledgeable enough about this topic to teach you what the difference between MTBF is relative to service life but I've provided a couple links about it and I'm sure you can find more information using the internet. Real world studies that are not long enough to determine the service life of equipment are not going to provide any valid data on service life. They can only provide MTBF data. It is very hard for you to communicate with others when you do not understand the difference between MTBF and service life.

SMA advertises a 100,000 hour MTBF and greater than 20 year service life - they're projecting a longer actual service life than their warranty. Yes, it's marketing info

Again you can't help but bring up MTBF.... You did finally find a source to support the idea of 20 year life spans. Good job!!! You deserve a cookie. Note that it is only saying they are designed for that so it isn't data proving this design. What would you say it means if a device has 11.4 year MTBF but claims to be designed for a 20 year service life?

It sure is funny that the one inverter brand that you've found sort of advertising a 20 year life span is also one of the ones that has an optional 20 year warranty. http://www.sma-america.com/en_US/products/grid-tied-inverters/sunny-boy/sunny-boy-2000hf-us-2500hf-us-3000hf-us.html" onclick="window.open(this.href);return false;

Because that's the industry standard for central inverters - that's all they 'need' to provide to entice sales in their niche. They're not competing with microinverters so the warranty rate in that market is irrelevant.

BTW: Did you notice how many inverter manufacturers already have or are coming out with microinverters?

RE: The small scale central vs microinverter study. I'm surprised how big of a difference they found. I question if that much of a difference could be had in real world systems of significant scale though. Although I saw 12% more production than was predicted on my first year.

On average, the microinverter system was able to
produce over 21% more power than the central inverter system at any given minute when
POA irradiation was above 650 W/m2. Within the same irradiance bins and with 3.2%
shading on one panel of each array (0.8% total array shading), the microinverters produced
an additional 97 W or 26.3% of power greater than the shaded central array. During this time,
the shaded central inverter lost an average 52 W or 12.3% in comparison to the unshaded
central inverter array.

 

[AndyH]

Queenbee - I came here for exactly one reason - to counter the suggestion that in order to get a long warranty one had to buy microinverters. It's not true, but I think you already knew that.

You can object to it, you can pick nits, you can twist things into knots but that doesn't change the facts.

And no - I don't consider being a salesperson dishonorable in the least. I know there are dishonorable salesfolk, though. I did not paint you with that brush.

Yes, I realize that you've keyed onto the misuse of MTBF. Mea culpa. And it's the culpa of many people in many industries as well. One thing you might have missed from the European paper is that the failure numbers were from actual field work and are not modeled estimates - and they were reported ALSO as an MTBF. No, it's not a perfect slam-dunk paper - but it meets my intended point - that central inverters do not drop dead at 10 years and 1 day of life. The point remains for that tangent that a 30 year life is achievable in off-grid service - it's been done on 1980s era equipment and it's more achievable for modern inverters - and not - they are not outliers. As I've tried in vain to explain to you, off-grid service is different than on-grid. The number one on-grid inverter killer is the grid itself. Next is heat.

And I'll simply leave it at that. In 30 years I'll hunt you down and we can compare notes. I'll bet I'll be using the same Outback VFX3524 that's sitting on the office floor at that time - because it'll be kept in the living quarters at a temp of about 75°F year round, it has about twice the capacity I'll need on a regular basis, and it won't be subjected to the dirty grid. Those factors add up to a very easy life for an electronic device. If not, I'll give you $50.

Why do you think that Enphase had to switch from electrolytic capacitors in their initial inverters in order to jump from a 15 year to a 25 year warranty? It's all about the heat.

Take care.

PS - Mr. Perez and the other principals at HomePower have been off-grid for close to 40 years, and the magazine has been off-grid from its beginning - more than 25 years. As he states in the talk, his home (which includes the Homepower publishing office) is a test bed where he's been doing side-by-side testing since before sinewave inverters arrived on the market. Most of the other writers are off grid as well. They run the equipment, they test the equipment, they meet with inverter manufacturers, and they have a firm clue about how they work and which ones don't. That's why I recommended you talk with him - I didn't expect you to believe a thing I said. That's also why I recommended connecting with Robin Gudgel at Midnite. Again - he's been in the inverter industry from the beginning as well and knows full well how long an Outback will operate in the field because he helped design it. Again - contact him. You can also catch bOB on the Midnite forum as well as Nrn Arizona Wind and Sun's forum - he's a principal at Midnite as well and will help you out. When it comes to reliable information, I'll take the word of these folks over ANY salesperson any day of the week. It's not personal, it's just that they don't have a dog in the fight, and they've been in the industry longer than 99% of installers and salespeople have been in solar. And longer than some solar salesfolk have been on the planet.

I'll leave you with that, and with these:
http://www.solartown.com/blog/2011/03/enphase-microinverter-warranty-claim-causes-heartburn/
http://www.sullivansolarpower.com/about/solar-power-blog/daniel-sullivan/dangers-of-micro-inverters

 

[QueenBee]

Really you are the only one interested in off-grid. The OP and the rest of us are all on grid so the service life of off-grid inverters is really not relevant. It's also not relevant when you are contrasting with on-grid only microinverters.

What exactly were you implying when you decided to call me a sales person? I assumed it was being used as an insult because clearly I have no profit motivation in this conversation.

Queenbee - I came here for exactly one reason - to counter the suggestion that in order to get a long warranty one had to buy microinverters. It's not true, but I think you already knew that.

Clearly I already knew that (Although I have not seen any 25 year warranties on central inverters) which was why that was EXACTLY what I said "Last I heard many central inverters still have less than 10 year warranties but the standard was 10 years and some are selling extended warranties doubling to 20." If that was the only reason you came here why did virtually every message you post bring up MTBF?? All you had to do was post a link to the SMA brochure like I did and point out that they sell a 20 year warranty.

The good news about the central inverter is that the modern high-frequency units are expected to last 30 years on average. There's good engineering behind that MTBF. I've yet to see anything, or hear anything from either inverter manufacturers or those that have been watching the industry for more than 40 years, that suggests micros will outlast central inverters.

Even in you very first post about this topic you can't communicate the difference between MTBF and service life. You have not provided a single piece of supporting evidence that supports your claim that central inverters are expected to last "30 years on average". You have one guy who says they will "last forever" and in that same talk he suggests drilling a hole in the wall and running an extension cord. Based on my experience with your lack of communication abilities I'm going to assume that when you said 30 years you meant off-grid central inverters so while thanks for your input I don't think anyone reading this thread will really care how long off-grid inverters will last since they are on grid....

You can object to it, you can pick nits, you can twist things into knots but that doesn't change the facts.

Object to what? Which facts are you talking about? The fact that you can not communicate about service life without bringing up MTBF, the fact that you have done nothing but bring up studies/stats/etc. which are not relevant and do not prove the points you are trying to make, the fact that NREL in 2006 said it was going to be difficult to break the 15 inverter life span barrier? The fact that NREL continues even to this day to recommend planning/budgeting on replacing inverters over the lifepsan of the PV?

Yes, I realize that you've keyed onto the misuse of MTBF. Mea culpa. And it's the culpa of many people in many industries as well. One thing you might have missed from the European paper is that the failure numbers were from actual field work and are not modeled estimates - and they were reported ALSO as an MTBF. No, it's not a perfect slam-dunk paper - but it meets my intended point - that central inverters do not drop dead at 10 years and 1 day of life. The point remains for that tangent that a 30 year life is achievable in off-grid service

Sorry, there you go again failing to communicate. You own up to misusing MTBF but then immediately misuse it again.... In one paragraph you say that your only point is that central inverters have long warranties too. But now you are trying to prove points that inverters don't die after 10 years and that off grid inverters last for 30 years. First of all a calculated statistical design MTBF or an MTBF from a real world study do not change that they are MTBF. I'll repeat my self. Please read up exactly what an MTBF can tell you and what it can't tell you. If you somehow got it into your head that I think that on day 3651 a central interver dies, you are having more trouble communicating than I thought. I honestly have no idea if non gird tie inverters live 30 years since you've done a horrible job providing evidence to support this claim. I doubt any have lived 30 years since apparently it wasn't that long ago that they died after only weeks....

I'll leave you with that, and with these:
http://www.solartown.com/blog/2011/03/enphase-microinverter-warranty-claim-causes-heartburn/
http://www.sullivansolarpower.com/about/solar-power-blog/daniel-sullivan/dangers-of-micro-inverters

The second link is basically just some guys biased opinion filled with information without sources and doesn't even mention the specific modeles and brands of microinverters he has experience with. His portrayal of what a microinverter replacement is like is an outright lie. "Now, when a micro-inverter fails, it is not an easy fix. Technicians have to get on the roof, rip out the entire array to get to the failed inverter under the array, install the new micro-inverter (God help them) and re-install the system." That's absurd. Best case is you are lifting up one panel, I'd guess on a worst case system you are lifting up 2 panels or if the roof was extra big with 4 rows, 3 panels. "It is disconcerting to see that several of our competitors have gone to offering micro-inverters standard. In about 2 years they will spend the majority of their time doing service calls to failed systems. This will likely result in their demise as businesses and we will then have to service these orphaned systems." That's clearly not been the experience of the Enphase systems that have been installed over the past 5 years. If that was the case then we wouldn't be having this discussion and Enphase would probably have already gone under. As for the installers, it would actually be a big boom for their business. They could have crews and crews of people going out replacing Enphase microinverters, getting paid by Enphase to do so, and have happy customers who like the check they get from the lost production. That is until Enphase goes under

The first link, it's not at all about the reliability of microinverters since the Envoy is not a microinverter but a networked computer. It's obviously not good to hear that they had a bad experience with Enphase technical support but computer technical support can be that way sometimes. I've had two interactions with Enphase technical support about details during my install and both times I was very satisfied with their knowledge of the product.

I'm not going to search for unhappy Outback customers because it adds no value to the discussion.

 

[AndyH]

Off-grid...*** I wasted our time comparing/contrasting different systems only to show that there are very significant differences in systems, operating environments, and in the relative weight of possible error modes. In order to interpret pieces from the NREL and other sources, it's not enough to fixate on '10 years' - it's vital to understand what type of system was analyzed, and whether the developed rule of thumb was developed to be a 'worst case' planning number or to define some other possibility. If we cannot do that, we cannot apply their numbers to our installations.

An example: There is a lot of work happening in the industry to reduce balance of system costs. Many of the quotes - including some you linked - say that a 20 year service life is impossible. Impossible how? Impossible for large-scale commercial service or for a 5KW home system? On, off, or grid-connected with battery backup? Impossible with a high-quality inverter or with an inexpensive inverter?


Let's leave the planner/think-tank mindset for a moment and flip back to being customers: What do WE want from our systems? Once we determine we'll be grid-tied, and then once we determine we'll be using microinverters, we get to figure out how long we want the system to last. If cost is no barrier - let's build for maximum life, we'll do things beyond a 'standard' installation to better protect the system. Maybe we'll make sure the inverters are kept as cool as possible.** Maybe we'll make sure we have a better than average ground system and install extra surge suppressors. Maybe we'll install extra filters between the grid and our sensitive electronics. While a significantly longer than average service life under these conditions might appear to be an outlier on a chart of all grid-tied microinverter systems, it's NOT an outlier on the chart of other similar systems. That's really my point about describing different systems - context is important before we latch-on to a 10 year expectation.

As both Nissan and First Solar have learned the hard way, context is important.

I tried to expand the context, tried to show the 'other side' of a warranty, and tried to suggest that we had the option to NOT accept an 'average' service life. I hope it helped the OP.


---
** It might be useful to remember that in some areas we're not going to get the roof 'cool enough'. Consider Leaf battery life in hot climates for a moment. Maybe, in places in the south, it would be better to split the array and use string inverters. Enphase's 15 or 25 year warranty has a 65°C (149°F) temperature limit. That doesn't mean they'll die if they're hotter than 149, but it does reduce their service life. A shingled roof will get hotter than 150°F in the southern US - before adding a solar panel. The panel shading should cool the roof provided the panels are mounted far enough above the shingles but the panels will become the heat 'source'. The inverter will run at ambient temperature when it's off, but will run hotter when working. Enphase reports that rise to be 5-15°C above ambient.


http://www.energyvanguard.com/blog-...f-Insulated-Rooflines-and-Shingle-Temperature
http://enphase.com/wp-uploads/enpha...er_Reliability_of_Enphase_Micro-inverters.pdf
http://www.azcentral.com/arizonarep...1first-solar-replacing-more-solar-panels.html
http://www.homeenergy.org/show/blog/nav/blog/id/370

*** edit...

It's difficult to have a series of remote conversations without some understanding of the backgrounds of the rest of the folks around the virtual desk. Maybe this analogy will work well enough to help bring the pieces together.

We're sitting in a small airplane, on the end of the runway, ready to depart. We open the manual for the airplane and it says we need a 500 feet ground roll in order to take off. We push the brake, push the throttle to full, release the brakes and start our roll. One hundred, 200, 300, 400..not fast enough...450...still not fast enough...500...600...end of the runway's coming up fast...so are the trees...too late - cut power jump on the brakes skidding sideways lost a wing on the trees gas on fire sorry about that good thing our life insurance is paid...[everything goes dark].

What happened? The numbers in the manual give performance information for standard conditions - a standard temperature, a standard atmospheric pressure, a standard weight, etc. What killed us is that we had full fuel and an extra 100 pounds of luggage behind the seat (we weighed more than standard), it's 80°F outside (warmer than standard), and we're taking off from a runway 2000' above sea level (higher than standard). All of those factors significantly lengthened our required ground roll.

The moral of the story? Blind adherence to specs without 1. understanding how the were derived and 2. applying them to our situation guarantees mission failure.

MTBF is another number derived from standard test conditions and assumptions. The same inverter that'll give us 200 years MTBF at standard conditions might give 250 when kept cooler than standard, but might provide only 150 when in a hotter climate. The same inverter that'll provide 200 years when operated at 75% of capacity might only provide 150 when run at 110% most of the time, and might provide 250 years when run at 50%. An inverter that'll provide 200 years with an average of 3 lightning strikes within 20 miles, might only provide 150 years if there are 6 lightning strikes within 20 on average.

The same inverter that'll provide 200 years in standard conditions might provide 400 years at 50% capacity, below standard temperature, not exposed to lightning surges.

Does that make sense to you?

 

[QueenBee]

I just had a friend come out and do my solar eval for my 2nd phase of solar PV. I'm going to take my 21 panel system and bump it up to around 65 in order to cover 100% of my electricity usage. That sounds like a lot but I've got some shading, am in the pacific northwest, and the ~44 new panels will be on the east roof. Anyway, I asked him the question when doing an ROI on central inverter systems what life span he tells his customers to use. He said conservatively use 10 years but realistically they'll probably last 15 years. This is coming from a guy who does 75% of his business in central inverters.

If that was your goal I think you failed to communicate it. If you would have said yeah most grid tied central inverters will probably last 10 or 15 years but IF you use it off grid, live in a mild climate, install it in your bedroom, keep dust out of the fans, install extra grounding, extra surge protection, tuck it good night, etc. then it can easily last 20 years I would have happily accepted that.

Does that make sense to you?

Yes, exactly why I thought it was comical how many times you brought up MTBF. The context matters but more importantly the MTBF does not tell you the usable service life since it is just the bottom of the bathtub and not the end of life phase.