The Argument for Enphase Micro Converters

RacerChrisRacerChris Registered Users Posts: 15
Hi all,

Just joined the Forum and signed a Contract to install a Solar PV System at our home in Fremont, Ca. Excited about starting our on Power Generating Plant :-) and doing our part to fight dependence on oil! :D

Being a Structural Engineer, I find the whole process quite interesting and learning alot thanks to this and other sites.

At this time, our PV system will consist of 27 SunPower 230W Panels with Enphase M210 micro-inverters. Although, I signed a contract for this install, I have about a week to make the final Inverter decision. Curious what those in-the-know thinks about whether the $2000 premium for Micro Inverters is a good decison for our site and situation.

Our location has a large 4:12 sloped roof that points southwest and gets good sun most of the day with only minor shading issues. The installer took sun measurements and has guaranteed in writing at least 8808 kwH annual production with micro-inverters and 8402 with a SunPower 5000 inverter. In additon, they warrant the components for 15 years.

According to my installer the advantages of micro-inverters includes:
- Per module tracking, making the system more efficient
- Maximizes system output, Optimizes MPPT
- Mean Life Expectancy of 120-330 years.
- Best monitoring system on the market included
- Easier to expand solar in the future
- Less power loss if any panels are shaded
- If micro inverter fails, only one panel goes down
- Inverters run cooler
- Better low-light production
- Easy return.replacement policy
- Competitive in ost per watt-hour

They also list the disadvantages as:
- Newer Product: Spring 2008
- Cost of monitoring $2/year per panel after 2 years
- Many potential points of failure
- More expensive per watt (not necessarily per watt-hour)

I've done my research and believe that most of these are correct, except the mean life expectancy which seems to be based on projected expectations based roughly on empirical results, not actual since micro-inverters are still in their infancy.

The real question, in my mind, is that if my site is not affected much by shading, will I see "real-world" increase in output with micro-inverters? Although there may be some truth to the longer life expectancy vs traditional inverters, in our situation, this does not hold as much weight since we have a 15 year warranty with either inverter and do not expect to keep this home that long.

Curious about what input you all would have on the PV system we are about to install. Three of the four quotes we received included SunPower 225 or 230W panels, except Sungevity which included BP Solar 175W panels. Only one of the four suggested considering the micro-inverters and according to them , 90% of their customer chose them over standard inverters. One of the installers provided a quote with micor-inverters when asked, but did not recommend them because they did not think we would see much increase in production. However, this installer did not take sun measurements like the one that is recommending them....

From my research SunPower panels are known to be the most efficient, but also the most costly. I like the idea that SunPower is in San Jose which suggests we are buying US Made panels, but suspect this may not be true. Anyways, since our roof space is limited, SunPower panels seems to be way to go to get the most production.

Whatever input anyone would have would be appreciated. Thanks all! :cool:
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Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: The Argument for Enphase Micro Converters

    Welcome to the forum.

    If you do a search of the forum for "Enphase" you'll see they've been discussed in depth, ad infinitum, ad naseum. :p Including doing things with/to them that is not recommended procedure.

    The main advantage of the microinverter is when you do not have single, clear exposure for the panels. They are good with multiple roof facets or for dealing with shading issues. They are simpler to install, as most of the wiring is "standard" AC connections which contractors tend to be familiar with already.

    Otherwise they're just more money, and the warranted lifetime has yet to be proven.
  • solarixsolarix Solar Expert Posts: 713 ✭✭
    Re: The Argument for Enphase Micro Converters

    Ditto on the enphase, I question their reliability. Sunpower is a good, high efficiency PV module, but you pay extra for it. There are many other choices that are of equal quality but lower efficiency that are much more cost effective - you will just need a few more of them. Try Canadian Solar, Trina, Solon, Scheuten, Conergy, ... I question getting only 8800 kWH from a 6.2kW system. Your area may be different, but the rule of thumb here is 1600 kWH per kW or 9920kWH for you. Check out SolarEdge for an alternative distributed inverter system.
  • BB.BB. Super Moderators, Administrators Posts: 33,327 admin
    Re: The Argument for Enphase Micro Converters

    If this is the German SunPower company (it sounds like it is)--What does the installer say about the positive ground requirement of SunPower panels for optimum power production (SunPower panels build up a charge on them if they are negative grounded. Positive grounding bleeds this charge off). The white paper that used to be out there a few years ago has been disappeared from the Internet--So, I cannot confirm that a single panel negatively grounded has this same problem of reduced power output over weeks/months as is known for negatively ground series strings of panels.

    Neat--Just found a PDF document from somebody else that quickly summarizes the SunPower positive ground requirement and what is happening. Unfortunately, it does not give the differences in losses for a single panel negatively grounded (I am not sure what Enphase does for panel grounding--negative, positive, floating, or configurable grounding). Major central inverters are available with configurable grounding.

    There are new non-isolated GT inverters--I wonder how the SunPower panels work with those types of GT inverters and what the panel ground referenced voltage looks like.

    Regarding the issues of central vs micro inverters... Personally, I would sill prefer a central inverter to replace a single inverter after 10-15 years (I hope) vs 15-20 years and replacing a one or a couple micro inverters at a time.

    But as you say, there is no real long term reliability studies of the micro inverters to know that they will or will not last XX years.

    I can understand people choosing micro inverters over a central inverter--It may take a decade or two to understand which was the better choice.

    Personally, I am cheap and I don't really like the requirement to power a local hub and Internet conectivity to know what my panels are doing. And paying $2 per year per inverter to see if everything is working correctly. The additional costs (initial and ongoing) would be something like 10% of the value of my yearly electrical bill (depending on lots of issues). My home, no A/C, I generate around $40-$50 per month (using flat rate billing--not TOU) and would pay $40 per month for monitoring and another $342 for the EMU.

    With solar, it is a game of numbers and it is very easy to add small costs here and there and swamp other decisions (i.e., pay more for SunPower panels for their ~3-6% advantage, then add a 10% hit on costs due to monitoring choices).

    I have BP 4175B panels now... However, I had BP 4175 or 4175A panels that failed after about 5 years. BP did supply new "B" production panels under warranty and paid some of my change out costs (I had to pay $500 for 20 panel change out on a 2nd story roof). So there is the good and bad experience for me (it did take 3+ months to get the new panels).

    One question I have of you--What is your plans for staying in the home?

    Personally, I do not believe solar panels add that much to the value of a home... They have a definite life (20-40 years) and can cause leakage problems in your roof.

    Many home buyers are not really thrilled to have a solar array on the roof--and for those buyers, the array may have close to zero, or even negative, value for them.

    I do not look at solar arrays as being and "investment". I believe that the typical conservation measures (insulation, windows, energy star appliances, more attic insulation, other generic home improvements) have a better return on investment.

    For me--Solar GT was a hedge against the state of California piling taxes/costs on our electrical power. Conservation has kept me below the ~300 kWH per month base line power cheap power (~$0.12 per kWH)... So, with solar, I am probably not saving any money.

    If, for example, I add A/C or an electric vehicle--My >1,000 kWH per month power costs are in the $0.40 to $0.60 per kWH--then Solar can be an actual money saver.

    But--there is always the possibility that the PUC will change the Net Metering rules (again) and wipe out some of the cost advantages and and the tax advantages of self generated electric power for EV cars.

    For California, they force people onto the E-6 Tariff plan... Which is a fairly complex set of Time of Use, Tiering, and seasonal matrix of charges.
    TIME PERIODS: Times of the year and times of the day are defined as follows:
    Summer (service from May 1 through October 31):
    Peak: 1:00 p.m. to 7:00 p.m. Monday through Friday
    Partial-Peak: 10:00 a.m. to 1:00 p.m.
    AND 7:00 p.m. to 9:00 p.m. Monday through Friday
    Plus 5:00 p.m. to 8:00 p.m. Saturday and Sunday
    Off-Peak: All other times including Holidays.
    Winter (service from November 1 through April 30):
    Partial-Peak: 5:00 p.m. to 8:00 p.m. Monday through Friday
    Off-Peak: All other times including Holidays.
    Holidays: “Holidays” for the purposes of this rate schedule are New Year’s
    Day, President’s Day, Memorial Day, Independence Day, Labor
    Day, Veterans Day, Thanksgiving Day, and Christmas Day. The
    dates will be those on which the holidays are legally observed.
    DAYLIGHT SAVING TIME ADJUSTMENT: The time periods shown above will
    begin and end one hour later for the period between the second Sunday in March
    and the first Sunday in April, and for the period between the last Sunday in
    October and the first Sunday in November.

    A few years ago, for people that were trying to get their feet wet and install a 1/2 sized or 1/4 sized solar system (1/2 or 1/4 of their monthly kWH usage) were finding out that their utility bill went up because of the wide TOU high rate tiers (elevated pricing can go from 10am to 9pm--not much sun at 9pm).

    So, if you cannot shift your heavy power usage to non-peak times--the TOU plan may hit you quite hard if your array is not large enough to offset most of your power usage.

    The issues with E-6 power would cause me to second guess installing GT solar in Northern California. I have the E-7 plan and it is much easier to teach family when to not use a lot of power (noon to 6pm Mon-Fri during "summer"). But E-7, I don't think, is available to new solar power customers.

    You probably have a smart meter now--I wonder if PG&E or your installer can download the hourly data and figure out your power costs on E-6 TOU with a spread sheet/website. And then overlay your solar production and see how the math works out.

    Remember, Solar GT makes sense (or not) based on a series of PUC tariffs and various laws/rulings. All of those can change when the state decides they want more money or the utilities go bankrupt (a second time).

    Personally, I would only install GT solar if I have done virtually everything possible to reduce power usage (including upgrading HVAC system, insulation, etc.).

    Lastly, remember that GT solar (without backup batteries and the correct inverter) does not operate during power failures. You will will be sitting around in the dark and/or using a genset for backup power.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SolarLurkerSolarLurker Solar Expert Posts: 122 ✭✭
    Re: The Argument for Enphase Micro Converters

    2000 dollars could buy you just shy of 4 more panels. I doubt the increase in production would beat have 4 more panels. Sunpower is a well built panel, I doubt you will see much variation in panels if shading is not a concern.
  • FrxddyFrxddy Solar Expert Posts: 113 ✭✭✭✭
    Re: The Argument for Enphase Micro Converters

    I am about to decide whether or not to install a PV system. I am leaning toward Enphase for two reasons. One is the idea that an inverter can go down & my system does not go down. Two is: Quiet. My pet peeve in life is things that hum. I honestly could not live in a house with inverters humming. I have been in two PV homes & perhaps I am sensitive to it, but the hum bothers me. With the Enphase there is no noise. Between them being outside the home and each one being so small, they are silent. I love that idea.

    I'm pretty sure you do no need to pay the $2 a month fee. The information is at your fingertips in your home on the monitor box. It is not as graphical as the $2 a month on line version, but all the information is there.
  • BB.BB. Super Moderators, Administrators Posts: 33,327 admin
    Re: The Argument for Enphase Micro Converters

    Some centeral inverters have cooling fans, and some do not... My Xantrex GT inverter does not use any fans and seems dead quiet--but I understand your concerns about background noise.

    From what I have read here, Enphase does not make all data available from the local EMU--because there are lots of people that would like access it. From what I understand/remember, Enphase actually removed some data sets from the EMU's a couple years ago with a software up grade.

    In any case--it is a personal choice and either can probably be justified. Long term, we really do not yet know how well either central or distributed inverters will last.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RacerChrisRacerChris Registered Users Posts: 15
    Re: The Argument for Enphase Micro Converters
    BB. wrote: »
    If this is the German SunPower company (it sounds like it is)--What does the installer say about the positive ground requirement of SunPower panels for optimum power production (SunPower panels build up a charge on them if they are negative grounded. Positive grounding bleeds this charge off). The white paper that used to be out there a few years ago has been disappeared from the Internet--So, I cannot confirm that a single panel negatively grounded has this same problem of reduced power output over weeks/months as is known for negatively ground series strings of panels.

    Neat--Just found a PDF document from somebody else that quickly summarizes the SunPower positive ground requirement and what is happening. Unfortunately, it does not give the differences in losses for a single panel negatively grounded (I am not sure what Enphase does for panel grounding--negative, positive, floating, or configurable grounding). Major central inverters are available with configurable grounding.

    There are new non-isolated GT inverters--I wonder how the SunPower panels work with those types of GT inverters and what the panel ground referenced voltage looks like.

    Regarding the issues of central vs micro inverters... Personally, I would sill prefer a central inverter to replace a single inverter after 10-15 years (I hope) vs 15-20 years and replacing a one or a couple micro inverters at a time.

    But as you say, there is no real long term reliability studies of the micro inverters to know that they will or will not last XX years.

    I can understand people choosing micro inverters over a central inverter--It may take a decade or two to understand which was the better choice.

    Personally, I am cheap and I don't really like the requirement to power a local hub and Internet conectivity to know what my panels are doing. And paying $2 per year per inverter to see if everything is working correctly. The additional costs (initial and ongoing) would be something like 10% of the value of my yearly electrical bill (depending on lots of issues). My home, no A/C, I generate around $40-$50 per month (using flat rate billing--not TOU) and would pay $40 per month for monitoring and another $342 for the EMU.

    With solar, it is a game of numbers and it is very easy to add small costs here and there and swamp other decisions (i.e., pay more for SunPower panels for their ~3-6% advantage, then add a 10% hit on costs due to monitoring choices).

    I have BP 4175B panels now... However, I had BP 4175 or 4175A panels that failed after about 5 years. BP did supply new "B" production panels under warranty and paid some of my change out costs (I had to pay $500 for 20 panel change out on a 2nd story roof). So there is the good and bad experience for me (it did take 3+ months to get the new panels).

    One question I have of you--What is your plans for staying in the home?

    Personally, I do not believe solar panels add that much to the value of a home... They have a definite life (20-40 years) and can cause leakage problems in your roof.

    Many home buyers are not really thrilled to have a solar array on the roof--and for those buyers, the array may have close to zero, or even negative, value for them.

    I do not look at solar arrays as being and "investment". I believe that the typical conservation measures (insulation, windows, energy star appliances, more attic insulation, other generic home improvements) have a better return on investment.

    For me--Solar GT was a hedge against the state of California piling taxes/costs on our electrical power. Conservation has kept me below the ~300 kWH per month base line power cheap power (~$0.12 per kWH)... So, with solar, I am probably not saving any money.

    If, for example, I add A/C or an electric vehicle--My >1,000 kWH per month power costs are in the $0.40 to $0.60 per kWH--then Solar can be an actual money saver.

    But--there is always the possibility that the PUC will change the Net Metering rules (again) and wipe out some of the cost advantages and and the tax advantages of self generated electric power for EV cars.

    For California, they force people onto the E-6 Tariff plan... Which is a fairly complex set of Time of Use, Tiering, and seasonal matrix of charges.



    A few years ago, for people that were trying to get their feet wet and install a 1/2 sized or 1/4 sized solar system (1/2 or 1/4 of their monthly kWH usage) were finding out that their utility bill went up because of the wide TOU high rate tiers (elevated pricing can go from 10am to 9pm--not much sun at 9pm).

    So, if you cannot shift your heavy power usage to non-peak times--the TOU plan may hit you quite hard if your array is not large enough to offset most of your power usage.

    The issues with E-6 power would cause me to second guess installing GT solar in Northern California. I have the E-7 plan and it is much easier to teach family when to not use a lot of power (noon to 6pm Mon-Fri during "summer"). But E-7, I don't think, is available to new solar power customers.

    You probably have a smart meter now--I wonder if PG&E or your installer can download the hourly data and figure out your power costs on E-6 TOU with a spread sheet/website. And then overlay your solar production and see how the math works out.

    Remember, Solar GT makes sense (or not) based on a series of PUC tariffs and various laws/rulings. All of those can change when the state decides they want more money or the utilities go bankrupt (a second time).

    Personally, I would only install GT solar if I have done virtually everything possible to reduce power usage (including upgrading HVAC system, insulation, etc.).

    Lastly, remember that GT solar (without backup batteries and the correct inverter) does not operate during power failures. You will will be sitting around in the dark and/or using a genset for backup power.

    -Bill

    Thanks Bill for the reply... I'm learning alot!

    Yes, California no longer offers the E7 plan; only TOU is E6, I believe. Didn't realize all the details though, Thanks, but not good news :grr

    Also not sure what specifically you mean by "Solar GT" is that different from Solar PV?
  • RacerChrisRacerChris Registered Users Posts: 15
    Re: The Argument for Enphase Micro Converters

    Thanks everyone for all your input. A couple of followup questions:

    - My Installer has recommended a SunPower SPM5000m Inverter. Is this sufficent for my 6.21kW system? Spec says “Recommended Array Input Power (DC @ STC) is 5300 W".

    - I have heard from someone at the Forum (private message) that "the SPR7000m Inverter will outperform Enphase by 10-20% in DC Watts". This a shocker and I have not found anything that supports this statement.
  • BB.BB. Super Moderators, Administrators Posts: 33,327 admin
    Re: The Argument for Enphase Micro Converters

    "Solar GT" = Solar Grid Tied Inverter (no battery bank).

    The 5000 sounds a bit small for a 6.21kW array--It will work fine (assuming panels are configure correctly)--But on sunny/cool days, the inverter will probably be hitting its (~5kW) power limits in the middle of the day and you will loose out on some energy harvest.

    The next size up may be a better fit. Check the price and see if 10-20% (SWAG) more solar collection is worth the XX% increase in system cost to you.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RacerChrisRacerChris Registered Users Posts: 15
    Re: The Argument for Enphase Micro Converters
    BB. wrote: »
    "Solar GT" = Solar Grid Tied Inverter (no battery bank).

    The 5000 sounds a bit small for a 6.21kW array--It will work fine (assuming panels are configure correctly)--But on sunny/cool days, the inverter will probably be hitting its (~5kW) power limits in the middle of the day and you will loose out on some energy harvest.

    The next size up may be a better fit. Check the price and see if 10-20% (SWAG) more solar collection is worth the XX% increase in system cost to you.

    -Bill

    Thanks Bill. Mine is definitely a Solar GT :cool:

    I did get a quote for using 238W E19 Panels in lieu of the 230W E18 and it's less than the cost of adding enphase, but again with a 6000, not a 7000 Inverter. This 'brand new" panels have a bit higher efficiency 19.1% compared to the 18.1 of the E18 series panels. That may be the best way to go with the extra money since our site is not subjected to much shade... Unfortuantely, i don't have room for more panels :cry:

    Do you agree that SunPower inverters will be 10-20% more efficient than enphase? That statement came from a "Solar R&D Engineer" that posts on this forum.

    Oh and BTW, what does SWAG mean?
  • BB.BB. Super Moderators, Administrators Posts: 33,327 admin
    Re: The Argument for Enphase Micro Converters

    I cannot say which will be more efficient--very few of us here have the tools or the site to do such measurements. Or access to every brand/model of inverter.

    SWAG--Scientific Wild A$$ Guess :blush:

    A 6kW inverter on a 6.2kW array should be fine.

    I am not in the solar biz... So I am really trying to help you understand and ask your installer(s) the right questions. Sometimes--people here will pick up just enough knowledge to be dangerous and figure out that the quoter/installer does not really know what they are talking about regarding solar RE.

    Not that you will have this problem (installer issues)--but an example of what can go wrong if you trust "the system" blindly:

    Panel Fire Question

    -Bill

    PS: As far as I know--there is no "SunPower" inverter--They just relabel inverters from various other manufacturers. Hopefully, they pick good vendors (just like you would hope too).
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • solarixsolarix Solar Expert Posts: 713 ✭✭
    Re: The Argument for Enphase Micro Converters

    The SunPower inverters I've seen are relabeled SMA Sunnyboys.
  • RacerChrisRacerChris Registered Users Posts: 15
    Re: The Argument for Enphase Micro Converters

    Thanks Bill for your candidness. Yes, I am learning alot and trying to circumvent incorrect advice/input. That was a scary thread!

    With all this good input, I think I've made my decision. There appears to be a uniform consensus that micro-inverters will improve performance when there is a shade issue, but that does not apply to my install.

    As for the longevity of the enphase inverters, although it has not withstood the test of time yet, for me this will not make much difference either since 1) I have a 15 year warranty - so if the standard inverter goes down after 10 years, it will be replaced and 2) if I lose performance, there is a performance guarantee - so a bad panel that affects a string will be addressed right away.

    So I am seriously considering going with the 238W E19 panels which will DEFINITELY increase the performance of the system!

    Having said all this, the enphase monitoring system is so cool, it's hard to resist the techno wiz part. Although it will cost only 27 x $2 = $54 per year, I keep thinking that this cost is at the mercy of enphase and will likely go up like everything else. Besides there is something fundamental wrong with paying for monitoring for the life of the system...

    I will see how my installer will respond to the questions I've asked above, then make my final decision.... THANKS TO ALL OF YOU FOR THE INPUT...
    On a completely different subject, what the heck do I do with a pool that we no longer use? Our backyard is landlocked, so I can't take the thing out. Is there any "green" way to use it? Maybe as a part of a heat-exchanger system?
  • BB.BB. Super Moderators, Administrators Posts: 33,327 admin
    Re: The Argument for Enphase Micro Converters

    The old pool may be a tough solution... knock out the concrete, fill 3/4 full with fly ash, put soil on top.

    Making a "pond" out of the pool (heat exchanger for heating/cooling the home)--you still have to treat it like a pond/pool (repair cracks, keep it clear of bugs, keep children out, etc.).

    I cannot think of any easy/cheap way to use it.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • FrxddyFrxddy Solar Expert Posts: 113 ✭✭✭✭
    Re: The Argument for Enphase Micro Converters

    Thanks for the comment that your Xantrex is quiet. I do not know what kind I saw ( heard), but both made a loud hum. Because I witnessed those I imagined they ALL hummed. I guess it's a question to ask before you buy .... "Is it quiet?"
  • jcgee88jcgee88 Solar Expert Posts: 154 ✭✭
    Re: The Argument for Enphase Micro Converters
    RacerChris wrote: »
    Thanks Bill for your candidness. Yes, I am learning alot and trying to circumvent incorrect advice/input. That was a scary thread!

    With all this good input, I think I've made my decision. There appears to be a uniform consensus that micro-inverters will improve performance when there is a shade issue, but that does not apply to my install.

    As for the longevity of the enphase inverters, although it has not withstood the test of time yet, for me this will not make much difference either since 1) I have a 15 year warranty - so if the standard inverter goes down after 10 years, it will be replaced and 2) if I lose performance, there is a performance guarantee - so a bad panel that affects a string will be addressed right away.

    So I am seriously considering going with the 238W E19 panels which will DEFINITELY increase the performance of the system!

    Having said all this, the enphase monitoring system is so cool, it's hard to resist the techno wiz part. Although it will cost only 27 x $2 = $54 per year, I keep thinking that this cost is at the mercy of enphase and will likely go up like everything else. Besides there is something fundamental wrong with paying for monitoring for the life of the system...

    If you have made your final decision, congratulations, having
    "been there done that," I know how difficult that can be.

    As a person who went through a similar decision process last
    year, and as an Enphase owner (apparently, the only person on
    this thread who has real life experience with Enphase) let me
    pass along some of my thoughts and observations.

    1. Central/string inverters

    Regarding 15 year warranty of central/string inverters...I
    understand you can take their base warranty from 10 years to
    15 years, essentially by paying for an extended warranty. If
    this is the case with your prospective central/string inverter,
    then you should realize that the underlying technology is still
    targeted for 10-year useful life. The extended warranty is
    simply a charge, likely buried somewhere in your contractor's
    balance of system costs, that will pay for the replacement.
    You would still bear the cost for the labor re-install and bear
    the inconvenience of your entire array being down.

    Regarding inverter efficiency, almost all the inverters on the
    market run about 95% efficiency at rated load. Central/string
    inverters, having a much higher rated load, take longer to reach
    their optimal range than micro-inverters. There is a site which lists
    the results of actual measurements, and I recall from that that
    below 30% of rated load, central/string inverters take a 10-15%
    hit, in other words, they're down in the mid-80's.

    Regarding SunPower inverters being 10-20% more efficient
    than Enphase, remember that Enphases run 95% efficient already,
    so 10-20% on top of that is only a point or two (it's not possible
    to go past 100%!). In other words, you'd never notice the
    difference, even assuming this unsubstantiated claim is true.

    2. SunPower PV modules

    SunPower manifests its added efficiency in the form of a smaller
    form factor. In other words, they might rate a given panel
    at 235w STC, and it is the functional equivalent of, say, a
    Sharp 235w module. The difference is that the SunPower takes
    less roof space.

    When I looked at SunPower during my decision process last
    summer, the smaller form factor would have enabled me to fit
    in two extra modules. My contractor estimated it would cost me
    $1/watt more for the SunPower. Thus, I would have gained 18%
    more capacity for 18% more cost. I didn't see this as a particularly
    good deal, so I passed on it.

    You haven't mentioned whether you are space constrained,
    is that why you are leaning towards SunPower?

    3. Enphase

    It is true that the major advantage of Enphase comes into
    play when you have shading issues. I would say that a
    very close second is the web-based management/monitoring
    capability.

    While you might not have shading, bear in mind that a PV
    string does not light up "instantaneously." In the morning,
    my western-most modules power up first, and in the
    evening, my eastern most power down last. Each
    sequence of power-up/power-down lasts on the order
    of an hour, and has a very similar performance profile
    to shading. My contractor told me that central/string
    inverters sync to the lowest common denominator
    (which is why shading is bad for them), and if true, then
    in my case I am gaining harvest every day during the
    start-up/shut down phases.

    I do have/did have shading issues, from three sources.
    Because Enphase monitoring enabled to see the actual
    effect on a per panel basis, I was able to take targeted
    remedial action. In other words, I knew exactly how much
    harvest was being lost, so I knew how much I could gain
    by taking action. This is one of the key attributes of the
    monitoring system - you can see historical performance
    down to the panel level. As a result, I removed two
    shading sources that were affecting production every day.
    But, I elected not to remove a tree that was clipping me
    only in winter when production is low anyways.

    I especially like Enphase because it is web-based, I can see
    my performance any time I want to: from a library, from
    Starbucks, from my car, etc. In fact, a week after my array
    was installed I was watching it on my cell phone while I was
    vacationing in Hawaii!

    As to cost... First, if you don't wish to pay Enphase's
    software fee, you can monitor from a PC at home.
    You simply connect the Enphase Envoy module to your
    router. This provides you with an instantaneous view,
    again down to the panel level. What this doesn't do
    is collect historical data. For that, you do pay the fee,
    and the Envoy sends all the realtime date to Enphase,
    where it is permanently stored for your future access.
    So, you are not paying for just the ability to monitor
    your own system with a nice web interface, but also
    for the storing the data itself. As to the software fee,
    my installation included a 5-year subscription. The
    fee rate you have been exposed to is an annually
    renewed rate; you can do a 5-year subscription, as
    well, which saves you 10%, as well as locks in the
    rate.

    --

    You should decide for yourself what is best. I can only
    say that going with Enphase has been a great decision
    for me, one that I take advantage of every single day.

    John
  • RacerChrisRacerChris Registered Users Posts: 15
    Re: The Argument for Enphase Micro Converters
    jcgee88 wrote: »
    If you have made your final decision, congratulations, having
    "been there done that," I know how difficult that can be.

    As a person who went through a similar decision process last
    year, and as an Enphase owner (apparently, the only person on
    this thread who has real life experience with Enphase) let me
    pass along some of my thoughts and observations.

    1. Central/string inverters

    Regarding 15 year warranty of central/string inverters...I
    understand you can take their base warranty from 10 years to
    15 years, essentially by paying for an extended warranty. If
    this is the case with your prospective central/string inverter,
    then you should realize that the underlying technology is still
    targeted for 10-year useful life. The extended warranty is
    simply a charge, likely buried somewhere in your contractor's
    balance of system costs, that will pay for the replacement.
    You would still bear the cost for the labor re-install and bear
    the inconvenience of your entire array being down.

    Regarding inverter efficiency, almost all the inverters on the
    market run about 95% efficiency at rated load. Central/string
    inverters, having a much higher rated load, take longer to reach
    their optimal range than micro-inverters. There is a site which lists
    the results of actual measurements, and I recall from that that
    below 30% of rated load, central/string inverters take a 10-15%
    hit, in other words, they're down in the mid-80's.

    Regarding SunPower inverters being 10-20% more efficient
    than Enphase, remember that Enphases run 95% efficient already,
    so 10-20% on top of that is only a point or two (it's not possible
    to go past 100%!). In other words, you'd never notice the
    difference, even assuming this unsubstantiated claim is true.

    2. SunPower PV modules

    SunPower manifests its added efficiency in the form of a smaller
    form factor. In other words, they might rate a given panel
    at 235w STO, and it is the functional equivalent of, say, a
    Sharp 235w module. The difference is that the SunPower takes
    less roof space.

    When I looked at SunPower during my decsion process last
    summer, the smaller form factor would have enabled me to fit
    in two extra modules. My contractor estimated it would cost me
    $1/watt more for the SunPower. Thus, I would have gained 18%
    more capacity for 18% more cost. I didn't see this as a particularly
    good deal, so I passed on it.

    You haven't mentioned whether you are space constrained,
    is that why you are leaning towards SunPower?

    3. Enphase

    It is true that the major advantage of Enphase comes into
    play when you have shading issues. I would say that a
    very close second is the web-based management/monitoring
    capability.

    While you might not have shading, bear in mind that a PV
    string does not light up "instantaneously." In the morning,
    my western-most modules power up first, and in the
    evening, my eastern most power down last. Each
    sequence of power-up/power-down lasts on the order
    of an hour, and has a very similar performance profile
    to shading. My contractor told me that central/string
    inverters sync to the lowest common denominator
    (which is why shading is bad for them), and if true, then
    in my case I am gaining harvest every day during the
    start-up/shut down phases.

    I do have/did have shading issues, from three sources.
    Because Enphase monitoring enabled to see the actual
    effect on a per panel basis, I was able to take targeted
    remedial action. In other words, I knew exactly how much
    harvest was being lost, so I knew how much I could gain
    by taking action. This is one of the key attributes of the
    monitoring system - you can see historical performance
    down to the panel level. As a result, I removed two
    shading sources that were affecting production every day.
    But, I elected not to remove a tree that was clipping me
    only in winter when production is low anyways.

    I especially like Enphase because it is web-based, I can see
    my performance any time I want to: from a library, from
    Starbucks, from my car, etc. In fact, a week after my array
    was installed I was watching it on my cell phone while I was
    vacationing in Hawaii!

    As to cost... First, if you don't wish to pay Enphase's
    software fee, you can monitor from a PC at home.
    You simply connect the Enphase Envoy module to your
    router. This provides you with an instaneous view,
    again down to the panel level. What this doesn't do
    is collect historical data. For that, you do pay the fee,
    and the Envoy sends all the realtime date to Enphase,
    where it is permanently stored for your future access.
    So, you are not paying for just the ability to monitor
    your own system with a nice web interface, but also
    for the storing the data itself. As to the software fee,
    my installation included a 5-year subscription. The
    fee rate you have been exposed to is an annually
    renewed rate; you can do a 5-year subscription, as
    well, which saves you 10%, as well as locks in the
    rate.

    --

    You should decide for yourself what is best. I can only
    say that going with Enphase has been a great decision
    for me, one that I take advantage of every single day.

    John


    John,

    Thanks so much for the reply, it is extremely helpful to hear from someone that balanced all these issues and made an informed decision.

    I followed the link in your signature and I see that your panels produce at maximum of 199W from your 235W Panels. I am not sure what this means.

    I would think this number is related to the actual output of the panel, but the STC rating of your panels are 211W. I have checked many other Enphase sites and all seem to be limited to 199W.

    Do you the correct intrepretation of what this number actually means?
  • mike95490mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: The Argument for Enphase Micro Converters

    panels seldom produce STC label spec, look for PTC , or deduct 20% from STC, to get real-life output
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • jcgee88jcgee88 Solar Expert Posts: 154 ✭✭
    Re: The Argument for Enphase Micro Converters
    RacerChris wrote: »
    I followed the link in your signature and I see that your panels produce at maximum of 199W from your 235W Panels. I am not sure what this means.

    I would think this number is related to the actual output of the panel, but the STC rating of your panels are 211W. I have checked many other Enphase sites and all seem to be limited to 199W.

    Do you the correct intrepretation of what this number actually means?

    I do know what this means, and this is the only bone I have to
    pick with the specific Enphase model I selected.

    My "M190" model has a max output of 190 watts, regardless of
    what the input panel wattage is. However, Enphase provides
    5% margin beyond the faceplate's 190 watts, so the M190 can
    actually output 199 watts. What you saw is my panels generating
    the most that an M190 can handle.

    I didn't know at the time that they also offer an M210 model.
    Presumably that would max out at 221 watts. If I had known
    that, I might have paid the nominal additional cost to get the
    M210. Some people on this board have opined that paying
    even this little bit extra would not be worthwhile, as it is
    very infrequent for a given panel to reach close to its STC
    rating. Also, my contractor later told me that Enphase only
    recommends (and certified) their M190 for my specific Sharp
    235w panel, so perhaps I wouldn't have the M210 as an
    option anyways. I see that you started with the M210,
    therefore, if you went with Enphase, you would get more
    than my 199w maximum.

    John
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: The Argument for Enphase Micro Converters

    To expand a bit on what John said, this is true of any inverter. No matter how much panel you have it hooked up to the inverter will only supply its rated Watts at most. Some people run slightly larger arrays because of what Mike said; the panels don't actually put out their nameplate rating. So if the panel(s) is (are) slightly over-sized then the inverter can be kept running at its maximum capacity for longer time each day. How cost effective this is depends on several factors.
  • RacerChrisRacerChris Registered Users Posts: 15
    Re: The Argument for Enphase Micro Converters
    To expand a bit on what John said, this is true of any inverter. No matter how much panel you have it hooked up to the inverter will only supply its rated Watts at most. Some people run slightly larger arrays because of what Mike said; the panels don't actually put out their nameplate rating. So if the panel(s) is (are) slightly over-sized then the inverter can be kept running at its maximum capacity for longer time each day. How cost effective this is depends on several factors.

    Cariboo,

    Thanks for the reply and input!

    Exactly my concern. It seems like clearly an undesirable thing to have an inverter that is rated to output less than what panel can provide. John's 235W Sharp panels have a PTC rating of 211, but the enPhase site reports a max panel output of 199 which MAY be limited by the Micro-inverter.

    Am I missing something here or is clearly a limitation of the micro-inverters?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: The Argument for Enphase Micro Converters
    RacerChris wrote: »
    Am I missing something here or is clearly a limitation of the micro-inverters?

    It's a limitation of all inverters, or more accurately a limitation of solar panels.
    Consider a 200 Watt panel. If you connect this to a 200 Watt microinverter you might expect to get 200 Watts * 'X' hours of daylight for, say, 1200 Watt hours per day.
    You won't see that.
    On average the 200 Watt panel will put out 180 Watts and the 'X' hours of daylight becomes 4 or 5 hours of "equivalent good sun" so the actual output becomes 720 to 900 Watt hours.
    Put a 230 Watt panel on the same inverter and it may average 200 Watts over the 4-5 hours for 800 to 1000 Watt hours, but the panel capacity at midday may exceed the inverter's output potential.

    Likewise if you have a 5000 Watt 'central' inverter with 6000 Watts of array or 8000 Watts of array all it will put out is 5000 Watts maximum.

    So do you spend the extra money to 'over-panel' the inverter so that it puts out peak production for more hours of the day? Depends on what you can buy the panels for vs. what you can sell the electric for.
  • RacerChrisRacerChris Registered Users Posts: 15
    Re: The Argument for Enphase Micro Converters
    It's a limitation of all inverters, or more accurately a limitation of solar panels.
    Consider a 200 Watt panel. If you connect this to a 200 Watt microinverter you might expect to get 200 Watts * 'X' hours of daylight for, say, 1200 Watt hours per day.
    You won't see that.
    On average the 200 Watt panel will put out 180 Watts and the 'X' hours of daylight becomes 4 or 5 hours of "equivalent good sun" so the actual output becomes 720 to 900 Watt hours.
    Put a 230 Watt panel on the same inverter and it may average 200 Watts over the 4-5 hours for 800 to 1000 Watt hours, but the panel capacity at midday may exceed the inverter's output potential.

    Likewise if you have a 5000 Watt 'central' inverter with 6000 Watts of array or 8000 Watts of array all it will put out is 5000 Watts maximum.

    So do you spend the extra money to 'over-panel' the inverter so that it puts out peak production for more hours of the day? Depends on what you can buy the panels for vs. what you can sell the electric for.

    Gotcha. This suggests that if the enphase inverters were rated higher, than I would get more net power right? OR if I used a 7000W Inverter on a 6000W panel array, that I would get more net power?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: The Argument for Enphase Micro Converters
    RacerChris wrote: »
    Gotcha. This suggests that if the enphase inverters were rated higher, than I would get more net power right? OR if I used a 7000W Inverter on a 6000W panel array, that I would get more net power?

    A 7 kW inverter would only peak at 6 kW if the array is only 6 kW (sometimes panels do put out more than their nameplate rating, such as under cold conditions or high altitude, but basically not).

    So what it comes down to is having enough panel to provide the maximum output of the inverter. This is unfortunately not a constant as panel output varies with conditions.

    If you have a 5000 Watt inverter with 2000 Watts of panel, you'll only ever see 2000 Watts (saving the above mentioned variable conditions).

    If you have a 5000 Watt inverter with 10,000 Watts of panel, you'll only ever see 5000 Watts - but you'll see it longer through the day as the potential is there from the time the panels reach 50% output on up.

    Nothing wrong with microinverter systems. But they aren't the solution to every problem any more than anything else is. Solar installs are highly site-specific and you need to select the right equipment for your particular circumstances.
  • solarixsolarix Solar Expert Posts: 713 ✭✭
    Re: The Argument for Enphase Micro Converters

    Even though modules are expensive relative to inverters, and it makes sense to have an inverter that can handle the STC rating of the array, a detailed analysis will show that there are very few hours per year that the array will produce more than 90% of its rating. Only at the noon hour, on cool/clear spring and fall days with the sun perpendicular to the array. The cost breakeven point is around 10% more array than inverter. Another factor is that inverters are a little more efficient at less than full power and reliability wise, operating an inverter below its rating should lead to longer life.
  • solar_davesolar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    Re: The Argument for Enphase Micro Converters

    My set up is exactly that way with 12.5 Kw of panels and a pair of 5.2 Kw kw of inverters, I have never seen it clip because when the optimal angle is achieved here the higher temps are already effecting the panel efficiency.
  • jcgee88jcgee88 Solar Expert Posts: 154 ✭✭
    Re: The Argument for Enphase Micro Converters
    RacerChris wrote: »
    Gotcha. This suggests that if the enphase inverters were rated higher, than I would get more net power right? OR if I used a 7000W Inverter on a 6000W panel array, that I would get more net power?

    Chris,

    Just do the math to figure if it is worthwhile. For me, my array has
    1-2 hours a day where the Enphases could be clipping. This is
    effectively the "very top of the bell curve," as you look at my output
    charts. Not every month yields clippable days, for example, from
    late fall to early spring, I never max out. Not every day yields
    clippable hours, for example, when it is cloudy.

    So let's say I get 7 months and 20 days/month of potentially
    clippable output. Let's say the panels would peak at 211 watts
    per panel instead of 199 watts if it weren't for the clipping. This
    works out to:

    1.5 hrs/day * 12 watts clipped/panel * 15 panels = 270 watt hrs/day

    Multiply by 20 days to get 5400 watt hrs/month

    Multiply by 7 months/year to get 37,800 watt hrs/year

    Divide by 1000 to convert to kwh and then multiply by
    $10/kwh to convert to dollars:

    37,800 watt hrs per year / 1000 watts hrs per kwh *
    $.10 per kwh = $3.78 additional per year

    --

    I'm not sure what an M210 costs vs an M190, but let's say it
    is $20. My payback period would then be:

    (15 inverters * $20 per inverter / $3.78 per year) = 79 years

    Since incentives and rebates on the equipment constitute 50%
    of my cost, let's divide the 79 by 2, so we're at 39.5 years.

    Since electricity rates will go up in the future, albeit by an
    unpredicatable amount, and your installation and/or area
    might be superior to mine, let's assume you, Chris, could do
    50% better than me. That would leave you at about 20 years
    payback period...that's a long time!

    --

    Some people might still do this. Why don't you plug in your
    numbers, using either or both types of inverters, and then
    show us what they are and whether it makes sense to
    go with a larger capacity inverter? I suspect you will find that
    this "extra power," while tempting to not let go to waste,
    is on the fringes of the decisions you need to make to
    optimize cost vs harvest.

    John
  • tonystewarttonystewart Solar Expert Posts: 54 ✭✭
    Re: The Argument for Enphase Micro Converters

    M190 inverters support 60 cell panels
    M210 inverters support 72 cell panels

    Sunpower SPR-230-WHT-U is a 72 cell panel therefore you must use the M210.

    There is no issue here, or choice . Either the M210 or a central inverter.
    If using this panel then the M190 cannot be in this discussion.
    It will work fine
  • RacerChrisRacerChris Registered Users Posts: 15
    Re: The Argument for Enphase Micro Converters

    Thanks ALL! This place is great!

    Ah, the law of diminishing returns. I get it now.
  • Solar GuppySolar Guppy Solar Expert Posts: 1,989 ✭✭✭
    Re: The Argument for Enphase Micro Converters

    The OP PM'ed me before this thread was started, I guess he didn't like my suggestion but I'll re-post for everyone

    The OP has 6200 watts of PV, the enphase limit to 199 AC watts or 5400 AC watts maximum. The installer claims of 10-20% more with Enphase is strictly based on comparing a 5000 watt sting inverter to the 5400 watts of Enphase units, not the the Enphase is more efficient

    Since the site has no shading, I recommended the SPR-7000m, which is the 7kw Sunnboy, the very highest performance inverter on the market, also backed by the largest and oldest inverter manufacture of GT equipment

    Yes you could use a 6kw and in cool weather or partly could conditions clip the output to that, in partly cloud conditions, you lose allot of generation, as with the edge of cloud effect going to +20% , it really hurts production on those day

    Also, inverter efficiency goes down as you approach maximum rated output, a 7kw inverter at 6kw output will out perform a 6kw unit by 2-4%, depending on the manufacture of the inverter

    If I was to buy this system, the 7kw Sunnyboy is the best choice, enphase has NO advantages in this proposed system
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