How Much Can I Underspec an Enphase Inverter ?

SageBrush
SageBrush Registered Users Posts: 19 ✭✭
in Grid Tie and Grid Interactive Systems #1
Hi All,

I'm tempted by two components for my soon to be flowing PV, 240 watt stc Sharp panels, and Enphase inverters. The problem (if it is a problem) is that these microinverters are spec'd for max 190 or 215 AC output, and up to 240 DC input depending on inverter.

I live in the SW at 6300 feet, and have heard more than one story of panel output over stc, I assume in part related to our elevation.

So what say the experts ?
Safe ?
Wasteful ?

The panels are going on top of a pole, and will be seasonally pitch corrected in spring and fall to 15 and 50 degrees. Although not wed to these component choices, I like the microinverters for usual reasons, and the module_area/pole is pretty much decided, so I want max module_area efficiency and output. The Sharps are 14.7% efficiency.

Thanks much! Eric
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,637 admin
    #2
    Re: How Much Can I Underspec an Enphase Inverter ?

    Enphase is a little bit different--As I understand, for their UL Listing--they have to provide a a printout of "approved" solar panels (brand/model number) for use with their inverters, so as to meet the listing requirements.

    Enphase Module Compatibility List (PDF)     Live link to Enphase

    The only Sharp 240 Watt panel listing I see is:
    Sharp Corporation    NU-U240F1  M190-72 or D380-72

    From my system (sea level near coast)--My system produces a maximum of 3kW / 3.5kW = 86% of rated array STC wattage (near San Francisco). We are at sea level and I don't clean my panels more than once a year--and I only see 3kW for a short time a couple times a year (on my 5 year old system). No logging--just wondering by the system a few times a day.
    • 240 watts * 0.86 = 206 watts
    Somebody here said that they have seen their 190 module actually output closer to 200 watts peak...

    So--for me, I am not loosing much in the way of power (a few cents worth a year?).

    For you, perhaps a bit more--but you are limited to specific/approved configurations.

    Regarding safety and long life--GT inverters are designed to output their maximum rated current (and have thermal overload protection).

    I would not worry... And you don't have much in the way of options anyway (cannot reconfigure array with 1 module per panel).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,637 admin
    #3
    Re: How Much Can I Underspec an Enphase Inverter ?
    SageBrush wrote: »
    ...and up to 240 DC input depending on inverter.

    By the way, 240 VDC what? I believe these are around 22-54 Vinput range (at least for the 380 watt dual unit--PDF Download).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: How Much Can I Underspec an Enphase Inverter ?

    Bill;

    He means 240 Watts on the DC input, as opposed to the Enphase's 190 Watts AC output.

    Nomenclature! Gotta love it! Especially when we start goofing up the abbreviations. :p

    AC can be Alternating Current or Air Conditioning, for example. Not interchangeable! :p
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  • SageBrush
    SageBrush Registered Users Posts: 19 ✭✭
    #5
    Re: How Much Can I Underspec an Enphase Inverter ?
    BB. wrote: »
    By the way, 240 VDC what?-Bill
    Sorry, I am not sure what question you are asking. The enphase sheet says up to 240 VDC input, max 190 VAC output.

    Thanks for the reminder that Enphase UL listing is linked to specific panels.
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    #6
    Re: How Much Can I Underspec an Enphase Inverter ?

    "The enphase sheet says up to 240 VDC input, max 190 VAC output"

    Can not imagine any rev of spec sheet with that bad of a mis-print.

    There is no spec on max input power, only recommended STC input power necessary to achieve rated AC power output.

    There is a spec on max input voltage.
    56 vdc for 190 watt unit
    62 vdc on 210 watt unit.
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  • SageBrush
    SageBrush Registered Users Posts: 19 ✭✭
    #7
    Re: How Much Can I Underspec an Enphase Inverter ?
    RCinFLA wrote: »
    "The enphase sheet says up to 240 VDC input, max 190 VAC output"

    Can not imagine any rev of spec sheet with that bad of a mis-print.

    There is no spec on max input power, only recommended STC input power necessary to achieve rated AC power output.

    There is a spec on max input voltage.
    56 vdc for 190 watt unit
    62 vdc on 210 watt unit.
    Ah, my mistake. I actually do know the difference between a watt and a volt. Now I understand why people were smirking :roll:

    230 watts in, 190 watts out -- I hope this is right. Does this mean 230 watts coming out of the cells, or into the inverter ? I hope the former, since that is a 18% drop in power. Perhaps a better way to ask this question, is that 18% drop the lions share of my derate fraction, mostly only leaving cabling to the meter to include ?

    And now, hopefully back to a sensible question: what happens if over 230 watts exits the module ? Say 240, or up to 250 watts.
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    #8
    Re: How Much Can I Underspec an Enphase Inverter ?

    250 watts will not hit inverter. The inverter will limit the draw off the panel to the inverters power capability.

    Will just waste some of the PV panel's wattage potential.

    The main reason for the seeming higher then necessary STC power is, with sun heating of panel, STC power is rarely the condition the panel is operating at. Heat will reduce the panels MPP power output. Normal sun heating will result in panels putting out max power about 10% below a 25 deg C panel temp.

    The 95% conversion efficiency on the spec sheet is not always the conversion efficiency.

    I believe somewhere on the Enphase site there is some info on what conditions reduce conversion efficiency. MPPT tracking hunting is one reason. I believe the switching efficiency drops a bit for a panel that has a lower MPP voltage at its rated power.
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  • SageBrush
    SageBrush Registered Users Posts: 19 ✭✭
    #9
    Re: How Much Can I Underspec an Enphase Inverter ?
    RCinFLA wrote: »
    250 watts will not hit inverter. The inverter will limit the draw off the panel to the inverters power capability.
    Thanks!

    Am I wrong in thinking that one of the reasons not to put an inverter below the peak rating of the PV is to avoid damage or premature failure ?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
    Re: How Much Can I Underspec an Enphase Inverter ?
    SageBrush wrote: »
    Ah, my mistake. I actually do know the difference between a watt and a volt. Now I understand why people were smirking :roll:

    230 watts in, 190 watts out -- I hope this is right. Does this mean 230 watts coming out of the cells, or into the inverter ? I hope the former, since that is a 18% drop in power. Perhaps a better way to ask this question, is that 18% drop the lions share of my derate fraction, mostly only leaving cabling to the meter to include ?

    And now, hopefully back to a sensible question: what happens if over 230 watts exits the module ?

    The maximum output of the Enphase is 190 Watts (actually a little more) regardless if the panel on the input side is in excess of this.

    The reason for having higher wattage on the input is because most of the time panels do not put out their rated Wattage. The idea is to find an ideal point that will keep the inverter at 190 Watts output for as long as possible, thus maximizing your return on investment.

    Roughly like this: 240 Watt panel at an average of 80% of its output over 4 hours of "good equivalent sun" = 192 Watts. If you drop to a "190 Watt" panel it will put out an average of 153.6 Watts over the same time. (Theoretical calculations here, not precise.)

    240 Watt output for the day: 768 Watt hours
    192 Watt output for the day: 614.4 Watt hours

    Now if you figure in one hour of "peak output equivalent" you get a "waste" of 48 Watt hours with the first panel and a gain of 38.4 Watt hours with panel two: 652.8 Watt hours per day, still less total harvest than with the larger panel.

    Again: data for comparative and explanatory purposes, not real information, your unit's actual performance will vary due to many mitigating factors (temperature, insolation, et cetera).

    (For some reason I have this sense of déjà vu! :p )
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    #11
    Re: How Much Can I Underspec an Enphase Inverter ?
    SageBrush wrote: »
    Thanks!

    Am I wrong in thinking that one of the reasons not to put an inverter below the peak rating of the PV is to avoid damage or premature failure ?

    It's all about maximizing the kWh's yielded from total $'s spent for panel + inverter.


    Running inverter below its rated power will not damage it. Actually, as it will reduce heat generated within inverter a bit, it may make inverter last longer. Heating from being outside, sandwiched between a hot panel and hot roof, probably dominates temp of inverter.

    A 230 watt panel on a 190 watt Enphase inverter only waste some of the panel's potential at high noon. Inverter will only load the panel to inverter's power capability.
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  • SageBrush
    SageBrush Registered Users Posts: 19 ✭✭
    #12
    Re: How Much Can I Underspec an Enphase Inverter ?

    Understood. Will an inverter have premature aging if it is connected to PV that has excess wattage ?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #13
    Re: How Much Can I Underspec an Enphase Inverter ?
    SageBrush wrote: »
    Understood. Will an inverter have premature aging if it is connected to PV that has excess wattage ?

    No.
    (Warning: the following explanation will make engineers cringe. :p )

    Solar panels are a current source; if there is no load, there is no current. The inverter can't draw any more than it can use. In that sense, they can not receive "excess Wattage" to the input side. The only potential hazard is from too high Voltage, but since Enphase inverters are designed on "one panel, one inverter" there should be no problem here. As RCinFLA pointed out, the maximum input Voltage is well able to handle the Voc from almost any single panel under normal conditions (very low temperature superconducting being one possible exception). If the panel is on Enphase's list of "acceptable" panels, it should work fine.
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  • SageBrush
    SageBrush Registered Users Posts: 19 ✭✭
    #14
    Re: How Much Can I Underspec an Enphase Inverter ?

    lol.

    I found this thread which goes over the same information I was seeking
    http://forum.solar-electric.com/showthread.php?t=8442&highlight=solectria+inverter

    I think it was in that thread that someone mentioned that PWM (?) inverters might suffer damage from a source power greater than spec, but PMMT inverters are ok because they switch to a higher voltage, and the inverter has a lot of voltage breathing room. I don't know how horrible and inaccurate that statement is, but until someone disabuses me of that explanation I'll take it.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #15
    Re: How Much Can I Underspec an Enphase Inverter ?
    SageBrush wrote: »
    lol.

    I found this thread which goes over the same information I was seeking
    http://forum.solar-electric.com/showthread.php?t=8442&highlight=solectria+inverter

    I think it was in that thread that someone mentioned that PWM (?) inverters might suffer damage from a source power greater than spec, but PMMT inverters are ok because they switch to a higher voltage, and the inverter has a lot of voltage breathing room. I don't know how horrible and inaccurate that statement is, but until someone disabuses me of that explanation I'll take it.

    Nomenclature again. :p

    PWM charge controllers "fed" a higher than system charge Voltage just wastes potential power.
    MPPT charge controllers are designed to "down convert" higher Voltages to greater current.
    Even so, they have a maximum input Voltage which should not be exceeded. In some cases they just shut down from "over Voltage". Go too high and, like anything else, they fry. The Outbacks have a 130 Volt (don't quote me; working from foggy memory) shut-down threshold with a maximum 150 Volt input. The Rogue has a much lower 34 Volt max.
    Charge controllers aren't inverters. What confuses people is that Grid Tie inverters also have MPPT function.
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  • drees
    drees Solar Expert Posts: 482 ✭✭✭
    #16
    Re: How Much Can I Underspec an Enphase Inverter ?
    SageBrush wrote: »
    The panels are going on top of a pole, and will be seasonally pitch corrected in spring and fall to 15 and 50 degrees. Although not wed to these component choices, I like the microinverters for usual reasons, and the module_area/pole is pretty much decided, so I want max module_area efficiency and output. The Sharps are 14.7% efficiency.
    What Sharp panel specifically are you looking at - you have a model #? The only 240w Sharp I see that's listed as compatible with Enphase is the NU-U240F1. The module efficiency is pretty standard for PV modules - just about all manufactures have panels at that efficiency rating.

    Looks like everyone else covered the other questions.
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  • SageBrush
    SageBrush Registered Users Posts: 19 ✭✭
    #17
    Re: How Much Can I Underspec an Enphase Inverter ?
    drees wrote: »
    What Sharp panel specifically are you looking at - you have a model #? The only 240w Sharp I see that's listed as compatible with Enphase is the NU-U240F1. The module efficiency is pretty standard for PV modules - just about all manufactures have panels at that efficiency rating.
    Yep, that is the module. I see lots of modules that range from 12 - 14% efficiency. 10% here, 10% there ... I can buy the sharp today for $2.60/watt delivered. If you know of a good brand with similar efficiency for less money, please let me know !

    I'm hoping to do a fair bit better than average doing the following:
    Enphase over standard inverter: 5%
    Keeping the panels clean: 5%
    14.7% rather than 13.5% efficiency: 9%
    Panel tilt changes with the seasons: 5% over optimal fixed tilt
    Bonus for my altitude: 5%

    If I am right, I'll keep my inverters pretty close to full for a lot of the year and produce 2 kwh/watt*year. That would be brilliant
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    #18
    Re: How Much Can I Underspec an Enphase Inverter ?

    The greatest avoidable risk to Enphase is overvoltaging the input.

    Just make sure that Voc of panels at your coldest temperature stays comfortably below the Enphase max voltage rating.
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  • Ralph Day
    Ralph Day Solar Expert Posts: 1,023 ✭✭✭✭
    #19
    Re: How Much Can I Underspec an Enphase Inverter ?

    RC,
    When you say overvoltaging the input do you mean the dc input? My supply wire was undersized for my 10kw installation, the result was inverters dropping out with overvoltage conditions (from the utility supply side). Enphase was able to re-program the inverters through the Envoy module and the problem was rectified. With the drop-outs I was only seeing about 75% of the production I get now. Goes to show, check everything you're paying for, even if someone else is supposed to be doing that for you.

    The acceptable level of line loss for a load service caused un-acceptable high voltage when putting power into the utility.

    Ralph
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #20
    Re: How Much Can I Underspec an Enphase Inverter ?
    Ralph Day wrote: »
    RC,
    When you say overvoltaging the input do you mean the dc input? My supply wire was undersized for my 10kw installation, the result was inverters dropping out with overvoltage conditions (from the utility supply side). Enphase was able to re-program the inverters through the Envoy module and the problem was rectified. With the drop-outs I was only seeing about 75% of the production I get now. Goes to show, check everything you're paying for, even if someone else is supposed to be doing that for you.

    The acceptable level of line loss for a load service caused un-acceptable high voltage when putting power into the utility.

    Ralph

    Yes, that's what he means: it's possible to put too much Voltage on the input of the inverter. I think the limit is 60?

    Your problem was at the other end: line Voltage reading too low, so the Enphase thought there was a power outage and shut down (as it should).

    They get you coming and going, don't they? :p
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,637 admin
    #21
    Re: How Much Can I Underspec an Enphase Inverter ?

    I think, the problem was the wire gauge was too small / too long and he had "reverse voltage drop" or a voltage rise when the 10kW inverters drove the AC line to over ~264 VAC--Causing a high grid voltage fault.

    Can also be an issue if the utility power from the street is already >>240 VAC--then even a few more volts from the GT Inverter(s) is enough to create the high AC line voltage fault.

    -Bill "my guess" B.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #22
    Re: How Much Can I Underspec an Enphase Inverter ?

    Let's go for the universally applicable "AC line Voltage outside specifications = inverter shutdown". :D
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  • Ralph Day
    Ralph Day Solar Expert Posts: 1,023 ✭✭✭✭
    #23
    Re: How Much Can I Underspec an Enphase Inverter ?

    That's right Marc, but on the high side. I had some voltage readings of 267vac plus...definitely out of spec. About 75% of inverters would run, always different mix and match of which, and others would trip out 5 minutes, then try and try again. I checked with Enphase and they said the fix they did to allow higher voltage operation would not have any deleterious effect on the inverters...and they are warranty-ing for 15 years remember.

    Ralph
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,637 admin
    #24
    Re: How Much Can I Underspec an Enphase Inverter ?

    That is pretty hot AC line voltage... Have you checked your household equipment to ensure that you are not running over 264 / 132 VAC anywhere?

    You may be shortening the life of some of your AC appliances/equipment.

    Not sure what the utility will say (are you raising the voltage to other homes in the neighborhood?).

    What is your high/low line voltage normally without the GT array? Is it high enough to complain to the power company?

    I am not sure that I would let them "get away" with upping the high line voltage.

    Others here with more regulatory experience than I can better address those issues (apparent violoations UL/NRTL Listing is not something a company does lightly).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #25
    Re: How Much Can I Underspec an Enphase Inverter ?

    How nice of Enphase to program there inverters on the fly to operate outside of the the UL1741 required range instead of fixing the real issue which is undersized wiring on the branch or possible the mains.

    So now you have a roof full of inverters running over voltage, yah that's a good fix:cool:
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  • Ralph Day
    Ralph Day Solar Expert Posts: 1,023 ✭✭✭✭
    #26
    Re: How Much Can I Underspec an Enphase Inverter ?

    Hmmm.

    Not on a roof, ground mount away from buildings. The voltages were a while ago, but I think it was because of undersized feed lines with no loads. The neighbour's were 240vac under normal conditions (40-50kwhr/day users) when mine were over 250. I'll check them again today when under full sun and see what it is when full pv production is operating (if it's a sunny day).

    The enphase extended range voltage for the 240v units is 206-269vac, wouldn't that be what they are UL listed for? Is the UL1741 regulation an absolute vac value or inverter specific?

    Thanks

    Ralph
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  • dancour
    dancour Registered Users Posts: 9 ✭
    #27
    Re: How Much Can I Underspec an Enphase Inverter ?

    My Enphase Inverters that are connected to 230 Watt Trina panels max out at 199 Watts. See attached pic.

    My 200 watt CSP6panels, using a SunnyBoy inverter, seem to match the Enphase Inverter's output.
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  • SageBrush
    SageBrush Registered Users Posts: 19 ✭✭
    #28
    Re: How Much Can I Underspec an Enphase Inverter ?
    dancour wrote: »
    My Enphase Inverters that are connected to 230 Watt Trina panels max out at 199 Watts. See attached pic.

    My 200 watt CSP6panels, using a SunnyBoy inverter, seem to match the Enphase Inverter's output.
    Hi Dan,

    When you look at your 24 hour power sinusoid graphs, does it appear as though the peak is cut-off because the top is flat ?
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  • dancour
    dancour Registered Users Posts: 9 ✭
    #29
    Re: How Much Can I Underspec an Enphase Inverter ?

    Yes you can see more clearly on this picture, the inverters maxing out.
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  • SageBrush
    SageBrush Registered Users Posts: 19 ✭✭
    #30
    Re: How Much Can I Underspec an Enphase Inverter ?
    dancour wrote: »
    Yes you can see more clearly on this picture, the inverters maxing out.
    Absolutely, thanks. Eyeballing suggests about 100 watts lost at the top, about 4.5% for a couple of hours.


    What fraction of the year does this happen, and how optimized are your collectors ?
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  • dancour
    dancour Registered Users Posts: 9 ✭
    #31
    Re: How Much Can I Underspec an Enphase Inverter ?

    I change the tilt seasonly - see winch pic in other post

    I know that I'm losing power over the noon hour because I'm maxing out the Enphase inverters, but I'm gaining before and after, as well on cloudy days, because of the larger size panels (230 watt).

    The rack could only hold a max of 12 panels.
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