My 7.5kWh micro Inverter (Build In Progress)

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Comments

  • solar_davesolar_dave Solar Expert Posts: 2,366 ✭✭✭✭
    Re: My 7.5kWh micro Inverter (Build In Progress)
    theo1000 wrote: »
    Thanx for that option solar dave, but those don't look like NEMA-3 boxes. Or am I missing something. I might be forced to buy new disconnects it looks like. Ugh!!
    My disconnect sits on my exterior wall.

    I purchased and installed 2 of these below. Originally planned on using just 1 as combiner but was advised to keep the strings separate.
    http://www.civicsolar.com/product/square-d-d222nrb

    WRT the Bare copper he wants to see it exposed all the way to the panel. I'm not sure why.

    Your right that was a nema 1 but this one is a nema 3
    http://www.ebay.com/itm/SQUARE-D-D221NRB-SAFETY-DISCONNECT-SWITCH-TYPE-3R-NEMA-ENCLOSURE-RAIN-PROOF-/190833639270

    If you can get the proper fuses to satisfy him then go there of course, but for 50ish bucks you can fix the argument.
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
    Re: My 7.5kWh micro Inverter (Build In Progress)

    Update on this systems performance.

    PG&E rated that the maximum power output of the system would be 6.1kWh. Just monitored the system last week at about 1:45 in the afternoon system hit a peak of 6.01kWh.
    Attachment not found.


    Client is happy, since energizing has only paid PG&E $5 per month for NEM agreement.

    March 21- April 20
    overproduction of 218KWH
    April 21 - May 20 overproduction of 330KWH

    This is a good indication that the system at the moment is over performing both PVwatts estimated calculations and enphases own derate calculations.
    The over production numbers are important to compensate for the winter months through winter solstice which will have a very adverse effect to the over production produced through out the year, so over production annualized will offset the lackign winter schedule. There has been more than enough over production that the client has been able to power teh Tesla S for 30kWh per day or more.

    Bad news is PG&E is paying out less for over production on the NEM term agreements at about .043 kWh
  • SkiDoo55SkiDoo55 Solar Expert Posts: 414 ✭✭✭
    Re: My 7.5kWh micro Inverter (Build In Progress)

    Just think what the bill would be without it.
    have to wait until end of True-Up Period (12 months) is up to see actual performance. He will need to be banking kWh's right now to carry thru winter.
    It all helps, still need to conserve!
    What was the CSI Annual forecast of the system. Need to compare that to Annual forecast Consumption.
    GT3.8 w/4600W Trina 230W, TX5000 w/5000W ET-250W, XW4024 w/1500W ET-250W, 4 L16, 5500W Gen. (never had to use) Yet!!
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
    Re: My 7.5kWh micro Inverter (Build In Progress)
    SkiDoo55 wrote: »
    Just think what the bill would be without it.
    Prior to the solar, client used the TESLA and charge station keeping the kWh's at roughly 33kWh. The utility bill prior to solar was roughly averaging $460~$520 per month and was easily approaching tier 4 structured pricing. Which makes this system at the grid parity thresh hold, and perfect for those getting off of fossil fuel, the ROI is accelerated and there are discrepancies not accounted for with electric cars such as stop and go traffic. Where fossil fuel engines require more load and idle at stop and go than fossil fuel generators, while electric cars when at stop don't require idle.

    SkiDoo55 wrote: »
    have to wait until end of True-Up Period (12 months) is up to see actual performance. He will need to be banking kWh's right now to carry thru winter.
    It all helps, still need to conserve!
    What was the CSI Annual forecast of the system. Need to compare that to Annual forecast Consumption.

    CSI=CEC (California Energy Commission)= Utility (sun edison,PG&E, etc...) Its all the same umbrella, PG&E takes the CSI calculation which actually is an incorrect value. Micro inverters are a technology very misunderstood, because while the CEC/CSI only account for the MPPT range at maximum harvest efficiency, the moment sun light makes contact with the panel Micro inverter will output power as low as 1 watt. The other misconception is the M215 actually will max out at 226watts, but isn't recognized by the CEC/CSI because @226watts the MPPT harvest efficiency falls to 93%. That's why it was called the M215, not the M226. Also 215 watts is with incoming voltage at exactly 120V per pole, while 226 watts is achieved if the incoming voltage is anything higher than 124 volts per pole.

    The problems accounted for are in summer use of the HVAC system. However now solar panels cover the roof so theoretically it was accounted that the attic would be cooler, hence making the living space cooler and the HVAC system running less.

    Winter condition is just lack of sun, and in the bay area there is a lot of over cast.

    The client also remodeled under california's title 24, so the wall insulation, floor insulation attic insulation, were improved, so technically the annualized bills from last years calculations should be reduced by 15% across the board. By winter the system should break the energy bill even, with the ROI by year 6.
  • SkiDoo55SkiDoo55 Solar Expert Posts: 414 ✭✭✭
    Re: My 7.5kWh micro Inverter (Build In Progress)

    My Central inverters start producing output with about 15 DC Watts input. That is with 20 panels feeding it.
    CSI PG&E etc use it at the 77% value and stay conservative for when they were giving rebates which I got on system out in in 2010. That system has produced 26+ MWh's since install. Both of my central inverter systems are producing 81-82 % yield vs the 77% in PV watts's which is imbedded in the CSI Calculator. It does give you some numbers to use for estimating.

    sounds like they are trying to save in many ways and that is all good.
    GT3.8 w/4600W Trina 230W, TX5000 w/5000W ET-250W, XW4024 w/1500W ET-250W, 4 L16, 5500W Gen. (never had to use) Yet!!
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
    Re: My 7.5kWh micro Inverter (Build In Progress)
    SkiDoo55 wrote: »
    My Central inverters start producing output with about 15 DC Watts input. That is with 20 panels feeding it.
    CSI PG&E etc use it at the 77% value and stay conservative for when they were giving rebates which I got on system out in in 2010. That system has produced 26+ MWh's since install. Both of my central inverter systems are producing 81-82 % yield vs the 77% in PV watts's which is imbedded in the CSI Calculator. It does give you some numbers to use for estimating.

    sounds like they are trying to save in many ways and that is all good.

    Enphase is actually working with CEC and NREL to change the PVwatts calculations for micro inverters because of the way power is harvested and inverted. DC voltage has to be up converted for 240V, while string inverters down convert voltage to meet 240V (for residential). The 2 methods are infact completely different. Due to the independence of each micro inverter micro inverter systems surpass PVwatts derate of 86.5%, in some instances some micro inverter systems are exceeding power as high as 88% which I have measured on a few days of monitoring.

    CSI/PG&E actually derated using PVwatts @85% according to micro inverter harvesting. The rule actually changed on the derate in November of 2013. String/central inverters are still recommended to be derated at 77% and no more than 80% if the conductors are engineered to decrease the voltage drop on DC side.

    String inverters are some what becoming a technology of the past, as there are to many limitations in string configuration for down converting voltage. Also sine wave AC power tends to have not only less voltage drop but is better regulated under higher temperatures. Alot of power loss in the string/central systems comes from DC side and high temperatures. AC power is a win, win when it comes to delivering power in smaller gauge conductors. Saves system cost loads of money, and no more need for NEC rules on DC disconnects. Overall micro is far superior on any scale.
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: My 7.5kWh micro Inverter (Build In Progress)
    Also sine wave AC power tends to have not only less voltage drop but is better regulated under higher temperatures.

    Can you elaborate? Is this about AC vs DC at any given voltage, or is this about higher voltage vs lower voltage?

    Of course, the higher the voltage the higher the voltage drop (in absolute terms), but I would think higher voltages would tend to reduce the amount of power that is lost.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
    Re: My 7.5kWh micro Inverter (Build In Progress)
    vtmaps wrote: »
    Of course, the higher the voltage the higher the voltage drop (in absolute terms), but I would think higher voltages would tend to reduce the amount of power that is lost.

    --vtMaps

    That's kind of what I was getting at, but not quite how the design came to the final conclusion of going micro, also take into account panel ISC. The original design for the 7.5kWh system for south and west bound systems was originally going to use a power one aurora dual MPPT, calculating the footages and combining at combiner, to inverter would of required 6AWG to the inverter to prevent any voltage loss to the system.

    Canadian solar no longer offers the 255M or the 260M but those are high ISC/IMP panels. With micro we were able to fine tune and get less panels in the order where as for the string configuration we would of had to add more panels, because between South and West Bound we have an odd number of panels.

    With micro inverter it is all a straight shot with 12AWG trunk cable, stepped up to 10AWG all the way to the load center. Not combining all the panels in the DC string configuration saved loads of mioney on panels, conductors, efficiency, disconnects, etc
  • SkiDoo55SkiDoo55 Solar Expert Posts: 414 ✭✭✭
    Re: My 7.5kWh micro Inverter (Build In Progress)

    My strings run @ 25 ft to string inverters bumped to #8 wire less than 1% drop! and I will never have to lift a panel to change an inverter.
    Not arguing but for my installs that is what I chose and would do the same again. If different install may go micro? Very happy with what I have, is producing more tha consumed, have about -3.5 MWh in my Net Account as of today. Have had multiple days of 100+ so A/C has been working.
    in your situation with all of the azimuth and roof slopes to contend with micro was probable a good decision.
    GT3.8 w/4600W Trina 230W, TX5000 w/5000W ET-250W, XW4024 w/1500W ET-250W, 4 L16, 5500W Gen. (never had to use) Yet!!
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
    Re: My 7.5kWh micro Inverter (Build In Progress)
    SkiDoo55 wrote: »
    in your situation with all of the azimuth and roof slopes to contend with micro was probable a good decision.

    Micro is the best decision. If you haven't built it you wouldn't know.
    Statistically, now this is FACT based on 4 years of micro inverter data. Micro inverter systems outperform string/central systems by 10%~14%.
    System costs are lower by an average of .13~.18 per watt depending on the scale (size of the system).
    Its an accelerated return on investment.

    Doesn't matter what slope, what plain, angle of azimuth, horizon, etc, micro wins hands down.

    Just for your viewing pleasure here is truth in R&D the grey line indicates "estimated power output" I purposely set that estimated spec at 78% PVwatts derate. The blue graph is the actual power of micro inverter system. LOOK at the number in p[ercentages anything over 100% exceeds the PVwatts 78% derate.

    Attachment not found.
  • fun2drivefun2drive Registered Users Posts: 6
    Re: My 7.5kWh micro Inverter (Build In Progress)

    Solar-Powered
    Very nice work by the way.
    I have a few questions regarding your comment regarding micro-inverters vs sting inverters. What about power conditioners sitting under the panels like the micro-inverters do? Have you installed any systems using power conditioners?
    The reason for my question is that micro-inverters sit in the environment while a regular inverter is typically in a mechanical room. I am planning a 10KW system and my biggest concern is that the heat where I live is significant so is the rain, humidity (Florida panhandle). I am concerned about reliability of Enphase since it sits in that environment (so do the power conditioners for that matter). Central inverters have been around for a long while but the micro's doing accelerated life testing have not. Accelerated life testing helps but it is not the same as the real world. I used to design electrical systems and we did this type of testing.

    My system will sit on a 35 ft tile roof making repair not an easy thing if a micro-inverter or power conditioner fails.

    Your installation pictures should be the poster child for how to do an installation. I am a EE by trade so I appreciate craftsmanship when I see it.

    Research is one thing but field use is another thus the reason for the questions and getting feedback from someone doing this day in and day out.
    My caution about reliability might be unfounded thus the request for some feedback.
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
    Re: My 7.5kWh micro Inverter (Build In Progress)
    fun2drive wrote: »
    Solar-Powered
    Very nice work by the way.
    I have a few questions regarding your comment regarding micro-inverters vs sting inverters. What about power conditioners sitting under the panels like the micro-inverters do? Have you installed any systems using power conditioners?

    Power conditioners are some what not worth the added value, to the power output. It just elevates the price per watt, which reduces the ROI. Also power conditioner is mechanical, it is more likely to have a point of failure more so than the micro inverter and its insulated circuitry.
    fun2drive wrote: »
    The reason for my question is that micro-inverters sit in the environment while a regular inverter is typically in a mechanical room. I am planning a 10KW system and my biggest concern is that the heat where I live is significant so is the rain, humidity (Florida panhandle). I am concerned about reliability of Enphase since it sits in that environment (so do the power conditioners for that matter). Central inverters have been around for a long while but the micro's doing accelerated life testing have not. Accelerated life testing helps but it is not the same as the real world. I used to design electrical systems and we did this type of testing.

    Micro inverters are protected by the panels shade. When I worked for another solar firm that I cannot discuss due to disclosure contract, there was testing done using a pyronometer. It was found that if the inverter is not exposed to direct sunlight/radiation the condition is typically 8.5* AVG cooler, rather than exposure to direct sunlight and its ambient condition.
    fun2drive wrote: »
    My system will sit on a 35 ft tile roof making repair not an easy thing if a micro-inverter or power conditioner fails.

    Your installation pictures should be the poster child for how to do an installation. I am a EE by trade so I appreciate craftsmanship when I see it.

    Research is one thing but field use is another thus the reason for the questions and getting feedback from someone doing this day in and day out.
    My caution about reliability might be unfounded thus the request for some feedback.

    I was a subcontracted R&D field technician, and construction manager for the EE's at 3 of the largest solar contracting firms in california. For 7 years I did nothing more but collect data, and improve patents. Some of which were my own patent idea's, but when you sign your life away under disclosure agreements, although being the proprietor of the idea, the firm owns the rights to the idea/patent pending. Reason why I no longer work for the big solar guys. I'm not an EE, but the greatest advantage not going to college to be an EE was atleast working side by side with the EE's, they were the book work, I was the hands on hard data. I have 4 patents in the process for production to improve harvest efficiency and reduce system sizing. I appreciate the compliment.
  • fun2drivefun2drive Registered Users Posts: 6
    Re: My 7.5kWh micro Inverter (Build In Progress)

    I appreciate the feedback on the micro inverter vs power conditioners and conventional inverter.
    I would prefer to use the micro inverter to reduce the space that is allocated for my mechanical room. What I read as being a failure point was the capacitors used by the company that sells the majority of the units. I think it was failing because it was unable to handle higher temperatures. I would think by now that this capacitor has been upgraded.

    You install micro inverters and I also thought not sitting in direct sunlight but under a panel would certainly help keep the temperature lower than direct exposure. Most of the systems I have been involved with when exposed to this type of environment were potted. That was done to act as a heat sink and also hermetically seal the unit. Expensive and heavy but typically reliable.

    New to solar PV and hope to learn enough that when my house is getting ready to be roofed in Jan or Feb I will have a suitable system ordered and ready for installation.

    I look forward to future installations by yourself and other members as this gives me a first hand insight as to how good installations should be done.
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
    Re: My 7.5kWh micro Inverter (Build In Progress)
    fun2drive wrote: »
    I appreciate the feedback on the micro inverter vs power conditioners and conventional inverter.
    I would prefer to use the micro inverter to reduce the space that is allocated for my mechanical room. What I read as being a failure point was the capacitors used by the company that sells the majority of the units. I think it was failing because it was unable to handle higher temperatures. I would think by now that this capacitor has been upgraded.

    Up conversion does not require the capacitance that string inverters require, its actually a very intricate series of MOSFETS, and thin film capacitors, which do not have voltage leakage in the conditions that most string inverters do. String inverters are electrolytic and are more susceptible and prone to capacitor leakage if the string inverter MPPT algorithm isn't matched so the string inverter is actually less efficient, as it bleeds more power in early morning and late evenings. Micro inverter in the up conversion is able to harvest more because of this factor.

    The problem with first and second gen enphase inverters that gave it a bad rap, was that the MPPT algorithms for lower wattage panels wouldn't deliver enough amperage. So the thin film capacitors would retain more heat until there could be a surge of 240V supplied power, there were also more significant voltage and efficiency losses because to constantly achieve 240V the algorithm was more likely to fall out of sync, mostly why the first gen M190 was in the realm of 94% efficiency, then the M210 was in the realm of 94.5% efficiency. Micro inverters are finally to a point of understanding that in order to maintain a constant algorithm and to stay within the 240V thresh hold the panel should essentially not have a name plate less than 240Wp.

    Hypothetically at 215 PTC a panel can yield 36V, but what would it take to get 240V a factor of 6.5 "meaning amps". A 215 watt (PTC condition) panel could provide 240V AC supplied power at .1 amp and that has been noted to be more efficient than down converting higher voltage to a lower 240V AC voltage at higher amps. Greater efficiency in smaller wiring with micro. This is what made the M190, and the M210 problematic, was that voltage would drop below 240V to maintain a .1 amp. Micro inverters start harvesting at 1 watt, where as most string inverters are in standby until 5 watts or greater are achieved by surface area's that are 5 times the meter sq of 1 independent panel. So a micro inverter although not within an MPPT algorithm yet, will make 1 watt of power which is 240V @ .0048amps, that is simply the greatest harvesting. This makes micro amazing that it harvests on the miliamp, rather than string inverters harvesting at a minimum of an amp.

    The way the technology has improved 1 in 200 Micro inverters should fail in or around year 5, that's much better than the 1 in 50 that would fail by year 2 from the first and second generation inverters.
  • CA SolarCA Solar Registered Users Posts: 2
    Re: My 7.5kWh micro Inverter (Build In Progress)

    Thanks for sharing this installation. This installation has two issues that cause me particular concern.

    One is the lack of flashing. An L foot on top of asphalt shingles with no flashing is placing the entire waterproofing reliability on sealant. A high quality sealant should be used in the lag holes, but a metal flashing is still required. Is your method acceptable with the roofing manufacturer?
    IBC 2012 1507.2.9 Flashings: Flashing for asphalt shingles shall comply with this section. Flashing shall be applied in accordance with this section and the asphalt shingle manufacturer's printed instructions.

    Second is the routing of the flexible conduit between arrays. It does not look like it is secured per NEC 300.11(A). Additionally it would look much cleaner if not run over the edge of the roof. Solardocks are a great way to transition between arrays if there is attic space. Perhaps that was the issue here. I would have liked to have seen a cleaner, more secured routing of the AC line.

    Since you have touted your project management experience, I hope you will seriously reconsider your weatherproofing methods. A small leak will not only eat up any profits you made on the job, but it degrades the entire PV industry. Flash properly.
  • sdoldsdold Registered Users Posts: 20 ✭✭
    Re: My 7.5kWh micro Inverter (Build In Progress)

    If you're looking for ways to improve your installs, it might be nice to start replacing these:

    Attachment not found.

    With these (UL 467 compliant):

    Attachment not found.

    Also thanks for sharing your install pics.
  • CA SolarCA Solar Registered Users Posts: 2
    Re: My 7.5kWh micro Inverter (Build In Progress)
    sdold wrote: »
    If you're looking for ways to improve your installs, it might be nice to start replacing these:

    Attachment not found.

    With these (UL 467 compliant):

    Attachment not found.

    Also thanks for sharing your install pics.

    That was going to be my 3rd issue with this install. I also wanted to say that all the critique is in the spirit of mastering our craft (which sometimes comes at the expense of mistakes). Keep sharing the lessons!
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
    Re: My 7.5kWh micro Inverter (Build In Progress)
    sdold wrote: »
    If you're looking for ways to improve your installs, it might be nice to start replacing these:

    Attachment not found.

    With these (UL 467 compliant):

    Attachment not found.

    Also thanks for sharing your install pics.


    OK if you like to spend more on stainless steel braid ground bonds that's your prerogative. Most racking now is compliant in (I.G) Inegrated Grounding. Which means if you want to spend more on redundancy..... Be my guest :D
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: My 7.5kWh micro Inverter (Build In Progress)

    Grounding is not needed at all for operation. It is a matter of code compliance. As such it may indeed be necessary to spend money on the braided connection straps in order to pass inspection.

    Do not give too much heed to what someone else has 'got away with'; what matters is what is safe and passes where you are.
  • sdoldsdold Registered Users Posts: 20 ✭✭
    Re: My 7.5kWh micro Inverter (Build In Progress)

    Well, if HX_Guy's system passes inspection, I will agree with you.
  • sdoldsdold Registered Users Posts: 20 ✭✭
    Re: My 7.5kWh micro Inverter (Build In Progress)
    Most racking now is compliant in (I.G) Inegrated Grounding. Which means if you want to spend more on redundancy..... Be my guest :D
    Two straps would be redundancy, but one good one that will last is safety in lightning and electrical faults. If by IG you are referring to Ironridge, they also use a similar braided strap IIRC. To me small things like this matter and show professionalism.
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
    Re: My 7.5kWh micro Inverter (Build In Progress)
    Grounding is not needed at all for operation. It is a matter of code compliance. As such it may indeed be necessary to spend money on the braided connection straps in order to pass inspection.

    Do not give too much heed to what someone else has 'got away with'; what matters is what is safe and passes where you are.

    This is also not what I could "get away with".

    According to code compliance micro inverters don't require the stainless steel bonding strap its just a waste of money. All micro inverter systems non IG require a continuous ground bond minimum 8AWG solid copper to 6awg GEC solid copper so the stainless steel splice bond is not required.

    For (I.G) systems the 6awg solid ground GEC is no longer required as the neutral and ground combined (using a 10awg thhn for the branch circuit) to service main is considered GEC and the EGC to AC side branch circuits.

    As long as the micro inverters makes contact with the spliced racking/railing the racking is bonded and considered part of a "continuous bonded, and grounded system".

    All string inverters when following code compliance on DC systems require the splice bonding as the DC conductor wires exceed 3' in length (from panel pigtails/combiner/inverter according to code.

    Micro inverters reduce costs for this reason. Some jurisdictions have confusion between how the code was written between 2008 and 2014, so just to keep inspectors happy I implement a splice bond on some not all of the systems and do not need to meet the UL compliance for micro inverter systems, because micro inverter systems do not call out a UL compliant splice bond for those systems.

    Its no different than the signage some jurisdictions request that I add on conduit/conductors/boxes etc, when infact when you read the code specifically the signs that are required are for DC side only, which means that the only sign truly required for micro inverters is a sign at the service main panel indicating that there is a photo voltaic generator on premises that back feeds into the main panel. City of Dublin is the first jurisdiction that I have actually dealt with out of 12 jurisdictions that is enforcing signage on everything as if it is a DC generating facility.

    Also to Sdold that has confusion of professionalism. That's the difference from me as a professional selling a system at grid parity for under $.20kWh production, and the "expensive professional" that sells solar at $.28kWh production, and above the grid parity thresh hold before fed tax credit. Big difference in the cost of professionalism. At the end of the year as a professional I definitely sell more systems, that pass code, and clients that keep passing me down to new clients as word of mouth. My costs out the door for even the LG300 B3 and G3 systems sell for under $3.67 per watt. No body beats my pricing on professionalism.
  • sdoldsdold Registered Users Posts: 20 ✭✭
    Re: My 7.5kWh micro Inverter (Build In Progress)

    The inverter bonding is different than the rack bonding. The rack bonding is to protect people and equipment from injury if a failure puts power on the rack, and to give a better path to ground for voltages induced during a lightning strike, instead of relying on the paths through the microinverters. The IG feature of the Enphase microinverter replaces the ground bonding of the microinverter chassis, not the rack bonding and grounding. Before IG, it had to be the wire you described or it could have been a WEEB washer between the inverter and rack. Wiley makes them for all of the popular racks (example WEEB-PMC for the Prosolar racks).

    My understanding of the NEC (690.43(c)) is the racking itself either has to be "identified" (evaluated by a testing agency like UL, etc.) as an "equipment Grounding Conductor" or must have "identified" bonding jumpers. Hence the requirement for the jumpers.
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
    Re: My 7.5kWh micro Inverter (Build In Progress)
    sdold wrote: »
    The inverter bonding is different than the rack bonding. The rack bonding is to protect people and equipment from injury if a failure puts power on the rack, and to give a better path to ground for voltages induced during a lightning strike, instead of relying on the paths through the microinverters. The IG feature of the Enphase microinverter replaces the ground bonding of the microinverter chassis, not the rack bonding and grounding. Before IG, it had to be the wire you described or it could have been a WEEB washer between the inverter and rack. Wiley makes them for all of the popular racks (example WEEB-PMC for the Prosolar racks).

    My understanding of the NEC (690.43(c)) is the racking itself either has to be "identified" (evaluated by a testing agency like UL, etc.) as an "equipment Grounding Conductor" or must have "identified" bonding jumpers. Hence the requirement for the jumpers.

    This is exactly my point.

    Where is a point of safety fault distribution going to go (if) I.G micro inverter systems do not require 6AWG GEC?

    In the case of non IG it is identified, and the splice/ground bonding exceeds bonding for series panels in string inverter installation. Where as some manufacturers like yingli only identify 12awg bare copper continous to 6awg GEC.

    Even in the case of iron ridge racking it is identified that the stainless steel splice bonds are to be used for non IG equipment such as string inverter DC systems.

    Its all arbitrary.

    The language for NEC has only gotten worse not better and is full of hypocacracy when you can get a UL/etl listed component such as a micro inverter that has defined that the 6awg GEC is not needed for installation. Enphase clearly identifies this issue. Hense no need for the splice bonds.

    I'm not here to argue. What I am saying is that the NFPA and engineers that write the language for NEC have taken it above and beyond to points that make (I.G) a hypocritical and arbitrary language in the solar industry. I've been in the business almost 9 years now and the language just gets more tricky and harder to identify when in relation to safety ground faults.
  • sdoldsdold Registered Users Posts: 20 ✭✭
    Re: My 7.5kWh micro Inverter (Build In Progress)
    Where is a point of safety fault distribution going to go (if) I.G micro inverter systems do not require 6AWG GEC?

    The three ways I know of are 1) A separate EGC running from inverter to inverter, like you described, 2) a WEEB washer etc. bonding the inverter to the rail, or 3) in the case you mentioned of the Enphase IG inverter, an EGC included within the trunk cable. But the racking is bonded and grounded separately from the inverters.
    Even in the case of iron ridge racking it is identified that the stainless steel splice bonds are to be used for non IG equipment such as string inverter DC systems.
    According to Ironridge, at least one rail per panel row needs bonding jumpers at the joints and rail grounding for any installation, no matter what type of inverter or inverter EGC style is installed.
  • bt999bt999 Registered Users Posts: 2
    I appreciate the comments on improvements in Enphase inverters. I was involved in a Habitat for Humanity project 4 years ago or so where we installed panels with Enphase micro inverters. At that time there were pretty high infant mortality rates on those units. According to the company's promotional white paper, those units used electrolytic capacitors yet you mention thin film capacitors (which ABB and Solar Bridge cites as reasons that their systems are superior to Enphase.). Have Enphase changed over to thin film?

    I intend to build a 15 x 300W panel array (perhaps using LG Neon 300W) on my house (to support a planned Tesla purchase, BTW) and was put off by the Enphase problems. leaning toward ABB but found that ABB micro inverters for higher output panels limit string size to 12 panels, apparently due to theirAC capacity being limited to 15A. The 17-panel limit of Enphase would solve that problem if their reliability issues have indeed been solved as you suggest above, and I would infer from your use of them on a big project that they have been.
  • bt999bt999 Registered Users Posts: 2
    On page 2 the pictures of racks with micro inverters, J-boxes and conduits in place seem to be showing an array of 17 micro inverters connected in a line. I wonder why you did not center-feed the array in order to minimize line voltage drop? If I read the Enphase Technical Brief on line voltage drop correctly, center-feeding a circuit into two sub-arrays would reduce voltage drop by about 70% or about 1.5V. Am I missing something?
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
    bt999 wrote: »

    I intend to build a 15 x 300W panel array (perhaps using LG Neon 300W) on my house (to support a planned Tesla purchase, BTW) and was put off by the Enphase problems. leaning toward ABB but found that ABB micro inverters for higher output panels limit string size to 12 panels, apparently due to theirAC capacity being limited to 15A. The 17-panel limit of Enphase would solve that problem if their reliability issues have indeed been solved as you suggest above, and I would infer from your use of them on a big project that they have been.

    The difference between the Enphase and the ABB that you need to pay attention to is the maximum power point tracking range. The Enphase micro inverter system is slightly more efficient per cycle/amp RMS than the ABB using panels under 310watts, now if you were to get a PV panel that was 310 watts up to 350watts then the ABB would be better suited. If you have to absolutely maximize a system for harvest and you need that 1 extra panel per branch string, its a no brainer, more inverters per branch string to maximize harvest.

    Enphase M215 60hz- 17 microinverters/panel total (not recommended to use greater than 60 cell panels over 270watt stc name plate max)
    Enphase M250 60hz- 16 micro inverters/panel total (not recommended to use greater than 60 cell panels over 310watt stc name plate max)

    ABB .25-I-OUTD 60hz- 15micro inverters/panel total ( 300watt stc)
    ABB .30-I-OUTD 60hz-12micro inverters/panel total ( 350watt stc)

    bt999 wrote: »
    On page 2 the pictures of racks with micro inverters, J-boxes and conduits in place seem to be showing an array of 17 micro inverters connected in a line. I wonder why you did not center-feed the array in order to minimize line voltage drop? If I read the Enphase Technical Brief on line voltage drop correctly, center-feeding a circuit into two sub-arrays would reduce voltage drop by about 70% or about 1.5V. Am I missing something?

    By design the entire system maintains efficiency, and exceeds estimates. Your numbers of 70%, and 1.5V are way off, at .61% there is a 1.5V drop after 60ft and that only accounts for the furthest inverter at end run NOT EVERY INVERTER IN THE TRUNK CABLE, even that calculation is hypothetical, because each inverter in the trunk cable has the potential for voltage rise, feeding voltage into the trunk cable at 2%. If it was a single generator (or string inverter) 60ft out before an additional branch interconnection into a branch circuit then the voltage drop of .61% at 1.5V is more accurately descriptive, but when you have a generator every 3.5' of cable its hypothetical, because the voltage is maintained in a chain, rather than travelling a long distance..
    It's more of a question to ask enphase why they just don't make a proprietary cable of 10AWG instead of 12AWG, makes more sense doesn't it? The voltage drop in trunk cable does not hold true, when each micro inverter is feeding power 3.5' between each micro inverter. So between voltage rise and voltage drop that is a difference (if) there is more voltage rise to the system when it was metered at main service.

    On PG.8 of the enphase installation manual
     Account for additional lengths of cable when calculating total voltage rise. Refer to the following documents to maintain AC voltage rise at less than 2%:
    o Applications of the Engage Coupler
    o Circuit Calculations for the M250 Microinverter (also available for M215)
    o Calculating AC Line Voltage Drop for M250 Microinverters with Engage Cables (also available for M215)


    In most circumstances when I first test voltage at the main panel (prior to installing solar system), I will typically get 115~125V per pole or 230~250V.
    When inverters are installed at a home location the installation occurs somewhere in between the grid infrastructure, this will cause voltage rise to the grid infrastructure. After solar system is installed at a location the voltage concentration becomes greater and the voltage metered will be 120~130V per pole or 240~260V. This is the same concept applied using trunk cable, because if voltage is rising at main panel due to concentrating grid voltage potential, that same effect occurs at the trunk cable because of the concentration of distributed generated power delivered through the trunk cable, within fractions of 60ft, not 60ft of distance.

    If the system main was under 118V per pole then the configuration would of changed in the trunk cable, however when the system main is metered at 124.5V per pole before the solar array is built then more than likely the potential for voltage rise in the system would be more predominant, as that is 249V for single phase. This means measured at the main, voltage rise at 2% is greater than the voltage drop that could occur at the trunk cable at .61%

    You may want to look into the the engineering concepts of the new enphase 60hz C250 277V/480 WYE, its advertised as enphases flagship commercial grade micro inverter capable of handling 350watts, and to utilize the the entire trunk per branch before entering into a combiner/distribution box, for ease of use and installation.
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