Micro Invertors

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System
System Posts: 2,511 admin
in Solar Skeptics, Hype, & Scams Corner #1
Are these the new wave for residential? I see them selling them on Ebay a lot. Can someone explain how they can plug into the AC outlet and provide elctricity to the house?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #2
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    Re: Micro Invertors

    Search through our archives for SWEA and Enphase... Google search

    Or, in Google type:

    SWEA Enphase site:wind-sun.com

    The SWEA plug into the wall ones will never be legal in the US (cannot meet NEC/Building Code requirements with a standard plug-in-the-wall type setup.

    Enphase is real (and can be legally installed in US/Canada)l--but not cheap.

    Enphase Micro-inverter Grid-Tie Systems

    In the end, small grid tied inverters will never save you money (the parts and installation and inspection costs are higher than the power generated).

    How does does Grid Tie Inverters work? Basically, they are a current mode generator that follows the AC wave form and pumps current back into your house wiring. Devices in the house and even out to the street in other's homes just the voltage and current just like any AC power.

    For all intents and purposes, the utility power grid acts like a giant AC battery. Obviously, from an engineering and business point of view--the actual GT/Grid issues are much more complex.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #3
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    Re: Micro Invertors

    texassolar,
    i think you could have asked this question that you had in this post by you,
    http://forum.solar-electric.com/showthread.php?t=6796
    try not to duplicate as it makes it difficult reading and these 2 threads are close to being a duplication.

    i wouldn't call it a wave, but more of an option for small scale solar gt.
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  • Robin Gudgel
    Robin Gudgel Registered Users, Solar Expert Posts: 58 ✭✭✭✭
    #4
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    Re: Micro Invertors

    I disagree that Micro inverters can't be cost effective. Some, like Enphase are very inexpensive. They just cost a bunch to hook up and monitor. Wait and see what shows up on the market this year! I'm also not sure that you won't be able to legally plug them into the wall. Wait and see. Wouldn't that be cool!
    Bob and I are working on more than just the Classic. We have 10 engineers that are very busy creating some pretty cool stuff.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #5
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    Re: Micro Invertors

    i agree with you robin as i believe them to be cost effective for small scale systems and boB may remember i indicated years ago that i felt there is a place for these small scale gt inverters when we were talking about the ok4you inverters. i don't believe a large scale system should incorporate them as then it is better to have the larger gt inverter(s). i do not like the idea of the inverter at the pv though, but i also see no reason the inverter can't be mounted inside the building with the pv wires fed a longer distance just as with the larger systems even though this could mean more sets of wires running into the house with multiple micro inverters. failures are less likely to occur and easier to detect with them inside imho.
    maybe rather than a micro inverter there should just be a mini inverter, that is, one that accepts around 400-600w as nowadays 2 pvs can exceed 400w and most people can accommodate 2 or 3 pvs easily. parallel a few more mosfets to a present type design or possibly use higher power mosfets in the present design maybe? i know i haven't a clue as to how you guys are addressing the layout of the micro inverter electronically and i'm just thinking out loud, but you get the idea.;)
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #6
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    Re: Micro Invertors

    It is my fault I said "Never"---I should know better and never ever say "never"... There are a lot of smart people working hard to prove every thing I say or predict is wrong. :roll:

    My point is to price out the system for your needs. Cheap inverters and expensive installation and support equipment is still not cheap (at least today). Typically, it is still cheaper per watt to build 1 larger GT inverter than to build 20 smaller ones.

    Regarding a "wall plug-in GT inverter"--I don't see how that can be legal with NEC/Building Codes in the US. Basically with today's wiring standards. You have the 15 amp breaker in the main panel for the branch circuit and if you attach a 15 amp GT system (really 12 amp maximum current or 1,440 watt output)--the branch circuit now has two energy sources and a wall outlet could have as much as 15+12=27amps available in a dead short... Way over the standard of 15 or 20 amps for a 14 awg branch circuit.

    I could raise other concerns (mounting, grounding, lightning protection, etc.)--but that first NEC issue would seem to prevent a "plug-in" GT system (and I could very well be wrong too--always ready to learn).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #7
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    Re: Micro Invertors
    BB. wrote: »
    It is my fault I said "Never"---I should know better and never ever say "never"... There are a lot of smart people working hard to prove every thing I say or predict is wrong. :roll:

    My point is to price out the system for your needs. Cheap inverters and expensive installation and support equipment is still not cheap (at least today). Typically, it is still cheaper per watt to build 1 larger GT inverter than to build 20 smaller ones.

    Regarding a "wall plug-in GT inverter"--I don't see how that can be legal with NEC/Building Codes in the US. Basically with today's wiring standards. You have the 15 amp breaker in the main panel for the branch circuit and if you attach a 15 amp GT system (really 12 amp maximum current or 1,440 watt output)--the branch circuit now has two energy sources and a wall outlet could have as much as 15+12=27amps available in a dead short... Way over the standard of 15 or 20 amps for a 14 awg branch circuit.

    I could raise other concerns (mounting, grounding, lightning protection, etc.)--but that first NEC issue would seem to prevent a "plug-in" GT system (and I could very well be wrong too--always ready to learn).

    -Bill

    don't worry too much about it bill as sometimes we word things wrong and there's always somebody out there that's going to say something about it. windsun said it best awhile back saying, "tough crowd". that's a good thing imo. they tend to jump me too if i say something out of whack in their opinion.

    as to the nec, they overdo things for i don't see extraneous efforts to be made when other outdoor items are pressed onto the home electrical system. do they make you jump the same hoops with flood lights for example? floodlights are about as apt to be "plug in" ready as any micro inverter as only a plug is needed if one overlooks their overstretched policing of solar.
    i'm starting to rant again so i'll shut up.:cry:
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #8
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    Re: Micro Invertors

    Oh--I am not worried... I made a good living proving people wrong myself when they said something could not be done....

    Regarding the NEC restrictions--Generally, when you dig through details and related stuff--the limitations usually makes sense when applying the rules to a broad base of electrical equipment/homes/industry/etc.

    -Bill ;)
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • halfcrazy
    halfcrazy Solar Expert Posts: 720 ✭✭✭
    #9
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    Re: Micro Invertors

    I think the Micro inverter like Enphase have a lot of merit. Take a look at the 15 pages of this thread http://forum.solar-electric.com/showthread.php?t=6394 this is a prime example of where the Micro inverter would shine there is terrible shading issues and the Micro inverter would make the best of each panel where a string inverter gets screwed up when one panel is shaded.
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  • System2
    System2 Posts: 6,290 admin
    #10
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    Re: Micro Invertors

    I am not sure what the quick answer reasons are that a person would want to have a micro inverter installation compared to a more traditional non-microinverter one? Can someone explain what a simple answer would be to this? Thanks
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #11
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    Re: Micro Invertors

    One might question if you have an install that needs micro inverters to deal with shading as to why your even putting PV in a location that has the shading in the first place.

    PV only make sense if you can generate power, mirco inverters won't do a lot for the shaded panels ....
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #12
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    Re: Micro Invertors

    Certainly, small Grid Tied installations (probably less than 2kW of panels) would be interesting. However, there is the cost of monitoring hardware (around $350) is a big hit for a small system. And if you want the "extended" monitoring--there is a website subscription fee every year or two.

    People talk about adding panels one at a time as funds allow--May be an issue if your location requires building permits and utility inspections (do you pull permits and call the utility every time 200 watts are added?).

    And, you can just look at the cost of the GT Inverter hardware on a $$$/Watt basis... Right now, the retail price is around $1 per watt for the GT inverters (Enphase and the more expensive SMA's). The less expensive units, such as the Xantrex GT 4.0 kW, are around $0.64 per watt retail (at least through NAWS)... That is "cheap" for a switching power supply (30 years ago we were looking at wholesale pricing of computer power supplies in the $0.50 per watt range--before overseas/outsourcing was popular).

    People can wave there hands about the life of 20 roof top inverters vs one wall mounted central inverter--and which would be easier to repair if/when they fail. Is it possible that the roof top inverters will last 20+ years while the wall mounted inverter lasts 10+ years... Don't know.

    The other issue is to think about alternate sourcing of hardware. If you need a new central inverter--it is pretty easy. You might end up with some electrical rerouting and/or mounting changes. And if you have monitoring--you may have to purchase mate (it has been 10 years).

    If you have a roof top inverter fail--are the vendors cross supporting the monitoring standards or are you going to have to purchase a new monitoring setup for the one inverter that failed and the other 19 working well? I don't know--there are not many vendors in the small inverter field yet.

    In the end, a product/vendor with good support and history. And watch the $$$/Watt and/or $$$/kWhr pricing of your quotes. You may not want to go for the "cheapest system"--but knowing your costs will help prevent surprises when the bill comes.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • tallgirl
    tallgirl Solar Expert Posts: 413 ✭✭
    #13
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    Re: Micro Invertors

    At $689 for a 400 watt inverter, it's about three times as expensive as a G-series OutBack inverter. Get the price down a ways and I might mount some out in my yard somewhere -- I've got a 20 amp circuit that terminates on my back porch I could use ;)
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  • tallgirl
    tallgirl Solar Expert Posts: 413 ✭✭
    #14
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    Re: Micro Invertors
    longtermsolar wrote: »
    I am not sure what the quick answer reasons are that a person would want to have a micro inverter installation compared to a more traditional non-microinverter one? Can someone explain what a simple answer would be to this? Thanks

    I've been working with building architects on using solar for car parks and covered walkways. Micro-inverters would work very well in those installations, depending on size, etc.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #15
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    Re: Micro Invertors

    But the part I wonder about is spreading 1 panel GT inverters around the home/city infrastructure vs just setting up 10's-100's+ in one central location (larger ones being single owner like a city). Installation, security, and maintenance--I would expect--to be much simpler and cheaper in a centralized location.

    Once 100% of the power of a civic center has been offset by solar power (if that ever happens)--then I can understand the billing/metering issues with net metering requiring "local offset" of power--on a "per fixture" basis--but it still does not address basic problems of simper/cheaper/maintenance issues with centralized systems.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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