Transformer Vs tranformer less inverters

Dapdan
Dapdan Solar Expert Posts: 330 ✭✭
in General Solar Power Topics #1
Hey Guy,

For my general education what is the main difference between transformer type inverters and non-transformer type inverters as it relates to off-grid type inverters. I know of one difference, the weight. Transformer type invereters tend to be quite heavy. Are they any worth while advantage of one over the other. If there is already a post like this, my apologies in advance. Thanks.

Cheers...
Damani
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #2
    Re: Transformer Vs tranformer less inverters

    Transformer designs give complete isolation from the input and output, so for example, you can ground a neutral connection on the output to earth ground safely, can't do that on a transformer-less design
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  • Dapdan
    Dapdan Solar Expert Posts: 330 ✭✭
    #3
    Re: Transformer Vs tranformer less inverters

    Thank gup,

    So therefore a tranformer base inverter is more suited to " whole house" or residential application where the ground maybe bonded to earth on the AC side of the wiring. Good to know.

    Cheers...
    Damani
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #4
    Re: Transformer Vs tranformer less inverters

    How's that work with the GT inverters, w/o transformers ? US uses the center tap of a 240V for ground/netural/return for the 120V taps.
    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 ||
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    solar: http://tinyurl.com/LMR-Solar
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  • bryanl
    bryanl Solar Expert Posts: 175 ✭✭✭✭✭
    #5
    Re: Transformer Vs tranformer less inverters

    re: "you can ground a neutral connection on the output to earth ground safely, can't do that on a transformer-less design"

    Don't confuse the earth ground with the chassis ground.

    What I think you refer to is the neutral to chassis ground bonding. That is only an issue with single phase non split (i.e. 110v in US) systems that don't have a neutral. A 240v volt split phase system has an actual neutral and that will need to be bonded to the chassis ground (green wire) at the service entrance if I recall correctly.

    The code for grounds and bonding gets a lot of folks confused so be very careful and know what is meant by 'separately derived systems' and also the manufacturer's instructions and caveats for your equipment.

    Modern electronics can somewhat alleviate a lot of the problems transformers used to be needed to solve. Older inverters, for instance, often used ferro-resonant transformers to help with line regulation over varying loads.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #6
    Re: Transformer Vs tranformer less inverters

    The issue with transformer-less designs is that the grounding must (usually) only be done on one side--If there is grounding done on both sides, it can end up with a high current path short (for example, off-grid, typically MSW, inverters if you ground the "AC neutral" and the "Battery negative" lead--it creates a short straight from the positive lead to the "neutral lead" on the MSW inverter--right through the switching electronics (at least that is how I understand it).

    With a isolated power transformer, you can ground reference any one output lead and it does not affect any input lead (Isolated Input/Output).

    In the US electrical code, they require the solar PV array to be ground referenced for ground fault detection (as well as ground referencing the neutral AC output)--I don't know--but that may complicate the design and approval of a transformer-less GT inverter.

    -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 ✭✭✭
    #7
    Re: Transformer Vs tranformer less inverters

    FWIW:

    There was an RSS Newsfeed a little while ago about SMA getting the first approval on transformerless GT units.

    http://www.altenergymag.com/news_detail.php?pr_id=17118
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #8
    Re: Transformer Vs tranformer less inverters

    On GT's and non-isolated designs, the array is "floating" side, unlike what most of us are use too with the negative line bonding to ground. This is all part of the NEC2008 update that allows both PV potentials to be floating relative to ground

    The major issue is how the new class of inverters handles both component failures ( PV panels are not going to survive 240 VAC across the string ) and ground fault detection, which is still required and can't be done with the cheap fuse method

    All for about 1% better efficiency :roll:
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  • AntronX
    AntronX Solar Expert Posts: 462 ✭✭
    #9
    Re: Transformer Vs tranformer less inverters

    SMA claims 98.3% peak efficiency of TL inverters. Their SB8000 gets 96.8% peak. Thats 1.5% higher eff. Over 15 years, equals 2874 KWh AC extra gain or $316 (at 11c/KWh). Resources and energy saved by not manufacturing transformers. Easier to install.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
    Re: Transformer Vs tranformer less inverters

    ... And perhaps cheaper to build, so the company makes more profit per unit?

    Oh dear; there I go being hopelessly cynical again! :roll:
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #11
    Re: Transformer Vs tranformer less inverters

    Want to go back to $10 per watt solar panels? :p;)

    A little interesting solar cell history:
    Although technical progress of silicon solar cells continued at breakneck speed - doubling their efficiency in eighteen months - commercial success eluded the Bell solar cell. A one-watt cell cost almost $300 per watt in 1956 while a commercial power plant cost 50 cents a watt to build at that time. The only demand for silicon solar cells came from radio and toy manufacturers to power miniature ships in wading pools, propellers of model DC-4's, and beach radios. With solar cells running only playthings, Daryl Chapin could not help but wonder, "What to do with our new baby?"
    ...
    Solar-cell technology proved too expensive for terrestrial use until the early 1970s when Dr. Elliot Berman, with financial help from Exxon Corporation, designed a significantly less costly solar cell by using a poorer grade of silicon and packaging the cells with cheaper materials. Bringing the price down from $100 a watt to $20 per watt

    -Bill "cheap to build cuts both ways" B.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • solarix
    solarix Solar Expert Posts: 713 ✭✭
    #12
    Re: Transformer Vs tranformer less inverters

    Along with the important considerations already mentioned, I would like to add that one advantage the transformer type has is lower susceptibility to surges, spikes and noise. It is nice to have some serious inductive impedance to knock down the high frequency spikes that can be on the power line. The high frequency switching circuits in a transformerless design are great at responding and controlling line regulation up to maybe 100khz but anything above that just rips right through and can wipe out your circuits. MOVS and filters are ok but that big heavy transformer really kills the high frequency noise. If reliability is important to you, take a good old heavy transformer design. Solar systems aren't portable, you only have to lift them once.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #13
    Re: Transformer Vs tranformer less inverters

    transformers also add isolation between the grid and you.
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