Microinverter to 220V-120V step down transformer to AC wall socket possible?

meridiansolar
meridiansolar Solar Expert Posts: 34
Can one use a 220V to 120V step down transformer to take the electricity from a microinverter solar panel system and feed it directly into a wall socket?

Are there 220v to 120V step down transformers that are effcient enough to do this?

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Microinverter to 220V-120V step down transformer to AC wall socket possible?

    No; this is not a good idea.
    The inverter possibly won't even function (if you're lucky). They test phase and try to "push" the Voltage high (above 240 VAC) and the "feedback" they'd get through a transformer should tell them the grid is out of spec which will make them shut down.
    That's the simple version. I hope RC or Bill or SG or someone will post the detailed explanation so you can see how complicated it is.
  • meridiansolar
    meridiansolar Solar Expert Posts: 34
    Re: Microinverter to 220V-120V step down transformer to AC wall socket possible?

    is there some sort of 220v by pass plug that you can put on a dryer/stove outlet that will allow you to wire a microinverter to then?

    kind of like those xmas tree lights where you can plug 3 or 4 ontop of one another.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Microinverter to 220V-120V step down transformer to AC wall socket possible?

    I have to say that both plans you're proposing are not legal. Even one microinverter needs to be permitted, inspected, and hard-wired to a dedicated line.

    Transformers, btw, can cause interesting Voltage variances when used in conjunction with, say, a motor; the residual magnetism in the motor can back feed through the transformer and actually increase the primary side Voltage momentarily. Using one to connect two Voltage sources is likely to have a similar effect.

    Those Christmas tree lights that you could plug together endlessly used to burn houses down as it was very easy to exceed the current limit of the wiring by adding more and more strings of bulbs. Good thing we have LED tree lights now!
  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    Re: Microinverter to 220V-120V step down transformer to AC wall socket possible?

    There are several reasons to get an install inspected and permitted:

    1) the utility has a right to know you are back feeding their grid, for safety sake at least. If you are back feeding the grid without their knowledge they can disconnect you.
    2) wiring into a non dedicated line is dangerous in that it is possible to overload the wire without tripping the line breaker, you are providing a source of generation as is the main panel, this could allow over the wire rating connection to the line with excess loads.
    3) many meters don't know which direction the electrons are flowing, you could actually get charged by the utility for your Excess generation instead of getting credit. The utility needs to install the proper meter to avoid this situation.
    4) if there is a fire and the work is not permitted and approved, the insurance company my deny your claim even if the source of the fire was not the solar.
    5) rebates and tax credits all require a permitted and inspected install.

    I am sure other will pipe in with there opinions as well.
  • solarix
    solarix Solar Expert Posts: 713 ✭✭
    Re: Microinverter to 220V-120V step down transformer to AC wall socket possible?

    Beyond the question of whether is legal or not (its not code legal) the question of how well it would work depends on the currents involved.

    The inverter and the grid act as voltage sources. They keep the voltage constant (well a good sinusoidal wave). and let the currents vary wildly in order to make the power required. The PV source of power is essentially constant, but the AC voltage is sinusoidal so even though there are storage capcitorss (those electrolytic ones we all worry about) in the inverter to smooth out the currents, the AC current is not sinusoidal.

    The grid side of your stepdown transformer is likewise not a sinewave current. All kinds of electric loads are nonlinear and require the source of voltage to vary its current greatly to meet the current demand. The computer you are using right now no doubt sucks all of its energy off the peak of the AC wave with a big surge of current right then and very little during the rest of the 8msec half wave. Remember : Power = Voltage x Current.

    OK, so the deal is that a transformer is an inductive device which fundamentally tries to oppose a change in current. This is why a sinewave is so good for transformers - the voltage and current have a constant change of speed (constant acceleration). Think of a spot going around a circle - constantly accelerating. Transformers etc, work very efficiently on sinewaves, poorly on everything else and not at all on DC. I haven't actually seen what the waveform of the current flow on an micro inverter looks like, but its probably not a real good sinewave even though its voltage waveform is. Because of that, it is going to lose efficiency forcing its power through a transformer.
  • Frxddy
    Frxddy Solar Expert Posts: 113 ✭✭✭✭
    Re: Microinverter to 220V-120V step down transformer to AC wall socket possible?

    I'm going to guess the reason that you are asking this question is because you own, or are thinking of buying, cheap inverters off eBay. (If not, please explain your situation in a bit more detail.) Those eBay inverters are NOT UL approved and as mentioned could get you in deep doo-doo if something goes wrong. The best scenario is they fail to function. The next to worst is you burn your house down & the insurance company says "Too bad". The worst is it costs a life and you are on the hook for it.

    Also, and I'm sorry if I'm being blunt... I mean, I'm glad you asked....but....if you are asking this question it means you don't understand enough to safely do what you are hoping to do. There comes a time when you need to use professional components and install them properly. I'm glad you asked because that means you want to install them properly, but you have missed the "use professional components".
  • meridiansolar
    meridiansolar Solar Expert Posts: 34
    Re: Microinverter to 220V-120V step down transformer to AC wall socket possible?

    no those ebay ones are so ineffcient it would be pointless to use them. Just trying to figgure out why some company doesn' t make plug and play solar panels.

    Taking out permits, hiring an electrician, etc, probably makes many many people give up on solar.

    If you could just plug them in like a TV, many many people would buy 500w or 1kw systems to help supplement their electricity usage.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Microinverter to 220V-120V step down transformer to AC wall socket possible?
    no those ebay ones are so ineffcient it would be pointless to use them. Just trying to figgure out why some company doesn' t make plug and play solar panels.

    Taking out permits, hiring an electrician, etc, probably makes many many people give up on solar.

    If you could just plug them in like a TV, many many people would buy 500w or 1kw systems to help supplement their electricity usage.

    True.
    There are such abominations as 120 VAC plug-in inverters. As far as I know none have the approval of any regulatory body.
    The reasons cited in the previous posts are why they are bad idea.
  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    Re: Microinverter to 220V-120V step down transformer to AC wall socket possible?

    This side of the pond, the mastervolt soladin is legal in the UK, Netherlands and Spain:
    www.mastervolt.com/solar/products/soladin-600/soladin-600-160-700-wp-model-for-use-in-spain/

    These are becoming quite popular in Spain because of the migraine inducing red tape that's required for normal grid connected systems.
  • meridiansolar
    meridiansolar Solar Expert Posts: 34
    Re: Microinverter to 220V-120V step down transformer to AC wall socket possible?

    "This side of the pond, the mastervolt soladin is legal in the UK, Netherlands and Spain:"

    this is awesome, they need to come up with a USA version! Why do they have different versions for UK, Netherlands and Spain? I thought all of those european countries used 220V?
  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    Re: Microinverter to 220V-120V step down transformer to AC wall socket possible?

    Yep they're all 230v but each have their own regulatory requirements which are slightly different. So the soladin would work in any country that supports 230v, it just won't be legal.
  • solarvic
    solarvic Solar Expert Posts: 1,071 ✭✭✭✭
    Re: Microinverter to 220V-120V step down transformer to AC wall socket possible?
    "This side of the pond, the mastervolt soladin is legal in the UK, Netherlands and Spain:"

    this is awesome, they need to come up with a USA version! Why do they have different versions for UK, Netherlands and Spain? I thought all of those european countries used 220V?
    If you clicked the website it was listed 50 cycle
    :Dsolarvic:D
  • Scott
    Scott Registered Users Posts: 1
    Re: Microinverter to 220V-120V step down transformer to AC wall socket possible?
    solarvic wrote: »
    If you clicked the website it was listed 50 cycle
    :Dsolarvic:D

    I don't necessarily disagree with the cautions all documented earlier, but I have to say as point of contrast that I have done what the original poster was asking about. We set up individual panels on our roof, connected them to UL-approved grid-tie inverters, pumped that into various models of 240V-120V step-down A/C transformers, and then just pumped into the A/C wall socket.

    We've had no problems; we've had it up there for almost 4 years now; and it's saved a bundle on our electric bill. I've also gone downstairs to the basement to see if the meter was really spinning backwards and decrementing, and all was confirmed. I then went on the utilities website to see whether they saw our power coming in, and it confirmed it as well. I even put some test equipment to see if our power wave was getting dirty, as well as voltage regulators to protect our critical equipment, and they've kicked on no more often when the solar was operating as when it wasn't. In fact, given the clean power-factor of the solar, it actually seemed to improve the profile, but that just might be the power of suggestion.

    So, I am not saying anyone's wrong here. I am just saying it can be done DIY without destroying your electrical setup or blowing yourself up.
  • jaggedben
    jaggedben Solar Expert Posts: 230 ✭✭
    Re: Microinverter to 220V-120V step down transformer to AC wall socket possible?

    From a functional point of view, my question is this:

    Why the heck would you go to all the expense and trouble of a transformer when it's not that hard to wire a 2-pole breaker into a panel?

    If you don't understand electricity well enough to wire up a breaker, then you almost certainly don't understand it well enough to be sure that you won't overload the receptacle's branch circuit with too much power. There is a fundamental reason why inverter outputs should have their own dedicated overcurrent protection without any possibility of loads connected. That's why plug and play will never be approved of by UL or the NFPA (regardless of the utilities' interests). There's a lot of stuff in the code that is superfluous but this is not one of those things.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Microinverter to 220V-120V step down transformer to AC wall socket possible?
    jaggedben wrote: »
    From a functional point of view, my question is this:

    Why the heck would you go to all the expense and trouble of a transformer when it's not that hard to wire a 2-pole breaker into a panel?

    If you don't understand electricity well enough to wire up a breaker, then you almost certainly don't understand it well enough to be sure that you won't overload the receptacle's branch circuit with too much power. There is a fundamental reason why inverter outputs should have their own dedicated overcurrent protection without any possibility of loads connected. That's why plug and play will never be approved of by UL or the NFPA (regardless of the utilities' interests). There's a lot of stuff in the code that is superfluous but this is not one of those things.

    Also, to be safe you would have to run a dedicated circuit to the wall plug anyway (or swear never to use any of the other outlets.) At that point there would be no reason not to hardwire while you are at it. :-)
    SMA SB 3000, old BP panels.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,422 admin
    Re: Microinverter to 220V-120V step down transformer to AC wall socket possible?

    Scott,

    The problem is you are adding available current to an existing branch circuit. If you have any other loads on that circuit, it will now "see" both the 15-20 Amp main breaker, plus any current from your solar array too.

    It is now possible to add more loads (coffee maker, microwave, portable heaters) to that circuit and over heat the wiring in your walls.

    Regarding the meter crediting your usage--Is that an old mechanical meter or one of the new Digital Meters?

    In Northern California they have been taking the last couple of years to convert everyone to "Smart Meters" (wireless digital meters)... And I would be surprised if they would go "backwards".

    It took them almost 1-2 years to upgrade my GT service to a digital meter. I presume to get the meter software and billing computer working correctly.

    Yes, doing what you said will work. And if no other loads are plugged into that branch circuit it will probably be fairly safe... But the utility (and probably city) do have the right to red-tag your house/pull your meter if they so decided (I have not read about this being done--So I do not know the risk of this happening in California).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Microinverter to 220V-120V step down transformer to AC wall socket possible?

    What you can get away with is not necessarily either legal or safe. And if it all goes wahoonie-shaped you are on the hook for absolutely everything because the install is not permitted or inspected. Even if the install is not at fault, it will be blamed and you will be toast.

    Your choice. But the host of professionals on this forum strongly advise against it.
  • plojm
    plojm Registered Users Posts: 7 ✭✭
    This definitely works I mocked up a setup just to show anyone. You do however lose efficiently so with solar it kinda sucks another 15% lose in efficiency. https://youtu.be/mKEN-LgWzgg

    But still I think way safer then Chinese grid 110 who's mosefts die so damn quick

  • BB.
    BB. Super Moderators, Administrators Posts: 33,422 admin
    Welcome to the forum PLOJM,

    I am guessing, but it looks like you are tying into a standard 120 VAC 60 Hz utility powered home plug, and connecting through a 120/240 VAC transformer to an Enphase micro inverter???

    In itself, there is nothing strange about that working.

    And, this setup will not supply AC power if the utility power fails (storm, car hits power pole, etc.).

    The other issues about legality (code/utility point of view) and safety (using a non-dedicated AC branch circuit for both GT solar and household loads) is not safe (as explained above). And, at least in pretty much any modern North American Home, we have split phase 120/240 VAC power anyway... So adding a double pole breaker (240 VAC) and running a dedicated branch circuit to the GT inverter/solar array is not that strange or difficult.

    If you have a very old home with 120 VAC only power--That does make it a bit more difficult to do GT Solar (note sure if there are any UL/NRTL Listed 120 VAC 60 Hz GT inverters out there)... Bringing out a 120 VAC line through a 120/240 VAC Step Up (Boost) Transformer--can be done but could be expensive (transformer, and extra transformer losses, limited amount of back feed into a small 120 VAC panel--Limited by code) are probably just the beginning of the issues (code building department, utility).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • plojm
    plojm Registered Users Posts: 7 ✭✭
    edited October 2018 #21
    I agree with most of ur comments in fact I run my solar system off 240v, I just hate when people say things cant be done or shouldn't be.  I started learning about solar with 120v (low quality) grid tie from China and 1 solar panel I made soldering cells, now I have a 3kw system and will probably soon be ac coupling with a 7.6kwh energi lithium battery I got. Learning is power and I have learned so much from the community. So I don't want anyone discouraged in trying. Yes there are many ways to do everything, this is just one if people wanted to. Thanks

  • BB.
    BB. Super Moderators, Administrators Posts: 33,422 admin
    We just lots a large number of homes in multiple areas in my state (California) from (possibly/probably) wind driven arcing utility lines. 

    Depending on where you live, a single house fire, while not only dangerous for the people/family living in the home, can also affect neighbors too.

    As said, there are reasons why code and insurance companies look very closely at what is "safe" and "legal" for power systems. Sure, one person, if doing thing correctly, can probably build a system that will work fine throughout its life.

    And, obviously, even code compliant/installed/inspected systems can catch fire. But generally, it is a relatively rare event and limited area of negative effects.

    And on to your next project... Li Ion battery bank. Do you know what the chemistry is (min/max voltages, ability to fail in a fireball, or not). Does it have a working BMS (battery management system)? Is the BMS integrated in such a way to limit the issues of over charging/over discharging?

    Generators and Battery banks--Are a relatively common source of fire. Lead Acid battery fires tend to be issues of electrical shorts and small explosion of hydrogen gas. Li Ion battery failures can be of the type where they just spray water and let it burn. Also, some Li Ion battery failures release Hydrofluoric Acid--A very nasty chemical that no organic life should ever be exposed to.

    Even single cell Li Ion battery failures (18650 and similar) have been known to cause terrible health problems and death in some instances (e-cigs, batteries on aircraft, etc.).

    I tend to go on the "don't do this if you do not know what you are doing" speech just once in a thread... So I will stop here and less you ask further questions specifically about safety.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • plojm
    plojm Registered Users Posts: 7 ✭✭
    Lol you're just that kinda guy nothing I can say, just be safe everyone and do your research. I do mine. Thanks for your comments
  • BB.
    BB. Super Moderators, Administrators Posts: 33,422 admin
    I am sorry... I am not trying to be Mr. Negative here. Just have seen too many fires and such from installations that had issues (including stuff done to code).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • MrM1
    MrM1 Registered Users Posts: 487 ✭✭✭✭
    Thanks Bill
    REC TwinPeak 2 285W 3S-3P 2.6kW-STC / 1.9kW-NMOT Array / MN Solar Classic 150 / 2017 Conext SW 4024 Inverter latest firmware / OB PSX-240 Autotransfomer for load balancing / Trojan L16H-AC 435Ah bank 4S connected to Inverter with 7' of 4/0 cable / 24 volt system / Grid-Assist or Backup Solar Generator System Powering 3200Whs Daily / System went Online Oct 2017 / System, Pics and Discussion
  • bill von novak
    bill von novak Solar Expert Posts: 891 ✭✭✭✭
    plojm said:
    I agree with most of ur comments in fact I run my solar system off 240v, I just hate when people say things cant be done or shouldn't be.  I started learning about solar with 120v (low quality) grid tie from China and 1 solar panel I made soldering cells, now I have a 3kw system and will probably soon be ac coupling with a 7.6kwh energi lithium battery I got. Learning is power and I have learned so much from the community. So I don't want anyone discouraged in trying. Yes there are many ways to do everything, this is just one if people wanted to. Thanks

    There are some very good reasons people shouldn't do things.  In medicine, people often hear something on the Internet and go demand a new drug or treatment without understanding their condition, the efficacy of the treatment, its side effects or its interactions with other drugs.  Sometimes they even get their hands on the new treatment and try it themselves.  This can be (and has been) fatal, either due to the unsafe treatment or deferring of an effective treatment.  So when people who are proficient with medical issues (like EMT's, doctors on forums etc) hear people asking for such advice online, they will generally say "TALK TO YOUR DOCTOR!"  And other people think they are being unhelpful or mean - but in fact they are trying to save the guy's life.

    Not much different here.  If you want to do an approved installation, there are plenty of companies out there who will do it safely and effectively.  If you want to do an UNapproved installation and you have the experience/knowledge to do it safely, you will do so no matter what we say here.  If you do not have the knowledge/experience to do it safely, the odds of you doing damage to your home's wiring, causing a fire or even electrocuting yourself are fairly high.  I personally have no desire to enable people to do those things, even if they get mad at me for not telling them how to do it.  And if a lack of advice causes the person to get mad and give up on the project - that may have just saved his home (or his life.)