Feedback for inverter I'm building for Solar Panels

Discussion in 'The Projects Forum' started by andrewsyc, Nov 26, 2011.

  1. andrewsyc

    Thread Starter New Member

    Nov 23, 2011
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    0
    After deciding to pursue a project of renewable energy I decided in order to make a project of building solar panels ROI worthwhile building the inverter myself would be necessary.

    I'm a EE student, my dad is a EE. He drew up the diagrams below. Some of it I'm not familiar with but the concepts are there and I understand the setup. He was fairly sure of himself but wasn't so sure on some of the particulars.

    The goal is to hook this up to the grid (of course) and roll back the meter on occasion. There will be approximately 600w peak attached to this.

    Could some of you provide some feedback off the diagrams or point to an internal link that would be helpful? Thanks...

    Excuse the crude handwriting, he's been told it's hard to read.
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    It is good to have isolation between the high voltage and low voltage circuits, like the op amp for measuring the AC voltage.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    A boost converter configuration would not really be suitable for 600W.

    You need more like a current-mode PWM bridge converter, preferably zero-volt switching to minimize losses in your switches.

    Have a read through here:
    http://elenota.pl/pdf/Texas_Instruments/slua122.pdf
    Laszlo Balogh has written quite a number of documents on SMPS design over on the Texas Instruments' website.

    As far as hooking it up to the grid and rolling back the meter - a pipe dream with only 600W available; that's about half what you need to run your refrigerator. Then there's the hot water heater. The big ticket item is your HVAC. Then you have your stove, washer/dryer, etc - that are more-or-less occasional demand items. After that come your lights.

    How about just trying to power your PC 24 hours a day, instead? That's probably around 600W or more.

    If you can ever get to the point where you actually had the excess capacity to sell power to the power company, you would need some sophisticated equipment in order to connect to the mains. The equipment would have to be approved by the power company. There have been power company employees killed because of people backfeeding the power company's lines.
     
  4. andrewsyc

    Thread Starter New Member

    Nov 23, 2011
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    0
    Thanks for the response SgtWookie, my goal is to only roll back the meter some of the time. This will only save $10-15 a month at best.
    It was discussed on how to cut the power for company lineman if the power were to ever shut off. Is 600W something we need to call and have them inspect then?
    This is just a fun project to build onto later.
     
  5. EB255GTX

    Active Member

    Apr 30, 2011
    54
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    There are standards and regulations you need to adhere to before connecting to the grid (regardless of whether you have excess power to sell back or not) - you leave yourself open to all kinds of bad legal stuff if you just hook something up that can source current to the grid.....not to mention the technical challenges inherent in grid connect vs stand alone.

    Stick with a stand alone inverter to get acquainted with the technology first, there is a lot of learning fun to be had with MPPT, the converter itself, the control and monitoring, the packaging and distribution of the DC and AC from the panels to the inverter and so on before even worrying about adding grid connect into the mix :)
     
  6. wayneh

    Expert

    Sep 9, 2010
    12,103
    3,036
    I hope you can see the humor in your own statement. No offense to your father - he might be 100% correct - but in my experience the devil is in the details. When 10% of the job remains, that's when you're just getting started. ;)
     
  7. andrewsyc

    Thread Starter New Member

    Nov 23, 2011
    3
    0
    I couldn't help but find your comment very humorous wayneh. Yes, I've built large projects before and the last 10% can take 90% of the time. :D
     
  8. Yako

    New Member

    Nov 24, 2011
    245
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    Looks mostly textbook to me. The first one is called a push-pull converter?

    I agree that 600W won't do very much.

    These converters literally kill the batteries too. The deep cycle discharging they cannot handle.

    Been there done all of this.
     
  9. EB255GTX

    Active Member

    Apr 30, 2011
    54
    2
    What batteries? Batteries are not needed to produce usable AC from solar module(s) when grid connected...
     
  10. cravenhaven

    Member

    Nov 17, 2011
    34
    2
    I'm appalled that a forum like this can happily discuss with or help someone build a device that is going to provide power directly to the power grid. There is a high probability of causing himself harm and a possibility of causing damage to the local electrical supply and putting their personnel in danger.
    The design is just someones casual scribble on an old piece of paper and is barely conceptual never mind functional.
    Yet this same forum will stop any discussion that even mentions the word 'automotive' unless its a repair question.
     
  11. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    I believe I addressed that in my first reply to this thread.
    There is no point in considering connecting it to the power grid, when it won't even be capable of powering a single major appliance; and even if they DO still want to connect it to the grid, the equipment must be approved by the power company.

    That was the expedient way for me to hand the ball off to their power company, who will have a long list of requirements that must be satisfied.

    Thank you, Captain Obvious.

    The rule on automotive modification topics is quite clearly defined, and has not been open to debate for some time now. If you wish to discuss automotive modifications, you most certainly may do so - but not on this board. We have even gone to the trouble of listing a number of sites where automotive modification topics might be welcomed, here: http://forum.allaboutcircuits.com/showthread.php?t=54400

    This Board is primarily oriented towards beginning to intermediate hobbyists. People at that level of experience have no business in attempting to make modifications to vehicles, nor do people who are not specifically trained to be automotive engineers.

    Repairs are entirely different; it is restoration to manufacturer's specifications.

    While this Board is open to the public, it is privately owned. It's their "house", so to speak - and they can choose what kinds of conversations they would like to host, and which kinds they will not, for whatever reasons they decide. I am not one of the owners, Adminstrators, nor Moderators. I just post quite frequently - and I follow the rules, without complaining about them. I invite you to do likewise.
     
  12. Wendy

    Moderator

    Mar 24, 2008
    20,765
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    Actually that was mentioned in several posts on this thread. It is not a banned topic, so instead of being a critic how about jumping and pointing to something that will work?

    We also point to other forums where automotive is allowed. Anyone who can not handle the rules here can always go elsewhere.

    To the OP:
    You are entering some dangerous legal waters here. If someone does get hurt because you didn't follow code (and there are regulations involved) they could own your house, not to mention jail time.
     
  13. cravenhaven

    Member

    Nov 17, 2011
    34
    2
    I have no wish to discuss the moderators decision about automotive topics. I was comparing the level of caution WRT the automotive topics against the apparent disregard for caution in discussing high voltage topics.

    I would have thought that such an audience should not be given tacit approval for attempting dangerous projects.

    I dont entirely agree but understand and accept the decision of the forum moderators on this subject. As I said above I have no interest in debating the decision about automotive topics.

    My reason for posting was to invoke the moderators awareness of a potentially dangerous topic. I believe that doing so is not just being critical of any of the responses but in fact adding to the understanding of other readers and possibly the OP that this is a dangerous subject.
     
  14. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    Believe it or not, there IS an assessment made of the capabilities of new posters. We care a great deal about the safety of our members. We frequently have to go on for a number of Q&A type replies until we get at least some kind of picture of where the member is in their skill level.

    In the opening statement, Andrewsyc stated:
    This implies that he is not only receiving formal training, he also has an EE Dad that is involved in this project, and he also has access to the faculty at his institution of higher learning. In this instance, his Dad will be looking over his shoulder when it comes to building/testing anything involving high voltage, so that Andrewsycs' safety is assured.

    Andrewsycs' situation is rather unique in this regard, as he has knowledgeable and qualified people to turn to everywhere in his environment. Most of our members don't have the advantages that he does. What we usually encounter is someone dabbling in electronics for the first time, and they are on their own, wondering how to make an LED flash on and off.

    Cautions have been given about the idea of connecting to the grid. As Andrewsyc is a serious student with an EE Dad, I have confidence that he will research the requirements in that regards. This is not something that I assume with most new members.

    Point noted. Thank you for your concern. :) Please realize that people who have been around here for a good while DO make the effort to analyze the capabilities of a member, along with the likelihood of success of a given project, and in particular, the safety risk a project may have for the level of experience the member has. We have to really spell it out for some people. In Andrewsycs' case, simply mentioning concerns should be a sufficient trigger for him to investigate/ask questions.
     
  15. jimkeith

    Active Member

    Oct 26, 2011
    539
    99
    Yes, wear your safety glasses in case your IED goes off in your face--as far as damaging your electric service, you could trip a breaker--shock hazard is significant too.

    The logistics of creating a regenerative converter are tremendous and there are many, many issues to deal with--the supervisory control, alone, is complex as it must deal with an intermittent and variable source of power.

    Don't want to throw cold water onto your ideas, but this is not a simple project and if successful, is unlikely to have a noticeable reduction on your power bill.
     
  16. Crispin

    Member

    Jul 4, 2011
    88
    2
    if I may be so bold as to bring this back on topic? :D


    To the OP –
    Why not try something slightly different? I am currently using a 1.6KW array which ultimately charges a bank of batteries. The PV panels drive a grid-tie inverter and a couple of battery chargers sit off that.

    These batteries then run a couple of invertors at night which power the lights and a couple of low usage ring-mains. Using a couple of latching contactors, when the inverter is turned on, the contactors which over from the mains to the inverter. On overload, the inverter drops out and in turn the contactor switches back to the normal supply. The same happens when the batteries are low, I can either switch the invertor off (using a W.I.P. MCU project) or its own built-in low voltage detection.

    That is the crux of the project. While it is not all homebuilt, it does the same thing but has all the safety built in as everything is approved for the specific use but there is lots of scope for homebuilt parts. The battery chargers are my next big thing.


    Unfortunately I have a new digital consumption meter so cannot see it go backwards but it does stop ticking for most of the day though :D
     
  17. Yako

    New Member

    Nov 24, 2011
    245
    2
    Usually batteries are part of the solar system setup. Somewhere along the line there has to be batteries to err ... store the energy for when it is required?
     
  18. Wendy

    Moderator

    Mar 24, 2008
    20,765
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    A common theme with these type of systems is to use the AC power grid as the storage, if you have a surplus of electricity you can sell it back to the grid (with the right equipment). The equipment is what we are talking about.

    Basically you have to convert the DC back into AC, match the phase, and make sure the proper safety equipment is included so if some poor line man cuts the juice he isn't electrocuted by your setup.

    It can be quite complicated, but if the surplus is enough very lucrative. No batteries needed.
     
  19. MrChips

    Moderator

    Oct 2, 2009
    12,439
    3,360
    This forum does not give anyone approval to attempt anything. There is no danger in discussing the design of a high voltage power supply. Whether you personally attempt to implement the design is another matter.
     
  20. Yako

    New Member

    Nov 24, 2011
    245
    2
    I see. I am a bit outdated it seems with solar.

    I just recall my days of building 12V to 240VAC inverters and running them off car batteries. 300VA would kill my batteries so quickly it wasn't funny.

    All I was running was a TV, radio and some lights and not much else.
     
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