Greenhorn question

On a nice bright sunny day, a car hits the power pole down the street. What would happen at my house with a gridtie system.

Would my house be automatically disconnected from the neighborhood, with my house being powered by my system?

or

Am I susposed to pull the disconnect at my house?

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,412 admin
    Re: Greenhorn question

    1. Car hits pole.
    2. Electrical lines are down/crossed at street.
    3. Your happily humming Grid Tied inverter watches voltage and frequency.
    4. Voltage falls out of ~180-264 VAC and or outside 60Hz +/- 0.5 Hz
    5. Inverter hardware sees out-of-spec. line and stops AC output within 6 cycles (1/10th of second).
    6. Inverter monitors line for 180-240vac AND 60.0 Hz +/- 0.5 Hz
    7. Inverter sees #6 and continue to monitor for 5 minutes. If #6 fails, inverter restarts 5 minute clock.
    8. End of 5 minutes with #6 true--turn on output.
    9. Wait for #6 to not be true and go back to #5 and start process over again.

    What do you have to do in the event of an accident/AC main failure?

    A) Nothing.
    OR:
    B) If you see "brownout" conditions (lights dim, fridge motor humming, etc.) or over voltage conditions (very bright lights from crossed lines, etc.), turn off main power until utility is on scene to protect your home appliances.

    With Grid Tied power, if you lose AC mains, you will lose power. Grid Tie power will not make your home power any more reliable.

    With a Grid Tie Inverter, you don't need to do anything different with your home electrical grid at all (assuming everything was installed to code and the Solar Panels + Inverter(s) are operating correctly).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Greenhorn question

    Sam,

    Assuming your utility-interactive system is battery-less, then the system would automatically shut down when the grid failed. This safety feature is called "anti-islanding", and your system would not power any loads in your home. The system would automatically reconnect to the grid and begin to generate power once the grid had been continuously active for five minutes.

    If your system were to include battery back-up, it would still disconnect from the grid following a failure, but your system would use energy stored in the batteries to continue operating and to power connected loads.

    HTH,
    Jim / crewzer
  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Greenhorn question

    Dueling posts! ;)

    Regards,
    Jim / crewzer
  • System2
    System2 Posts: 6,290 admin
    Re: Greenhorn question

    Thanks that helps, but leads to another question.

    So if I have a dedicated circuit in my house powered by the inverter (no batteries), what happens as the sun light starts to drop?

    Does the inverter shut down at a predetermined output voltage?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,412 admin
    Re: Greenhorn question

    A Grid Tied (or utility interactive) inverter is a bit different than your normal 120/240 VAC inverter you connect to your batteries and run your TV from your car's cigarette lighter.

    To the inverter, the utility looks like a huge "AC" battery. And the inverter's job is to take all of the energy generated by the solar panels and push it out into your breaker panel. A Grid Tied inverter does not have a "regulated" output in the conventional sense. What regulates the voltage in your home/grid tie system is the utility mains themselves (and your utility's network of generators). Kind of like a car battery, you can input 1 amp, 10 amps, or even a 100 amps, and (within reason) the car battery will stay between 13-14 volts DC.

    Your car inverter's job is to simply output 120 VAC at 60 Hz (i.e., a regulated output).

    As the solar power drops, the inverter is looking at the equation of Power=Voltage*Current (from the solar panels)... The inverter is constantly adjusting the current it takes (and by extension, the voltage output by the panels) and trying to keep Power from the panels at a maximum (MPPT=Maximum Power Point Tracking)...

    The power from the solar panels will eventually drop enough until the inverter cannot convert any power at all... The inverter and its electronics are still running and monitoring the solar panels... But the voltage and current will eventually drop enough to where there is not even enough solar power to run the inverter itself (typically somewhere around 10-50 watts or so)...

    For my inverter (a Xantrex unit--just my guess from watching it operate--I do not know the internals), when the voltage/current falls enough for the electronics to shut down--the AC side of the inverter goes into a 5 minute count down and rechecks if there is enough solar power available... Eventually, it gets dark enough where the unit does not even try to restart the DC side of the system and it goes to sleep for the rest of the night.

    Now, regarding the "dedicated circuit" in your home...

    In reality, all of your loads are connected in parallel to your 120/240 VAC 60 Hz mains (Assuming North America). Imagine a 12 volt car battery supplying the power, and lights, radio, etc. all drawing their electricity from the "main" battery.

    Each major load will have its own dedicated circuit breaker (or fuse) to protect against short circuits--but they all are eventually connected to that one battery.

    Now imagine we have a 12 VDC generator. That is also connected to the battery through its own dedicated circuit breaker. As the engine starts running and turning faster, the current from the battery goes into the "fuse panel" / Breaker Box and either helps power the loads and/or starts also to recharge the battery.

    If you "turn off" the generator, all the loads are still connected to the battery (aka Utility Mains) and everything continues to run just fine (you may notice a bit of voltage drop--like when head lights are on and you turn off the car engine).

    But in a normal home setup--you will never be able to know if your inverter is working or not except by looking at the inverter's LCD Display and, if it is generating more power than the home is using, you will see your utility meter running backwards (or at least turning slower than normal if your home is drawing more power than the grid tie inverter is generating).

    The Grid Tie inverter does monitor your home's voltage and frequency--but only as a safety measure as I previously described. It does not "regulate" the voltage or frequency of the power in your home--and that is why a true utility interactive / GT inverter cannot supply power to your home if a car hits the pole outside of your home.

    There are other ways of adding solar power to your home--where you can use solar panels and inverters that behave like a giant UPS (uninterruptable power supply). And may folks do that on this board (off-grid cabins and systems that are GT but also go off-grid if power is lost in a storm--for example).

    But these Off-Grid and Hybrid systems require battery banks, different (and somewhat more expensive) inverters, transfer switches, etc... too. The concept is pretty straight forward, but getting into the details can get very confusing to get it all right (works well and is safe).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2
    System2 Posts: 6,290 admin
    Re: Greenhorn question

    I've always wondered how the "anti-islanding" features work.

    Is the 5 min window the anti-islanding? Or is there something else involved as well?

    The answer on the output shutting down brings up another question. What sort of phantom power do most inverters draw at night?

    I've got my house down to 30W overnight*. Hopefully an inverter isn't more than a watt.

    * I've got one of the T.E.D. units and it works wonders on getting consumption under control!
  • BB.
    BB. Super Moderators, Administrators Posts: 33,412 admin
    Re: Greenhorn question

    My post #2 is the anti-islanding function (I probably described it 90% accurately--I don't have the specs.).

    The five minute timer I mentioned in my last post is probably just a byproduct of the fact that the power has to valid for 5 minutes and if the inverter electronics (a portion of which are supplied by the solar panels) are non-functional as the sun goes down/comes up--then the five minute timer probably start over again.

    From here (pdf file link--I think it will click correctly) the Xantrex XT models have a 1 watt nighttime load.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2
    System2 Posts: 6,290 admin
    Re: Greenhorn question

    Are there GT inverters that allow you to have a dedicated circuit that remains up when the street is down?
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Greenhorn question

    if you are asking about defeating the anti-islanding then the answer is no, there aren't any, as that would take the inverter out of compliance and pose a shock hazard to linemen. if you are asking of any other types of operations while the grid is down then you might be refering to a grid-tied battery backed type of inverter as this will feed power to batteries on a primary basis and the grid (if there) on a secondary basis.
    i must add here that only an inverter that is made to connect to the grid is able to be fed to the grid as those other inverters, even if they're sinewave, will blowout.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,412 admin
    Re: Greenhorn question

    Here is a short and sweet diagram of the difference between a Grid Tied and a hybrid system (grid tie/off-grid capable) system. This is for Xantrex, but I am sure other companies have similar diagrams.

    Remember Off-Grid and hybrid systems cost quite a bit more to operate than a pure grid tied system. In my area (SF CA), a retail priced / installed grid tied system costs around $0.25 per kWhr to operate (~$0.14-$0.17 per kWhr with California solar rebate).

    A pure off grid system will cost $1.00 per kWhr (or more) once the costs of of the lower efficiencies and the batteries (and their replacements) are taken into account.

    A grid tied hybrid system will probably somewhere between the above two systems in costs...

    Right now, my power is around $0.115 per kWhr (flat rate) or between $0.09 to $0.49 per kWhr (off peak/peak winter/summer tiered pricing).

    -Bill

    By the way, there are inverters that are intended to operate with generators and/or grid power--and they basically behave like a large UPS system... Plug your AC main into the 2-4 kWatt inverter. Plug a battery bank into the inverter. Plug/wire your load(s) into the output of the inverter.

    With AC mains on... Inverter just connects AC input to AC output and provides AC power to your loads. It also has an internal battery charger that takes the AC Mains and keeps your batteries charged.

    AC Mains fail, within 1/2 a cycle or so, the inverter turns off the AC mains switch and turns on its inverter to supply power to your AC loads from the battery bank...

    Optionally, you can connect solar panels and charge controller to your battery bank (solar power). You can also connect a generator to the Inverter and program the inverter to start the generator set if the battery bank voltage falls too much.

    You can do almost anything you want--within reason. Solar, Grid, Generator, etc... Backup, off-grid, grid-tie or mix. Only one circuit for your home, or the whole building.

    The question is what do you need and how much do you want to pay... The cheapest solar solution--Grid Tied inverter (no battery backup) costs about $10 per watt installed (retail). And your electricity will cost ~$0.25 to $0.35 or more (depending on the amount of sun you get). Can be installed for less. Not all utilities allow Grid Tied systems or 1 year net metering... Solutions tend to be based on personal needs and exact location.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2
    System2 Posts: 6,290 admin
    Re: Greenhorn question

    I was hoping not have any batteries. Feed the power company when I'm at work and the sun shines. Run my tv on the weekend when the drunk hits the pole. I don't mind sitting in the dark at night. But I don't want to miss TV during the day.
    I guess by your description. A GT with battery back up runs solely from the batts when the neighborhood goes down. Wouldn't that waste several hours of sunshine on the panels?
  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Greenhorn question

    Links to “anti-islanding” info: http://www.google.com/search?hl=en&q=anti-islanding+inverter&btnG=Search
    Are there GT inverters that allow you to have a dedicated circuit that remains up when the street is down?
    Yes. For example, the OutBack GTFX (sealed) and GVFX (vented) utility-interactive (U-I or GT) inverters require a battery bank, and, subject to battery capacity and loads, they will power a “downstream” AC load when the “upstream” grid is disconnected. The batteries can be recharged from external sources (i.e., PV), and/or from the inverter's built-in charger once the grid is restored.These particular inverters have two AC connections: “AC In”, for connection to the grid, both both “buying” and “selling”, and “AC Out” for connection to downstream loads.

    See these links for more info: http://www.outbackpower.com/GT_Inverters.htm and http://store.solar-electric.com/oupogrsiwain.html

    I believe the new Xantrex XW series inverters can operate in a similar manner. See: http://www.xantrex.com/web/id/1858/docserve.asp

    HTH,
    Jim / crewzer
  • BB.
    BB. Super Moderators, Administrators Posts: 33,412 admin
    Re: Greenhorn question

    Sam,

    Look at my PS in post #11 (and/or Jim's links) for details (dueling posts and edits again). :cool:

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mikeo
    mikeo Solar Expert Posts: 386 ✭✭✭
    Re: Greenhorn question

    "I guess by your description. A GT with battery back up runs solely from the batts when the neighborhood goes down. Wouldn't that waste several hours of sunshine on the panels?"

    No, when the sun is shining the charge controller will be charging the batteries, and the charge current subtracts from the load current from the batteries point of view. If your PV's are putting out more current then your load currents, then the battery will actually be charging up. You would not need a very large battery bank if all you want to do is watch TV when the sun shines and the grid is down.