Grid tie lag time.

Newbie here. I have read that there is a certain lag time from the point at which a turbine will not provide enough juice to the time time the inverter will switch back to the grid, and visa versa. Is this always true, or will certain models of inverters make this transfer seamlessly?

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,748 admin
    Re: Grid tie lag time.

    Your question is a little confusing... I understand what you are trying to ask though...

    The 5 minute "time-out" is a regulatory requirement such that the "Grid" or Utility power has to be stable (within voltage and frequency specifications) for 5 minutes before the inverter is allowed to start providing energy to the grid.

    It appears that many of the "wind turbine" Grid Tied Inverters are inverters that were designed for solar panel use, but with different firmware (and perhaps some hardware changes), converted to support wind turbines.

    The basic design, when applied to solar panels seems to use the solar panel energy to power the inverter--and ~5 minutes after the inverter gets enough power from the solar panels (and monitors AC line), then it will start converting (assuming there is enough solar panel energy).

    When converted to wind turbine use--there are many times when the wind turbine actually goes to zero output (lull in wind, gust, 180 degree wind shift, etc.). Each time this happens, I am guessing, the inverter processor is reset and starts the 5 minute timeout (watching AC main volt and Hz) all over again.

    During the day, a solar panel will almost never go to zero power (even under heavy clouds)--so the grid tie inverter processor never gets reset during the day and as soon as there is enough sunlight--the inverter starts conversion immediately.

    For solar, this is great because there is no power wasted when there is no sunlight.

    For Wind, the good thing is there is no wasted power when there is zero wind--but the problem is 5 minutes of straight line/non turbulent, continuous wind before GT Inverter conversion starts can loose a significant amount of available wind power for generation.

    Following the Is Wind The Answer? Read This First from NAWS' wind turbine page:

    Massachusetts Small Wind Report (PDF):
    • The average capacity factor for 191 existing small wind turbines currently installed and reporting to the Production Tracking System (PTS) is 4%. This is less than half of the target capacity factor of 10%.
    • Installers, on average, are significantly overestimating annual energy production. On average installers are overestimating energy generation by a factor of 3 to 4.
    • The most prolific small wind installer, with 6 installations included in this analysis, is Installer 10. These systems are performing with an average capacity factor of 3%. The most commonly installed small turbine, using MTC funds, is the Bergey Excel‐S, with an average capacity factor of 4%.
    • The cause of the overall poor performance of installed small wind energy systems is not known with complete certainty. Known contributing factors include inverter synchronization/standby time, higher than expected site turbulence, and lower than expected average wind speeds.
    • Of the 19 systems analyzed, 16 have been inspected by Cadmus. Of these 16, only 6 were found to meet the estimated 10% capacity factor requirement of the SRI program, based on Cadmus’ site survey and use of the SWEET modeling tool.
    Are there other GT Inverters for Wind Turbines out there that don't reset the 5 minute timer every time the turbine stops? Possibly--but you will probably have to check with your turbine mfg. of choice and see which GT Inverters support their turbines. I don't do not design or sell any solar/wind equipment.

    A bit more on small grid tied wind turbine inverter options in this thread.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • n3qikn3qik Solar Expert Posts: 741 ✭✭
    Re: Grid tie lag time.

    A local town here has a Skystream 3.7 at their park. I watched it last year as it spun the meter both backwards and forwards. There was no 5 min. delay. When stopped the meter would spin forward then as the wind picked up, the meter would stop then start backwards. I think the 5 min. delay maybe only if the grid drops out.
  • NoodlesNoodles Solar Expert Posts: 30 ✭✭
    Re: Grid tie lag time.
    n3qik wrote: »
    I think the 5 min. delay maybe only if the grid drops out.

    You are correct, sir.
  • System2System2 Posts: 6,290 admin
    Re: Grid tie lag time.

    Ok, I understand what you mean about the inverter making sure the grid is stabilized before generated power can be "sold" back to the grid. What I am actually asking about is the automatic switching from turbine to grid power when you have lulls in the wind, or if the wind slows to a point that no power is being generated. When this switch happens, is there any break in power supply to the home, either momentarily or perhaps for 5 to 10 seconds? I assume there would not be, because in the event that power demand is higher than what the turbine would supply, you would actually be "co-mingleing" power from the turbine and the grid.
  • BB.BB. Super Moderators, Administrators Posts: 32,748 admin
    Re: Grid tie lag time.

    Kel,

    If I understand your question correctly... No, there is no "break" or interruption in the power as the inverter switches between selling power or not.

    Basically, for all intents and purposes, the AC power from the utility looks like a giant AC Battery, and the wind turbine/inverter are just an "AC Battery Charger".

    I have not seen anyone complain that their home lights flicker as the turbine/inverter energy production goes up and down--but, the voltage at your home will vary by a couple of volts as the inverter sells or not sells... Just like you may see the headlights on your car brighten and dim as you rev the engine from idle to medium speed and back down, or turn the engine off and the headlights dim a little.

    But the chances that you will notice this in your home lights or not is not very great... Imagine you took your 300 watt dinning room chandelier and turned the dimmer up and down and watched the rest of the lights in your home--you probably will not see any difference between the chandelier on or off.

    With a grid tied inverter (wind or solar), there is no "switching" of your AC power, just the effective power current flow from the inverter changes from 0 amps to XX amps as the wind/sunlight vary. So, the loads on your home do not see any power glitches as the inverter output changes over time.

    It really is just like an "AC Battery" charger/alternator version of your car's DC alternator/battery setup. The loads do not "know" where the current/electrons come from.

    Regarding the 5 minute delay--N3qik is saying that the Skystream appears to be properly designed and its internal Grid Tie Inverter does not suffer the 5 minute delay every time the turbine stops and starts in gusts--a very good thing.

    Lastly, you have not asked, and we have not said anything in this thread--but research your wind turbine purchase well... Because of the nature of wind and electromechanical devices, Wind Turbines tend not to produce as much power as people think, and good quality "home sized" turbines are few and far between--plus good or bad, they will need servicing (tilt tower or a crane) every so often for lubrication and repair/replacement.

    I don't have a wind turbine and I am no way connected with any RE mfg. or retails--this is just based on my readings and understanding of the components involved.

    -Bill

    PS: Here is a thread where a couple of different brands of wind generators with good histories are mentioned.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Grid tie lag time.
    PS: Here is a thread where a couple of different brands of wind generators with good histories are mentioned.

    Odd, no thread appears, hmmm what could it mean.... !
    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 ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • BB.BB. Super Moderators, Administrators Posts: 32,748 admin
    Re: Grid tie lag time.

    It's the MISSING LINK. :p

    Thank you Mike. Previous post corrected...

    By the way, that thread is titled "Windmill Bashing" and also features our first known "sock puppet" (at least, that I have seen).

    As with everything on the Internet--verify everything you read. As reporters are told (and appear to have forgotten):
    "If your mother says she loves you, check it out"
    -Bill :blush:
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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