Does MPPT apply to grid tie?

jza80
jza80 Registered Users Posts: 13
I see this value in the SG-view software I'm running, it seems this value tracks to the panel output by about a volt or less.

Is there a purpose for this for a non-battery system? Inverter is Sunpower/Xantrex GT-series.

Thanks!

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Does MPPT apply to grid tie?

    I am not quite sure of your question... But MPPT (Maximum Power Point Tracking) is very useful for Grid Tie system...

    Both because we need to "transform" (DC to DC switching power supply) from XXX Volts DC of the solar panels to 240 VAC of the utility lines, the inverter has to figure out the optimum DC Voltage*Current=Max Power of the solar panels...

    MPPT Voltage can be simply programmed into a solar inverter / charge controller, or just measure the maximum open circuit voltage and take XX%, etc...

    But the Xantrex (and others) are actively checking the V*I to figure out the maximum energy--some are a few times an hour, others are many times a second (60x a second for the Xantrex GT???).

    SG knows the various algorithms for some of the manufacturers--but I am sure some are patented and other are "trade secrets".

    In the end, part of the way to get the maximum performance from your solar panels (or should I say $olar panel$) is because of the MPPT function.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jza80
    jza80 Registered Users Posts: 13
    Re: Does MPPT apply to grid tie?

    Thanks, I did not know the purpose of MPPT for grid tie. I read about it in discussions regarding battery systems but not for grid tie. So if I understand you correctly, the MPPT is just the inverter "reference" adjusting to the changing voltage output of the solar panels?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Does MPPT apply to grid tie?

    Pretty much yes... The switch mode power supply has the ability to change its internal behavior (typically the duty cycle of the high frequency switch module)... So it has to pick some operating parameters--so why not match the optimum I*V point of the solar panels for that moment in time (amount of sun and temperature both affect the Vmp/Imp point for the solar panels).

    And switch mode power supplies are used specifically for inverters because it allows for a smaller isolation transformer (because of the 20-50kHz--or whatever frequency--allows smaller transformers and components).

    For Battery Chargers, they don't need the electrical isolation between the solar panels and the battery bank (most share a common negative ground lead). So, there are other types of power supply circuits that can be used also...

    For example, PWM, think of nothing more than a switch that turns on 100% (more or less a dead short from the solar panel to the battery bank). The switch stays closed until battery becomes mostly charged, when that voltage point it reached, the switch starts to open (typically a some sort of transistor)... First it may only open for 10% of the cycle (dozens or hundreds of time a second), then 50% open, and eventually 90%+ open duty cycle (only 10% of the current from panels flows to the battery bank)....

    A PWM type solar charge controller is less efficient at matching a solar panel's Vmp*Imp point (it cannot), but the circuit is also simpler and cheaper to build (plus it uses less solar panel power to operate). And it works just fine for charging a battery. Especially for smaller systems (typically around 400 watts or less--thre are some new small MPPT controllers that may be efficient even below the 400 watt level).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Does MPPT apply to grid tie?
    BB. wrote: »
    Especially for smaller systems (typically around 400 watts or less--three are some new small MPPT controllers that may be efficient even below the 400 watt level).

    -Bill


    Any model #'s for the lower power MPPT charge controllers ?

    Any feedback on how they are actually working out ?
    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: 33,431 admin
    Re: Does MPPT apply to grid tie?

    The 400 watt lower limit is based on the recommendations (as I recall) for the Outback MX 60 because of tare/overhead power loses to run the unit...

    I think the smaller units are the New Morning Star or Blue Sky(?)--not that I have looked at them--I was just leaving an out for those folks that may find those smaller units that meet their needs.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Does MPPT apply to grid tie?

    for the record, the blue sky products are not new and were under the company name of rv power products before they changed it. though i don't know of the best transition point for these products, i believe they would be lower than the mx60.
  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    Re: Does MPPT apply to grid tie?

    The MorningStar Sunsaver Mppt is really the only 200watt 12v/15A /400watt 24v/15A mppts out there.

    The BlueSky are Good units, built well and comformal coated .. there Mppt is different on the newer units ( 25A ) , more of a mini-sweep mppt, the older units are VOC based.

    Efficiency and harvest wise the Morningstar Mppt is top in this power class, one of the reasons is its a dual-phase synchronous switcher, very efficient typology. The BlueSys is a non-synchronous design and about 3% less efficient