GT modules

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minabenyamin
minabenyamin Solar Expert Posts: 45 ✭
in Grid Tie and Grid Interactive Systems #1
Hello everybody,

someone told me that Solar modules are two types, GT modules and off-grid modules, is that right?

when I buy solar panels for a GT system it's different than solar panels for off-grid systems??

Thanks

Mina
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #2
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    Re: GT modules
    minabenyamin wrote: »
    Hello everybody,

    someone told me that Solar modules are two types, GT modules and off-grid modules, is that right?

    when I buy solar panels for a GT system it's different than solar panels for off-grid systems??

    Thanks

    Mina
    The difference it not quite as clear cut as that.
    For off grid systems, the panels will drive a charge controller (CC) to charge a battery bank.
    If a PWM type CC is used, then a 12V system requires panels with approximately 18V Vmp. That would be a 36-cell panel using silicon cells.
    A panel which is limited in output voltage to 18V is referred to as a "12V battery charging panel" or simply a 12V panel. If 36 each of 6"x6" cells are used, the resulting panel will be only about 3' by 3' in size and will cost more per watt than a 60 or 72 cell module.
    Those higher voltage panels are only suitable for off-grid use is you have an MPPT CC, but are suitable to be used in series strings to go to a Grid Tie Inverter (GTI) which can accept input voltages up to ~600V (more under the 2014 version of the NEC).
    The result of designing either a GT system using high voltage panels in series or an off-grid system using high voltage panels in series and an MPPT CC is that larger, less expensive to manufacture per watt, panels can be and generally are used.
    This adds the the market demand for those larger panels, also helping to drive the per watt price down by allowing economies of scale in manufacturing and distribution.
    SMA SB 3000, old BP panels.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #3
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    Re: GT modules

    PP
    minabenyamin wrote: »
    someone told me that Solar modules are two types, GT modules and off-grid modules, is that right?

    Did you mean "solar panels" instead of solar "modules"?
    when I buy solar panels for a GT system it's different than solar panels for off-grid systems??

    Yes and no... The solar cells/panels themselves operate exactly the same between GT and Off Grid solar panels.

    The difference is that (for example) a 12 volt battery bank and a PWM charge controller (pulse width modulation) for optimum use of solar power from the panels needs Vmp~18 volts (Voltage maximum power for 36 cell panels). If the panel has Vmp less than ~17.5 volts, the panel voltage will be too low to recharge a battery bank on a very hot day (Vmp-panel falls as its solar cells get hot--by upwards of 20% from standard test conditions/marketing numbers).

    For Grid Tied AC inverters (and larger off grid solar power systems), the GT inverters (and charge controllers) have MPPT (maximum power point tracking) inputs for the solar array. So, instead of being limited to a specific voltage--They can take a wide range of input voltages and still function correctly.

    A MPPT type charge controller on a 12 volt battery bank (high end controller) can have an Vmp-array voltage of ~17.5 to 100 VDC and work just fine. There are some that can take >400 VDC input too.

    A MPPT type GT inverter can (approximatly) take Vmp-array of 200-400 volts (+/- --- depending on brand/model).

    So--for a GT based solar panel, their design is no longer tied to a 12/24/48 volt battery bank and PWM charger's limitations for optimum efficiency... The MPPT controller allows the panel manufacturer to make "any" Vmp-panel voltage that is optimum for their process (size of solar cell, amount of copper in panel, size of panel, etc.)... A very common Vmp-stc (standard test condition) voltage is around 30 VDC for GT panels (~60 cell panels). 72 cell panels are another common standard too (Vmp~36 volts). And there have been solar panels with Vmp up near 100 VDC.

    As long as the series/parallel configuration of the panels gives a Vmp-array / Imp-array that matches the input range of the MPPT input for the GT inverter--Everyone is happy. The panel mfg. builds the lowest cost panel they can. The GT inverter gets high voltage (easier for them to use), and the installer uses less copper wire (higher voltage, lower current, less copper needed to run cable from array to GT inverter).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #4
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    Re: GT modules
    BB. wrote: »
    PP

    Did you mean "solar panels" instead of solar "modules"?

    She meant modules, which is the correct term, although colloquially modules are often called panels. See the definitions at the beginning of 690.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #5
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    Re: GT modules

    "He"... :-)

    No problem... I was just trying to make sure Mina was not talking about distributed GT Inverters (Micro Inverters) or something else.

    A "solar module" is not specifically Off Grid or Grid Tie except by the application.

    -Bill "trying to be clear" B.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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