They dun discontinued mah solar panels - help me find a replacement!

cupcakecupcake Solar Expert Posts: 254 ✭✭✭

Hi Pals, cake here again...


They dun disocniued mah panels. Was tryn to add 1 mo'

the spex of the existing 1's are 35.8 Vmpp

Does anyone out there know ANY panel that is AVAILABLE that runs at 35.8 Vmpp?

Mah panels are hooked in parallel so I need to match the 35.8 Vmpp...


Thanks


-cupz caxe


~1.5Kw PV in parallel
Morningstar MPPT-60 controllers (2) in parallel
3 Trojan tr-1275's in parallel 450ah total
Samlex 2,000 watt 12-volt inverter hardwired


Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,489 admin
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • cupcakecupcake Solar Expert Posts: 254 ✭✭✭
    BB. wrote: »




    Bill... the vmpp of the first panel you posted is Vmp: 36.5 Volts, I need 38.5


    Will it be an issue doing 3 38.5 panels AND a 36.5 panel in PARALLEL

    I thought he Vmpp had to be EXACT when doing a parrallel connection..

    Please advise...


    --icing
    ~1.5Kw PV in parallel
    Morningstar MPPT-60 controllers (2) in parallel
    3 Trojan tr-1275's in parallel 450ah total
    Samlex 2,000 watt 12-volt inverter hardwired


  • BB.BB. Super Moderators, Administrators Posts: 29,489 admin
    More or less, Vmp (for parallel) and Imp (for series) should match within ~10%, and 5% or better for a "near" perfect match (given manufacturing variations).
    • 38.5 volts +/- 5% give you 36.6 to 40.4 volts as a very good match
    • 38.5 volts +/- 10% give you 34.7 to 42.4 volts as a "good enough" match
    And this one is a 40.3 volt Vmp panel:

    http://www.solar-electric.com/solar-panels-mounts-kits-accessories/solarpanels/kyocera-solar-panels/kyocera-kd325gx-lfb-325-watt-polycrystalline-solar-panel.html

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • cupcakecupcake Solar Expert Posts: 254 ✭✭✭
    BB. wrote: »
    More or less, Vmp (for parallel) and Imp (for series) should match within ~10%, and 5% or better for a "near" perfect match (given manufacturing variations).
    • 38.5 volts +/- 5% give you 36.6 to 40.4 volts as a very good match
    • 38.5 volts +/- 10% give you 34.7 to 42.4 volts as a "good enough" match

    And this one is a 40.3 volt Vmp panel:

    http://www.solar-electric.com/solar-panels-mounts-kits-accessories/solarpanels/kyocera-solar-panels/kyocera-kd325gx-lfb-325-watt-polycrystalline-solar-panel.html

    -Bill




    Bill,

    Say I gitt the 40.3 vmpp panel you posted - my panels are 35.8 -- what happens to the 'extra voltage' in this case (when all panels are wired in parallel) ???


    Does all voltage go to the 'lowest' voltage in the system?
    Where does the extra voltage 'go'?
    Is there any harm/over-heating/other wanton issues I should know about?

    Do tell...

    --Cakeie



    ~1.5Kw PV in parallel
    Morningstar MPPT-60 controllers (2) in parallel
    3 Trojan tr-1275's in parallel 450ah total
    Samlex 2,000 watt 12-volt inverter hardwired


  • BB.BB. Super Moderators, Administrators Posts: 29,489 admin
    For PWM charge controller--They only "pass current"--So the "extra available voltage" does not do anything--It is never there (the battery bank "clamps" the voltage to whatever is it is (12-15 volts + wiring+controller voltage drop). Solar panels are current sources... So it "is up to the load" to set the voltage.

    For MPPT controllers, it is much more complicated... In theory, the MPPT charge controller "sweeps" the solar array every X minutes. Basically running from zero to maximum current it can draw from the array, while measuring the voltage. Then using the equation:

    Power = Voltage * Current

    It calculates the V*I for the data points and finds the largest result.

    So--Two issues... First, if you have (for example) an 18 and 36 volt panel in parallel, there is no "optimum" voltage where you will get rated power. You will (probably) get several spikes where you have maximum power. One with Vmp~18 volts, another with Vmp~36 volts, and probably a third maximum somewhere in between.

    Which maximum will the MPPT controller select? I do not know. It could pick the "real" maximum or one of the several other local maximums.

    Putting a 35 volt and 40 volt Vmp pair of panels in parallel and connecting them to an MPPT charge controller will not break anything. You just may not get the absolute maximum available power (P=V*I).

    Best case, the controller finds a maximum that is "good enough" for your needs (you will get a little bit less power--5-10% or so less than rated wattage)--But that is the price of having "slightly unmatched panels". Worst case, it picks a really bad voltage (say Vmp~40.4 volts and none of your 35 volt panels will supply any current).

    If you have "worse case"--Your choices are to get a second MPPT charge controller and put the "higher" voltage panels on one controller, and the rest of the "lower voltage" panels on the second.

    Or, you sell your "non-optimum" set of panels and buy a matching set that you can get "today" for a reasonable price.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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