PV Modules manufacturer wattage tolerance and performance calculations

We install utility sized PV generating facilities, 10 MW+. Our client is proposing to furnish 280W "nominal" modules with a tolerance of +5%/-3%. In other words we could end up with 272 watt and 294 watt modules in the same crate. It is my understanding that our performance calculations should be based upon the lowest wattage module in the string? The manufacturer has taken the position that sorting the modules is not necessary???? What say the experts, I'm the site layout and civil guy, so sorry in advance for my ignorance of all things electrical, it just smells wrong to me.:confused::confused::confused:


  • BB.BB. Super Moderators, Administrators Posts: 33,140 admin
    Re: PV Modules manufacturer wattage tolerance and performance calculations

    That specification is pretty standard... In California, we have to use the PTC ratings as documented by the state (PTC is a more reasonable day to day power number based on actual solar array temperature in full sun--Usually somewhere around 80-85% of manufacturer's marketing spec. I have not seen any +/-% Watts spec'ed with the PTC numbers).

    You do not need to sort the panels to match their Vmp/Imp specifications.

    The Vmp*Imp power curve is pretty flat around the Pmp (peak power) and panel Vmp and Imp rating variations that are within ~10% or less are not going to really cause any overall power reduction issues.

    There are some vendors that sell a "magic brick" that are supposed to balance parallel strings with slight Vmp/Imp/Shading issues to increase/optimize total power output. (i.e., such as Solar Edge).

    Are these devices needed and/or a good investment... I really don't know--but I would need convincing.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • NorthforkerNorthforker Registered Users Posts: 15
    Re: PV Modules manufacturer wattage tolerance and performance calculations

    Thanks for the reply Bill
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