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PVWatts Instructions

The NREL PVWATTS® Calculator tool is used to calculate estimated system production from a solar photovoltaic (PV) system.

(2015 Notice from NREL) “NREL released a new version of PVWatts® in September 2014 which changes the results significantly to more accurately reflect PV performance outputs from current systems. Note that the results will typically increase 7 to 10 percent. This version updates the default derate/loss values, uses a modern inverter curve and adds several options. You can read more about this update here. The old versions PVWatts V1 and PVWatts V2 have been retired.”

There are two versions available for analyzing solar PV grid-tied system production estimates. The PVWatts Calculator is simpler to use and is typically adequate for system evaluation. The System Advisor Model (SAM) is more advanced, requires professional knowledge and extensive data input, and is recommended for certain array types utilizing reflector technologies to maximize solar PV production.

To use the NREL PVWATTS Calculator, use the following guidance:

  • Current NREL Versions accepted by the NJCEP

     NREL PVWatts Calculator

     NREL System Advisor Model (SAM)

 

  • Click here for a slideshow of instructions that offer basic guidance on how to obtain the results that the NJCEP requires for the Final As-Built paperwork.
  • Specific instructions and descriptions of sections in the PVWatts Calculator are provided by NREL through integrated website interfaces, or by using the website’s “Help” menu.
  • NJCEP Requirements for PVWatts: further guidance is provided within the instructions section of the “Solar SRP Final As-Built Forms”, within the “Tech Worksheet Instructions” tab.  Downloadable forms can be found on this webpage.

    Program-mandatory changes within PVWatts
  • “Ideal” PVWatts
    –    DC System Size (kW)
  • “As Built” PVWatts (Per Array Plane)
    –    DC System Size (kW)
    –    Array Type (fixed, 1-axis, 2-axis, etc.)
    –    System Losses % (DC-to-AC Derate Factor)
    –    Tilt (°)
    –    Azimuth (°)
    –    Inverter Efficiency (%)
  • “As Built” Loss Calculator (derate calculator)
    –    (PV Module) Nameplate (DC) rating (%)
    –    Shading (%) [not “Solar Access” %]
    Do not alter any further values or options when submitting to the NJCEP.
  • The guidelines have changed regarding hard-copy submittal of PVWatts and Shading Report.  Hard copies are not required to be submitted with the final As-Built packet.  BUT…
    The NJCEP reserves the right to request a complete copy of production estimates, a full shade analysis, or any relevant documentation from the installer at any time.  Save a copy of the “Results” pages for permanent record with the project file.

 


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