If the default overall DC to AC derate factor of 0.77 is not appropriate for your PV system, you may use this calculator to determine a new value by changing one or more of the component derate factors in the table and clicking the "Calculate Derate Factor" button. You may enter values within the ranges shown in the table. Values outside the ranges are reset to to the default values by the derate calculator. The new overall DC to AC derate factor may be hand entered, or copied and pasted, into the "DC to AC Derate Factor" field on the PV Systems Specifications section of the PVWATTS input form. Click on HELP below the table for information about DC to AC derate factors.
Calculator for Overall DC to AC Derate Factor

Component Derate Factors Component
  Derate Values   		Range of
Acceptable Values
  PV module nameplate DC rating 0.80 - 1.05
  Inverter and Transformer 0.88 - 0.96
  Mismatch 0.97 - 0.995
  Diodes and connections 0.99 - 0.997
  DC wiring 0.97 - 0.99
  AC wiring 0.98 - 0.993
  Soiling 0.30 - 0.995
  System availability 0.00 - 0.995
  Shading 0.00 - 1.00
  Sun-tracking 0.95 - 1.00
  Age 0.70 - 1.00
  Overall DC to AC derate factor            0.77                       (PVWATTS Default)


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