Overview and comparison with PV Watts

Sighten‘s production model incorporates key aspects of the industry’s most sophisticated models while maintaining simplicity of user inputs.

Highlights

• Simple and non-assumptive user inputs required: module and inverter quantities/models, pitch, azimuth, and shading

• Hourly production calculations with granular weather data

• Module and inverter-level electrical behavior modeled 

Overview

Full description of Sighten's production calculation

• production is simulated for each array on an hourly basis
• primary sources of input:
  • TMY weather data (8760 hours) based on system location
  • PV module electrical specifications per manufacturer spec sheet
    • includes parameters we calculate to construct IV curve (DeSoto)
  • inverter electrical specifications per manufacturer spec sheets
  • array details (e.g. tilt, azimuth, string size, shading, etc)
• for each hour of a TMY dataset:
  • determine the solar radiation incident on the tilted surface
    •  "unshaded" radiation includes beam radiation component
    • "shaded" radiation assumes no beam radiation
  • determine solar cell temperature based on PV model specifications in both shaded and unshaded conditions
  • construct I-V curve of solar cell based on IV curve parameters calculated as functions of solar cell temperature for both shaded and unshaded conditions (Desoto)
  • determine the AC power generated from the array:
    • NOTE: the percentage shading implies the percentage of PV modules IN EACH STRING that receive "unshaded" radiation versus "shaded" radiation
    • if the array uses a string inverter:
      • the string voltage is calculated as a composite of the unshaded and shaded PV modules
      • find array max power (DC) by calculating string voltage as a function of a universally-applied string current
      • find module voltage on the I-V curve for unshaded module
      • find module voltage on the I-V curve for shaded module
      • string voltage is the sum of voltages generated by unshaded and shaded modules in their respective proportion
      • iterate until maximum of product of string voltage and array current is found
    • convert array power (DC) into array power (AC) based on inverter efficiency specifications (per spec sheet) and derate assumptions applied to all string inverters:
      • wiring_dc = 0.980
      • mismatch  = 0.980
      • diodes    = 0.995
      • soiling   = 0.950
      • wiring_ac = 0.990
  • if the array uses microinverters:
    • find array max power (DC) by calculating unshaded and shaded module voltages as functions of a individually-managed current
      • find module max power (DC) on the I-V curve for unshaded module
      • find module max power (DC) on the I-V curve for shaded module
      • convert module power (DC) into module power (AC) for unshaded and shaded modules based on inverter efficiency specifications (per spec sheet) and derate assumptions applied to all microinverters:
        • wiring_dc = 0.995
        • mismatch  = 1.000
        • diodes    = 0.995
        • soiling   = 0.950
        • wiring_ac = 0.990
      • array power (AC) is the sum of power (AC) generated by unshaded and shaded modules in their respective proportion of the array