PV Solar Specific aspects: Performance Ratio, Life expectancy and Irradiance

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Performance Ratio: It is used to assess the installation quality, which is calculated as follows:

PR= Esys÷ Eideal


Esys = the actual yearly energy yield from the system

Eideal = the ideal energy output of the system

The PV array ideal energy yield (Eideal) can be determined by two ways:

Method 1:

Eideal l = Parray_STC × Htilt


Parray_STC = the rated output power of the array under standard test conditions, in watts

Htilt = yearly average daily irradiation, in kWh/m2for the specified tilt angle

Method 2:

Eideal = Hpv ×ɳpv


Hpv = actual irradiation that falls on the array surface area

ɳpv = efficiency of the PV modules


Hpv= Htilt × Apv


Apv = total area of the PV array

Htilt = yearly average daily irradiation, in kWh/m2for the specified tilt angle

Life Expectancy:

The recommended life expectancy used in life cycle assessment of photovoltaic components and systems is different for components:

  • Modules: 30 years for mature module technologies
  • Inverters: 15 years for small size plants (residential PV); 30 years with 10% of part replacement every 10 years
  • Structure: 30 years for roof-top and facades and between 30 to 60 years for ground mount installations on metal supports.
  • Cabling: 30 years


The irradiation depends on the location and orientation of the modules.


  • Direct Normal: Measured by a pyrheliometer on a sun following tracker.
  • Global Horizontal: Measured by a pyranometer with a horizontal sensor.
  • Diffuse: Measured by a shaded pyranometer under a tracking ball.

Solar Irradiance Components

Global = Direct Normal* Cos (Z) + Diffuse

Posted by: Prateek Sikka

2 Responses to "PV Solar Specific aspects: Performance Ratio, Life expectancy and Irradiance"
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