Sunlight Story (2)

Editor : Optomon

 On my previous article, Sunlight Story (1), I explained about sunlight which we receive everyday from the Sun, that is Solar Energy. In this article, I am going to talk about a Solar Simulator.

What is Solar Simulator?

 Power and Efficiency of Solar Cells or Modules which convert sunlight to electricity must be expressed by values which are measured under internationally recognized Standard Test Condition (STC). Standards for Light Intensity is 1 kW/㎡, Solar Radiation Spectrum is AM(AirMass)1.5 and temperature of solar cell is 25 ℃. Measurement Test must meet the standards. If not, the test has to be calibrated. When solar cells are tested for their performance at authorized test organization or manufacturing facility, instead of natural sunlight, a solar simulator is used which is very similar to the real sunlight in terms of light intensity and wavelength distribution. The reason is that natural sunlight varies depends on time and location thus accuracy is low. Also, manufacturing facilities cannot use is in real time measurement.

 A solar simulator is manufactured in accordance to IEC 60904-9 test regulations which are International Standards.

Construction of Solar Simulator

   Xenon short arc Lamp : Light source similar to sun wavelength
  ? Reflector : Reflects Point Light Source from a lamp in one direction
  ? Plane Mirror : Changes light path in 45°
  ? Special Filter : Filters light to make it similar to AM1.5G spectrum wavelength. (Selective Block-off capability)
  ? Integrating Lens (Fly eye lens) : Create uniformed illuminance (focus light and reduce brightness differences)
  ? Collimating Lens : Changes irregular incident light rays into parallel rays


Solar Simulator and its light irradiance shape(SimuLightTM XE330, McScience)

Standards for Solar Simulator

 Three international organizations have been setting standards for Solar Simulator and the organizations and standards are as below.
? American Society for Testing and Materials(ASTM, Standard Reference # E927 – Standard Specification for Solar Simulation for Terrestrial Photovoltaic Testing ? Standards for USA
? International Electrotechnical Commission(IEC, Standard Reference # IEC 60904-9 – Solar simulator performance requirements) ? Standards for Europe
? Japanese Standards Association (JSA) – Japanese Industrial Standards(JIS C 8912 – Solar simulators for crystalline solar cells and modules, JIS C 8933 Solar simulators for amorphous solar cells and modules)

 Three classes are defined. – Class A – Class B – Class C
Each class defines degree of conformity of Light Beam against real sunlight in the fields of followings.
? Integrated irradiance in a specific wavelength range (AM1.5G, 400 ~ 1,100nm)
? Non-Uniformity of Irradiance
? Temporal Instability of Irradiance
? Spectral Match against sunlight within specified wavelength for each AirMass

 To be classified as “Class A”, a solar simulator has to satisfy three requirements under “Class A” section such as Non-Uniformity of Irradiance must be less than 2 %, Temporal Instability of Irradiance must be less than 2 % and Spectral Match has to be ± 25% or better. Also, Integrated irradiance under AM1.5G must be 1000 W/m2 (100 mW/cm2)

 Even if there is big deviation in each wavelength range overall Integrated irradiance must match to specifically defined solar irradiance. Even if standards allows deviations in wide ranges, a solar simulator with the best quality has much better spectral match in each wavelength ranges.

Solar simulator standards classifications

 IEC Standards classify solar simulators in three alphabets such as AAB. That are the first letter represents class of Spectral Match, the second letter represents Non-Uniformity of Irradiance and the third letter represents Temporal Instability of Irradiance. The standards also allow another way of expression. For example, a solar simulator which satisfies all of three requirements can be described as “Class AAA”.

To be continued on January’s issue in 2015…