Talk:Solar simulator

• Why it should be changed:

The current introduction does not sufficiently include all major areas where solar simulators are used, nor does it adequately cite sources/examples of these applications.

• References supporting the possible change (format using the "cite" button):

1. spectral content
2. spatial uniformity
3. temporal stability

Each dimension is classified in one of three classes: A, B, or C. The specifications required for each class are defined in Table 1 below. A solar simulator meeting class A specifications in all three dimensions is referred to as a Class A solar simulator, or sometimes a Class AAA (referring to each of the dimensions in the order listed above).^[16]

The solar simulation spectrum is further specified via the integrated irradiance across several wavelength intervals. The percentage of total irradiance is shown below in Table 2 for the standard terrestrial spectra of AM1.5G and AM1.5D, and the extraterrestrial spectrum, AM0.

These specifications were primarily intended for silicon photovoltaics, and hence the spectral range over which the intervals were defined was limited mainly to the absorption region of silicon. While this definition is also adequate for several other photovoltaic technologies, including thin film solar cells constructed from CdTe or CIGS, it is not sufficient for the emerging sub-field of concentrated photovoltaics using high-efficiency III-V semiconductor multi-junction solar cells due to their wider absorption bandwidth of 300–1800 nm.

New:

The standards specifying performance requirements of solar simulators used in photovoltaic testing are IEC 60904-9^[17], ASTM E927-19^[18], and JIS C 8912^[19] These standards specify the following dimensions of control for light from a solar simulator:

1. spectral content (quantified as spectral match)
2. spatial uniformity
3. temporal stability
4. Spectral Coverage (SPC) (IEC 60904-9:2020 only)
5. Spectral Deviation (SPD) (IEC 60904-9:2020 only)

A solar simulator is specified according to its performance in the first three of the above dimensions, each in one of three classes: A, B, or C. (A fourth classification, A+, was introduced by the 2020 edition of IEC 60904-9 and only applies for solar simulators evaluated in the spectral range of 300 nm to 1200 nm^[17]). For ASTM E927, if a solar simulator falls outside the A,B,C criteria, it is considered Class U (unclassified)^[18]. Although these standards were originally defined specifically for photovoltaic testing, the metrics they introduced have become a common way of specifying solar simulators more broadly in other applications and industries^[20][21][22].

The ASTM E927-19 specifications required for each class and dimension are defined in Table 1 below. A solar simulator meeting class A specifications in all three dimensions is referred to as a Class AAA solar simulator (referring to the first three dimensions listed above).^[18]

The ASTM E927 standard specifies that whenever this triple-letter format is used to describe a solar simulator, it needs to be made clear which classification applies to each solar simulator metric^[18] (e.g. a Class ABA solar simulator needs to make clear which parameter(s) are Class A vs B). The IEC 60904-9 standard specifies that the three letters must be in order of spectral match, non-uniformity, and temporal instability^[17].

• Why it should be changed:

Updated links to the solar simulator standards need to be provided, as well as the inclusion of the JIS C 8912 standard which was absent. The recent update to the IEC 60904-9:2020 standard added spectral coverage and spectral deviation metrics which needed to be added as well, along with the definition of a new A+ classification which required clarification of which spectral range it must be applied to. Since spectral coverage and spectral deviation are optional metrics at this time, clarity was needed around which metrics are mandatory to achieve Class AAA classification.

Spectral content needed to be made clearly equivalent to spectral match since that is how it is referenced in the standards.

Also clarified details around Class AAA nomenclature which are not necessarily consistent in the nomenclature.

The content referring to spectral match is recommended to be moved to its own subsection.

• References supporting the possible change (format using the "cite" button):

See in-line citations above.

• What I think should be changed (include citations):

This subsection did not previously exist, but I will show the original content that will be moved and included in this new subsection.

Original:

The solar simulation spectrum is further specified via the integrated irradiance across several wavelength intervals. The percentage of total irradiance is shown below in Table 2 for the standard terrestrial spectra of AM1.5G and AM1.5D, and the extraterrestrial spectrum, AM0.

These specifications were primarily intended for silicon photovoltaics, and hence the spectral range over which the intervals were defined was limited mainly to the absorption region of silicon. While this definition is also adequate for several other photovoltaic technologies, including thin film solar cells constructed from CdTe or CIGS, it is not sufficient for the emerging sub-field of concentrated photovoltaics using high-efficiency III-V semiconductor multi-junction solar cells due to their wider absorption bandwidth of 300–1800 nm.

New:

A solar simulator’s spectral match is computed by comparing its output spectrum to the integrated irradiance in several wavelength intervals. The reference percentage of total irradiance is shown below in Table 2 for the standard terrestrial spectra of AM1.5G and AM1.5D, and the extraterrestrial spectrum, AM0. Below is a plot of these two spectra.

A solar simulator’s spectral match ratio, ${\displaystyle R_{SM}}$ (i.e. ratio of spectral match), is its percentage output irradiance divided by that of the reference spectrum in that wavelength interval. For example, if a solar simulator emits 17.8% of its total irradiance in the 400 nm - 500 nm range, it would have a ${\displaystyle R_{SM}}$ in that wavelength interval of 0.98. If a solar simulator achieves a spectral match ratio ${\displaystyle R_{SM}}$ between 0.75 and 1.25 for all wavelength intervals, it is considered as having class A spectral match.

These wavelength intervals were primarily intended for the solar simulator application of testing silicon photovoltaics, hence the spectral range over which the intervals were defined was limited mainly to the originally-developed absorption region of crystalline silicon (400 nm - 1100 nm).

The solar simulator standards have some requirements for where the illumination spectrum must be measured. For example, the IEC 60904-9 standard requires that the spectrum be measured at 4 different locations in a pattern given below^[17].

Recent material science developments have expanded the spectral responsivity range of c-Si, multi-c-Si and CIGS solar cells to 300 nm - 1200 nm^[17]. Therefore, in 2020, the IEC 60904-9 standard introduced a new Table of wavelength intervals (given in Table 3 below) aimed to match solar simulator output to the present needs of a wide variety of photovoltaic devices^[17].

While the above definition of spectral range is adequate for addressing the testing needs of many photovoltaic technologies including thin film solar cells constructed from CdTe or CIGS, it is not sufficient for testing multi-junction solar cells using high-efficiency III-V semiconductors that have wider absorption bandwidths from 300–1800 nm.

For accurate spectral data outside the above-mentioned ranges, the data tables in ASTM G173 (for AM1.5G and AM1.5D)^[23] and ASTM E490 (for AM0)^[24] can be used as reference, but the specifications of solar simulators unfortunately do not yet apply to anything outside 300 nm to 1200 nm for AM1.5G, and 300 nm to 1400 nm for AM0. Many solar simulator manufacturers produce light outside these regions, but the classification of light in these external regions is not yet standardized.

• Why it should be changed:

This topic is large enough to merit its own subsection. Added how the ratio of spectral match is computed in order for the spectral match classification to be determined. Corrected percentage values to the latest values from the standards. Added required detail that measurements need to be made in multiple locations for a valid spectral match measurement, and updated context and information around the previous comments about photovoltaic technology types and the applicability of solar simulators.

• References supporting the possible change (format using the "cite" button):

${\displaystyle S_{NE}=100{\frac {{\text{max}}(I_{s})-{\text{min}}(I_{s})}{{\text{max}}(I_{s})+{\text{min}}(I_{s})}}}$

Here ${\displaystyle I_{s}}$ is the array of normalized short-circuit current values detected by a solar cell or array of solar cells. The three solar simulator standards have slightly different requirements for how the array of measurements is gathered for computing spatial non-uniformity. ASTM E927 specifies that the illumination field must be measured at a minimum of 64 positions. The area of each test position, ${\displaystyle A_{TP}}$, is the illumination test area divided by the number of positions. The area of the detector used must be between 0.5 and 1.0 of ${\displaystyle A_{TP}}$^[18].

• Why it should be changed:

Specification of how to measure and calculate spatial non-uniformity should be added in order for a reader to understand how a solar simulator is classified, similar to the provided explanations for how to compute spectral match.

• References supporting the possible change (format using the "cite" button):

${\displaystyle T_{IE}=100{\frac {{\text{max}}(I_{T})-{\text{min}}(I_{T})}{{\text{max}}(I_{T})+{\text{min}}(I_{T})}}}$

Here ${\displaystyle I_{T}}$ is the array of measurements gathered over the period of data acquisition. The solar simulator standards do not specify the required time interval or sampling frequency in absolute terms.

• Why it should be changed:

This subsection is needed to inform readers how a solar simulator can have its temporal instability classified, similar to the explanations provided for how to calculate spectral match.

• References supporting the possible change (format using the "cite" button):

${\displaystyle SPC=\left(\sum _{E_{SIM}(\lambda )>0.1\cdot E_{AM1.5}(\lambda )}E_{AM1.5}(\lambda )\cdot \Delta \lambda {\Bigg /}\sum _{\text{300 nm}}^{\text{1200 nm}}E_{AM1.5}(\lambda )\cdot \Delta \lambda \right)\cdot 100\%}$0.1\cdot E_{AM1.5}(\lambda )}E_{AM1.5}(\lambda )\cdot \Delta \lambda {\Bigg /}\sum _{\text{300 nm}}^{\text{1200 nm}}E_{AM1.5}(\lambda )\cdot \Delta \lambda \right)\cdot 100\%}"/>

• Why it should be changed:

This subsection is needed to inform readers how a solar simulator can have its spectral coverage calculated, similar to the explanations provided for how to calculate spectral match.

• References supporting the possible change (format using the "cite" button):

• Why it should be changed:

This subsection is needed to inform readers how a solar simulator can have its spectral deviation calculated, similar to the explanations provided for how to calculate spectral match.

• References supporting the possible change (format using the "cite" button):

The second type of solar simulator is the flashed simulator which is qualitatively similar to flash photography and use flash tubes. With typical durations of several milliseconds, very high intensities of up to several thousand suns are possible. This type of equipment is often used to prevent unnecessary heat build-up in the device under test. However, due to the rapid heating and cooling of the lamp, the intensity and light spectrum are inherently transient, making repeated reliable testing more technically challenging. The temporal stability dimension of the standard does not directly apply to this category of solar simulators, although it can be replaced by an analogous shot-to-shot repeatability specification.

The third type of solar simulator is the pulsed simulator, which uses a shutter to quickly block or unblock the light from a continuous source. This category is a compromise between the continuous and flash, having the disadvantage of the high power usage and relatively low intensities of the continuous simulators, but advantage of stable output intensity and spectrum. The short illumination duration also provides the benefit of the low thermal loads of flashed simulators. Pulses are typically on the order of 100 milliseconds up to 800 milliseconds for special Xe Long Pulse Systems. Those systems are being offered for different segments such as quality control in production for solar cells and modules as well as independent laboratories or manufacturer R&D. Laboratory systems typically offer enhanced functions like temperature cycling and configurable irradiation levels. ^[36]

New:

Solar simulators can be divided into two different categories according to their emission duration: continuous (or steady-state), and flashed (or pulsed). Solar simulators are also sometimes categorized according to the number of lamps used to generate the spectrum: single-lamp or multi-lamp^[37].

• Why it should be changed:

There is enough to discuss about each type of solar simulator that the information should be moved to their own subsections. Furthermore, there is no distinction between 'flashed' and 'pulsed' solar simulators in the standards, so the content around 'pulsed' solar simulators should be removed. Shutters for solar simulators are an optional accessory that do not bring about a new classification.

• References supporting the possible change (format using the "cite" button):

See in-line citations above.

• What I think should be changed (include citations):

This text should be given its own subsection, and the examples of solar simulator manufacturers removed to put into a list at the end of the entire article.

Original:

The first type is a familiar form of light source in which illumination is continuous in time. The specifications discussed in the previous section most directly relate to this type of solar simulator. This category is most often used for low intensity testing, from less than 1 sun up to several suns. In this context, 1 sun is typically defined as the nominal full sunlight intensity on a bright clear day on Earth, which measures 1000 W/m². Continuous light solar simulators may have several different lamp types combined (e.g. an arc source and one or more halogen lamps) to extend the spectrum far into the infrared. ^[25] Examples of low-intensity and high-intensity continuous solar simulators are available from Solar Light Company, Inc. (inventor of the original solar simulator in 1967,) Atonometrics,^[26] Eternal Sun,^[27] TS-Space Systems,^[28] WACOM,^[29] Newport Oriel,^[30] Sciencetech,^[31] Spectrolab,^[32] Photo Emission Tech,^[33] Abet Technologies,^[34] infinityPV ^[35]

New:

The first type is a familiar form of light source in which illumination is continuous in time, also known as steady-state. The specifications discussed in the previous sections most directly relate to this type of solar simulator. This category is most often used for low intensity testing, from less than 1 sun up to several suns. The total integrated irradiance for the AM1.5G spectrum is 1000.4 ${\displaystyle W\cdot m^{-2}}$ (280 nm to 4000 nm bandwidth)^[23] which is often referred to as ‘1 sun’. Continuous light (or Continuous-Wave, CW) solar simulators may have several different lamp types combined (e.g. an arc source and one or more halogen lamps) to extend the spectrum far into the infrared. ^[25]

• Why it should be changed:

Examples of solar simulator manufacturers do not belong in this section, and clutter the information being presented. The definition of 1 sun needs to be less ambiguous as it has strict definitions.

• References supporting the possible change (format using the "cite" button):

See in-line citations above.

• What I think should be changed (include citations):

This discussion of flashed solar simulators merits its own subsection.

Original:

The second type of solar simulator is the flashed simulator which is qualitatively similar to flash photography and use flash tubes. With typical durations of several milliseconds, very high intensities of up to several thousand suns are possible. This type of equipment is often used to prevent unnecessary heat build-up in the device under test. However, due to the rapid heating and cooling of the lamp, the intensity and light spectrum are inherently transient, making repeated reliable testing more technically challenging. The temporal stability dimension of the standard does not directly apply to this category of solar simulators, although it can be replaced by an analogous shot-to-shot repeatability specification.

New:

The second type of solar simulator is the flashed or pulsed simulator which is qualitatively similar to flash photography and uses flash tubes. With typical durations of several milliseconds, very high intensities of up to several thousand suns are possible. This type of equipment is often used to prevent unnecessary heat build-up in the device under test. However, due to the rapid heating and cooling of the lamp, the intensity and light spectrum are inherently transient, making repeated reliable testing more technically challenging. Solid-state lamp technology such as LEDs mitigate some of these heating and cooling concerns in flash solar simulators^[38]. The solar simulator standards provide guidance for steady-state compared to flashed solar simulators. For example, ASTM E927 section 7.1.6.3 provides guidance on temporal instability measurements for flashed solar simulators^[18].

• Why it should be changed:

The discussion is long enough to warrant a visible break from other solar simulator discussions in its own subsections. The text about temporal stability of the standards not applying to this type of solar simulator is false as per 7.1.6.3 of ASTM E927 which specifies that for flashed or pulsed simulators "repeat 7.1.6.2 for a minimum of 20 successive pulses" where Section 7.1 specifies test methods for temporal instability of irradiance.

• References supporting the possible change (format using the "cite" button):

1. Light sources (lamps) and power sources
2. Optics and optical filters, to alter the beam and obtain desired properties
3. Control elements for operation

• Why it should be changed:

This section needs to be added to inform readers of the basic building blocks of a solar simulator, in order to provide better context for subsequent sections where lamp types are discussed.

• References supporting the possible change (format using the "cite" button):

Xenon arc lamp: this is the most common type of lamp both for continuous and flashed solar simulators. These lamps offer high intensities and an unfiltered spectrum which matches reasonably well to sunlight. However, the Xe spectrum is also characterized by many undesirable sharp atomic transitional peaks, making the spectrum less desirable for some spectrally sensitive applications.

Metal Halide arc lamp: Primarily developed for use in film and television lighting where a high temporal stability and daylight colour match are required, metal halide arc lamps are also used in solar simulation.

QTH: quartz tungsten halogen lamps offer spectra which very closely match black body radiation, although typically with a lower color temperature than the sun.

LED: light-emitting diodes have recently been used in research laboratories to construct solar simulators, and may offer promise in the future for energy-efficient production of spectrally tailored artificial sunlight.

New:

Several types of lamps have been used as the light sources within solar simulators. The lamp type is arguably the most important determining factor of a solar simulator’s performance limits with respect to intensity, spectral range, illumination pattern, collimation and temporal stability^[1].

• Why it should be changed:

There is much more discussion and content needed for each lamp type that merit their own subsections, and putting the lamp types into alphabetical order removes implicit bias from the order the information is presented in.

• References supporting the possible change (format using the "cite" button):

See in-line citations above.

• What I think should be changed (include citations):

Original:

There is currently no content for this

New:

Argon arc lamps were used in early solar simulation studies (1972) and have a high color heat emission of 6500 K well-matched to the sun’s blackbody temperature, with a relatively broad spectral emission from 275 nm to 1525 nm^[1]. High-pressure argon gas cycles between an anode and a cathode, with a water vortex flowing along the inside quartz tube wall to cool the arc edge^[14]. Argon arc lamps carry the disadvantages of short lifetimes and poor reliability^[1]. A sample spectrum is included below^[39].

• Why it should be changed:

This type of solar simulator lamp was absent in the past.

• References supporting the possible change (format using the "cite" button):

See in-line citations above.

• What I think should be changed (include citations):

Original:

There is currently no content for this

New:

Carbon arc lamps have an emission similar to AM0 and are therefore used for solar simulators designed to produce extrasolar spectra (being used for NASA’s first space simulators)^[1]. Carbon arc lamps benefit from higher-intensity UV emission. However, they have the disadvantage of being generally weaker in intensity than similar xenon arc lamps ^[1]. In addition, they have a short lifetime, are unstable during operation and emit high-intensity blue light mismatched to the solar spectrum^[1]. An example spectrum is included below^[40].

• Why it should be changed:

The carbon arc lamp was absent from the previous article.

• References supporting the possible change (format using the "cite" button):

See in-line citations above.

• What I think should be changed (include citations):

Original:

LED: light-emitting diodes have recently been used in research laboratories to construct solar simulators, and may offer promise in the future for energy-efficient production of spectrally tailored artificial sunlight.

New: Since approximately the year 2000, Light-emitting diodes (LEDs) have become commonly used in PV solar simulators^[37]. LEDs emit light when electron-hole pairs recombine^[41]. They are low-cost and compact with low power consumption^[1]. They typically have narrow bandwidths of the order of 10 nm - 100 nm, so multiple LEDs need to be combined to make a solar simulator^[42]. As such, the spectral match of a LED solar simulator is largely determined by the number and type of LEDs used in its design. LEDs can be accurately controlled to time windows less than a millisecond for steady or flashed solar simulator applications^[1]. Additionally, LEDs have a very long life cycle compared to all other solar simulator lamp types and are very efficient in energy conversion^[1]. Ongoing research and development on LEDs is continually driving down their cost^[1] and expanding their spectral coverage^[42], allowing them to be increasingly employed in wider-spectrum solar simulators. LED solar simulators are unique in that their spectra can be tuned electrically (by increasing or decreasing the intensity of various LEDs) without the need for optical filters^[43]. Compared to xenon arc lamps, LEDs have demonstrated equivalent results in IV testing of photovoltaic modules, with better stability, flexibility and spectral match^[44]. Because LED emission is somewhat sensitive to junction temperature, they have the disadvantage of requiring adequate thermal management^[45]. Two example spectra are included below, showing the capability for low^[43] or high^[46] spectral match depending on the number and type of LEDs used.

• Why it should be changed:

The state of the art of LED solar simulators has changed dramatically, and the current article does not reflect existing research and commercially-available LED solar simulators.

• References supporting the possible change (format using the "cite" button):

See in-line citations above.

• What I think should be changed (include citations):

Original:

Metal Halide arc lamp: Primarily developed for use in film and television lighting where a high temporal stability and daylight colour match are required, metal halide arc lamps are also used in solar simulation.

New:

Metal Halide arc lamps were primarily developed for use in film and television lighting where a high temporal stability and daylight colour match are required. However, for these same properties, metal halide arc lamps are also used in solar simulation. These lamps produce light through a high-intensity discharge (HID) by passing an electric arc through vapourized high-pressure mercury and metal halide compounds^[14]. Their disadvantages include high power consumption^[1], high electronic driver costs^[1], and short life cycles^[1]. However, they have the benefit of relatively low costs^[14], and because of this low cost, many large-area solar simulators have been built with this technology^{[47] [48]}. An example spectrum is given below^[49]

• Why it should be changed:

There was much detail absent from the original article on metal halide solar simulator lamps.

• References supporting the possible change (format using the "cite" button):

See in-line citations above.

• What I think should be changed (include citations):

Original:

QTH: quartz tungsten halogen lamps offer spectra which very closely match black body radiation, although typically with a lower color temperature than the sun.

New:

Quartz-tungsten halogen lamps (QTH lamps) offer spectra which very closely match black body radiation, although typically with a lower color temperature than the sun.They are a type of incandescent lamp where a halogen such as bromine or iodine surrounds a heated tungsten filament^[14]. Their disadvantage is that they have a maximum color temperature of 3400 K meaning they produce less UV and more IR emission than sunlight^[14]. They are high-intensity^[1] and low-cost^[1], and are widely used in less spectrum-sensitive applications like concentrated solar collector testing^[14]. An example spectrum is included below^[50].

• Why it should be changed:

There was significant detail absent from the original content.

• References supporting the possible change (format using the "cite" button):

See in-line citations above.

• What I think should be changed (include citations):

Original:

There is currently no content for this

New:

A super continuum laser is a source of high-power, broadband light that can range from the visible range to the IR^[1]. Lasers are high-intensity and easy to focus, but have the disadvantage of only illuminating very small areas^[1]. Their high intensities, however, allow for testing of photovoltaic modules in solar concentrator applications. An example spectrum is included below^[51].

• Why it should be changed:

This is a type of solar simulator which needs to be mentioned along with all other lamp types.

• References supporting the possible change (format using the "cite" button):

See in-line citations above.

• What I think should be changed (include citations):

Expansion of discussion of properties, advantages and disadvantages, better schematic drawing, and better spectrum to enable comparison to other lamp types.

Original:

Xenon arc lamp: this is the most common type of lamp both for continuous and flashed solar simulators. These lamps offer high intensities and an unfiltered spectrum which matches reasonably well to sunlight. However, the Xe spectrum is also characterized by many undesirable sharp atomic transitional peaks, making the spectrum less desirable for some spectrally sensitive applications.

New: Xenon arc lamps are the most common type of lamp both for continuous and flashed solar simulators. They are a type of high-intensity discharge (HID) lamp where light is produced from an electric arc through ionized, high-pressure xenon gas ^[14]. These lamps offer high intensities and an unfiltered spectrum which matches reasonably well to sunlight. Furthermore, these lamps exhibit no significant spectral balance shift due to differences in power, reducing the need for power source stability^[1]. Because they emit high intensities from a single bulb, a collimated high-intensity beam can be produced from xenon arc lamps^[14]. However, the xenon arc lamp spectrum is characterized by many undesirable sharp atomic transitional peaks, as well as generally stronger emission in the infrared^[14] making the spectrum less desirable for some spectrally sensitive applications. These emission peaks are typically filtered using glass filters^[1]. Xenon lamps carry many disadvantages including a high power consumption^[1], a need for constant maintenance^[1], a short life cycle ^[1], a high cost^[14], an output sensitivity to power supply instabilities^[14], a risk of bulb explosion due to their operation via high-pressure gas^[14], and an ozone respiratory hazard due to ozone production from UV radiation^[14].

A schematic of the components of a typical xenon-arc-lamp solar simulator is given below, along with a typical spectrum^[44].

• Why it should be changed:

Significant detail was absent from the original content and the quality of the images was very low.

• References supporting the possible change (format using the "cite" button):

• Abet Technologies^[34]
• Atonometrics^[26]
• Eternal Sun^[27]
• G2V Optics Inc.^[52]
• infinityPV^[35]
• Newport Oriel^[30]
• Photo Emission Tech^[33]
• Sciencetech^[31]
• Solar Light Company, Inc. (inventor of the original solar simulator in 1967) (citation needed)
• Spectrolab^[32]
• TS-Space Systems^[28]
• WACOM^[29]
• Wavelabs^[53]

• Why it should be changed:

De-clutter the presentation of companies, decouple them from basic information about solar simulators and their operating principles, and update the list of current companies to include latest technological advances.

• References supporting the possible change (format using the "cite" button):