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What is a Solar Simulator?


Ossila Solar Simulator

A solar simulator is a light source which simulates natural sunlight and is used in research to test processes which are activated or catalysed by visible (or near visible) light. Solar simulators are calibrated so that they replicate the distribution or the intensity of the sun's irradiance as closely as possible. You can use solar simulators in any situation where you want to evaluate the effect of visible light on your sample - whether this be in a biological system, a photochemical reaction or for an optical device. However, it is extremely important that a solar simulator has a consistent output and radiates uniformly over a well-defined area.

Solar Simulator I-V Test System Bundle

Solar Simulator Test System Bundle
  • Unbeatable Value
  • Easy Cell Characterization
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Buy Online £3,500.00

Purpose of a Solar Simulator


Solar irradiance spectra. AM1.5G is often used as the standard for solar simulators
Solar irradiance spectra (ATSM G173-03 and IEC 60904). AM1.5G is often used as the standard for solar simulators.

Our sun radiates electromagnetic energy all over the earth's surface with an average power density of 1000 W/m2 on a spectrum approximated by the AM 1.5 spectrum (shown in the figure above). Solar power is well utilized within nature, providing energy to all living things through photosynthesis. Photovoltaic materials can also use this energy to generate electrical current. However, this constant radiation can damage some materials, such as polymers and other organic materials. There are many areas of research where it is vital to accurately characterize these light-dependent reactions.

While the solar spectrum is well defined on average, the exact solar irradiance at any point on the earth surface varies significantly by hour, day, week, or month. This variation is due to varying weather conditions and the relative position of this point to the sun at a given time. Additionally, spectral intensity will differ depending on your relative position to the equator (zenith angle) at time of measurement. Essentially, solar irradiance is not consistent across the earth's surface. These inconsistencies mean that if you use natural sunlight as a light source, you cannot easily compare or quantify light-dependent processes if they are measured at different points geographically or at different points in time. 

Alternatively, you can use a solar simulator in laboratory environment to supply a constant, reliable light source, which closely matches the solar spectrum. This will allow you to characterize light-dependent responses accurately and reliably.

Solar Simulator Design


There are three main things to consider when evaluating a solar simulator:

  • Spectral match

    How closely does this spectrum from this light source replicate the energy given out by the sun?

  • Spatial Variation

    Is the light distributed evenly? Over what area is this light distributed uniformly? 

  • Temporal stability

    Is the light given out from this light source consistent? Does the spectrum change over time?

Every solar simulator will have classification grades for each of these criteria - either A, B, or C, with A being the highest grade. The best solar simulators have AAA classification. Manufacturers should also quote the area that these ratings are valid over. For example, the small-area Ossila Solar Simulator has AAA classification over a 15 mm diameter, but ABA or ACA classifications over 25 mm and 32 mm areas, respectively.

The main component of a solar simulator is the calibrated light source. The most commonly used light sources are Xenon arc lamps, but the development of high intensity LEDs has meant that LED-based solar simulators are becoming more popular. LED light sources have longer lifetimes than their arc lamp alternatives. They are also more compact and are less expensive. Other components of a solar simulator may include:

  • Optical filters or lenses to improve light uniformity.
  • Fan or cooling system to stop the light source from overheating.
  • A fixed or adjustable stand and testing stage.
  • Specific control elements and power source.
Solar Simulator Diagram
Solar simulator diagram

The types of control systems and power sources you will need for your solar simulator depend on the type of light source that you use. For example, a Xenon arc lamp will require an expensive power source to reduce any spectral changes in the output with time. An LED-array light source won't need this, but it will require a more complex control system as each LED will have to be controlled individually.

Want more information about solar simulator design? See solar simulator design, working principles & optics

Solar Simulator Uses


Solar Cell Measurement

Solar simulators are most commonly used to characterize solar cells. The performance of solar cells will vary significantly depending on the intensity or spectral distribution of incident light. It is therefore very important to use a well-defined, calibrated light source for testing optoelectronic devices, especially during the research stage of development.

Natural sunlight varies significantly over days, weeks, and months, and it also varies geographically. Solar simulators allow you to compare measured device efficiencies, independent of where and when they are tested.

Additionally, early development solar cells may not be robust enough to withstand harsh outside conditions. New solar materials still need to be rigorously and reliably characterised before they are tested under "real life" conditions. Therefore, most situations require solar simulators to measure devices in controlled laboratory conditions.

Photodegradation

You can also use a solar simulator to measure material stability under solar irradiance. There are plenty of materials which degrade under solar irradiation, especially after long periods of exposure. Most of these reactions occur in the presence of oxygen or moisture. For example, most organic chemicals can degrade when exposed to oxygen, but these reactions are often accelerated in the presence of light.

Photodegradation occurs due to photochemical reactions. Often in these photochemical reactions, the absorbance of a photon excites an electron within a molecule into an excited state. This excited molecule will then oxidise or reacts with moisture, causing it to decompose into another (sometimes unwanted) product.

Photodegradation often happens with organic materials, such as organic dyes, food and for some polymers (such as polystyrene). However, it can also occur within some inorganic materials, such as TiO2. When photodegradation occurs within a fluorophore, it is referred to as photobleaching.

Photobiology

Solar simulators can also be used to study the behaviour of natural organisms and plants under illumination. The most obvious example of a light-dependent reaction occurring in nature is photosynthesis, but there are other biological processes which depend on sunlight. An example is photomorphogenesis. Additionally, continuous illumination can have harmful effects on biological materials, such as sun damage to human skin.

Solar simulators can be extremely helpful in understanding exactly what happens in these biological processes. One benefit of using artificial sunlight for these purposes is that you can test materials under various light intensities or wavelength ranges. This can help you to evaluate the exact energy levels and reactions which happen when these processes occur.

Solar Simulator I-V Test System Bundle

Solar Simulator Test System Bundle
  • Unbeatable Value
  • Easy Cell Characterization
  • Worldwide Shipping

Buy Online £3,500.00

 

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Contributing Authors


  • Mary O'Kane
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