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A Solar Simulation system also known as sun simulator reproduces full spectrum light equal to natural sunlight. The ground level spectrum of natural sunlight is different for various locations on earth. The constituents of the atmosphere affect both absorption and scattering. Elevation is another factor that affects the ground level spectrum, since the elevation determines how far the sun's radiation must pass through the atmosphere. For any given location the distance the sun's radiation must travel through the atmosphere changes as the day progresses, due to the changing angle of the sun. With the sun directly overhead the direct radiation that passes through travels the shortest distance through earth's atmosphere to reach the earth. The spectrum of this radiation is referred to as "Air Mass 1 Direct" (AM1D). For standardization purposes sea level is used as a standard reference site. The global radiation with the sun overhead is referred to as "Air Mass 1 Global" (AM1G). The spectrum of sun's radiation in space does not pass through any air mass hence it is referred to as "Air Mass 0" (AM0).
Since solar radiation reaching the earth's surface varies significantly with atmospheric condition, location, time of the day, earth/sun distance, and solar activity, standard spectra have been developed to provide a basis for standardization of theoretical evaluation of the effects of solar radiation. The most widely used standard spectra are those published by The Committee Internationale d'Eclaraige (CIE), the world authority on radiometric and photometric nomenclature and standards.
The American Society of Testing and Materials (ASTM) has published three spectra, AM0, AM1.5 Direct and AM 1.5 Global for a 37o tilted surface. The conditions for the AM 1.5 spectra were chosen by ASTM because they are representative of average conditions in the 48 contiguous states of the United States. In addition to the standards for different air masses, standards for Non-Uniformity, Temporal Instability of Irradiance, Total Irradiance within 300 Field of View, and how closely the system's radiation spectral distribution matches the sun's radiation have been established by various organizations. In the USA, American Society for Test and Measurement (ASTM) has established such standards for Solar Simulators.
FEATURES
PET solar simulators consist of a Light Source and a Power Supply. The light source has an ellipsoidal reflector that surrounds the lamp and collects most of the lamp output. The radiation from the lamp is focused onto an optical integrator that helps produce a uniform diverging beam. The beam is diverted 90° by a mirror onto a collimating lens. Special filters are placed between the mirror and the collimating lens to shape the radiation spectra to match various air masses. The output is a uniform beam that closely matches the sun's radiation spectra for a given air mass. Various models offer different areas of illumination. Each model can be manufactured to simulate the sun's radiation for different air masses.
The power supply unit provides constant electrical power to the xenon arc lamp. All of our systems come with a standard closed loop light intensity controller. This helps in assuring very stable light intensity. In addition the power supply unit houses control circuitry for several control features. Some of the control features are discussed here.
Exposure Control
Each Solar Simulator has a shutter that can be operated manually from a switch on the front panel or remotely with a foot pedal. The shutter can also be programmed to open from 0.1 second to 999 seconds with a built in timer control.
Light Intensity
The light intensity can be adjusted with a control on the front panel. This feature is useful to help compensate for lamp aging. In addition, each system has a Constant Light Intensity Controller as a standard feature. This control system maintains a constant level of light intensity for long-term exposures.
Output Power
It is possible to factory set the system light output higher than one sun when the lamp is new. If the system output is higher than one sun, then the intensity control is used to adjust the system output at one sun. As the lamp ages, the intensity control can be adjusted to maintain one sun output.
Safety Interlocks
The Light Source unit has safety interlocks. The door for lamp replacement has an electrical interlock to shut down the system if the door is opened without turning the system power off. This prevents access to the lamp when it is on thus preventing operator exposure to the radiation and protects against inadvertent contact with the hot lamp. There is a thermal interlock that turns the lamp off in the event the temperature within the housing exceeds safe operating levels. In addition there is a safety interlock that turns the system power off in the event the cooling fan fails.
Lamp Aging
The xenon arc lamp should be replaced every 1,000 hours to ensure spectral fidelity and proper level of intensity. There is an hour meter that monitors and displays the lamp age. It serves as a convenient reminder of when the lamp should be replaced. PET Solar Simulators have a lamp alignment feature that allows the lamp to be aligned without the lamp being turned on. This feature makes it very easy to align the lamp for the best uniformity for the area of illumination.
APPLICATIONS
Photovoltaic Cell Performance
Determining electrical performance of photovoltaic cells Comparison of cell characteristics among group of cells or different cell designs Repeated measurement of the same cell to study life cycle performance changes
Photochemistry/Photobiology
Environmental Exposure Testing
Evaluating the effect of solar radiation on various materials and finishes Accelerated testing for cross-linking of polymers and embrittlement of plastics Testing for color fading of paints and fabrics Qualifying and life-time testing of materials for space
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