Introduction to Solar Simulation
Solar simulation are mainly for the purpose of characterizing photovoltaic devices in a controlled and consistent environment. Solar simulators can themselves be characterized in three categories based on how well their optical output matches that of the sun. Recent developments in this field point towards a potential business opportunity in the commercial lighting industry, whereby indoor light sources can be made to closely replicate the colour and overall atmosphere provided by natural light. This proves useful due to the adverse health effects associated with chronic exposure to artificial light sources.
Photovoltaic characterization occurs by measuring the electrical characteristics of the device while light is incident upon the active region. The efficiency of the device is then obtained by measuring the output electrical power as a fraction of the power provided by the incident light. This can be carried out with a sufficient degree of accuracy only after the characteristics of the solar simulator are known.
To characterize the solar simulator itself, three characteristics are of utmost importance, namely: spectral match (SM), spatial non-uniformity (SNU), and temporal instability (TI). These components are central to most, if not all, optical systems. Spectral match refers to the distribution of intensity across the wavelength emission spectrum of the solar simulator. Spatial non-uniformity refers to the degree of inconsistency as one moves along the length and width of the entire test region at an instant in time. Temporal instability refers to the degree of inconsistency in one spot of the test region over time. The goal in creating a good solar simulator is to have these parameters match the sun’s parameters as closely as possible.
The American Society for Testing and Materials (ASTM) has published documentation outlining the requirements for each of these three categories, and allows scientists to assign a letter-grade to each category based on a solar simulator’s performance in that area. This provides a simple way of immediately communicating how well a solar simulator performs in each category. The quantities associated with these properties are obtained by conducting optical measurements pertaining to each property. Spectral match is addressed via a spectral analysis while spatial non-uniformity and temporal instability are both addressed via an optical detector array. The two measurements are determined by controlling each of two variables; time is held constant for spatial non-uniformity, and a spatial average is analyzed over a time interval for temporal instability. The following table outlines the characteristics of each category corresponding to each letter grade.
Typically solar simulator can be made of Xenon Arc Lamp and LED. LED light source has very high electrical-to-optical conversion rate, making is highly energy efficient and low cost for operating. LED simulators are more favourable than xenon-lamp-based simulators, especially in the spectral match category. Xenon arc-lamps are the most popular optical source in most solar simulators. Although widely used, these lamps do not necessarily provide the best spectral match.
Common Terms For Solar Simulators:
Lm/w (流明/瓦): lumens per watt 流明/瓦
Luminous efficacy is a measure of how well a light source produces visible light. It is the ratio of luminous flux to power, measured in lumens per watt. Depending on context, the power can be either the radiant flux of the source’s output, or it can be the total power (electric power, chemical energy, or others) consumed by the source. The former sense is sometimes called luminous efficacy of radiation, and the latter luminous efficacy of a source or overall luminous efficacy.
Optical Power (光功率)
The energy per unit time, e.g. transported by a laser beam, or a focusing power. Alternative terms: radiant power, focusing power. Both dBm (decibel-milliwatts) and mW (milliwatts) are units of optical power. They can be converted as follows:
dBm=10xlgP (P indicates optical power, in mW.)