# Design and Validation of an Adjustable Large-Scale Solar Simulator
## 1 Introduction  
The transient nature of environmental parameters, especially solar radiation, makes outdoor technology testing uncontrollable. Solar simulators are devices that provide approximately natural sunshine with an artificial light source and allow controllable indoor testing under desirable conditions. In fact, solar radiation, in a natural environment, changes continuously over days and seasons, while indoor tests are programmable, repeatable, and stable under laboratory conditions. This way it is possible to change a single parameter (for example, the intensity or the incidence angle of the luminous flux) and to analyze how the system is affected by each of them. Crucial aspects of the design of a solar simulator are the correct spectral matching, irradiance uniformity, and temporal stability. When testing PV cells, the spectrum is paramount since it influences the conversion efficiency of the incident radiation. Flux uniformity and stability have to be acceptable so that the average value is as stable as possible on the target area. Early solar simulators were designed in the 1960s by the National Aeronautics and Space Administration (NASA) for spacecraft ground-testing. Recently, solar simulators have been used in testing, calibrating, and characterizing photovoltaic panels and testing dashboards, steering wheels, and airbags in the automotive industry. Indeed, they have been used in many different applications, such as conducting aging tests on PV materials, investigating the effects of light on the growth of plants and algae, and testing of thermal or thermo-chemical devices for use in chemical reforming. In thermal applications, solar simulators are classified as low and high flux, depending on the output flux, for a few sums (1 sun = 1 kW/m\({}^{2}\)) to more than 30 sums, respectively. The major components of a solar simulator are the light source with power supply and the optics and filters to modify the output beam. Light-source selection is the primary step to obtain suitable simulated radiation. Generally, four types of lamps are used in asolar simulator: xenon arc lamps, metal halide arc lamps, light-emitting diodes (LEDs), and quartz tungsten halogen lamps. In the literature, examples can be found of solar simulators employing tungsten halogen [1,2], argon arc [3], metal halide [4,5], xenon arc [6,7], and LED lamps [8,9] or several light sources [10,11]. Many differences are present even regarding the number of lamps and target area. [PERSON] et al. [1] designed and built a solar simulator for testing flat-plate thermal collectors (0.5 \(\times\) 0.5 m). They utilized a small number of lamps and a reflected light tube that generates multiple virtual images. This way, the standard deviation in illumination over the collector area is 5.3% of the mean level. [PERSON] et al. [5], instead, designed and built a large-scale solar simulator based on 188 lamps. The simulated radiation can be adjusted between 150 and 1100 W/m\({}^{2}\) by varying the number of lamps on and the lamp-to-area distance. At the height of 1.75 m, the nonuniformity of illumination is 4.91%. [PERSON] et al. [8] used a combination of different light sources to cover the solar spectrum. Red, green, and blue light-emitting diodes (LEDs) matched the visible range, and then UV and near-infrared lamps completed the spectrum. [PERSON] [10] used 9 warm-white LED lamps, 9 cool-white LED lamps, 20 UV LED (410 nm) lamps, 20 IR-LED (700-800 nm) lamps, 20 IR-LED (800-900 nm) lamps, and 20 IR-LED (900-1100 nm) lamps. The calculation results of nonuniformity on the test area of 32.5 cm \(\times\) 28 cm is equal to 1.915%, showing a high uniformity because of the LEDs' symmetrical position. [PERSON] et al. [12] compared LED and xenon lamps by measuring the current-voltage (IV) response and spectral response (SR) for a variety of solar cells. The results demonstrate that the LED-based simulator produced a more stable, flexible, and accurate match to AM1.5G than the xenon lamp-based simulator. [PERSON] et al.