Pseudo Sun Instrument
The Pseudo-Sun Instrument (PSI) is an LED based solar simulator used in testing solar cells and solar panel boards. Currently, many LED based solar simulators use a hybrid system of LEDs and halogen bulbs. This leads to lower customizability and control of the light spectrum. The temporal instability (variation of the source with time) of halogen bulbs creates an inconsistent testing environment unfit for serious scientific analysis. To combat this, a design utilizing only LEDs with a wide range of wavelengths was proposed.
The goal for the project was to conform to the ASTM International standards for solar simulators. This meant that to create the best performance possible the device must have the correct spectral power distribution as defined by ASTM. Additionally, the testing area must have equivalent power at all points within its borders. The largest benefit of using LEDs to simulate the Sun’s spectrum is the temporal stability. LED’s have a long life without degradation of the LED’s output. Because of this, conforming to the ASTM standard for temporal stability is significantly easier than hybrid halogen-LED designs.
The project’s end result will produce a device completely capable of autonomously generating a characterization of a solar cell. PSI will be able to test variable loading efficiency (the efficiency at which the cell converts solar energy into electrical energy depending on its load). It can also test individual spectral response by turning on one type of LED at a time from ultraviolet to infrared. These are all tests that common solar simulators perform; however, PSI will have the built in capability to thermally cycle the cells by cooling them. Additional possibilities in the far future would be making the device vacuum sealable to allow for the complete reproduction of space environment.
PSI utilizes USB communication that is controlled through a graphical user interface. The device’s spectral output is completely software defined allowing for a variety of applications such as reproducing the spectrum in low Earth orbit (air mass zero or AM0) or the average global spectrum on the surface (air mass 1.5 global or AM1.5G). The 21 individual LED spectrums are each programmable leading to a full 480 LED array producing well over 1353 watts per square meter (power of Sun).
As of July 2017, the first revisions of the PSI circuitry have been acquired and are currently being tested. The formal structure is still in the development phase.
The project was conceived by Brandt Lomen, an undergraduate electrical engineering major, who was originally tasked with testing the solar cells used on the Alaska Research CubeSat 2. He became the lead on the project that would become PSI. He completed all research, electrical design, and electrical fabrication for this project. Additionally, he completed the software interface. Sarah Riopelle, an undergraduate mechanical engineering major, produced all mechanical designs for the PSI housing compartment through the integration of electrical components and the device requirements. This included the design, fabrication, and testing of the PSI’s structure.