Advantages in using LEDS as the main light source in solar simulators for measuring PV device characteristics

Advances in photovoltaic technology resulted in increased complexity of device calibration, largely being affected by deviations of test spectrum from natural spectra. While the output spectrum of some solar simulators is adjustable, generally only light intensity and module temperature can be varied. This is due to the light sources used in current simulators. LEDs offer an additional degree of freedom, when using an appropriate combination of wavelengths. This paper presents the advantages of this lighting technology for solar simulation and backs these up through results of the prototype unit developed at the Centre for Renewable Energy Systems Technology. The ability to keep LEDs stable for a long time and dim them with minimal changes in the spectrum allows generation of a spectrum closely matched to AM1.5G standard test spectrum or indeed even realistic variations of the outdoor spectrum. LEDs can be controlled very fast within microseconds or operated continuously, combining a steady state and a flash solar simulator with additional functions such as variable flash frequencies and flash shape. Combined with the life expectancy exceeding 50.000h, LEDs are a strong candidate for solar simulator light sources introducing a significant improvement in calibration lifetime as well as significantly reduced running cost. The usage of LEDs can enhance today’s characteristic measurement functions and even opens possibilities to fully characterise solar cells indoors within a much shorter time than is possible today, over a range of conditions previously only available through outdoor characterisation.