The importance of a good spectral match or 'close-match' solar simulator for accurately measuring and investigating multi-junction solar cells was clear and has since been thoroughly demonstrated in the research literature:

"The photovoltaic characterization of triple-junction InGaP2/GaAs/Ge solar cells is presented. Measurements made using a single light source solar simulator are compared with other measurements made using a multi-light source solar simulator that provides a close match to the air mass zero (AM0) solar spectrum. The output spectrum of the solar simulators has been measured, and two methods for calibrating the simulator output intensity haven been employed. The spectral response of the solar cells has been characterized through quantum efficiency measurements. These data are analyzed to determine the effect of the simulator spectrum on the measured photovoltaic response, and in particular, areas where spectral mismatch between the simulator and AM0 can lead to inaccurate performance predictions are highlighted."[3]

At TS-Space Systems, when we made the worlds first multi-source close match solar simulator back in 1997 [2], we also made the world's first multi zone solar simulator by definition. What is a "zone" when it comes to solar simulators? It's a good question and one we get asked quite a lot of the time.

Modern multi-source solar simulators follow a general pattern of combining an arc lamp (traditionally Xenon) with one or more  incandescent lamps. At TS-Space Systems we've lead the way by adopting Metal Halide arc lamps for our latest range of solar simulators which are cheaper and much more stable than Xenon sources without using feedback controllers.

But where our solar simulators really excel is their division of the spectrum into independently controllable wavebands. We call these spectral "zones". As an example, the measured spectrum of a TS-Space Systems Unisim, quad-source (four zone) solar simulator is shown to the left.

The intensity of each "zone" can be adjusted independently in a TS-Space Systems Unisim solar simulator. Being able to adjust discrete portions of the spectrum while a device is under test allows for specific sub-cells to be limited or saturated with their appropriate wavelength of light. Thus the behaviour and characteristcs of the device can be fully investigated.

A further distincition can therefore be drawn between advanced solar simulators which provide a close-match and those which not only provide a close-match, but divide the spectrum into controllable "zones" which are suited to the spectral response of each band gap within the solar cell. 

What happens when you need more than four "zones"? That's where our Unisim N-Zone comes in.

For the uninitiated, when selecting a solar simulator, there seems to be a huge number of manufacturers and models available. While there are standards in place that require simulators to be classified according to their performance, these have not kept pace with the advances of solar simulator technology or the devices they are used to test. Our guide to solar simulators attempts to list the basic terminology and elements of solar simulators, how they are classified by the existing standards and, finally, how advanced solar simulators differ and the advantages they provide. It is in no way a complete work, but is intended to help those who are new to the field by giving them a good entry-level knowledge of the subject.

We recommend downloading and reading the international standards (listed under 'Standards' here) to assist with the terminology and concepts described throughout this site.

If you have a suggestion for additional content you'd like to see here, or if you have questions, please feel free to contact us. We would like to hear from you.