Tools of the Trade #5 — Non Contact Thermometer

Jane Wonders Jane.Wonders@altenergysolutions.com

The temperature of the solar modules has a dramatic effect on their output. For a standard crystalline or polycrystalline silicon PV module the temperature coefficient of power is about –0.5% / ºC. That means that a 120W module (as measured at 25ºC) will actually only produce about 105W when running at 50ºC. The question then becomes “what temperature are the cells”. I have used thermocouples attached to the back of modules to measure temperature (there is normally about a 3 – 5 ºC drop between the cell and the back of the module) when I can get to the back of a module, but this is often not possible. Enter the non-contact thermometers. I use a Raytek ST60, though there are many choices out there. Just point the thermometer at the module, press the button and read the temperature!) You can even use the thermometer to scan for “hot-spots” if you suspect a cell is bad etc.

Now that line-tie systems are giving so much information about power production it is important to understand the factors that affect PV performance, and cell temperature is one of those factors that is often overlooked.