difference between measured module temperature & calculated by NREL method

[vilasgpacharne]

1. we are using bifacial solar module in one of our project.

2. The module temperature ( of bifacial module) is being measured by CS240 temperaure sensor( make-compbell scientic) . This temperature sensor is fixed at back side of solar module.

3. The module temperature ( of bifacial module) is also calucated by NREL method/ sandia module temperature model.

We are finding large difference between these two values

Difference= MOD_TEMP (Measured by CS240) - NREL_MOD_TEMP (Calculated-NREL method)

this difference is i the range of -9% to 36% based on irradiance during the day.

Request you to support to resolve below query

1. Why there is difference?

2. is suitable to measure module temperature of bifacial solar module ( since it is fixed at only one side).

3. What is suitable module temperature sensor to measure module temp of bifacial solar module so that the measured & calculated temperature(NREL) values should match.

Regards,

Vilas Pacharne

vilasgpacharne@gmail.com

[André Mermoud]

The measurement of modules temperature in a field is a delicate operation.

To my mind, just gluing the sensor on the backside of the module is not quite correct. The layout of the measurement is very important. Remember that a temperature sensor always measures its own temperature !

See our FAQ "How is evaluated the Module temperature during the simulation ? ".

At the end of this post you have a paragraph with our advices: "PV array temperature measurement"

Now PVsyst doesn't use the Sandia or NREL thermal model.

It proposes a model in which you can adjust the "Thermal Loss factor" (U-value) in order to match you measurements at best.

Please read the help "Project design > Array and system losses > Array Thermal losses".

NB: expressing temperature differences in terms of percentages doesn't make sense. Percentage with respect to what ?

If it is 0°C, this doesn't have a physical meaning. The reference could be anything else (25°C, -273°C, etc)

The only way is to express the temperature differences in terms of °C.