How to measure roof temperature for solar calibration?

[eegz]

How do I measure the roof temperature so I can calibrate my solar sensor readings?

Do I just lay a thermometer on the roof or should it be on the panels?
Should the thermometer glass touch the roof tiles or is it ok to have it in a plastic housing?

Tried using a laser thermometer and it gave a reading 20 degrees higher than the mercury one.

Sorry if it's obvious, but didn't find anything in the manual, Youtube, Google or in the TFP search.

 

[ajw22]

@JamesW @JoyfulNoise How to?

 

[eegz]

Bump?

 

[mas985]

Normally the temperature sensor is attached to one of the pipes supply or return. It doesn't really matter as long as it is in direct sun and close to the panels.

 

[eegz]

Thanks Mark!