Short answer- YES. Sunlight shining on your sensor will definitely cause a higher than actual temperature reading. Depending on the accuracy needed, you can probably just shield the sensor with a cover of low emissivity (e.g. gloss white). Make sure the sensor is mounted such that air can circulate freely.

Brad Waybright

It's all okay as long as it's okay.

Your transmitter will have temperature compensation. The spec sheet should show the limits of the temperature compensation.
The transmitter will give accurate readings as long as the transmitter temperature is within the limits of the internal compensation circuit.
We had an issue of an application of a temperature transmitter which would be used in an ambient temperature that at times would be below the compensation range.
We conducted some tests by cooling the transmitter and checking the indicated temperature against the actual temperature.
We found that the error matched the amount that the temperature was below the compensation limit.
The intended use was a safety shutdown of a stack. We reasoned that if conditions caused to stack temperature to rise to a dangerous level on a cold day that it would not be a problem and may actually be advantageous if the process shut down at a lower stack temperature.
The transmitter was used and worked well.
Measure the temperature of your transmitter on a day when the sunlight is shining brightly on the transmitter. Reconcile this with the listed limits of the internal compensation.

Bill
--------------------
"Why not the best?"
Jimmy Carter

What does your datasheet even say about sunlight?

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

Google instrument sunshield

Dumb, cheap transmitters might very well have no temperature compensation. You get what you pay for.

The device's spec sheet will tell you over what (ambient) temperature range it can be used, but "ambient" means the temperature of the transmitter housing (and the transmitter inside), not the air around it. Housing can be hotter than ambient air.

Thanks a lot for the explanations :)