Interesting question. I think there is nothing wrong with using the estimation from NASA POWER; these estimations have been validated against meteorological measurements. You need to, of course, cite in your material and methods that NASA POWER was used. Many governments have meteorological stations and services that you can use for your research but, if you can get a direct measurement. In my opinion, the NASA POWER is a great option.

best of luck

Here are some papers discussing the use of NASA POWER

Article Evaluation of NASA satellite- and assimilation model-derived...

Article NASA/POWER and DailyGridded weather datasets—how good they a...

Thank you, Avraham.