Mark here from Self Sufficient Me offers extremely easy-to-follow instructions for drying turmeric. I agree with him in the end (spoiler alert!): Leave the skins on, then wash, boil, slice, dehydrate and grind them: https://www.youtube.com/watch?v=4u9bFxD4EGY
If the video is too lengthy for you, perhaps try this very quick read, instead. It covers the same steps that Mark does: https://www.sunoven.com/step-by-step-to-making-turmeric-powder/
I will be drying my turmeric sliced in the oven at it's lowest temperature (175˚ F) until they are cracking dry (supposedly 2-3 hours), and then grinding them in my food processor, as I've yet to purchase either dehydrator or a spice grinder. Would you recommend them?
Also, note! The powder may store best in a dark jar, in the fridge for up to 2 years; however, the most beneficial compound in turmeric--curcumin--appears to have a shelf life of about 6 months (1).
Image from: https://naatigrains.com/product/lakadong-dried-turmeric-slices/
(1) https://pdfs.semanticscholar.org/305b/5667ed272493088f990761263285ac5e98ee.pdf