Granada does not have an official free  park and ride system.

This is my personal idea of the best park and ride.

If my advice became too popular I would have to take down this advice because it might block up this free parking but if only one or 2 people follow my advice there will be no problem.  So don't tell anyone else about this. 

Here are instructions:

The Sacromonte Abbey is about 40 minutes walk from Plaza Nueva (the absolute centre of Granada)
The Abbey has a large free parking area.

Leave the A92 at EXIT 253 (GRANADA ESTE - EL FARGUE)  Drive through el fargue.
Take a left into Camino Viejo de El Fargue

Take the next left at the football pitch. (If you go past the electricity substation you have gone too far)

Drive down the road until you get to the abbey.
Park your car.

You are now at the M on the top part of this map
https://granadamap.com/4.htm

If you want to get a bus get on a 35 which will take you to Plaza Nueva.
The 35 goes every 30 minutes.
For more frequent buses walk down to Cuesta Chapiz where there are buses every 15 minutes.

Another tip: There is an outside restaurant at the start of El Fargue called the Caldero. (not far from the turn off to the abbey)  It does a menu del dia and it can be a pleasant place to eat.