My climate in western Oregon is somewhat similar to Sacramento but not quite as hot. My shop is well insulated and shaded by trees.  In the summer it never gets above 75 F (23  C) even after several days in the 90s F (92 C). It cools to the low to mid 50s F at night so if the shop does get warm I can cool it by opening the windows at night.
 In the winter I heat it with a wood stove. It usually takes a couple of days to burn up all the wood scraps I have generated over the summer then I go to my fire wood pile for fuel. I have a custom made air cleaner for dust with a furnace fan in it that blows across the wood stove and circulates the heat. 
One shortcoming of the mini splits is, as with regular heat pumps, that they work best when the temperature is set to a narrow bracket between high and low of say 6 degrees or less 24/7/365.