I put a post on this forum about building a walk in fridge using an a/c unit with a modified controller. I would like to add a dimension to that. I would like to build a trailer to be the fridge, with walls that are r30 and a ceiling with r60. Furthermore, I want the unit to be self contained, with solar panels on the top to keep the room cool. I will install batteries, but hope to have to not buy more than 4 days worth of batteries to keep things chilled. The area is high plains desert in northern Nevada. There are 231 days of sunshine. Does anyone know of a formula that I can use to calculate electricity needs? I want to find a better way than to use hunches.