Solar powered bit coin mine

I have a fully paid for solar rig generating EXCESS 10 kwh in my backyard. Essentially free electricity I can't use or sell to grid. I wanted to purchase 1-2 antminer (total 300-600 terahash 5-10 kwh). I was hoping to break even in a year and profitably generate $5-10K per year thereafter. Online calculator shows this is possible but there must be a catch.

Is this a good idea? My investment is about $10K in the mining rigs. I particularly worry mining will get more expensive and so I will never break even or make far less than $5-10K per year in the long run.