So in the UK, Can you install this system yourself and put power back into the grid? In the US you can't unless a contractor does the install and it is all verified, which kind of inflates the price exponentially. I work with similar battery powered systems and had always wanted to do something like this, it would have to be stand alone though for me. I'm curious as to how long you will have to stick with it to break even. I ended up here on your 2015 xbox controller/pi zero blog that i have turned into a project all of my own 🙂 I should probly just read more into what your doing! Cheers!