Big screen able to be turned off

Wanting a large display, say 800x480 or more, 5"+ for displaying data from an off grid solar system.
Lots of numbers and charts required.
Being able to completely disable the display for power saving is a must. I bought a bunch of megas and 3.5" tfts but they cannot be switched off.

I'm open to using a android tablet and Bluetooth but my coding skills are basic. I already have a 7" tablet. Wouldn't know where to start with an app so is this feasible?

Also, I know there are 40x4 lcd displays but is there anything bigger?

See here.

And this Android App here which provides example code.