Read up on the uxn project, which is a platform designed to be run
minimally. Can be run on gameboys. offline only(/mostly?). The
people behind the project work off the grid in a sailboat,
requiring them to meter their electricity and data usage carefully.
Video edit on sunny days, etc. Power usage by computers is remarkable.
MacBooks alledgedly use 6-12 W, but this little RPi uses 2.8.