low energy? look at EOMA68 (note: may not be a realistic solution for you, yet, but its a good cause to support) http://www.crowdsupply.com/eoma68
Basically that's a project I've sunk big $$$ into and raised a lot more money to get off the ground. It's basically about freedom and control of our computing devices, but it also so happens to be ultra low power. A single cell battery can power the laptop for maybe 8-10 hours. A normal 4 cell battery might do a typical laptop for 3-4 hours.
If you want government out of your life it's the way to go. Though technically in the mean time I'd still recommend my companies government-infected devices, because they're more usable and for the moment still better than anything else out there freedom wise (almost, there is one other better freedom option, but I'd avoid it cause it's built off refurbished systems and really are at the end of the line as far as working go- 10 year mark means computers start to fall apart-literally- certain pieces degrade due to government regulations in materials used which means certain parts will fail/not work properly etc).