Improve energy consumption with Ubuntu and Lenovo IdeaPad Z370 (sandy bridge-chipset)

Update 2015-03-15: As Antiplex mentioned in the comments, the resources are slighlty out of date. An update is pending I use my laptop (Lenovo Z370, with Ubuntu 11.10) a lot in the college. Unfortunatly there aren’t enough plugs in the wall for all students and I’m not willing to bring a plug board with me every time. So my approach to the problem was to improve the energy consumption of my laptop.