Among the many No-Cost energy conservation methods using a computer, shutting down you PC or Laptop is the best way.
Many individuals and organizations tend to leave their computers switched on during the night to download updates automatically and save time during the day.
Leaving computers running during nighttime consume massive amounts of energy reaching $2.8Bn and release 20 tons of CO2 per year in the US alone, according to a recent study by 1E and the Alliance to Save Energy.
So, unless you need to access your computer remotely from home, or have information on your device that people need to access over the network, then please turn off your computers before going home