1: Switches between the power lines
A switch which you can craft for activating/deactivating the power on the power line.
use = unknwon... atm

2: Electric doors
A door you can place betwen walls. The door dan be closed with electrical power (oh... there is the usage for the switch

3: An enemiedetector / warning lamp
Something that detects nearby enemys. If enemies are detected it sends power to ... maybe to an electric door(?).
And maybe it's blinking if enemies nearby

4: Electric fences/walls
An electric fence/wall powered by electricity which hurt enemies if touched.
edit:
5: Repair robots which repairs damaged buildings (like walls)
edit 2: (srsly.. this game has so many potential... its soo epic <3)
More ways to get electricity:
6: Wind turbine (if there is wind on this planet...?)