Word before "power" or "system" (5)
I believe the answer is:
solar
'word before power or system' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for solar that I've seen before include "Of the sun, as ray or panel" , "Coming from the sun" , "type of radiation" , "Concerning the sun" , "Sun-powered" .)