Green Party finally contrived to get power (6)
I believe the answer is:
Here is my best explanation:
'power' is the definition.
('energy' can be a synonym of 'power')
'green party finally contrived' is the subsidiary indication.
'finally' indicates one should take the final letters.
'contrived' is an anagram indicator.
The final letter of 'party' is 'y'.
'greeny' is an anagram of 'energy'.
'to get' is the link.
(Other definitions for energy that I've seen before include "Go, zip", "Vigour, power", "Pep", "Capacity for activity", "Fuel", "Seventeen forty six defeat for Bonnie Prince Charlie", "Capacity for action", "Zip", "It's measured in joules or ergs" and "exertion".)