Friends:

   What is the Origin & Cause of Energy?

The Blessed Buddha once said:
Where, Friends, is the ability of Energy to be seen & found?
The Energy ability is to be found among the Four Right Efforts...
SN V 196 http://What-Buddha-Said.net/drops/What_is_Right_Effort.htm

 What is Right Effort?
The effort to overcome already present disadvantageous mental states..
The effort to prevent future disadvantageous mental states from arising..
The effort to develop yet unarisen advantageous mental states..
The effort to maintain already arisen advantageous mental states..
That is Right Effort! SN V 2
http://www.accesstoinsight.org/ptf/dhamma/sacca/sacca4/samma-vayamo/index.html

Damaging mental states should be seen & battled in every moment!
Beneficial states should be sought and cultivated in every moment!
The enthusiasm in doing that, conditioned by that, is right energy!  

For a full Study on Energy (Viriya): The root Hero of all Success:
http://What-Buddha-Said.net/drops/III/The_Definition_of_Energy.htm
http://What-Buddha-Said.net/drops/III/The_Arising_of_Energy.htm
http://What-Buddha-Said.net/drops/III/The_Ability_of_Energy.htm
http://What-Buddha-Said.net/drops/III/The_Origin_of_Energy.htm
http://What-Buddha-Said.net/drops/Enthusiastic_is_Energy.htm
http://What-Buddha-Said.net/drops/III/Power_of_Energy.htm
http://What-Buddha-Said.net/drops/III/Ballanced_Energy.htm
http://What-Buddha-Said.net/drops/III/The_Chief_Hero.htm
http://What-Buddha-Said.net/drops/III/Energetic_Effort.htm
http://What-Buddha-Said.net/drops/III/Avoiding_Effort.htm
http://What-Buddha-Said.net/drops/III/Feeding_Energy.htm
http://What-Buddha-Said.net/drops/III/Energy_Viriya.htm
http://What-Buddha-Said.net/drops/III/Dual_Energy.htm