energy
The German word for energy is 'Energie'. It is used in the same way as in English, to describe the capacity of a physical system to perform work. It can also refer to the resources available for use, such as fossil fuels or renewable energy sources. In physics, it is often measured in joules.
I have no energy today.
This sentence expresses the speaker's physical or emotional state of exhaustion or lack of vitality.
The sun is a renewable energy source.
This sentence expresses an environmental concern or principle by highlighting the sun as a perpetual provider of energy.
He put his energy into the project.
In this case, energy represents someone's figurative force or vitality that is directed towards accomplishing a task.