waste of energy vs wastefulness

waste of energy and wastefulness both are nouns.

Word	Noun	Adjective	Verb	Adverb
waste of energy	Yes	No	No	No
wastefulness	Yes	No	No	No

As nouns, wastefulness is a hypernym of waste of energy; that is, wastefulness is a word with a broader meaning than waste of energy:

waste of energy: a useless effort
wastefulness: useless or profitless activity; using or expending or consuming thoughtlessly or carelessly

Other hypernyms of waste of energy include dissipation, waste.

waste of energy (noun)	wastefulness (noun)
a useless effort	useless or profitless activity; using or expending or consuming thoughtlessly or carelessly
	the trait of wasting resources