This is the 648th most frequent Romanian word.
energiei
The Romanian word "energiei" means "of the energy" (genitive/dative form).
In this sentence, 'energiei' is used in the genitive form to indicate possession or association, showing that the efficiency pertains to 'energy'.
Eficiența energiei poate contribui la economisirea resurselor naturale.
The efficiency of energy can contribute to saving natural resources.
Here, 'energiei' is again in the genitive case, specifying that the study is about 'alternative energy'.
Studiul energiei alternative este crucial pentru viitorul nostru.
The study of alternative energy is crucial for our future.
In this instance, 'energiei' is used in the genitive to mark that the importance is related to 'solar energy'.