As nouns the difference between shortage and excess
is that
shortage is a lack or deficiency; an insufficient amount while
excess is the state of surpassing or going beyond limits; the being of a measure beyond sufficiency, necessity, or duty; that which exceeds what is usual or proper; immoderateness; superfluity; superabundance; extravagance; as, an excess of provisions or of light.
As an adjective excess is
more than is normal, necessary or specified.