Energy is lost between trophic levels. Energy is lost in the following ways; in respiration (mostly lost through heat), energy still present in egested food, through movement, through digestion, energy still present in excreted materials etc
Of the 100% sunlight energy that reaches plants, ~5% is converted into NPP. Energy is lost in the following ways; reflected light, light of wavelengths not useful to plants, passes through leaves, lost in respiration, lost as heat etc.