The primary way in which energy is transferred in food chains is through trophic levels. Energy originates from the sun and is captured by producers, like plants, during photosynthesis. This energy then moves to consumers, which can be herbivores or carnivores, as they eat the producers or other consumers. Each transfer of energy results in a significant loss, typically around 90% due to metabolic processes, illustrating the inefficiency of energy transfer and emphasizing the importance of understanding food web dynamics.