You may feel exhausted in the winter and so on... It has many points, reasons and facts we can focus on and by doing this we can get to some general understanding.
Nature has a lot of influence over our energetic health, since we draw energies from nature and the summer and the winter do have differences between their natural appearance, content and criterions... Thus, we draw the energies differently in each season depending on the natural criterions that each of them includes in their appearance. The difference makes the amount of the energies that we may draw depending on the sort of natural energy that we're attracted to and so on. It also makes general energetic differences which aren't too relevant to this particular thread so I guess I'll have to skip on those concepts.
As an example, personally I'm attracted to solar energy and I enjoy drawing energy from the sun, so I'll obviously have more energy on the notes of amount, effectiveness, qualification, and so on...The sun is a very strong embodiment of the fire element, while you can tap into the energy by channeling the energy by different methods that always include energy work. For an instance Sun meditation is a form of meditation that allows a person's body to draw energy from the sun into itself. It typically is practiced in the morning and evening just after the sunrise and before sunset by gazing into the sun and meditating. Although it takes a significant amount of practice to master this type of meditation, anyone can participate as each individual can begin at a low level and work his or her way up to longer and more powerful sessions.
That's my case in this situation... However Of course that there are many other examples of uses of energy obtained in natural sources which change and transform depending on each season specifically, I just gave you a specific one which is fairly clear and understandable. Moon, sun, things related to earth (grounding and centering is very associated to that), are all sources of natural obtained energy. In the winter things go differently with nature so that's why you see the difference in association with your energy. I think that you get the point.
If you have already noticed our emotions change in each season differently due to various circumstances. Emotions are actually strongly associated with your spiritual health and especially your energy (the emotions actually "create" energy and sometimes are considered to "be" the energy). Thus, our emotions strongly affect this type of thing including the amount of the energy as far as I'm concerned. Your emotions happen to be a type of energy- and an important one. Your emotions bridge areas of your awareness from the physical to the spiritual when it comes to the energy, and if your emotions are chaotic or imbalanced, the energy around you will be as well... So having your emotions changed in each season basically strongly affects your energy and spiritual health in a very noticeable way.
I hope this answers your question.