Solar energy is not always effective, in winter there is little use of it. Although I often go on hikes and in summer it is really useful to have with you something that will help recharge the devices during long walks. I take with me a couple of powerbanks, and in my backpack I have a built-in solar panel. But in the cold seasons, when the sun is far from the earth, as I already said, the efficiency of solar batteries drops to 20% -30% of the norm.
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