100w is not a lot and, of course that is it’s optimal output. If there is any shade or cloudiness the output will fall off dramatically. A rainy day could put you into a deficit that 100w can’t recover from. It might be adequate if all you need is to run a few lights for an hour or two before bed. Bob is right, we need to know what will be using your battery at night. Any solar web site should link to a calculator that will help you determine how much solar you need to meet your needs. Good luck
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