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We have plants that need watering
(slrpnk.net)
But if your expense for the power station is higher than what you will save on the electricity bill you are actually losing money. Especially if you consider batteries lifetime, you can risk throwing the whole thing away before you saved enough bill money to recover the expense. So there are cases in which simply paying the bill is cheaper. I did the math a while back for my house and I would break even in like 7 years, which gives me only 3 years of actual saving before the battery wears out.