Most solar calculators give you a number and leave you hanging. Ours shows the math behind it — watts needed, battery storage, daily sun hours for your actual ZIP code, and whether your setup will actually make it through a cloudy stretch. But before you open the calculator, here’s the short version of how the math works so you know what you’re looking at. The Short Answer The number of solar panels you need depends on three things: how much power you actually use per day, how many p