The  first thing to consider when wondering how big of a solar system you need to run a house off-grid is whether or not you plan to use another alternative source of energy to power the home. If you are going to be using off-grid solar energy for smaller needs, then you won’t have to invest in such a big system.
You want to invest in at least 20-25 solar panels for the average home. Available online through numerous forums, however, are solar system calculators to determine the size of the system that is required to power your current residence!