First you need to know “how much stuff you have”, then you need to know “How Solar works”. Additionally, but not such a critical factor is “where you live”, it’s fair to assume you will get about 6 hours of direct sunlight a day on average considering clouds, rain, and other weather conditions that might exist in your specific area.

You can start by figuring out how much power your home consumes on average. Your energy bill should provide you with a summary of your energy consumption trends over a period of time. A typical home has the basics, a water heater, stove/oven, dish washer, clothes dryer, electric heater , TV, lights, computer, etc. If we say these items average out to 600 watts. Over the course of 24 hours, you need 600 watts * 24 hours = 14,400 watt-hours per day.

Now a bit about solar. An average solar panel can generate 70 milliwatts per square inch * 5 hours = 350 milliwatt hours per day. Therefore you need about 41,000 square inches of solar panel for the house. That's a solar panel that measures about 285 square feet (about 26 square meters).

Unfortunately this only covers you the part of the day the sun shines, approximately 6 hours, and most likely not the 6 hours your home. So what do you do when the sun isn’t shining? A battery bank is a good solution but very costly to an already costly endeavor. The original question, how much do I need, is a moving target. Solar by itself is not a reasonable cost effective, practical solution.

NOAA Solar Calculators: http://www.srrb.noaa.gov/highlights/sunrise/gen.html