You can buy devices that measure your electrical power usage. I used one once to figure out the power draw of a toaster for a research project I was working on. The one I used is called the "WattsUp" and it was apparently expensive. Cheaper one:
P3® Kill A Watt Power Meter (P4400) - Electrical Testers - Ace Hardware
You should know from the outset that solar power isn't something you do because you want to save money.
Your available sunlight is primarily determined by your latitude and the time of year. There are a few ways to estimate your average daily incident solar radiation. Some are based on historical meteorological data combined with theory and some are all theory. I don't recall them being particularly straightforward. Once you have a reasonable estimate of the amount of energy available to you, you could use this to spec your solar panels.
However, if I were you, I'd look into local solar equipment contractors, since they do this type of thing for a living and could tell you what you need (along with a few things you probably don't need) with more certainty.