You should be able to gather a rough estimate with knowledge of your yearly electricity use, and some general facts about solar panels. The quickest and easiest way for you to do this is by actually contacting some solar installers in Union City, who can more accurately gauge your needs.
Let's make some assumptions here. The average house in the United States consumes approximately 8,900 kWh per year of electricity.
A 1 kW solar system generates about 1,000 kWh per year in cloudy places, and almost double that on sunny days. Let's say you're trying to generate enough solar energy to make up for about 4,400 kWh per year (a little under 50% just to make it easier).
Assuming you're looking at a 2-3 kW solar system in a sunny place like Union City, you can expect to install anywhere from 16 to 20 120 Watt solar panels on your roof to meet your needs.