In order to install an effective solar panel system you must know your current energy consumption. You can acquire this information from your current utility company. You should use the data given by the company as the starting point of your solar panel system. You will be able to create your system to accommodate your house requirements. You will also have to take into consideration the direction your roof is facing, the amount of objects around your house, amount of trees around your house, and the different appliances you will want to operate through your solar panel system.
The area you resign in will also play a factor. If you live in an area that goes through harsh winters or extreme summers, you will have to consider the increase consumption of heat or cooling in your home than if you lived in an area with mediocre climates.
The littlest things like older trees providing shade and helping lower cooling consumption, or bare tree limbs allowing sunlight in during the winter can make a difference and should be taken into consideration.
An additional option to assist in decreasing electricity consumption is to replace your appliances with energy efficient models. The newer appliances usually use less than 50% less energy than older models. Changing your light bulbs to fluorescent light bulbs will also make a difference.
After taking into account all obstacles and energy consumptions, you can stay on the safe side by building a solar panel system that generates the electricity needed to operate your household appliances times a quarter more than what your utility company reported to stay on the safe side. So you should go about multiplying your (average) daily kilowatt hour usage by .25. This will give you a fairly accurate estimate of the amount of energy you will need to build a system that can accommodate all your electricity consumption.