Carefully consider the types of solar panels you plan on having installed. Long ago, if you didn't have enough roof space, you'd need very expensive high efficiency mono-crystalline panels. There are now more advanced polycrystalline panels and even thin film panels. If you've got enough roof space, you might wish to look at the size of the panels in relation to their output capacity to avoid having insufficient panels that you need more of later.
This video provides a detailed look at California’s most popular type of solar water heating system – the close-loop active system.
The amount of energy your solar panel will produce is rated by watts. For example, if your solar panel is rated 100 watts, then on a clear day, your solar panel will produce 100 watts per hour. To find out how much electricity you need to produce, look at your electric bill and divide the total by 30 days and then divide it by 3 as there is generally bright sunlight one third of the day.
Your solar panels' density will impact their efficiency. Getting high density solar panels may cost you quite a bit, but after a while they'll pay for themselves because they produce more power. Be sure and compare densities before choosing a solar panel.