While solar panels can continue to work on days when it is not sunny, you should not have them installed if you live in an area that is cloudy most of the time. The amount of energy you save with them will not be worth the amount you paid for them.
Find a reputable company. With the rapidly rising popularity of solar energy, new companies are springing up left and right to take advantage. A solar energy installation is a big purchase that should last you many years. When shopping for your system, look for a company that you can be confident will still be around ten or even twenty years from now.
Solar Radiation (Chapter 7) ABE 474 Indoor Environmental Control Dr. Angela Green University of Illinois at Urbana-Champaign.
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.