Putting solar panels on your roof can save a lot of money in the long term. But having somebody come over to your house and tell you whether or not your house is a good house for solar panels can cost a lot of money in the short term. It's a classic Catch 22, provided that you don't quite understand what a Catch 22 is.
But now Google, helpfully, is ensuring that none of ever has to learn the exact definition of "Catch 22" by creating an online tool, called Project Sunroof, wherein you plug in your address and it tells you the hours of usable sunlight per year based on day-to-day analysis of weather patterns, and the total area available for solar panels based on 3D modeling of your roof and nearby trees, and then calculates the estimated net savings. With a free tool like this, you can't afford not to get solar panels, or at least kill a little time plugging in the address of every house you've ever lived in.