It's better to get a solar system when you own a home. Don't overextend! If you have a mortgage and you need to finance your solar energy system, you could endanger your financial security.
The best time to incorporate solar power into the design of a home or building is in the initial construction. Windows are best facing south to let maximum sunlight (hence greenhouse heat) in during the winter. Likewise, avoid windows facing directly into the summertime sun to keep things cooler, so less power is needed for fans or air conditioning. The maximum roof space, however, should always get sunlight exposure.
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.