You should never feel pressured to buy something, especially an expensive solar energy system. These types of salespeople are pretty common in this industry. You can tell them you'll be back later, and they should be fine with it. If they are persistent about making a deal now, tell them that the deal should be just as good in the future. Making decisions under pressure can be more costly later on.
Before installing solar panels on your roof, check with your home owners association. Some associations have restrictions on what you are allowed to do to the outside of the property, and this might mean solar panels are not an option for you. It is better to have this information up front than to purchase the panels and be forced to remove them at a later time.