The following is a web site that allows you to calculate the cost of putting in solar power for a given % drop in your electric bill as a function of your zip code. I can't vouch for the accuracy of its findings but in running it for my home it seemed pretty accurate from what I have read. Right now solar power seems to cost about 4 times more per kilowatt to produce then the power line. We pay a little over $.10 per KW in Florida. Some solar panel company out West claims to have made a break through and can now match the power line costs. I have no way of sustantiating this.
In looking at solar panels you always have to keep in mind that they need to be clean, free of snow and have optimal sun hitting them to produce the maximum rating that they claim. It would always be best to ask for "real life" output when dealing with the suppliers.
Right now solar power even with all sorts of tax credits, which I'm against (I don't want to help pay for someone else's electric bill), still doesn't make sense. Where as solar hot water appears to have good potential for saving money at a reasonalbe investment, especially if it is combined with a large storage tank of water to be used for assisting the heating of the home. As others here have pointed out, spending more money on better planning with more insulation in the roof, thicker logs, premium glazed windows, energy Star appliances and led and flurescent lighting is the most cost effective ways of saving on cooling and heating costs which in turn helps the earth.
Dig out your electric bill before running the calculator as it wants to know your dollars spent or kilowatts use. Enter the dollar amount in even amounts like 145 no decimals.