Residential Solar Energy in Washington, DC
I created two Excel worksheets to aid first myself and others in assessing the financial impacts (they are generally quite positive) of installing photovoltaic power (click here) and solar hot water (click here) particular to the non-state of Washington, DC. One can plug in their own variables to determine the potential simple paypack, return on investment and net present value of going solar.
The key is to think of solar power as an investment (and a tax-free one at that!) rather than a cost. One can likely get better returns investing some of your money in the sun rather than the stock market, bond market or a savings account.
Here is PDF of a PowerPoint slide show I gave to the Solar Hot Water Homeowner Education Forum on June 26, 2012 that was sponsored by Capitol Hill Energy Cooperative and DC Sun and entitled: Financial Benefits of Residential solar Hot Water in Washington, DC.