the idea is to sell your excess electricity to the power company on sunny days when brown outs occur and consumption goes up... then at night you buy the juice from the grid, some months you may make a profit, but you have to pay for the installation and materials...
Here in New Orleans the deal the city council made with Entergy mandates they hook up solar systems...
The state however has met a set number, "allows an electric utility to reject applications from homeowners proposing to install solar once the overall percentage of electricity produced from solar in that utility exceeds 0.5%." and that number has been reached so outside new orleans you cannot hook into the grid and pay off your investment.
Now you could hook up , use what you need and give the rest to the companies, but that would be socialistic and frowned upon...