From this Bloomburg Businessweek story:
The shift toward distributed rooftop power hasn’t yet made a big dent in the profits of large utilities, but they’re beginning to feel the bite. Arizona’s largest utility recently reported quarterly electricity sales had dropped 1.3 percent from a year earlier, in part due to distributed generation. To head off the threat of rooftop solar, utilities in at least five states have asked regulators to begin taxing rooftop solar installation or tacking on fees to connect to the regular grid in order to recoup lost revenue.
The problem is your monthly electric bill isn’t just the number of kw you use times the per kw rate, although they present it to you that way. Behind the scenes, your utility pays less for the electrons than it sells them to you, and uses most of the “profit” to pay for expanding and maintaining the grid. So if you go solar on your roof, you no longer use – nor help pay for – maintaining the grid. And the grid costs the same as it did before you left it.