Net metering (bi-directional meter whereby the consumer is credited for energy fed into the grid) and high electricity rates are two important factors in making solar feasible. California at $0.25/kWh is among the highest, and has the largest # of installed systems. Idaho with abundant hydro at $0.06/kWh is among the lowest, and doesn't pencil out. Some states Florida, Hawaai are solar unfriendly. Also, you must have lots of sunlight and a good location for the panels. Utility companies are threatened by solar and are hoping to change the rules in their favor.
Several interesting articles:
Net metering - Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Net_metering
Wikipedia
Net metering (or net energy metering, NEM) allows consumers which generate some or all of their own electricity to use that electricity anytime, instead of when it is generated. This is particularly important with wind and solar, which are non-dispatchable.
?History · ?Controversy · ?Comparison · ?Time of use metering
Ditching Net Metering Is in the 'Best Interest' of Solar, Say MIT ...
http://www.greentechmedia.com/articles/read/MIT-Economists-Say-We-Should-Ditch-Net-Metering
Greentech Media
May 5, 2015 - Net metering compensates distributed solar generators at the retail price for electricity they supply to the grid, rather than at the wholesale price ...
Net Metering 101 - IER
instituteforenergyresearch.org/analysis/net-metering-101/
Institute for Energy Research
Jan 14, 2014 - Selling the excess electricity to the grid is called “net metering.” Net metering is one of the hottest topics for utilities today because of the way the ...