Idaho has relatively cheap power (8 cents/kWh winter, 10 cents summer), and no time of use, so the ROI on Solar is twice or more as long as a lot of places. That said, Idaho is also ideally situated for solar, because peak demand is during the summer season, when production is at maximum (as opposed to, say, Vermont, where peak demand is in winter). Also, solar daily production and export peaks right in the heat of the day in summer, when AC demand is highest. Rises and falls with cloud cover, too! Idaho Power's dams cannot keep up during that time and they have had to build gas fired peaker plants (Idaho has no natural gas reserves, so they have to ship gas in from out of state to fuel the plants) to meet the demand. This will only get worse as Idaho grows and temperatures keep climbing. These costs could be mitigated by encouraging widespread rooftop solar adaption, but IPC won't do it because they can't control it.
If IPC ever comes out with true numbers I would bet that they would show that solar setups cost them nothing and actually add to their bottom line through the summer peak. They want every penny they can get, though, so they won't admit it. To my knowledge, after their defeat in front of the IPUC a couple of years ago going after net metering they haven't tried again, because they don't want this known. They'd be paying ME!
In the long run, I also like solar as a hedge against rising power costs. Hard to pencil that in, but it does help with peace of mind for those of us near retirement.