WHEN President Obama proclaimed in his State of the Union address last month that “solar is saving Americans tens of millions of dollars a year on their energy bills,” he clearly wasn’t talking about Nevada.

In late December, the state’s Public Utilities Commission, which regulates Nevada’s energy market, announced a rate change drastic enough to kill Nevada’s booming rooftop solar market and drive providers out of the state. Effective Jan. 1, the new tariffs will gradually increase until they triple monthly fees that solar users pay to use the electric grid and cut by three-quarters users’ reimbursements for feeding electricity into it.

More startlingly, the commission made its decision retroactive. That means that the 17,000 Nevada residents who were lured into solar purchases by state-mandated one-time rebates of up to $23,000 suddenly discovered that they were victims of a bait-and-switch. They made the deals assuming that, allowing for inflation, their rates would stay constant over their contracts’ 20- to 30-year lifetimes; instead, they face the prospect of paying much more for electricity than if they had never made the change, even though they’re generating almost all their electricity themselves.

The commission justified its decision by citing grid construction and maintenance costs that rooftop solar users haven’t been charged for, but circumstantial evidence suggests that other factors played a role. All three commission members were appointed or reappointed by Gov. Brian Sandoval, a Republican, whose two election campaigns have received a total of $20,000, the maximum allowed donation under Nevada law, from NV Energy, the Berkshire Hathaway-owned utility that is a major beneficiary of the rate changes. Two of Mr. Sandoval’s closest informal advisers, Pete Ernaut and Gregory W. Ferraro, are NV Energy lobbyists.