To understand why major solar companies are leaving Nevada in the wake of the state’s decision to cut the value of net-metered solar, concentrate on these two words -- no grandfathering.

The Nevada Public Utilities Commission’s decision last month to apply rate cuts and higher fixed charges to existing solar customers, not just future customers, is a huge problem for solar installers like SolarCity, Vivint Solar and Sunrun. It’s also a big problem for their customers, who are likely to see the value of their solar-generated electricity evaporate, as NV Energy cuts their compensation from full retail rates to wholesale rates over the next five years.

No other state has applied net metering changes to existing solar customers, given that it could undercut the economic case for making the 10- to 20-year investment into rooftop PV. Even Hawaii, which pushed through some significant cuts opposed by solar groups when it replaced its net metering program in October, applied them only to future customers.

And no other state has seen the same solar exodus as Nevada has. SolarCity, which leads the state in rooftop PV installations, announced it would shutter its Nevada operations the day after the ruling came out, and announced this week it’s cutting 550 jobs in the state, its first significant staffing reduction.

Vivint Solar closed its Nevada operations mere months after opening them, citing the uncertain market climate it faced under NV Energy’s proposal. CEO Greg Butterfield defended the decision in a Wednesday statement, saying that with the new rules, solar “customers would lose money, limiting adoption only to those willing to make an environmental statement.”

On Thursday, competitor Sunrun followed suit, announcing that it’s closed its Nevada operations, resulting in the loss of “hundreds of jobs” at the company and affiliated installers. And according to Lauren Randall, Sunrun’s public policy manager, the no-grandfathering part of the PUC’s decision was a big part of the reason why it left.

“The retroactivity piece is extraordinarily problematic,” she said in a Thursday interview. “Nevada essentially baited solar companies into the state, and baited homeowners to go solar, and then switched the rules of the game. It’s the most egregious anti-business, anti-solar decision that we’ve seen promulgated in any state in the country.”

Since the decision came out, Sunrun has been getting calls from customers worried that their solar systems are going to be draining, rather than adding to, their monthly budgets, she said. “What’s most problematic for this retroactivity piece is homeowners on fixed income, retirees that have budgeted for solar, and have trusted the state’s government to make that possible.”

Shayle Kann, senior vice president of research at GTM Research, noted Thursday that the lack of grandfathering is “by far the most dangerous part of this ruling.”

More than half of the states in the country are involved in studying or considering changes to net metering policy, which has traditionally rewarded solar customers for the power they feed back to the grid at the same retail rates they pay for energy. In two closely-watched decisions in recent months, Hawaii chose to reduce solar compensation well below the retail rate, while California chose to retain retail-rate payments, with only minor additional costs.

But in these states, and every other actively studying changes to net metering policies, utility regulators have “recognized that solar is by its nature a long-term investment,” Kann said. For customers considering that investment, “I think it’s reasonable for them to assume that the basic structure under which they’re compensated isn’t going to change. If you take that away, you’ve made it so that it doesn’t make sense for anyone to install solar anywhere.”

Meanwhile, the departure of the country’s biggest solar installers is likely to put a serious crimp in Nevada’s recent spectacular solar growth. There were roughly 10,000 solar customers in Nevada as of the third quarter of last year, according to GTM Research, driven by a 2015 growth spurt that put the state in second place in the country in terms of residential solar market share. That’s up from 14th in 2014 and 28th in 2013, and “no other state has risen in the rankings as quickly,” according to Cory Honeyman, senior solar analyst at GTM Research.

Of that recent growth, much has been driven by national installers offering third-party power purchase agreements and leases such as SolarCity, Sunrun and Vivint, he said -- about 90 percent of all installations in recent quarters, in fact. SolarCity alone accounted for about three-fifths of solar installations in Nevada in the first three quarters of last year, he said.

SolarCity and its fellow installers have vowed to fight Nevada's net metering changes. Randall noted that SunRun has joined the state’s Consumer Advocate in motions to ask the Nevada PUC to stay the implementation of the decision and reconsider it, and intends to pursue legal action in the event that effort fails.

Sunrun has also sued Nevada Gov. Brian Sandoval for failing to comply with a public records request showing communication between him and his staff and NV Energy employees and lobbyists. It's also a member of solar lobbying group The Alliance for Solar Choice, which has been criticized of late for what detractors call overly aggressive tactics in fighting net-metering changes in Hawaii and other states.

These tactics have led to complaints from some groups that the solar industry is using the threat of job losses to push states to adopt net metering policies favorable to them and their customers, to the detriment of utility customers who can't afford rooftop solar. Solar industry groups counter by citing studies that show a net positive impact of distributed PV for the grid and utility operations.