"All indicators internally are showing a really strong recovery from what was essentially a drop to zero," said Jonathan Cohen, the government liaison for SUNation Solar Systems, one of the largest installer of solar panel on Long Island, in New York state.

That's an especially meaningful statement in New York, which saw the nation's most severe solar downturn.

Not only was the state the epicenter of contagion, but solar businesses went into a near-coma as the state declined to name solar installation as an "essential business," even as it achieved that status in most other states.

Statewide, 65% to 70% of the 10,000-person solar workforce was furloughed, according to Shyam Mehta, the executive director of the New York Solar Energy Industries Association.

"We had no idea when we'd be able to work again," Mehta said, pointing out that smaller solar businesses often have enough cash on hand to last a few months. "There was real existential concern for the industry as a whole."

New York's solar lockdown was lifted in May. Before, SUNation had furloughed two-thirds of its 170 employees.

Now it has brought back all but 20 of its workers. The remainder, Cohen said, didn't want to come back. The company has hired some new people and is advertising for six more.