As the calendar is poised to turn to a new year, Jon Costanza, owner of Sunpower Builders in Collegeville, shares the anxiety of many Pennsylvania solar installers.

It's an uneasiness born of concern that with a new administration in Harrisburg, years of financial incentives that have nurtured the fledgling, yet steadily growing, solar industry will disappear.

There are 700 solar contractors now. "We're going to see three-quarters of those guys go by the wayside," Costanza said.

Then there's the other transition that gnaws at him.

This one has nothing to do with politics or policy debate, but instead covers even trickier terrain: encouraging the ambitions of a daughter, even when they come at the expense of the family business.

As Costanza braces for the uncertainty of what Gov.-elect Tom Corbett's administration will mean to his company, he also is trying to find his bearings after the defection of oldest daughter, Kira.

Family-business owners long have been disappointed by the decision of a son or daughter, brother or sister, to leave the company. This one, perhaps, comes with a bit more sting for Costanza, because his daughter has opted to stay in the solar business - just not his.

The Costanzas' working relationship is well known in the state, where a few years ago there were just 11 certified solar installers. In terms of solar advocacy, father and daughter have been an influential pair, working and lobbying together the last three years to promote solar as a viable form of alternative energy and to help the industry grow in Pennsylvania.

The state now is believed to be second or third in the country in the number of solar jobs, due to grant initiatives such as the popular Sunshine program that the Costanzas, along with other installers, pushed for in Harrisburg.

But with future public solar-financing options in question, so, too, might be opportunities for growth. Without renewed state incentives, industry experts agree, the ranks of solar installers in Pennsylvania might thin drastically.

Kira Costanza's decision to leave the family business for one with work in other states might just be the start of a trend, her father suggested.

Not that it has made her choice to join Solardelphia in Bucks County as director of marketing any easier for him to take. Usually as outgoing and talkative as his daughter, Jon Costanza, a solar contractor since the 1970s, would not respond last week when asked how he reacted to her decision to move on.

Asked to describe his daughter, however, the spurned boss found his voice: "She's just a fantastic and dedicated person. As a parent, there's nothing that I could possibly look for or ask for in any of my children than to know they are following something they are passionate about."

Still, he added from his home office, "I miss [her] every moment without her here."

For Kira Costanza, 26, the decision to leave was strictly business.

"To pursue my interest in policy, I just wanted to get a broader sense of where the industry is going, expand my professional experience," she said last week at Solardelphia's headquarters, a converted house just north of downtown Doylestown.

While her father's company, with 20 employees, has concentrated mainly on Montgomery County and nearby areas - "Just portray that positively," she added protectively - Solardelphia, started in 2001, is working in Pennsylvania, New Jersey and Delaware, with plans to expand into Massachusetts and Connecticut next year.

Founder Jude Webster said he expected to grow the company from 25 employees now to 40 by the end of next year.

Kira Costanza first caught his attention a few years ago when she had the temerity to run for secretary of one of the solar trade groups - defeating an industry veteran, Webster said. It was only as the solar field became increasingly crowded and marketing more important to getting business that Webster thought to offer her a job.

That prompted a phone call from Jon Costanza. What followed was a conversation between Webster, 34, and Costanza, 55, not unlike one in which a father has been asked for his daughter's hand in marriage. Though in this case there is no romantic relationship, and Webster did not ask for Costanza's permission to hire his daughter.

"I don't think he was exceptionally happy about that," Webster said. "But he said he loves his daughter and wants her to do well."

"Dilemmas of family business" - that's how T.L. Hill, a professor of strategy and general management at Temple University's Fox School of Business, summed up the situation as described to him.

"From the father's perspective, it's sort of wonderful and horrible at the same time," Hill said. "To see your daughter flourish and enter a field you love and do well enough that a competitor will hire her and allow her to spread her wings - this is what you look for.

"From a business perspective, if she's that good, you don't want to lose her."

Kira Costanza insists the only thing her father has lost is the obligation to pay her.

Intact is their shared passion for an industry that has enabled them do what they love most: help others. With her father's assistance, two years ago Kira created Sunpower Afrique, a nonprofit dedicated to bringing solar power to the small West African nation of Togo.

There's one other change in their relationship, though: "We don't talk about business," she said.

Contact staff writer Diane Mastrull at 215-854-2466 or dmastrull@phillynews.com.