The number of new residential solar-power installations on Long Island so far in 2017 has declined by more than 50 percent compared with the period in 2016 as national companies have fled the market or retuned their businesses.

The number of residential solar installations declined to 2,975 for the first six months of this year, compared with 6,722 in the same period last year, according to figures from PSEG Long Island, which oversees the programs for LIPA. That’s a decline of 55 percent, after two prior years of triple-digit growth.

“It was a bubble,” said Mike Voltz, director of energy efficiency and renewables for PSEG. He blamed this year’s tumbling sales on a sharp drop-off in aggressive promotions by solar leasing companies, combined with a decision by the state in 2016 to end a popular LIPA solar rebate.

In addition, a state loan program upped its interest rates for most customers.

Nonetheless, Voltz said, “You’re now at a level where it’s more sustainable.” He noted that most of the business is being done by local companies that established the market over nearly two decades.

Also, he said, while leased systems made up 75 percent of the market last year, with the balance sold, this year the reverse is true: Systems that are sold are leading the market.

Voltz said commercial systems are also seeing an uptick as home systems recede. For the first six months of 2016, only 29 commercial systems were connected to the LIPA grid. This year, the number rose to 39 through the end of June, he said.

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LIPA last month awarded contracts for 20 megawatts of commercial rooftop solar agreements for 31 locations around Long Island. It also contracted for more than 58 megawatts of utility scale solar in Calverton.

About 40,000 of LIPA’s 1.1 million customers have rooftop solar.

SUNation Solar Systems of Ronkonkoma, one of the largest installers on Long Island, has grown its business this year, in part by taking on installations for other companies, said vice president Mike Bailis.

The company has learned lessons from the leasing companies by using canvassers who knock on doors to sell systems, and a telephone call center, Bailis said. An average 7,000-watt residential system costs around $25,000.

“Maybe we’re bucking the trend,” said Bailis, noting his commercial business also is on the upswing. Rivals who haven’t branched out “are down because they aren’t as aggressive as we are,” he said.

David Schieren, chief executive of EmPower Solar, a large installer in Island Park, said the fever pitch of sales in 2016 led to “customer backlash” with solar that established companies like his have worked this year to reverse. Still, he said, his sales are up 20 percent year over year.

“There was consumer fatigue from customers getting door-knocked and cold-called,” Schieren said. “That sector of the market that the lease appealed to has been saturated.”

EmPower has been able to grow by branching out into consumer battery systems while expanding the commercial sector of the business, Schieren said.

Earlier this year, EmPower installed a 51-kilowatt system on remote barns at Paumanok Vineyards in Aquebogue. It uses a remote net metering system that allows the solar panel energy to be applied to the winery’s primary electric account, saving $8,000 a year.

EmPower also is about to start a 1-megawatt community net metering project at Academy of St. Joseph in Brentwood. The system will allow the cheap solar power benefits to be shared among seven separate accounts and the many Roman Catholic nuns who live there, he said.

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With net metering, customers with solar systems generate energy to power their home appliances, and send excess power to the grid.

That excess is banked in special net meters, and when the sun isn’t shining, customers draw energy from the LIPA grid against their banked excess energy.