The 40 panels on the roof cost the couple about $53,000, and they paid about $5,000 upfront. They received $11,200 back, thanks to federal, state and city incentives and tax credits. The couple decided to take out two loans to pay off the rest of the bill. One loan is from the state energy authority and is paid at the same time as their monthly Con Ed bill, totaling less than $200 per month.
Mrs. Tornquist said the electricity bill averaged about $320 per month before they went solar. After the system was installed in May 2015, the bills dropped to $18 a month during the summer and about $50 a month during the winter.
Solar power first took off in Staten Island, Long Island and Westchester County, largely because many residents own houses with large pitched roofs that face south, optimal conditions for generating the most kilowatts. It hasn’t been as easy for homeowners in more built-up areas. Shade from neighboring buildings is the most limiting factor, and many solar installers are not interested in setting up systems on small flat roofs, according to Mr. Neidl.
“The large national installers would see a small roof on Google Maps and they would say: small system, big hassle, no thank you,” he said.
The city’s fire codes also made it difficult for installers to place enough panels to yield sufficient power, said Ronnie Mandler, the president of Best Energy Power, a Long Island solar installer.
The New York City Fire Department requires a clear path of six feet from the perimeter of the roof, as well as from all doors, skylights and hatches, so firefighters have enough room for themselves and their equipment. That limits the amount of usable space on a typical townhouse with a 20-by-45-foot roof.
“The city’s stringent fire codes are the reason the solar market hasn’t gotten bigger here,” Mr. Mandler said. That said, installers have come up with some innovative solutions.
Gaelen McKee, the president of Brooklyn SolarWorks, worked with a structural engineer and a design firm to create a solar canopy that raises the entire PV system off the roof by about 10 feet with aluminum frames.
Mr. McKee said fire codes limit the typical rowhouse to about 16 roof panels, but a canopy system can more than double the number of panels by elevating the panels over the roof, thus using most of the building’s footprint. He said he now installs about eight canopy systems a month and expects to double his business over the next year.
Owners of apartment buildings are also eyeing the sun. Jac Zadrima, a principal of Genesis Realty Group in the Bronx, placed solar systems on 21 of the 40 rental buildings the company owns. He estimates that he saves about $6,000 to $10,000 per building a year, and said that savings helps maintain other building operations.
“When you’re maintaining an older housing stock, a maintenance issue is never minor,” he said, “so it’s nice to have that extra money to offset a good portion of your common-area costs.”
Similarly, after spending $1.7 million to install solar systems on nine rental buildings in the Bronx, Brooklyn and Queens, Daniel Benedict, the founder of Benedict Realty Group, estimated that the investment will have paid for itself in about five years.
“Solar is great for long-term owners,” he said. “I’m saving 70 percent on my annual electricity bill.”
The 552 panels across the four buildings that make up the firm’s Alpine Apartments in Jackson Heights, Queens, generate about 157,000 kilowatt-hours of electricity per year. Between January and August, the Con Ed bill for the buildings’ common areas totaled $5,334, significantly less than the $18,850 he paid during the same period last year before he went solar.
Cecil D. Corbin-Mark, the deputy director of West Harlem Environmental Action, a community organization, said he worried that the less affluent would be left behind in the city’s solar revolution.
The organization has urged several Housing Development Fund Corporation co-ops in the neighborhood to go solar, but convincing people to spend money for future savings is difficult. “Many of these buildings don’t have much in reserves, so boards are hesitant to take out loans,” he said.
Even if co-ops and condominiums have sufficient reserves, getting the residents on the solar bandwagon is often difficult, said McGowan Southworth, 41, a founder of Zero Carbon Corporation, a green energy consultancy that has helped co-ops go solar.
Mr. Southworth understands the struggle: When he was president of his co-op board, it took him over a year to obtain shareholder approval, install a solar system and switch meters at his own building in Sunset Park, Brooklyn.
“It was a lot of collaboration, which included many informal chats in the hallways,” he said. “But now it’s an identity. We are known as that Sunset Park solar co-op.”
An earlier version of this article misstated the program through which Ann Schaetzel and four other homeowners formed a solar purchasing group. It was Here Comes Solar, organized by Solar One, a nonprofit, not the city’s Solarize NYC, organized by Brooklyn Community Board 6 and Solar One. The article also misstated the electricity generated by the 552 solar panels at the Alpine Apartments in Jackson Heights, Queens. It is about 157,000 kilowatt-hours per year, not 157,000 kilowatts.