Could solar water heating work in NYC apartment buildings?

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In 2013, the Mayor's Office of Sustainability published a report on energy and water use in the city with surprising findings, chief among them this environmental takeaway: that multifamily properties account for more than half the energy consumed by NYC's buildings, with two-thirds of that going toward heating and hot water. The report identifies old, inefficient steam heating systems as one of the primary reasons for the high percentage of energy used, noting that refurbishing or replacing these methods could present significant savings. 

One California-based nonprofit has a suggestion: solar water heaters. The Center for Sustainable Energy administers an initiative for San Diego homeowners to install solar water heating systems on their roofs; in a press release, CSE notes that for buildings where daily hot water use is high, supplementing existing systems with solar could reduce heating costs by 60 to 80 percent.

San Diego, though, is famously one of the sunniest cities in the country—plus, CSE incentivizes installing solar water heaters for Californians by offering rebates and tax credits. 

Nicholas Oliver, a project manager with the CSE, says such a project could still be viable in NYC, despite the city's comparatively gloomier weather. "California has more sun than the northeast, but the solar thermal technology is better at capturing indirect, diffuse sunlight," he says. 

Per the Department of Energy, solar water heating systems can work efficiently in any climate. And the New York State Energy Research and Development Authority notes that solar heaters function even when the weather is overcast, harnessing sunlight through roof panels that heat cold water and transfer it to water tanks. Hot water is then provided by a combination of conventional heating and solar heating, as the systems are integrated with one another. 

In fact, points out Paul Gottsegen, president of Halstead Management Company, in some countries like Ireland, developers can't build new construction without incorporating solar technology. "That shows you that it's definitely doable," Gottsegen says. (Halstead doesn't manage any properties using solar power yet, though Gottsegen says they recently recommended it to a 640-unit complex.) 

In multi-family buildings, Oliver says, "solar works quite well with central boiler units. You'd have mutiple solar collectors on the roof feeding a storage tank. Water would come into tank and would be heated indirectly usually, with heat exchange fluids. The resulting hot water would then be drawn by the building before there was any draw from the boiler. It's a way to reduce the amount of use the boiler gets on a daily basis, which is where the savings come from." 

This system works best when there's ample roof space relative to the size of the building, he says, so the benefit would likely be greater for low-rise buildings than for tall apartment towers.

Gottsegen says that there's a promising alternative to individual city properties installing solar where they can: solar sharing programs. "To me, this is the way to go, because not every building has the roof print to accommodate enough solar panels," he explains. With solar sharing, community members, including those who don't have the space to install panels on their own properties, contribute to the cost of placing them elsewhere in the area where there is more room, like the roof of a school.

"What happens is all the energy collected goes back into the grid and is calculated so that people who have contributed get a proportionate reduction in their energy costs," Gottsegen says. 

An initiative called the NYC Solar Partnership, a collaboration between Sustainable CUNY, the Mayor's Office of Sustainability, and the New York City Economic Development Corporation, is trying to get such a program up and running. The partnership is now fielding requests for information from potential suppliers of community solar power. (DNAInfo wrote about the program in October 2016, and spoke to one landlord's representative, who confirmed that they'd installed panels in nine of their rent-stabilized buildings in the Queens, Brooklyn, and the Bronx.)

And according to the state Department of Energy Conservation, there are benefits for New York homeowners who adopt solar water heating, including incentives for installing systems and income tax credits. And in the city, Solarize NYC invites communities interested in installing solar power systems to apply for resources and grant money. 

And the process for installing the technology sounds rather low-stress: "It may involve turning off the building's hot water for an hour or two for connections to be made, but that's it," Oliver says. "In general, the technology is pretty simple, and applicable in all areas of the United States."