Solar hot water heating is the redheaded stepchild of the renewable energy world. Most people have no idea what it is. Or, they confuse it with its attention-grabbing cousin, solar photovoltaics, the solar panels we all know about that convert light into electricity and glint on a rapidly increasing number of American roofs.
Despite its obscurity, solar hot water heating is a great technology—cost-effective, pollution-free, climate-resilient. And that’s why we’re celebrating New York City’s recent installation of solar hot water systems on the roofs of five firehouses in the Rockaways section of Queens. All five had been damaged by Hurricane Sandy, with four of them suffering from extensive flooding that required repairs to equipment housed in their basements, including furnaces and boilers.
That’s where solar hot water heating is coming to the rescue. “The firehouses in the Rockaways are ideal sites for solar hot water heating,” explains Kristin Barbato, Deputy Commissioner of the city’s Department of Citywide Administrative Services, which initiated and financed the project. (The project was managed by the New York Power Authority, the state’s public power provider and a national leader in energy efficiency.) “Firehouses,” Barbato says, “operate 24-7 and they use a lot of hot water for showers and laundry. The addition of the solar thermal systems makes each facility independent of the need to use natural gas or other fossil fuels to heat water for showers and general use.” In other words, should we face another storm like Sandy, Engine Companies 264, 265, 266, 268, and 329 will have functioning hot water systems when they need them most.
Current solar hot water heaters are based on a technology that’s more than 100 years old. (It was invented in Baltimore, actually, and was quite prevalent in the U.S. before it was supplanted by cheap hot-water heaters that use natural gas.) The heaters rely on a phenomenon we all know from parking cars in un-shaded spots: “Something left out in the sun is going to get hot,” explains Tim Merrigan, a solar hot water expert at the National Renewable Energy Laboratory. “If you put glazing over it, that’s going to trap the sun’s heat.”
The way the solar hot water heaters on the firehouse roofs work is relatively simple. Water from the building is piped up to the roof and then through a series of panels containing evacuated glass tubes. While inside the panels, the water absorbs the radiant heat of the sun. Then, it’s piped back down to a storage tank in the basement.