Mirrors to Take BPC Park Out of Darkness

By Barry Owens

The future home of Teardrop Park South, which will sit in building shadows almost year-round and seemed destined to be the darkest of Battery Park City’s urban valleys, might have offered gloomy planting prospects. But tomorrow, there will be sun.
The heliostats, mirrors that track the sun and reflect the rays to the ground below, were manufactured in Germany and their use to brighten a park will be a first for New York City. Photo: Courtesy Bomin Solar
“No hocus pocus about it,” said landscape designer Michael Van Valkenburgh, explaining the trick. “Only mirrors.”

Van Valkenburgh was the lead designer for Teardrop Park North and the man behind the plan to extend the park south across Murray Street, into the courtyard of a horseshoe-shaped building slated for construction next year. Once complete, the building will completely shield the park from the sun for much of the year.

“Not exactly a people magnet,” Van Valkenburgh said of the space. But he hopes that a trio of mirrors installed atop a nearby building will reflect enough sunlight for trees and other living things to thrive there.

“This is an idea that very oddly has yet to come to New York,” he said of the mirrors. “There are a number of places in the city that could benefit from the devices.”

The disc-shaped mirrors, called heliostats, are eight feet in diameter and mounted on top of the 24-story Verdesian
building, which is under construction at Murray Street and North End Avenue. The computer-programmed and motorized mirrors, custom-manufactured by Bomin Solar, a German company, track the sun’s movement and reflect its rays like spotlights to the ground below. The heliostats were installed last month.

“Sunlight is escaping many of our neighborhoods,” said Tim Carey, president of the Battery Park City Authority. “This is a technology whose time has come for New York City.”

The Authority paid $355,000 for the heliostats. Their use is in keeping with Battery Park City’s “green” goals, Carey said, likening the neighborhood to “an urban renewable energy lab.”

To help brighten the park he designed, Van Valkenburgh tapped architect and “daylight consultant” David Norris, who used similar technology to bring sunlight into buildings in Boston and Washington, D.C.

Norris, of Tribeca-based Carpenter Norris Consulting, said in an interview that he first focused on harnessing existing light at ground level. The park can be made brighter, he said, by incorporating reflective materials, such as a shiny, red brick, into the park’s design.

A crane hoists the heliostats May 31 in Battery Park City. The mirrors will reflect sunlight to the ground below. Photo: Allan Tannenbaum.

He is also working with the architects of the building that will be constructed next to the park to “punch holes in the building to create solar portals.” But portals and brilliant bricks would not be enough to sustain a green park space if it lacked sunlight year-round.

“That’s where the heliostats came in,” he said. “Really, they’re nothing more than big Boy Scout signal mirrors, the kind you sort of line up and shine into Bobby’s eyes.”

The mirrors, though, will reflect enough of the sun’s rays to keep the park in sunlight year-round, he said, and in some ways will be more effective than broad daylight since the rays can be directed to different spots at different times of the day or season, as needed. The light will shine in large pools or in well-defined spotlights, but will not be concentrated enough to blind or burn, he said. “It’s nothing more than once-reflected sunlight, somewhere on the order of 70 to 80 percent of the power,” he said.

Though plans for the new park have not been drafted and the park’s construction will not begin until next year, the project’s designers and the Authority were eager to have the mirrors up now.

“We want to put them in play, to discover what they can and can’t do,” Norris said.

Van Valkenburgh said he hopes to put the light in play in the treetops, on grass and rocks, and perhaps a fountain—now that he has been promised that sunlight will dapple the water.

Fully assembled, but with their reflective surfaces wrapped in clear plastic, the heliostats were installed on May 31. Engineers from Bomin Solar will return in August to cut away their wrappings and program the devices to follow the sun.

“People are always amazed and very happy when they see how they work,” said Michael Kroeffges, with Bomin Solar.

“Could we unwrap just one?” Norris asked. “And can they be rotated by hand?”

They answers were “yes,” so the pair planned an afternoon of mirror tilting and shadow chasing in the construction zone that will one day be a park.