Light detection and ranging (Lidar) has been employed by the US military since the 1970s. Now, New York City is using the 3-D laser technology to pinpoint its photovoltaic potential - and is creating the first solar map of the Big Apple.Photon Magazine | October 9th, 2010
During nine separate nights last spring, a small twin-engine Shrike Commander soared over the city that never sleeps. Equipped with a lidar system, which sent out laser pulses to track every point of space between it and the Earth some 3,500 ft below, the flight collected data to produce a glowing never-before-seen solar map of New York – making this, researchers hope, one of the most photovoltaic (PV) module-studded cities of the future.
The map, currently being developed by the Center for Advanced Research of Spatial Information (CARSI) at Hunter College, is the result of a dual effort by Sustainable CUNY and New York City. It represents part of Mayor Michael Bloomberg’s PlaNYC – a plan to cut emissions and reduce energy use by 30 percent in New York City by 2017.
Only 10 years ago, laser-generated mapping data of this type was too dense and heavy for any civilian or commercial software systems to process.
But now, says Llana Hines, general manager of Sanborn, the Colorado Springs, Colorado-based company that carried out the lidar flight project, applications have caught up with hardware to provide better storage, more memory and greater precision tracking. And all for a relatively low cost. In New York City’s case, the price tag totaled $450,000, almost half of which was funded by grants from the US Department of Energy.
Â»For a lot of cities that have to answer the question of [PV] capacity, it becomes a return on their investment. This can be more cost effective, with a higher definition and finer resolution mapping [of solar energy’s potential],Â« says Hines.
So how does lidar technology actually work – and why is it more useful than, say, regular aerial photography for a city that’s trying to get ahead in generating solar power on a large scale?
Basically, it comes down to a laser and a pulse. As opposed to aerial photographs, which are two-dimensional and can’t be turned on their side, the lidar sensor sends out a pulse that scans in all directions, that is, vertically and horizontally. When the pulse returns, it contains the dimensional data of every object in that three-dimensional swath of airspace: trees, door canopies, light posts and, most importantly, buildings.
In terms of its potential for mapping out wide-scale PV installations, says Hines, lidar Â»allows you to completely visualize the entire terrain, including the tall buildings and urban canyons [so] you can do calculations and figure out where would be the best location to put the solar panels.Â« After receiving the data that’s been collected from all points of space, technicians are left with what Hines calls a Â»point cloud.Â«
Â»We look at this point cloud – think of it as one big chunk of points – and we turn it on its side, see the skyline, get a rendering of the landscape, and are able make a precise picture image from this data because we not only have its true position in latitude and longitude but we also know its elevation,Â« she says. The New York project represents a leap forward not only in terms of accuracy, she adds, but in terms of speed as well.
Â»You can say, â€ºThis building is 25 stories off the ground and its dimensions are such-and-such,â€¹ which is far smarter than what you get from photometric aerial images where there’s always a margin of error,Â« says Hines. And in terms of turnover, Â»10 years ago it would take most states 3 to 5 years [to finish] a mapping cycle. You couldn’t capture the area and process it in time to make it relevant to anybody,Â« Hines says, adding, Â»Now, we can map entire states and acquire and deliver the solar map data in 6 months.Â«
Naturally, New York is not alone in adopting this new technology. After its trial run here, lidar-equipped flights may well be taking off and creating solar maps of cities throughout the country. Â»In those urban canyons, you have to get as much detail as possible [to maximize your PV],Â« says Hines.
Â»I suspect we’ll be having a lot more of this.Â«