Green roofs are not news. In fact, ever since the early 2000’s, green roofs have been spreading across America, and the world, like weeds (no pun intended). A recent editorial in the New York Times (http://opinionator.blogs.nytimes.com/2012/05/23/in-urban-jungles-green-roofs-bring-relief-from-above/?src=recg) illuminated the spread of green roofs with an interesting analysis. By combining not only quantitative measurement of temperature differences with electrical savings, the piece makes an interesting case for why green roofs, and their less illustrious sister, white roofs, could be an easy and immediate solution to the energy reductions necessary.
However, beyond the number tossing and analysis, the article did shed light on one of the greatest issues with green roofs… there are just so many solutions that are called Green roofs.
The first, and most intuitive green roof is that of the garden. These roofs are coated with vegetation that not only reflect most of the sunlight, but they also use a process known as phototranspiration to cool the roof top surface. Numerous studies have been conducted to measure the effectiveness of these green roofs. When all factors are considered, including the fact that ‘green roofs’ are naturally more effective in the summer, allowing for the winter roofs to maintain a warmer temperature, it was shown that the roughly $15 dollar per square foot price tag for a green roof pays itself back in less than 3 years. This is astounding when we consider that a building ownership cycle is on average 17 years.
Of course, green roofs also clean the air (through photosynthetic processes) and help reduce the burden of urban water flash runoff, not to mention urban heat island.
White roofs are simply roofs painted with white paint. Not a particularly complex idea, but the heat reduction on the roof is astounding, and the option is so cheap that many building owners are flocking to it.
Blue roofs are ponds on the roof. These systems combine the natural cooling capacity of evaporation with a monitored flow to not only help cool but also mitigate storm overflow issues.
And of course, there are our old friends photovoltaic’s that are ‘green’ in the sense that they create a renewable energy source on site. Not too shabby.
However, what The New York Times article fails to present are some of the interesting ‘fushion’ green roof options out there. First up, is algal solar shades. These large sheets of parallel plastic contain floating algae that grown in a small amount of water. Not only does the green algae provide a shaded environment, effectively cooling the building, but it can also be used as a carbon sink or as a source for biofuel stock. Interesting idea, no?
Secondly, there are solar thermal water heaters which not only cool the house but also reduce the electricity or gas bill by mitigating the amount of energy needed for showers, washings, etc.
Finally, we should not forget the possibility of microdesalination facilities on rooftops. Especially in cities such as NYC which have ample access to salt water, desalination through controlled evaporation offers a way to easiliy cool roofs which simultaneously producing a valuable commodity. Of course, NYC is not in a water shortage prone region, but perhaps cities such as LA or San Diego could benefit from this desalination roof even more.
All in all, the option for green roofs are immense. When you have a controlled environment with access to so much solar, and thermal energy, it seems as though you have a situation primed for opportunity. I just hope that more people take advantage of the opportunities atop their buildings.
As always, check back in with www.energygridiq.com for all your energy thoughts and news.
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