Recently, Ryan Miller and Green Roofing Technology help construct a roof for the NY Parks and Recreation Department. The goal of the green roofing system was to provide solar energy for building use. Other portions of the project included a rainwater collection system and vegetation on the roof. One aspect of the project that complicated things was the fact that they could not pierce the underlying membrane and instead had to rely on a ballasted system. In 2012 Hurricane Sandy hit the area and the original build crew went out to assess the effectiveness of the green roofing system.
Many Components to the System
In order to prevent piercing of the underlying membrane the team has to ballast the roof, which means it was essentially perfectly balanced. The sheer weight of the roofing system keeps everything in place. Vegetation was also located on the roof, fed naturally by sunlight and rainfall. Excess rain was captured by a water collection system and used to regularly irrigate roof vegetation. Finally, photovoltaic panels were installed to generate usable energy for the building during the day and lights for the roofing system during the evening.
The entire system was well configured to be an effective use of evaporation aspiration to keep the building cool. In this process water was stored through the water collection system, located under the upper roof where vegetation and solar panels were located. The water was warmed by the internal heat of the building. As the water evaporated from the system it released the building's heat, in a similar mechanism as sweating.
The water collection system also extended the operating life of the photovoltaic cells by lowering the overall operating temperature on the surface of each panel. By providing a cooling effect, the system was able to generate more power, on average, than bigger solar system.
Considering the roofing system was built in the northeast and not College Station, TX, the power generation results was outstanding. The total square footage of the roof was divided between pedestrian space, vegetation space, lights, and solar panels. When compared to a solar roofing system that is completely solar panels, the combined green roofing system produced 8.3% more power.
What about the Costs?
The total cost of the combined roofing system was equal to the cost of a traditional solar power roofing system. The space saved by fewer solar panels and better operating efficiency, allowed costs to be saved from less required mounting equipment. That space was converted in living space for plant life.
By the year 2021 the building will have saved over $ 359,431 in savings at a rate of $ .20 kWh. Additionally, the federal government offers many tax incentives that make these roofing systems financially attractive. One program in particular, called the Business Energy Investment Tax Credit can allow up to a 30% tax concession on the roofing system. Savvy building owners can also tax advantage of carbon credits, which can be sold with the aid of investment firms and brokers.
Combined green roofing systems have found a special place in the roofing industry. Future ramifications of this system could prove to be a consistent source of revenue after the system has paid for itself. In this particular study, the system generated full ROI within 5 years.