Plants on Green Roofs Help Solar Panels Keep Cool
Despite being an abundant untapped resource for distributed renewable energy production, rooftops sometimes aren't the best place to install photovoltaic (PV) panels. Heat has a negative impact on voltage, which affects power production on extremely hot days. But, by integrating a rooftop PV system with a green building technique designed to keep roofs cool and manage stormwater, Maryland-based Green Roof Technology may have found a solution to this problem.
Its new “Sun-Root solar-living roof system” is described by the company as the first fully integrated, non-penetrative solar and extensive green roof system in North America. Besides reportedly improving a building's energy efficiency by keeping it cool, the Sun-Root, its developer states, combines the benefits of a vegetative roof with the power production of a solar roof.
Essentially, it is like taking a ground-mounted PV system and putting it on a roof, while still maintaining the integrity of the green roof’s moisture seal and water management systems. Through evaporation, the system creates a cooler micro-climate around the PV panels, enabling them to operate more efficiently.
“Heat is the enemy of energy production,” said Jörg Breuning of Green Roof Technology in a statement. “Any time atmospheric temperatures on a roof begin to rise, PV elements lose their efficiency and can shut down if temperatures rise too high. We sought a way to counteract this negative phenomenon by combining solar modules with an extensive green roof.”
The sun-root system works by mounting the panels onto a drainage element stabilized by "root stiffeners". This ensures that the PV system is attached to the roof without compromising its waterproof integrity. The green roof material (soil, plants, etc.) act as a counter-load to the wind lift on the panels.
Rainwater is channeled underneath the panels by a capillary fleece and the suction provided by a slight slope in the roof. This provides water to the plants, and cools the panels through evaporation. The water then drains off the roof in the surrounding drainage system.
Elements of the sun-root can be tailored to meet the needs of different sites. The installation's specifications depend on site-specific factors like wind zone, building height, terrain category, distance to the edge of the roof, dry weight of the substrate and the size of the solar modules. The module racking structure is set at a default tilt of 30 degrees, but can be adjusted with the optional "root flex" retrofit kit.