Green Roof Integrated Photovoltaic
Green roof integrated photovoltaics (GRIPV) is a system that combines the benefits of solar and green (or vegetative) roofing. Prospect Solar has the unique ability to operate as a solar and green roof installer through partnership with our sister company, Prospect Waterproofing. A green roof integrated photovoltaic system allows for a relaxing and therapeutic roof space that provides environmental benefits in addition to what solar contributes.
Advantages of Green Roofs and Solar
- Reduced building heat envelopes mitigating Urban “Heat Island” Effect
- Green roofs reduce HVAC bills and allow for solar to increase energy offset
- Vegetative roofs can retain 50-90% of rainfall, avoiding storm water runoff
- Reduces the amount of impervious surfaces in a city
- As natural biofiltration devices, green roofs remove airborne toxins and re-oxygenate air; water retention allows for filtration of pollutants
- Green roofs can reduce the noise levels of a facility by as much as 40%
- Extended roof life can be possible due to moderation of temperature swings
- Warmth from solar panels provides vegetation a longer growing season
- GRIPV systems can increase solar production by as much as 16%
Green Roof Construction
Green roofs are typically installed on an Inverted Roof Membrane Assembly (IRMA) roofing system. Sometimes referred to as a Protected Roofing Membrane Assembly, this system places the waterproof membrane directly onto the roof substrate (decking), and then uses a protective foam layer above it to prevent puncture of the waterproofing layer. From here, one of three types of green roof systems is installed:
- Extensive – The most prevalent green roof system utilizing 3-6″ of growing medium. This low-maintenance approach can even be installed on sloping roofs, and is ideal for growing hardy drought, wind, and frost-resistant plants such as sedums, herbs, and grasses.
- Semi-Intensive – Also referred to as shallow-intensive, this system creates roof top lawns and common areas that are ideal for foot-traffic and human interaction. Planted in 6-12″ of growing medium, these rooftop greenways provide a firm construction that handles continual pedestrian interaction.
- Intensive – Intensive green roof systems are the most in-depth vegetative roof system. Sometimes referred to as “urban agriculture,” these systems incorporate 6-36″ of growing medium that can accommodate sod grass, perennial and annual flowers, shrubs, and even small trees. Intensive green roofs require built-in irrigation and additional upkeep. However, the result is a flourishing green rooftop environment full of varied plant species.
Green Roof Integrated Photovoltaic System Installation
In a GRIPV system, the solar modules are secured to the rooftop through ballasted mounting. The weight of the green roof’s engineered soil and plants provides a non-penetrating anchor and helps conceal these ballast mounts.
Made of recycled high-density polyethylene (HDPE), this layer is fabricated similar to a waffle or egg-carton form. The lowered cells provide water retention cups, while the raised domes provide ventilation and evaporation through a series of holes. Drainage channels on the top and bottom allow transport of rain water across the drainage layer to a water retention layer below where rain and nutrients are absorbed and stored. The ballasted mounts for the solar panels are placed on this layer before adding the engineered soil.
This growing medium is specially designed soil that is lightweight and porous allowing for absorption of moisture and minerals without compromising structural integrity. Engineered soil consists mainly of inorganic nutrients and minerals, and avoids compression due to settling. Because it is a non-compacting medium, excess water is able to drain with little effort and is distributed to the retention layer. Between the drainage layer and engineered soil is a system filter which prevents drainage holes from clogging and soil from washing into lower levels.
Solar and Vegetation
Once the solar mounting is ballasted with the engineered soil, horizontal rails (similar to struts) are placed across ballasted feet. Mechanical fasteners allow for the solar panels to be attached to these rails, and secured for high winds. Electrical cables are run through a buried underground conduit. The row of gravel in front of the solar module prevents soil washout as rain water flows down. Sedums are planted into the engineered soil.