Solar and Green Roof with Green Roof Plants

News-brief from Environmental Building News

Green Roofs Improve Solar Panel Efficiency 

By Erin Weaver 

Green roofs are known to extend roof life, conserve energy, and reduce stormwater runoff and air pollution; new studies show they can also boost the performance of solar panels. Plants reduce a roof’s contribution to the urban heat-island effect by lowering the surrounding air temperature through evaporation; this cooling can also make photovoltaic panels perform more efficiently. Plants also reduce airborne pollutants and dust particles, allowing the panels to absorb more sunlight. 

Studies vary in the efficiency boosts reported, from 3% to 16%. This is in addition to green roofs’ known effect of cooling indoor air, which reduces annual energy use by 6%, according to a recent French study. 

New designs for solar arrays allow water to drain evenly across the roof, and research suggests that the biodiversity created by including shade-tolerant plants below the panels can improve a green roof’s overall performance. A recent British study in Building and Environment found that broad-leafed plants such as lamb’s ear, which can thrive in partial shade, outperformed the traditional sedum in cooling the substrate and surrounding air. 

 

December 1, 2012

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DISCUSSIONS, Comments

Reader-contributed comments related to Green Roofs Improve Solar Panel Effciency - EBN: 21:12. Comments are listed with newest at the top.

Green Roof Plants Posted by Jorg Breuning on Dec 2, 2012, 06:12 PM  
 
Sedums are a large genus of flowering plants commonly known as stonecrops. They are found worldwide from tropical regions to the Polar Circle. There are more than 400 different Sedum species known and most of them survive in locations that have hardly soil. The survive-ability of Sedums under extreme conditions with a thin layer of soil and almost endless varieties makes them to the ideal, perennial ground-cover for extensive green roofs.

The British study over less than two years with broad-leafed perennials like (mentioned Stachys byzantina, Bergenia cordifolia and Hedera hibernica) require deeper soil profiles. More green roof growing media (soil) increases the costs of the green roof, the structure and the maintenance dramatically and so decrease the likelihood of having a green roof to start with. Comparing Sedums with the mentioned type of perennials is like comparing wild strawberries with apples.

The readers of this Solar/Green Roof (Sun-Root)article also must understand that the climate conditions in Great Britain are unique and generously supported with moderate temperatures by the golf stream all year around.

As a green roof expert with over 40 years of experience I can clearly say that this research is worthless and proves only common sense. If this study would have been done by experienced researches the plant selection would have considered broad-leafed, perennial plants that grow in the same conditions as the compared Sedums.
In modern green roof technology there are multiple choices of herbaceous perennial plants that supplement the fundamental Sedum carpet.

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