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.
Photo © Shunji Ishida
Studies vary in the efficiency boosts reported, from 3 to 16 percent. This is in addition to green roofs’ known effect of cooling indoor air, which reduces annual energy use by 6 percent, 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.
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