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London Build 2015



Studies show green roofs boost PV output
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Vegetated roofs can improve the output from photovoltaic solar panels, according to two recent studies. One study in Germany showed an average of 6% increase in power and the Bronx Design and Construction Academy in New York City found that green roofs boosted production by 3%.
Studies show green roofs boost PV output

In the German study, various green roofs had been installed on the Cultural Center of the Ufa-Fabrik in Berlin Tempelhof, during the 1980s. During the late 1990s several types of PV array were added with the intention of comparing their performance over time to determine which was the most efficient.

Voltages characteristically depend on temperature levels. Lower operating temperature means better PV efficiency. In this research the PV cells over a green roof were compared with cells over Bitumen roofs. In over 5 years of recording, the panels over the green roof showed an average 6% increase in yields. But the green roof was only one factor in enhancing the efficiency of PV-panels, taking other factors into account, the total range of increased energy output varied between 1 and 10%.

PV over green roofs can be mounted on fixed frames. The costs are lower in comparison to the tracking systems, which follow the sun, but the output is slightly less.

Under the PV panels, a variety of extensive green roof vegetation can be grown. In Berlin it was originally a Sedum roof but this was subsequently changed to include a wide variety of plantings. Minimum garden roof maintenance is required to reduce taller growing plants. The solar panels must be without shade.

The estimated benefit of a higher Power output from a green roof can help to offset the cost of green roof installations. Additionally installing solar panels on a green roof will result in a shorter payback period and higher ROI than installing them on a black, bitumen roof.

It is also important to note that green roofs are shown to reduce building energy use by reducing temperature fluctuations, or heat island effect, on the roof. This means that the heating and air conditioning systems do not have to work as hard to heat or cool the building, which saves energy.

Therefore, not only do green roofs boost solar panels' productivity, but they also decrease the amount of energy that the building needs to operate - which means the solar panels need to do less work to meet the building's electric load.



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