Solar panels don't have to fight for space on green roofs. Two experts suggest combining solar with green roofs works best.
If a solar roof is placed over plants, both the roof and the plants do better. The plants make the solar panels more efficient, because their evaporation cools the back of the exposed panels. Solar panels work better when they are cool.
Likewise, the dappled shade that the solar panels provide the plants below is similar to the canopy effect of taller trees protecting plants underneath from harsh direct sun.
That is the finding of Neubrandenburg Professor of Landscape Ecology Manfred Köhler, who has been involved with research on green roofs and façade greenery since 1981.In his paper, Positive Interaction between PV-systems and Extensive Green roofs Dr. Köhler says (rough translation)
On some of these greened roofs a photovoltaic –research power plant (PV) was installed in 1999.The CEO of nanosolar has said the same thing. Solar panels can be arranged to drip water for plants underneath:
Results: Under the shade of the PV panels the vegetation is modified significantly. It changed from a Moss-Sedum roof to a vegetation stand dominated by higher taller plant species likArtemisia and other. The biomass of plant species increased through the years.
A green roof reduces the maximum temperature during the day time. This has a positive influence on the production of electricity by the PV-panels and makes them more efficient in the summer months.
"In a municipal solar power plant, solar panels are mounted onto rails above the ground so that grass and flowers can continue to flourish in between and below the rows of panels. Care is taken that sufficient amounts of rainwater can drop through between adjoining panels so that the flowers and organisms below are not starved. In fact, in dry regions, the solar panels even benefit the ecosystem by increasing the moisture level in the soil.This synergy is good news, not just for us as homeowners going green, but also for us as a nation.
The Solar Grand Plan published in Scientific American last December said we could power 1/3 of the nations electricity with 30,000 square miles of photovoltaic arrays.
That sounds like a lot of space, but that is actually less square miles than coal per gigawatt produced, when you include the mined areas, not merely coal power stations. It seems like a lot because its all in one place, unlike coal mines.
More than enough land in the Southwest is available without requiring use of environmentally sensitive areas, population centers or difficult terrain, says the NREL. More than 80 percent is not privately owned. Arizona is very interested in developing this solar potential because coal is water intensive. This could eliminate the need for more than half the nation's coal plants.
And even better for the solar grand plan to be designed to allow some desert plant growth underneath in the dappled shade that could cool the panels in that hot Southwest sunshine. If the installation were designed as recommended by the green roofing professor and the solar CEO, we might have the best of both worlds.
Photo from Green Roof Magazine
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