As quoted in the Spring 2007 Green Roof Magazine, Manfred Köhler, Founder of the Green Roof Centre in Neubrandenburg, Germany said that if a solar roof is placed over plants, both the roof and the plants perform 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.

Köhler, Professor of Landscape Ecology at Neubrandenburg, 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):

The vegetation dynamics of the extensive green roofs is one of the main issues and has been monitored since 1992. On some of these greened roofs a photovoltaic –research power plant (PV) was installed in 1999. At that time it was the largest in PV- installation in Berlin. Ten different types of PV-panels were tested. Some of these panels are installed above the green roof, similar panels above a typical black Bitumen roof on a comparable building. So the interaction between green roofs and PV panels was tested for several years. 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 like Artemisia 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.

This April, Martin Roscheisen, the CEO of Nanosolar, blogged about the same synergistic arrangement, that solar panels can be arranged to drip water for plants underneath:

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, considering much larger solar installations, like the Solar Grand Plan published in Scientific American last December. For that to be implemented, 30,000 square miles of photovoltaic arrays would be needed.

When you include mining area in assessing the square miles coal uses, solar would actually take less space than coal per gigawatt hour of power produced, according to Scientific American, based on power being produced from solar installations already in place in the Southwest.

The Solar Grand Plan has backing from studies by the NREL in Colorado showing that more than enough land in the Southwest is available without requiring use of environmentally sensitive areas, population centers, or difficult terrain. Arizona’s Department of Water Conservation has noted that more than 80 percent of his state’s land is not privately owned and that Arizona is very interested in developing its solar potential.

But still, it is a large area of our beautiful land. Some environmentalists are discouraged by the size of solar installations such as the Grand Plan envisions, even though those 30,000 square miles could supply a third of our national electricity requirement. How much better for it to be designed to encourage plant growth underneath as well as cooling the panels in that hot Southwest sunshine. If the installation were designed as recommended by the green roofing professor and the solar CEO, we could have the best of both worlds.

Photo by Flickr user dotcommodity