Green Roofs - Living Architecture Monitor - Spring 2020 - 34

ON SPEC

WHY HAVE EUROPEANS EMBRACED
SOLAR PANELS AND GREEN ROOFS WHILE
WE ARE STUCK IN EITHER/OR MODE?
BY STEVEN W. PECK

olicies and business practices that support the best possible
use of roof space are needed now, more than ever. The
doctrine of "Best Possible Use" for roofs means getting the
most public and private benefit from our rooftop real estate
assets. Yet the rooftop solar panel market is capturing a growing
portion of roof space, effectively squeezing out other uses. The
problem is exacerbated when policies demand one technology,
or the other. It should not be so! Solar panel green roof combinations have been implemented on hundreds of buildings across
Europe.The best possible use of our roof assets is supported by
the many synergies between green roof and solar panels which
are ecologically, socially and economically impressive:

*S
olar panels are four to 10 per cent more efficient at producing electricity when placed above extensive green roofs. The
green roof keeps them cooler due to evapotranspiration and
shading. For every 1°C above 25°C, solar panels lose 0.5 per
cent energy output. The temperature on green roofs stays
below 35°C, keeping the surrounding air temperatures and
solar panels cooler.
*G
reen roofs help keep foreign particles off solar panels, helping them become more efficient and reducing maintenance
costs.
* The plants and growing media provide the ballast required
to anchor the racking system that secures the solar panels,
thereby eliminating the need for heavy point loads of
concrete ballast or worse, roof penetrations that are prime
spots for future leaks. Since the green roof extends the life
span of waterproofing, it can reduce or eliminate the need for
a costly waterproofing roof replacement that would disrupt
energy production.
*S
olar panel green roof projects can create micro climates
under the panels, which in turn create micro habitats that
increase plant and insect diversity.
LIVING ARCHITECTURE MONITOR / SPRING 2020 / 34

Millions of square feet of combined solar/green roofs have been
implemented in Europe but North America still seems to be
stuck in an either/or mindset. "The lack of implementation may
be because the awareness isn't in the market yet," said Michael
Krause, of Kandiyo Consulting, a solar industry consultant in
Minnesota. "Solar panel green roof projects are more prevalent
in countries like Germany, Switzerland, Austria and the UK,
primarily due to good policy on green roofs and renewables,"
said Dusty Gedge, President of the European Green Roof
Association. "Professionals are more aware that integrating the
two approaches is achievable because of good systems developed
by leading green roof companies," he added. Big companies
like Optigrun, Bauder and Zinco have had proven systems for
more than a decade. Jorg Bruening of Green Roof Technology
has developed solar panel green roof projects in North America
since 2008. "Some solar panel companies don't like green roofs
because it means they can't sell quite as many panels. We also
need more data to prove the benefits," he added.
San Francisco's Better Roof Ordinance recognizes combined
solar panel green roofs in its compliance requirements (30 per
cent green roof area, or 15 per cent solar panels, or a combination). A roof with 15 per cent green roof area, half covered
in solar panels would meet the full requirement, leaving the
remaining roof area for other purposes, such as amenity decks,
rooftop farming, or sky lights.
Integrating solar panels and green roofs makes greater use
of our roof assets than just solar panels, and the efficiency
gains often pay for the green roof assembly. Smart designers
and policy makers should embrace the integration of these
technologies and maximize the benefits of their roof assets.
Steven W. Peck, GRP, Honorary ASLA is the founder and president of
Green Roofs for Healthy Cities. Register for our free webinar on solar
panel and green roof synergy April 22.
LIVINGARCHITECTUREMONITOR.COM

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Green Roofs - Living Architecture Monitor - Spring 2020

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