Rooftop Agrivoltaics
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twelve years ago we discovered
the synergy between green roofs and
solar panels
here’s a picture of me on the epa
region 8 headquarters in downtown denver
colorado
behind me you see a solar panel array
and in front of me is a series of plants
that i’m taking data on
these plants ended up benefiting from
the solar array
to the point where we had to evaluate it
very closely so we put a whole bunch of
sensors
under that solar array and found out
that there were really three things that
influenced the success of those plants
it was cooler under the solar panels in
the summer
warmer in the winter it was also
less wind and of course there’s a lot
less sunlight not
plants don’t need a hundred percent of
the sunlight all day long
so they thrived under there we also
found out that the panels benefited from
the fact that the plants were there
solar panels operate most efficiently
at 72 degrees fahrenheit
and the the rooftops are typically up to
170 degrees fahrenheit
plants can’t survive those conditions so
they
evaporatively cool the air around the
solar panels
and end up providing some cooling
benefit to the panel so they operate
more efficiently now
i’m studying drought tolerant native
and non-native plants on that green roof
but i want to take this a little bit
further
i want to substitute those plants for
food crops
so this is a term called rooftop
agrovoltaics that’s literally the
combination of
agriculture and photovoltaics
photovoltaics is another term
for solar panels so i want you to say it
with me
rooftop agri-voltaics
that’s literally growing food under
solar panels
on top of buildings we already know
that agrovoltaics work on the ground
in farm fields so us green roof
researchers we call that at grade
since we’re used to being up in in
higher elevation
so here’s a picture of some research my
colleague dr mark uchanski
at colorado state university has
performed the past
couple of years he evaluated food crops
under solar panels and in adjacent full
sun areas
and he found relatively equal
yield under the panels and in full sun
interestingly though foliage crops
such as lettuce ended up having
slightly larger leaves under solar
panels and that’s because the plants
themselves were growing
and trying to reach more sunlight so in
theory
we might end up with more marketable
produce under solar panels
now i want to take this further growing
in agri-voltaic systems on the ground is
one thing
it’s much more extreme up on rooftops
so here’s a picture of my graduate
student thomas hickey
he’s collecting data in green roof
systems under solar panels
this past summer he did a pilot study
where he screened
crops of all kinds and actually native
plants of all kinds which are
of course food crops for pollinators
and he found some really interesting
results
so the water limiting environment of
green roof systems
meant that the plants out in full sun
actually didn’t
didn’t survive it was only the crops
grown under solar panels
that actually uh produced
so you might be wondering why am i so
interested in rooftop agrivoltaics
well besides the fact that i’m a green
roof researcher so
that that’s my my primary area of
expertise
however i’m really convinced that
rooftops are the place
that we need to be looking at for
growing food
half of our world population lives in
urban areas
already by mid-century
two-thirds of our population will be
living in urban areas
all those people eat and very little
ground is available for growing food
on the ground or at grade so i really
want to push for
producing food in the only available
space remaining
rooftops so in 2017
i was one of the technical advisors for
the green roof ordinance that occurred
for the city and county of denver
it passed and one of the things we did
was a rough analysis of how many low
slope
or what looks like flat rooftops there
are
in the city and county of denver we
found out it’s about
5 000 acres that’s a lot of space
imagine if just 20 percent of that
area a thousand acres could be used
for rooftop agraval tanks and also
consider
a a modest yield of about
five thousand pounds per acre
over a thousand acres that’s five
million pounds of food that can be grown
in just the city and county of denver
imagine how many households
that can can feed
also there’s another aspect i have this
great quote here and i’ll read it for
you
urban spaces are pivotal nodes of the
global ecosystem
and it is in cities where the majority
of humans and influential decision
makers
experience nature so
while growing food crops isn’t exactly
nature
it’s on the way to nature and a lot more
alive
than a black membrane rooftop so imagine
if people could
experience the benefits of being around
plants
even more in their rooftop environments
nearby
so if you want to help me lead a
revolution
in rooftop agri-voltaics i have four
things that you can do
today so the first thing you can do is
educate yourself on green roofs go to
green roofs.org
that’s a website by the non-profit
greeners for healthy cities
you can also go contact your local
government
so your local government asks them what
do you do
to support rooftop agri-voltaics
you might have to do a little bit of
defining for them because they may not
know what that means
but you can ask them three separate
things you can ask them
what do you do to support green roof
installations
what do you do to support rooftop
solar installations and what do you do
to support
a local food system you can also contact
your energy provider
they are in control of what renewable
energy sources are are invested in
in their area and finally
you can seek out and buy local food go
to your local farmers market
go to your local grocery store and ask
for local
local food sources we need to support
these local food sources as well as
rooftop solar
as well as green roof development in
order to get to the larger goal
of rooftop agri-voltaics thank you
[Applause]
you