Rooftop Agrivoltaics

t minus 10 9 8 7

6 5 4 3

2 1 0

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