Jennifer Bousselot is a gardener, but her crops aren’t in the ground – they’re on the roof of one of the Colorado State University buildings in downtown Denver.

On the roof are rows of native plants, colorful flowers and ripe vegetables. It’s not exactly a quiet garden scene as cars zoom past the building on Interstate 25. But Bousselot has a vision for it.

I want to use plants to provide better conditions for living in cities,” he said. “So it’s about providing additional benefits to areas that are often underutilized.”

Bousselot, an assistant professor of horticulture, conducted research on rooftop agrivoltaics – how plants grow under solar panels. His fascination began 15 years ago, but it was unintentional.

“I was very disappointed to see that another scientist put a solar array next to my research plots,” said Bousselot. “But in the next two or three growing seasons, I saw a remarkable response of the plants around the space.”

    Jennifer Bousselot, an assistant professor of Urban Horticulture and Green Roof Culture at Colorado State University.

Jennifer Bousselot, an assistant professor of Urban Horticulture and Green Roof Culture at Colorado State University.

This is because of their synergy, he said. Solar panels tend to be too hot on conventional roofs, which can reach 150 degrees or higher, and that heat reduces their efficiency. Plants help cool them down.

When you have plants under there, they cool their surrounding areas so they can survive,” Bousselot said. “So usually the plants under a solar panel get conditions close to what the ambient conditions are and so the panels benefit.”

The same goes for the panels that support the plants.

“In the West, where we have a lot of sun, we basically provide the same protection as a slightly cloudy day by putting solar panels – especially semi-transparent panels – on top of the plants ,” he said.

One way to see how the plant is doing is to measure chlorophyll. This is a substance that makes plants green and helps them absorb sunlight to grow. Bousselot and his graduate students used a thermometer-like tool to measure it.

“It’s called a chlorophyll fluorometer,” he said. “This helps us measure between different treatments, [shows us] how effective or how healthy that plant is under those conditions.”

Their tests showed that plants growing under or near solar panels were able to withstand higher humidity, using less water overall. Leafy greens are especially promising.

“It’s not urban versus rural,” he said. “Really trying to grow plants near people. And most of our population is in urban areas and not enough of our green [spaces are] in urban areas.”

Bousselot’s agrivoltaics research at CSU has brought to new heights the growing interest in “green roofs,” the term for those at least partially covered by vegetation. the Latter-day Saints Conference Center in Utah has a green roof of over 200,000 square feet. In Idaho, there is one above St. Luke’s Magic Valley Hospital.

    Jennifer Bousselot, a researcher at Colorado State University, measures chlorophyll in native plants using a Chlorophyll Fluorometer.  It shows how effective the plant is growing.

Jennifer Bousselot, a researcher at Colorado State University, measures chlorophyll in native plants using a Chlorophyll Fluorometer. It shows how effective the plant is growing.

Bousselot hopes the fast-growing region will see more as cities and architects rethink the utility of rooftops.

“Is the roof used for much other than storage? No,” he said. “So for me, it’s really amazing to see scenarios where we contribute a lot of things that we need as a human society.”

He wasn’t the only one who felt this. Back in 2017, Denver voters passed an initiative to mandate green roofs on new and existing buildings over 25,000 square feet. Bousselot is one of the initiative’s technical advisors.

“The ordinance seeks to achieve significant environmental benefits for the city, primarily through the reduction of urban heat island effect and greenhouse gas emissions,” said Amanda Weston, spokeswoman for Denver’s planning department.

But it is difficult to enforce that ordinance, especially in the existing buildings.

“If the building can’t hold the weight of the structure, it’s not something we can approve and say it’s okay to do that because it’s not safe,” he said. “When pen goes to paper, and everybody starts making plans, we’re like, ‘Oh, wait a second, that’s not going to happen.'”

Therefore, in 2018, the city expanded the ordinance and renamed it the Green Buildings Ordinance. This gives building owners more options and flexibility while keeping sustainable development goals in mind. The city estimates it will create 3.5 million square feet of green space by 2050 compared to the old ordinance and reduce cost requirements by up to 90%.

Among the requirements of the new ordinance is that every building — new or existing — must install a so-called “cool roof ‘ “.

“A cool roof is made of a very careful material,” says Weston. “And so it reflects more sunlight and absorbs less heat than a typical roof.”

After that, you have a range of compliance optionsincluding payments to the green building fund and the purchase of offsite solar power.

“We don’t want to just say, here are the rules, deal with it,” Weston said. We want to give project teams the resources and tools to see this as an opportunity, an opportunity to design more sustainable buildings.

Since the ordinance was implemented, 28 buildings have opted for onsite green spaces, according to the city. “Green space” usually means trees and shrubs – not a garden with solar panels.

    The green roof atop CSU's Terra Building in downtown Denver.

The green roof atop CSU’s Terra Building in downtown Denver.

“It’s actually a small percentage of projects that are able to comply with the green building ordinance’s required roof plants,” said Jeff Stoecklein, a Denver-based landscape architect.

Stoecklein’s goal as a designer is to balance usable outdoor space with plants. But the an ordinance is required either 60% of the total roof area, or 10% of the gross floor area devoted to green space. That leaves little space to add chairs or a pool, for example, so clients often choose the easier option.

“Sometimes it just takes little tweaks to the HVAC or mechanical systems of the project, the architectural systems, to put them in a place where they’re close enough to meet the credit option,” he said. . “And therefore the value of contributing a little more reasonable instead of translating it all to the vegetated roof area.

However, Stoecklein is concerned about long-term success due to the city’s intense sun exposure.

“Any assembly plant needs things like irrigation, long-term maintenance,” he said. “So the viability of these systems is challenged where we are in our climate.”

In any case, Stoecklein sees the benefit.

“We’re becoming more dense than we were 5, 10, 20 years ago,” he said. “And that’s why it’s so important to provide, I think, daily access to the landscape and outdoor space.”

Despite the challenges, Bousselot hopes more people will embrace green roofs.

“If we can bring a little life back into that city, choose to use some of the remaining space our cities have left — rooftops — we can really make an incredible impact,” he said.

This story was produced by the Mountain West News Bureau, a collaboration between Wyoming Public Media, Nevada Public Radio, Boise State Public Radio in Idaho, KUNR in Nevada, the O’Connor Center for the Rocky Mountain West in Montana, KUNC in Colorado , KUNM in New Mexico, with support from affiliate stations throughout the region. Funding for the Mountain West News Bureau is provided in part by the Corporation for Public Broadcasting.

Copyright 2022 KUNC. To see more, visit KUNC.

Leave a Reply

Your email address will not be published. Required fields are marked *