As solar panels devoured the winter sun from the rooftop of North Market on a recent morning, a new set of panels nearby beamed power directly skyward.
Equipped with a 3M-made film that reduces temperatures without electricity, these reflective panels can dramatically improve the efficiency of power-hungry refrigeration systems.
For the North Minneapolis grocery store – the first in Minnesota with a SkyCool Systems installation – that means money saved. For a warming planet, this means that greenhouse gas emissions are reduced while cooling needs increase.
The world now faces “multiple unavoidable climate risks” in the coming decades, according to the latest UN climate report. Adaptation to a changed climate in which air conditioning will play a greater role has become more important as efforts to mitigate global warming have failed.
SkyCool and 3M are working together to sell the cooling panel systems to grocery stores and other users who use a lot of electricity keeping things cool – although the concept could expand to other energy-efficient uses .
“Grocery stores operate on thin margins – anything over 10% energy savings will be very significant,” said 3M business developer Billie Pritzker. The panels can provide savings of 15% to 20%, she says.
Air conditioning and refrigeration consume a quarter of the world’s electricity and contribute 7% of global greenhouse gas emissions. SkyCool claims its panels can save twice as much energy as similarly sized solar panels can produce.
General Manager Eli Goldstein knows the claim raises a few eyebrows.
“There’s always skepticism around new technologies,” said Goldstein, whose company is based in Silicon Valley. “This is a technology that can directly cool the environment. It’s a very clear cost-benefit ratio.”
A few big-box retailers are testing the panels as a way to meet ambitious carbon reduction targets. 3M is installing the technology at one of its factories in California. A data center also drives the cooling panels.
“There’s a lot we can do just by having these highly reflective surfaces on rooftops,” Goldstein said. “Now, how do you incorporate it into a product, and who do you sell it to? »
How the technology works
3M’s high-tech piece that looks like plastic – actually hundreds of nano-layers of precise thickness that work together to reflect solar energy – is borrowed from the natural world.
“This same structure is found in the wings of butterflies and fish scales,” said 3M scientist Tim Hebrink.
The type of film used to reflect sunlight and return heat to the atmosphere relies on “passive radiative cooling”, another natural phenomenon observed when frost appears on windows even when the air temperature remains at above freezing point.
“The two key properties are solar reflectivity and thermal emissivity,” Hebrink said. “It’s what gives us the ability to radiate heat skyward.”
SkyCool racks work by cooling a fluid that travels under the panels and is pumped through the refrigeration systems. Cooling helps reduce the running time of motors in the refrigeration system to reduce electricity consumption. In total, the SkyCool system saves about 100 watts per square meter, which is twice the average output of a solar panel.
The film emits heat in a specific wavelength that allows it to escape into space – a property that could be used to cool urban centers if the film were on enough buildings, research shows.
Arizona State University researchers installed 3M passive radiative cooling film directly over a bus stop last summer and found it cooled the air temperature in the shelter by up to 4 degrees.
“Based on these positive results, the City of Tempe is considering incorporating cooling films into the future design of bus shelters, bus roofs and other shade infrastructure,” the university announced last month. .
A team of researchers from the University of Minnesota sought funding to simulate how much 3M film on downtown Minneapolis and St. Paul rooftops it would take to lower summer daytime temperatures by 2 degrees .
Pritzker said 3M is testing more ways to apply the film directly, including shipping container-based housing units and potentially electric vehicle batteries.
Most uses have been pilot projects so far. For the film to be successful in adapting to or stemming climate change, it must sell.
Drivers expand use
North Market’s non-profit owner, Pillsbury United Communities, saw an easy decision when 3M approached with a new way to cut energy costs during the warmer months.
“The main reason we are participating is to help advance this technology,” said Vanan Murugesan, director of transformation at Pillsbury United Communities. “Refrigeration is one of the biggest expenses for a grocery store – they are energy-intensive – and we couldn’t pass up the opportunity to participate in this pilot project and promote this technology.”
Depending on the level of energy savings, this could help control rising food prices, he said.
The Federal Department of Energy says $300 billion is spent worldwide on cooling systems every year, and the environmental impact could increase by an order of magnitude over the next few decades as developing countries will begin to use more air conditioning and data centers will continue to be built.
“Currently, 1 gigatonne of CO2 emissions per year comes from electricity needed for cooling applications,” according to the department’s Advanced Research Projects Agency. “This will rise to over 10 gigatonnes of CO2 emissions per year by 2050 if improved cooling technologies are not developed.”
In 2018, the agency awarded 3M more than $2.7 million to refine the passive radiative cooling film first developed by researchers at Stanford University. Last year, SkyCool provided a $3.5 million grant to deploy the technology.
Government support – through funding or policy – can be crucial for widespread adoption of passive radiative cooling. 3M Anti-Smog Roofing Granules benefited from a Los Angeles requirement that new homes have environmentally friendly roofing.
While 3M and SkyCool declined to say how much the systems cost – each installation was a custom project – the companies say the average time to recoup expenses from energy savings is two to five years. The payback period for solar panels averages eight years.
“The idea is that it can be cheaper than a solar panel and save more energy,” Goldstein said. “Everyone benefits.”