Scientists reveal all-day cooling tech that also generates clean electricity
The dual cooling and power strategy can work round the clock and deliver savings of 30 percent electricity compared to only using solar cells.
Researchers at Penn State University in the US have developed a ‘dual-harvester’ that generates clean energy and directs heat away from the Earth. The harvester consists of a solar cell and uses radiative cooling to save more than 30 percent of electricity compared to standard solar cells.
What is radiative cooling?
Radiative cooling is the process through which objects on Earth shed their thermal energy into outer space without warming their surroundings. Heat is emitted in the form of infrared light, which escapes directly from the Earth’s atmosphere.
The team leveraged this principle to develop a dual cooling and power strategy, generating clean energy through a solar cell while simultaneously getting rid of heat.
“In radiative cooling, the infrared light radiates from a piece of transparent, low-iron glass,” explained Linxiao Zhu, assistant professor of mechanical engineering and leader of the research team. “The light bounces off the glass, passes through the atmosphere without warming the surrounding air, and lands in outer space, which we call the cold universe.”
While this does not directly help generate energy, cooling generated using this approach can be used in place of air-conditioners and refrigerators and reduce the consumption of electricity that would have otherwise been used to do this work.
How does a dual-energy harvester work?
Zhu was part of the team that invented daytime radiative cooling a decade ago. The technique is currently being explored as a zero-carbon cooling method.
In their recent work, Zhu’s team designed a new ultrathin, transparent radiative cooler that transmits most of the light through it. This way, a solar cell placed below the radiative cooling material can continue to generate electricity while the radiative cooler does its thing.
“At night and during the day, the radiative cooler works as a 24/7 natural air conditioner,” highlighted Pramit Ghosh, a doctoral student in mechanical engineering at Penn State. “Even on a hot day, the radiative cooler is cold to the touch.”
Tests carried out by the researchers showed that the cooler could drop ambient air temperature by as much as five degrees Celsius during the day. The cooling produced in this manner can be pumped using a fan to keep a building cool round the clock, acting as a natural air conditioner.
The key advantage of such a system is that dual-energy harvesters occupy the same space and can continue to work in tandem, irrespective of the time of the day. The setup is also minimal and can be placed on a rooftop or the ground, much like solar cells are installed.
“Based on these experimental results, using the two harvesters together has the potential to significantly outperform a bare solar cell, which is a key renewable energy technology,” Zhu added.
The research findings were published in Physical Science earlier this month.
Study Abstract
Daytime radiative cooling to below ambient air temperature relies on radiating heat while reflecting most sunlight. Thus, subambient daytime radiative cooling has been largely incompatible with solar energy harvesting. Despite the great theoretical potential of coharvesting the cold universe and the sun as renewable resources, subambient daytime radiative cooling and significant solar power generation have not been achieved simultaneously. Here, we introduce and demonstrate simultaneous subambient daytime radiative cooling and photovoltaic power generation from the same area. Outdoor experiments show that the radiative cooler reaches 5.1°C below the ambient temperature under ∼1,000 W/m2 sunlight, and the photovoltaic cell produces 159.9 W/m2 simultaneously and from the same area. The radiative cooling power at ambient temperature is measured to be 63.8 W/m2 under peak sunlight and 87.0 W/m2 at night. The results highlight the great potential of simultaneous radiative cooling and sunlight harvesting for renewable energy.
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