In a world where traditional energy methods become increasingly expensive and have a significant impact on the environment, researchers at Pennsylvania State University are exploring two underutilized renewable resources: the sun and outer space. Its goal is to generate electricity and passively cool structures in an innovative way.
Sun and space: Harnessing the cold of the universe and solar power for renewable energy
Led by Linxiao Zhu, assistant professor of mechanical engineering, the team has developed and tested a dual strategy that enables both cooling and power generation. This strategy involves capturing solar energy using a solar cell and simultaneously directing the heat away from the Earth through radiative cooling. The details of this energy solution, which turns out to be more efficient than the individual use of each component, were published in Cell Reports Physical Science.
Radiative cooling works by sending infrared light directly into outer space instantly, without heating the surrounding air. Zhu explained the concept with the help of a thermal camera, which makes it possible to visualize infrared light, loaded with heat, which is normally invisible. This thermal infrared radiation, also known as blackbody radiation, is the energy that people and objects release when they cool.
In radiative cooling, infrared light is radiated from transparent, low-iron glass. The light bounces off the glass, passes through the atmosphere without heating the surrounding air, and reaches outer space, which we refer to as the cold universe.
Linxiao Zhu
This process cools the surface of the radiative cooler, which can be directed toward an object, such as the inside of a building or a refrigerator.
Daytime radiative cooling was invented a decade ago and is being developed as an emerging zero-carbon cooling method. Zhu was part of the research team at Stanford University in 2014 that first developed daytime radiative cooling.
Whether at night or day, the radiative cooler works as a natural air conditioner available 24 hours a day. Even on a hot day, the radiative cooler feels cool to the touch.
Pramit Ghosh, lead author and doctoral student in mechanical engineering at Pennsylvania State University.
Below the radiative cooler, the researchers placed a solar panel, so that during daylight hours, sunlight passes through the transparent radiative cooler and is absorbed by the solar cell to generate electricity.
The team tested their system last summer at the Sustainability Expertise Center at Pennsylvania State University’s Sustainability Institute. They found that the combined electricity generation and cooling benefit of the dual harvesting system could exceed the electricity savings of a single solar cell by up to 30%. In other words, leveraging the resources together as a pair outperforms the performance of using either resource separately.
Based on these experimental results, using the two harvesters together has the potential to significantly outperform a single solar cell, which is a key renewable energy technology.
Linxiao Zhu
Another benefit is the size of the unit: since the two harvesters are stacked, they take up minimal space on a roof or floor.
At the same time and in the same place, we can take advantage of these renewable resources together, 24 hours a day.
Pramit Ghosh
Via psu.edu
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